"Mad Roger" wrote in message
news
What's the *performance* difference between 15 inch, 16 inch and 17 inch
tires (all else being equal)?

Let's say that the stock wheel is 16 inch and let's ignore sheer looks,
and
the fact the speedometer will read differently, and let's ignore obvious
non-performance wheel-well fitment issue since they're obviously not
performance changes.

What *performance* changes will the one inch larger or smaller tire cause?

Basically, I'm wondering why people almost universally want larger wheels,
where all I'm asking about are what the performance tradeoffs are.

Bigger wheel = less gasoline for a given distance and less tire wear.

On 7/19/2017 7:36 AM, dadiOH wrote:
"Mad Roger" wrote in message
news
What's the *performance* difference between 15 inch, 16 inch and 17 inch
tires (all else being equal)?

Let's say that the stock wheel is 16 inch and let's ignore sheer looks,
and
the fact the speedometer will read differently, and let's ignore obvious
non-performance wheel-well fitment issue since they're obviously not
performance changes.

What *performance* changes will the one inch larger or smaller tire cause?

Basically, I'm wondering why people almost universally want larger wheels,
where all I'm asking about are what the performance tradeoffs are.

Bigger wheel = less gasoline for a given distance and less tire wear.



Folks might like to know that just putting the question as posed into
google will get results like this:

https://www.cars.com/articles/what-d...1420680318902/

On Wed, 19 Jul 2017 08:55:29 -0400,
Frank wrote:

https://www.cars.com/articles/what-d...1420680318902/

Thank you for that article, where the 3 main takeaways are...

"If the wheel diameter increases by one inch, the height of the tire
should decrease accordingly to compensate, in order to keep the overall
diameter the same."

"With larger wheels and lower profile tires ¡X and the resultant shorter
sidewalls ¡X they¡¦re stiffer and there¡¦s less of an air and rubber cushion
than before, increasing the chances that hitting a large pothole could
damage the tire, wheel or both."

"An 18-inch tire, for example, will probably weigh at least a couple of
pounds more than a 16- or 17-inch tire. That could also be true of a larger
wheel."

To summarize what the article said for moving to larger-diameter wheels...
+ The overall vehicle suspension remains at the same ride height
+ Tire air "cushioning" is greatly reduced
+ Unsprung weight goes up appreciably

On Wed, 19 Jul 2017 07:36:14 -0400,
dadiOH wrote:

Bigger wheel = less gasoline for a given distance and less tire wear.

I would intuitively agree with you but the two referenced articles do not
agree with our intuition.

Combined, the two articles said (for a one-inch difference)...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration & decrease in fuel economy
+ And there will be a decrease in handling (mostly in cornering)
+ And that unsprung weight goes up appreciably
+ In addition to tire air "cushioning" being reduced
+ While the overall vehicle suspension remains at the same ride height

On 7/19/2017 11:17 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 08:55:29 -0400,
Frank wrote:

https://www.cars.com/articles/what-d...1420680318902/

Thank you for that article, where the 3 main takeaways are...

"If the wheel diameter increases by one inch, the height of the tire
should decrease accordingly to compensate, in order to keep the overall
diameter the same."

"With larger wheels and lower profile tires ¡X and the resultant shorter
sidewalls ¡X they¡¦re stiffer and there¡¦s less of an air and rubber cushion
than before, increasing the chances that hitting a large pothole could
damage the tire, wheel or both."

"An 18-inch tire, for example, will probably weigh at least a couple of
pounds more than a 16- or 17-inch tire. That could also be true of a larger
wheel."

To summarize what the article said for moving to larger-diameter wheels...
+ The overall vehicle suspension remains at the same ride height
+ Tire air "cushioning" is greatly reduced
+ Unsprung weight goes up appreciably


I found it interesting and first sentence says it, "They look cool."

On Wed, 19 Jul 2017 15:51:22 -0000 (UTC),
Mad Roger wrote:

Bigger wheel = less gasoline for a given distance and less tire wear.

I would intuitively agree with you but the two referenced articles do not
agree with our intuition.

Combined, the two articles said (for a one-inch difference)...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration & decrease in fuel economy
+ And there will be a decrease in handling (mostly in cornering)
+ And that unsprung weight goes up appreciably
+ In addition to tire air "cushioning" being reduced
+ While the overall vehicle suspension remains at the same ride height

I need to correct the summary based on a distinction trader_4 brought up
that there may or may not be an increase in overall diameter.

Since I'm not the one putting 20 inch wheels on a Honda Civic, I have to
ask here whether the general trend is to maintain the overall diameter of
the wheel-and-tire assembly, or if most people increase the overall
diameter?

On Wed, 19 Jul 2017 12:17:36 -0400,
Frank wrote:

I found it interesting and first sentence says it, "They look cool."

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.

If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
+ And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".
I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.



I would tend to look at the drivers who over-size their wheels
and conclude that it is _not strange at all_ that the mods
are based solely on image ..
John T.

On Wed, 19 Jul 2017 13:36:23 -0400,
wrote:

I would tend to look at the drivers who over-size their wheels
and conclude that it is _not strange at all_ that the mods
are based solely on image ..

I'm having a hard time fathoming that there are zero performance benefits
from putting a one-inch larger diameter tire-and-wheel assembly.

Most things done for "looks" have a semblance in reality, I thought.

For example, low-profile tires give better steering response, so, that's
why (I presume) I see SUVs with super low profile tires (because they want
to look like a better steering vehicle).

Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).

Same with dual exhaust, or a hood scoop, both of which allow the engine to
bring in and shove air out easily (which is essentially what an engine
does).

So the whole performance-look thing is a bit confusing to me.

Unlike the examples above where the look is to replicate situations where
there is actually a performance gain, if there are no performance gains to
larger wheels, then how does the *look* of larger wheels look like you get
performance gains?

On 7/19/2017 9:53 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 12:17:36 -0400,
Frank wrote:

I found it interesting and first sentence says it, "They look cool."

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.

If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration

+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

My understanding is that low profile tires are being used because they
have lower rolling friction - the rubber is flexing less, so there is
less loss to heating the tire.

+ And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Yes, it is astounding. In fact, I would suggest it is unbelievable.


Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.

On 7/19/2017 9:52 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 15:51:22 -0000 (UTC),
Mad Roger wrote:

Bigger wheel = less gasoline for a given distance and less tire wear.

I would intuitively agree with you but the two referenced articles do not
agree with our intuition.

Combined, the two articles said (for a one-inch difference)...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration & decrease in fuel economy
+ And there will be a decrease in handling (mostly in cornering)
+ And that unsprung weight goes up appreciably
+ In addition to tire air "cushioning" being reduced
+ While the overall vehicle suspension remains at the same ride height

I need to correct the summary based on a distinction trader_4 brought up
that there may or may not be an increase in overall diameter.

Since I'm not the one putting 20 inch wheels on a Honda Civic, I have to
ask here whether the general trend is to maintain the overall diameter of
the wheel-and-tire assembly, or if most people increase the overall
diameter?


Some people that increase tire size will change the gearing to
compensate. Otherwise, your shift points will change, your speedometer
will be in error.

On Wednesday, July 19, 2017 at 12:53:09 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 12:17:36 -0400,
Frank wrote:

I found it interesting and first sentence says it, "They look cool."

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.

If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)

I don't see the decrease in fuel economy. Just because a car
accelerates slower doesn't mean that it will use more fuel.
I think there is a difference in rolling resistance between tires
of different diameters, but as said previously, when going to
larger diameter wheels, the tires other characteristics, eg profile
change too. That would have an effect on rolling resistance.



+ And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.

Again, torque does not translate directly into fuel economy. I
could apply less torque over a longer time period, get to the same
speed and not necessarily use more fuel.

Bob F actually wrote:

+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Maybe I read the article wrong that was referenced by Ed Pawlowski?
https://www.carthrottle.com/post/how...t-performance/


Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

I understand your intuition, which is the same intuition we all have but if
it's true what that article from Ed says, then 25% less torque at the
contact patch means 25% less torque to combat increased wind resistance at
highway speeds.

That means, in the words of the article, the engine has to 'work harder' to
combat that wind resistance.

You tell me how making the engine work (presumably a lot) harder increases
fuel efficiency.

My understanding is that low profile tires are being used because they
have lower rolling friction - the rubber is flexing less, so there is
less loss to heating the tire.

Neither of the two articles mentioned that factor.

And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Yes, it is astounding. In fact, I would suggest it is unbelievable.

That's a fair assessment since 25% less torque for a one-inch increase in
diameter is astounding.

Can you take a look at the article to see if I did my math wrong?
https://www.carthrottle.com/post/how...t-performance/

360 Newtons is 78% of 460 Newtons.
460 Newtons is 128% of 360 Newtons.

That's roughly 1/4 if my math is right.
(I never know which direction to quote but both end up being about 1/4.)

On Wednesday, July 19, 2017 at 2:06:41 PM UTC-4, Bob F wrote:
On 7/19/2017 9:53 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 12:17:36 -0400,
Frank wrote:

I found it interesting and first sentence says it, "They look cool."

I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".

I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
noted.

If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Yeah, that number seems suspect to me too.



Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration

+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

My understanding is that low profile tires are being used because they
have lower rolling friction - the rubber is flexing less, so there is
less loss to heating the tire.

I think that's true. It's not clear to me anymore what is being
discussed here. Is it the hypothetical and unusual case where
the same profile and width tire is use, just larger diameter?
Or is the most common case, where with a larger wheel, you go to
a different profile tire, so the overall rolling diameter stays
about the same?



+ And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Yes, it is astounding. In fact, I would suggest it is unbelievable.


+1




Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.


And I don't believe less torque translates into lower fuel economy either.
Yes, it will accelerate slower with a larger diameter wheel, but that
just means you have less torque applied over a longer period. It's
not torque, it's energy that you need to look at.

On Wednesday, July 19, 2017 at 2:22:17 PM UTC-4, Roy Tremblay wrote:
Bob F actually wrote:

+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Maybe I read the article wrong that was referenced by Ed Pawlowski?
https://www.carthrottle.com/post/how...t-performance/


Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

I understand your intuition, which is the same intuition we all have but if
it's true what that article from Ed says, then 25% less torque at the
contact patch means 25% less torque to combat increased wind resistance at
highway speeds.

That means, in the words of the article, the engine has to 'work harder' to
combat that wind resistance.

You tell me how making the engine work (presumably a lot) harder increases
fuel efficiency.

Look at the energy required to lift a 100 lb rock two feet. I can do
it two ways, with a 2ft lever that provides low torque, or a 10 ft
lever that applies higher torque. Which takes more *energy* to lift
the rock? Answer: they both take the same amount. Now apply that
to the fuel economy issue.

Or take the example of a bicycle with different gear ratios. While
the ratios vary, and with some ratios you couldn't get up a hill,
while with other ratios it's possible or even easy, it doesn't
change the energy input required.

On 7/19/2017 1:42 PM, Mad Roger wrote:
On Wed, 19 Jul 2017 13:36:23 -0400,
wrote:

I would tend to look at the drivers who over-size their wheels
and conclude that it is _not strange at all_ that the mods
are based solely on image ..

I'm having a hard time fathoming that there are zero performance benefits
from putting a one-inch larger diameter tire-and-wheel assembly.

Most things done for "looks" have a semblance in reality, I thought.

For example, low-profile tires give better steering response, so, that's
why (I presume) I see SUVs with super low profile tires (because they want
to look like a better steering vehicle).

Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).

Same with dual exhaust, or a hood scoop, both of which allow the engine to
bring in and shove air out easily (which is essentially what an engine
does).

So the whole performance-look thing is a bit confusing to me.

Unlike the examples above where the look is to replicate situations where
there is actually a performance gain, if there are no performance gains to
larger wheels, then how does the *look* of larger wheels look like you get
performance gains?


There are little to no performance gains for any of the above. It is
all about looks. Duel exhausts? Ever look at the pipes underneath?
They may end up with two termination points but that is after it all
goes through the same single pipe. Duals go back to the V-8s in the
1950s.

A car manufacturer sends me (and many others) an occasional survey.
They may ask what I think looks better. Two pipes on opposing sides
versus two pipes next to each other on one side versus two pipes in the
center. They never ask what I think of performance, mostly style once
in a while ergonomics on control location but that is for style of the
dashboard.

Its all about style. If people don't like the looks they won't go to
the showroom.

On Wed, 19 Jul 2017 11:14:46 -0700 (PDT),
trader_4 wrote:

I don't see the decrease in fuel economy. Just because a car
accelerates slower doesn't mean that it will use more fuel.

I will agree with you that most people say that you get better gas mileage,
but we haven't seen a reliable article that says that yet.

All we've seen is the two articles that say nothing good performance-wise
will come out of increasing the overall diameter.

I understand your intuitive argument that one spin of the wheel is a few
inches more but if that one spin comes at a cost in the engine working
harder, then we may not get the economy we intuit.

The wind resistance has to be overcome.
Torque isn't only for starting at a dead stop.
Torque is also needed to overcome wind resistance (which gets appreciable
at speed).

I think there is a difference in rolling resistance between tires
of different diameters, but as said previously, when going to
larger diameter wheels, the tires other characteristics, eg profile
change too. That would have an effect on rolling resistance.

I did not consider when I originally asked that there are two situations:
+ Larger wheels with lower profile tires resulting in the same diameter
+ Larger wheels resulting in a larger diameter

Again, torque does not translate directly into fuel economy.

Maybe. Maybe not. It's fair to ask whether fuel economy is increased when
the overall diameter of the tire-and-wheel assembly is increased.

So far, neither of the two articles has said that.

I agree with your intuition - but our intuition isn't good enough for a
correct answer. We need to find a reference that reliably backs up our
intuition.

I
could apply less torque over a longer time period, get to the same
speed and not necessarily use more fuel.

I guess what you're saying is that everything is relative.
I think we all intuit that larger diameters mean fewer inches per
revolution which we associate with overdrive gears, which, to our
intuition, mean better gas mileage at cruising speed.

However ..........

Cruising speed isn't free.
You still have to overcome wind resistance (which is appreciable).

What overcomes wind resistance?
Torque at the contact patch, right?

If that's what overcomes wind resistance, and if the engine has to work
harder to achieve that torque to overcome the wind resistance, then we may
not get the gas mileage we intuit.

I don't know the answer.
I only know what the two articles said.

On Wed, 19 Jul 2017 11:04:20 -0700,
Bob F wrote:

Some people that increase tire size will change the gearing to
compensate. Otherwise, your shift points will change, your speedometer
will be in error.

I tried to phrase the original question to keep compensation out of the
picture because with compensation, anything can change.

I just wanted to know more about the physics of larger overall diameters.

So far, no reference has given a single good performance impact that
results from just the one change of diameter.

On Wednesday, July 19, 2017 at 1:42:49 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 13:36:23 -0400,
wrote:

I would tend to look at the drivers who over-size their wheels
and conclude that it is _not strange at all_ that the mods
are based solely on image ..

I'm having a hard time fathoming that there are zero performance benefits
from putting a one-inch larger diameter tire-and-wheel assembly.

Most things done for "looks" have a semblance in reality, I thought.

Why would that be? I see lots of things done for styling and eye
appeal that are just for that purpose.




For example, low-profile tires give better steering response, so, that's
why (I presume) I see SUVs with super low profile tires (because they want
to look like a better steering vehicle).

How many people looking at a stylish SUV think that those wheels look
like they steer better?




Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).

Same with dual exhaust, or a hood scoop, both of which allow the engine to
bring in and shove air out easily (which is essentially what an engine
does).

So the whole performance-look thing is a bit confusing to me.

Unlike the examples above where the look is to replicate situations where
there is actually a performance gain, if there are no performance gains to
larger wheels, then how does the *look* of larger wheels look like you get
performance gains?

Who ever said that it did?

On Wednesday, July 19, 2017 at 2:31:49 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 11:14:46 -0700 (PDT),
trader_4 wrote:

I don't see the decrease in fuel economy. Just because a car
accelerates slower doesn't mean that it will use more fuel.

I will agree with you that most people say that you get better gas mileage,
but we haven't seen a reliable article that says that yet.

I never said that most people say that you get better gas mileage.
I have no idea what most people would think.




All we've seen is the two articles that say nothing good performance-wise
will come out of increasing the overall diameter.

I understand your intuitive argument that one spin of the wheel is a few
inches more but if that one spin comes at a cost in the engine working
harder, then we may not get the economy we intuit.

I didn't say that either, in fact I said the opposite. You're looking
at torque, not energy expended. If I lift a 100 lb rock with a 2ft
lever or with a 10 ft lever, one involves 5 times the torque, but
the energy used is exactly the same.





The wind resistance has to be overcome.
Torque isn't only for starting at a dead stop.
Torque is also needed to overcome wind resistance (which gets appreciable
at speed).

I think there is a difference in rolling resistance between tires
of different diameters, but as said previously, when going to
larger diameter wheels, the tires other characteristics, eg profile
change too. That would have an effect on rolling resistance.

I did not consider when I originally asked that there are two situations:
+ Larger wheels with lower profile tires resulting in the same diameter
+ Larger wheels resulting in a larger diameter

Then you must not pay much attention to all those wheels out there.



Again, torque does not translate directly into fuel economy.

Maybe. Maybe not.

No, it definitely does not, per the rock example.


It's fair to ask whether fuel economy is increased when
the overall diameter of the tire-and-wheel assembly is increased.

So far, neither of the two articles has said that.

I agree with your intuition - but our intuition isn't good enough for a
correct answer. We need to find a reference that reliably backs up our
intuition.


Clearly you don't agree with my intuition, which is backed with physics.

On Wed, 19 Jul 2017 11:38:24 -0700 (PDT),
trader_4 wrote:

How many people looking at a stylish SUV think that those wheels look
like they steer better?

Maybe I'm wrong that people try to replicate an image of speed and handling
(e.g., why do people put M3 badges on a non-M3 bimmer then?).

Anyway, I just want to know what the performance impact is of a larger
diameter change of one inch.

This Car and Driver article tries to answer the question:
Effects of Upsized Wheels and Tires Tested
http://www.caranddriver.com/features...d-tires-tested

"What¢s immediately apparent from the results is that as the wheel-and-tire
packages get larger and heavier, acceleration and fuel economy suffer.
Neither is a huge surprise, but we measured a 10-percent drop in fuel
economy and a four-percent degradation in 0-to-60-mph acceleration from the
15s to the 19s"

On Wed, 19 Jul 2017 11:29:19 -0700 (PDT),
trader_4 wrote:

Look at the energy required to lift a 100 lb rock two feet. I can do
it two ways, with a 2ft lever that provides low torque, or a 10 ft
lever that applies higher torque. Which takes more *energy* to lift
the rock? Answer: they both take the same amount. Now apply that
to the fuel economy issue.

The problem is that the math is non linear.
The physics forum said it this way.
https://www.physicsforums.com/thread...wheels.406860/

"attempting to spin a 2x larger wheel at the same speed would be attempting
to move the car 2x faster. Since energy is force x distance, traveling 2x
faster for 1 hour necessarily requires at least 2x more energy (since you
covered 2x more distance)...."

Or take the example of a bicycle with different gear ratios. While
the ratios vary, and with some ratios you couldn't get up a hill,
while with other ratios it's possible or even easy, it doesn't
change the energy input required.

The physics forum said otherwise.
https://www.physicsforums.com/thread...wheels.406860/

"Even more bad news is that in the real world, air resistance is actually a
square function! (2x more speed means 4x more air resistance!). This means
you would actually probably need at least 4x more energy..."

I am not a physicist so I'm just looking for the answers like everyone else
where my intuition isn't good enough to answer the question correctly.

On 7/19/2017 11:33 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 11:04:20 -0700,
Bob F wrote:

Some people that increase tire size will change the gearing to
compensate. Otherwise, your shift points will change, your speedometer
will be in error.

I tried to phrase the original question to keep compensation out of the
picture because with compensation, anything can change.

I just wanted to know more about the physics of larger overall diameters.

So far, no reference has given a single good performance impact that
results from just the one change of diameter.


It will be like always driving with a slightly higher gear.

Prius cars are using low profile tires. Do you suppose they have a
reason for that? They aren't necessarily larger tires.

Just putting a bigger tire on your car is going to decrease your
acceleration, and likely increase your highway mileage, depending on the
car engine's power curve, unless you re-gear to compensate.

It also may increase your turning radius, or damage your front tires if
you forget and turn too tight.

On Wednesday, July 19, 2017 at 3:02:03 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 11:29:19 -0700 (PDT),
trader_4 wrote:

Look at the energy required to lift a 100 lb rock two feet. I can do
it two ways, with a 2ft lever that provides low torque, or a 10 ft
lever that applies higher torque. Which takes more *energy* to lift
the rock? Answer: they both take the same amount. Now apply that
to the fuel economy issue.

The problem is that the math is non linear.

The problem is that you don't understand the physics.



The physics forum said it this way.
https://www.physicsforums.com/thread...wheels.406860/

"attempting to spin a 2x larger wheel at the same speed would be attempting
to move the car 2x faster. Since energy is force x distance, traveling 2x
faster for 1 hour necessarily requires at least 2x more energy (since you
covered 2x more distance)...."

Or take the example of a bicycle with different gear ratios. While
the ratios vary, and with some ratios you couldn't get up a hill,
while with other ratios it's possible or even easy, it doesn't
change the energy input required.

The physics forum said otherwise.
https://www.physicsforums.com/thread...wheels.406860/

"Even more bad news is that in the real world, air resistance is actually a
square function! (2x more speed means 4x more air resistance!). This means
you would actually probably need at least 4x more energy..."

Now you're just deliberately throwing obfuscation into the problem.
Sure there is more wind resistance at higher speeds. But you were
talking about a car moving at the *same speed* down the highway
and saying that it involves more or less energy because of differing
torques. The bicycle example still applies. The bicycle moving at
the same speed will need the same *energy* input to get up a hill
but with different gear ratios, the torque applied at the peddles
will be different. You apply less torque over a greater peddle
movement distance or higher torque over a shorter distance, but
the energy input is the same. It's physics 101.

On 7/19/2017 11:38 AM, trader_4 wrote:
On Wednesday, July 19, 2017 at 1:42:49 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 13:36:23 -0400,
wrote:

I would tend to look at the drivers who over-size their wheels
and conclude that it is _not strange at all_ that the mods
are based solely on image ..

I'm having a hard time fathoming that there are zero performance benefits
from putting a one-inch larger diameter tire-and-wheel assembly.

Most things done for "looks" have a semblance in reality, I thought.

Why would that be? I see lots of things done for styling and eye
appeal that are just for that purpose.




For example, low-profile tires give better steering response, so, that's
why (I presume) I see SUVs with super low profile tires (because they want
to look like a better steering vehicle).

How many people looking at a stylish SUV think that those wheels look
like they steer better?




Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).

Same with dual exhaust, or a hood scoop, both of which allow the engine to
bring in and shove air out easily (which is essentially what an engine
does).

So the whole performance-look thing is a bit confusing to me.

Unlike the examples above where the look is to replicate situations where
there is actually a performance gain, if there are no performance gains to
larger wheels, then how does the *look* of larger wheels look like you get
performance gains?

Who ever said that it did?


My father once told me a story about meeting a tire tread designer for
one of the big tire manufacturers. He said she was a little old lady who
could draw pretty treads. Admittedly, this was probably 30-40 years ago.

On 7/19/2017 11:56 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 11:38:24 -0700 (PDT),
trader_4 wrote:

How many people looking at a stylish SUV think that those wheels look
like they steer better?

Maybe I'm wrong that people try to replicate an image of speed and handling
(e.g., why do people put M3 badges on a non-M3 bimmer then?).

Anyway, I just want to know what the performance impact is of a larger
diameter change of one inch.

This Car and Driver article tries to answer the question:
Effects of Upsized Wheels and Tires Tested
http://www.caranddriver.com/features...d-tires-tested

"What¢s immediately apparent from the results is that as the wheel-and-tire
packages get larger and heavier, acceleration and fuel economy suffer.
Neither is a huge surprise, but we measured a 10-percent drop in fuel
economy and a four-percent degradation in 0-to-60-mph acceleration from the
15s to the 19s"


Without adjusting the gearing? Clearly, they are operating the engine
way out of it's efficiency range. Why would anyone do this?

On Wed, 19 Jul 2017 12:13:37 -0700 (PDT),
trader_4 wrote:

The problem is that you don't understand the physics.

I am not going to disagree with you.

That's why I want a reliable reference that backs up any claim of better
gas mileage with a larger diameter tire.

This article from Cooper Tire says that our intuition is wrong for example.
Do larger tires improve gas mileage?
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage

"The common belief is that a tire with a larger diameter will cover more
ground per revolution, thus reducing overall gearing and enabling the
engine to run at lower revolutions per minute (RPM). People generally
associate lower RMP with less fuel used to travel the same distance. While
this may be true in a few instances, it is not the case for most vehicles.
There are too many variables to make a universal statement that larger
tires are more fuel efficient."

They then explain that the torque curve is critical, which makes the
equation too complex for a Usenet discussion instantly (because of the huge
number of variables involved).

Now you're just deliberately throwing obfuscation into the problem.
Sure there is more wind resistance at higher speeds. But you were
talking about a car moving at the *same speed* down the highway
and saying that it involves more or less energy because of differing
torques.

Huh? You misinterpreted what I said versus what was quoted but that doesn't
really matter since all we need is a reliable reference that backs up both
our intuition that the larger diameter setup will result in better fuel
economy.

So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

So let's just look for a reliable reference that actually claims that
better gas mileage results from just changing overall diameter.

Here's the best I can find, from that Dunn/Cooper reference above:
"In a nutshell, the vehicles which stand to benefit from a larger diameter
tire are those that produce more torque than they need to in order to
maintain speed."

However, it concludes, probably correctly, that...
"There are just too many factors to consider to make general statements
that larger or smaller tires are more fuel efficient."

On Wednesday, July 19, 2017 at 3:25:24 PM UTC-4, Bob F wrote:
On 7/19/2017 11:56 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 11:38:24 -0700 (PDT),
trader_4 wrote:

How many people looking at a stylish SUV think that those wheels look
like they steer better?

Maybe I'm wrong that people try to replicate an image of speed and handling
(e.g., why do people put M3 badges on a non-M3 bimmer then?).

Anyway, I just want to know what the performance impact is of a larger
diameter change of one inch.

This Car and Driver article tries to answer the question:
Effects of Upsized Wheels and Tires Tested
http://www.caranddriver.com/features...d-tires-tested

"What¢s immediately apparent from the results is that as the wheel-and-tire
packages get larger and heavier, acceleration and fuel economy suffer.
Neither is a huge surprise, but we measured a 10-percent drop in fuel
economy and a four-percent degradation in 0-to-60-mph acceleration from the
15s to the 19s"


Without adjusting the gearing? Clearly, they are operating the engine
way out of it's efficiency range. Why would anyone do this?

+1

On 7/19/2017 11:22 AM, Roy Tremblay wrote:
Bob F actually wrote:

+ The engine delivers ~25% less driving force to the wheel contact patch

That's crazy! Where on earth did that come from. 1" diameter increase
would only cause that change if you started with 4" O.D. tires.

Maybe I read the article wrong that was referenced by Ed Pawlowski?
https://www.carthrottle.com/post/how...t-performance/


Low profile tires compensate for the wheel diameter increase, so no
increase in tire diameter occurs, and no torque loss should occur.

+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
It should increase economy. Just like driving in a high gear does.

I understand your intuition, which is the same intuition we all have but if
it's true what that article from Ed says, then 25% less torque at the
contact patch means 25% less torque to combat increased wind resistance at
highway speeds.

Actually read the article. They are changing from a 15" to a 19" tire.
That's a 26% increase in diameter. The torque goes down 26%, the engine
RPM goes down 26%. The power required to go THE SAME speed stays
virtually the same. But now, the engine may be operating at a lower part
of it's efficiency curve. Or maybe not.

These days, cars are geared for efficiency generally, with possible
choices to change the shift points for performance. So changing tire
O.D. is not likely to help mileage.


That means, in the words of the article, the engine has to 'work harder' to
combat that wind resistance.

It delivers more torque at lower RPMs. The work to go the same speed
remains the same. Work is force x distance.

You tell me how making the engine work (presumably a lot) harder increases
fuel efficiency.

My understanding is that low profile tires are being used because they
have lower rolling friction - the rubber is flexing less, so there is
less loss to heating the tire.

Neither of the two articles mentioned that factor.

And unsprung weight goes up by a few pounds

The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.

Yes, it is astounding. In fact, I would suggest it is unbelievable.

That's a fair assessment since 25% less torque for a one-inch increase in
diameter is astounding.

Can you take a look at the article to see if I did my math wrong?
https://www.carthrottle.com/post/how...t-performance/

360 Newtons is 78% of 460 Newtons.
460 Newtons is 128% of 360 Newtons.

That's roughly 1/4 if my math is right.
(I never know which direction to quote but both end up being about 1/4.)

On 7/19/2017 12:27 PM, Mad Roger wrote:
On Wed, 19 Jul 2017 12:13:37 -0700 (PDT),
trader_4 wrote:

The problem is that you don't understand the physics.

I am not going to disagree with you.

That's why I want a reliable reference that backs up any claim of better
gas mileage with a larger diameter tire.

This article from Cooper Tire says that our intuition is wrong for example.
Do larger tires improve gas mileage?
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage

"The common belief is that a tire with a larger diameter will cover more
ground per revolution, thus reducing overall gearing and enabling the
engine to run at lower revolutions per minute (RPM). People generally
associate lower RMP with less fuel used to travel the same distance. While
this may be true in a few instances, it is not the case for most vehicles.
There are too many variables to make a universal statement that larger
tires are more fuel efficient."

They then explain that the torque curve is critical, which makes the
equation too complex for a Usenet discussion instantly (because of the huge
number of variables involved).

Now you're just deliberately throwing obfuscation into the problem.
Sure there is more wind resistance at higher speeds. But you were
talking about a car moving at the *same speed* down the highway
and saying that it involves more or less energy because of differing
torques.

Huh? You misinterpreted what I said versus what was quoted but that doesn't
really matter since all we need is a reliable reference that backs up both
our intuition that the larger diameter setup will result in better fuel
economy.

So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

So let's just look for a reliable reference that actually claims that
better gas mileage results from just changing overall diameter.

Here's the best I can find, from that Dunn/Cooper reference above:
"In a nutshell, the vehicles which stand to benefit from a larger diameter
tire are those that produce more torque than they need to in order to
maintain speed."

However, it concludes, probably correctly, that...
"There are just too many factors to consider to make general statements
that larger or smaller tires are more fuel efficient."


If you have a car geared for drag races, putting larger tires on it will
give you better highway mileage. Backing off on the leadfoot will give
you better mileage in the city.

If you own a car designed for mileage, not performance, the larger tire
will probably not improve the mileage, because that's not what the
manufacturer designed it for.

On 07/19/2017 11:42 AM, Mad Roger wrote:
Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).

I owned a '60 Plymouth which was the bitter end of the fin craze.
Plymouth even referred to them as stabilizers:

http://www.allpar.com/history/plymouth/1960.html

I never managed to get the car up past 110 and didn't notice any more
stabilizing effect than my '65 Dodge which was back to the basic 3 box
model:

https://en.wikipedia.org/wiki/Dodge_...5.E2.80.931967

Style is style. I did go to an outlaw kart race a couple of weeks ago
and found out the real use for the wings -- when they roll the wind up
on their side with the wing preventing them from going over completely.

On Wednesday, July 19, 2017 at 3:27:57 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 12:13:37 -0700 (PDT),
trader_4 wrote:

The problem is that you don't understand the physics.

I am not going to disagree with you.

That's why I want a reliable reference that backs up any claim of better
gas mileage with a larger diameter tire.

This article from Cooper Tire says that our intuition is wrong for example.

You keep saying "our intuition" when it's clear that both Bob F and
I don't agree with your intuition.




Do larger tires improve gas mileage?
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage

"The common belief is that a tire with a larger diameter will cover more
ground per revolution, thus reducing overall gearing and enabling the
engine to run at lower revolutions per minute (RPM).

That's not belief, it's fact. Assuming of course that you do change
the gearing.




People generally
associate lower RMP with less fuel used to travel the same distance.

Maybe they do, but it's not correct. Following that logic, you
could bog an engine down into the low RPM range and with it
struggling, it would use less fuel, even with the throttle wide
open.



While
this may be true in a few instances, it is not the case for most vehicles.
There are too many variables to make a universal statement that larger
tires are more fuel efficient."

They then explain that the torque curve is critical, which makes the
equation too complex for a Usenet discussion instantly (because of the huge
number of variables involved).

But you're the one making the incorrect and simplistic assumption
that less torque means less fuel used.




Now you're just deliberately throwing obfuscation into the problem.
Sure there is more wind resistance at higher speeds. But you were
talking about a car moving at the *same speed* down the highway
and saying that it involves more or less energy because of differing
torques.

Huh? You misinterpreted what I said

I didn't misinterpret anything. I gave you an example of where you
can ride a bike up a hill at two different gear ratios and with
the lower gear ratio, it will take less torque at the pedals, but
the energy used is exactly the same. You then proceeded to throw
another variable in, going up the hill at different speeds and
the effect of wind resistance. The car example you keep bringing
up, you're talking about different diameter tires, but driving
at the same speed and how much energy is used. Changing the speed
is just obfuscation.



versus what was quoted but that doesn't
really matter since all we need is a reliable reference that backs up both
our intuition that the larger diameter setup will result in better fuel
economy.


"our" intuition again.


So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

Wow, imagine that.

On 07/19/2017 12:56 PM, Mad Roger wrote:
"What¢s immediately apparent from the results is that as the wheel-and-tire
packages get larger and heavier, acceleration and fuel economy suffer.
Neither is a huge surprise, but we measured a 10-percent drop in fuel
economy and a four-percent degradation in 0-to-60-mph acceleration from the
15s to the 19s"

Taking this a little further even in the same size aftermarket alloy
wheels are often heavier than OEM pressed steel wheels with the
resulting increase in unsprung mass and rotational inertia. But they
look kewl.

On Wed, 19 Jul 2017 12:34:29 -0700,
Bob F wrote:

Actually read the article. They are changing from a 15" to a 19" tire.

I completely misquoted the article.

I agree with you that they lost about 25% in torque going up in four
inches, not one inch.

That's a 26% increase in diameter. The torque goes down 26%, the engine
RPM goes down 26%. The power required to go THE SAME speed stays
virtually the same. But now, the engine may be operating at a lower part
of it's efficiency curve. Or maybe not.

That's what the Cooper Tire article said.
http://www.dunntire.com/blog/Do-larg...ve-gas-mileage
"the vehicles which stand to benefit from a larger diameter tire are those
that produce more torque than they need to in order to maintain
speed...[but] There are just too many factors to consider to make general
statements that larger or smaller tires are more fuel efficient."

These days, cars are geared for efficiency generally, with possible
choices to change the shift points for performance. So changing tire
O.D. is not likely to help mileage.

This Consumer Reports report says that the OEM tires are designed for fuel
efficiency where the replacement tires can have a few mpg impact, so, that
seems to back up the claim that too many things change even if all you do
is change the tire diameter.
http://www.consumerreports.org/cro/n...nomy/index.htm
"Consumer Reports recently tested a few all-season tire models with low
rolling resistance and found that those tires can improve fuel economy by
an additional one or two mpg."

On Wed, 19 Jul 2017 12:45:50 -0700 (PDT), trader_4
wrote:



"our" intuition again.


So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

Wow, imagine that.

Trader, why do you feel the need to insult and pick fights with
everyone you encounter on Usenet?

Are you unusually short? Did your parents not allow you to attend
kindergarten? Never play team sports? Never served your country?
Flunk out of kindergarten? Were you raised by howler monkeys?

Not every discussion has to result in a fight and insults. You need
to learn how to play in the sandbox with others. I wouldn't be
surprised if this has been a problem your entire life.

On 07/19/2017 12:01 PM, Bob F wrote:
My understanding is that low profile tires are being used because they
have lower rolling friction - the rubber is flexing less, so there is
less loss to heating the tire.

Many manufacturers use low rolling resistance tires as OEM equipment to
improve their CAFE numbers. One of the best is the Bridgestone B381
which has a 65 profile. Low profile is usually considered to be 50 and
under.

On 07/19/2017 01:01 PM, Mad Roger wrote:
"Even more bad news is that in the real world, air resistance is actually a
square function! (2x more speed means 4x more air resistance!). This means
you would actually probably need at least 4x more energy..."


Even worse news... Drag is a square, horsepower is a cube of velocity.

On Wednesday, July 19, 2017 at 3:54:54 PM UTC-4, Stormin' Norman wrote:
On Wed, 19 Jul 2017 12:45:50 -0700 (PDT), trader_4
wrote:



"our" intuition again.


So far every reference I can find (e.g., Car & Driver & Cooper/Dunn Tire
and the Physics Forum) say that is not the case.

Wow, imagine that.

Trader, why do you feel the need to insult and pick fights with
everyone you encounter on Usenet?

I don't. But after a few back and forth's with some posters,
enough is enough. And you do worse, getting nasty with them
on the first retort, typically because they dared to do something
you say isn't allowed, like mention Hillary negatively. You hit
them with a sharp retort. Calling people "trumptard" is an
example.



Are you unusually short? Did your parents not allow you to attend
kindergarten? Never play team sports? Never served your country?
Flunk out of kindergarten? Were you raised by howler monkeys?

Not every discussion has to result in a fight and insults. You need
to learn how to play in the sandbox with others. I wouldn't be
surprised if this has been a problem your entire life.

Go **** yourself hypocrite. How's that?

On 07/19/2017 01:12 PM, Bob F wrote:

Prius cars are using low profile tires. Do you suppose they have a
reason for that? They aren't necessarily larger tires.

https://www.toyota.com/prius/features/tires/

That shows P195/65R15. Those are low rolling resistance tires, not low
profile. P215/45R17 would be low profile but that is showing as not
available. LRR and low profile are two different things.

On Wed, 19 Jul 2017 13:24:51 -0700 (PDT), trader_4
wrote:


I don't. But after a few back and forth's with some posters,
enough is enough. And you do worse, getting nasty with them
on the first retort, typically because they dared to do something
you say isn't allowed, like mention Hillary negatively. You hit
them with a sharp retort. Calling people "trumptard" is an
example.


You have a condition son, Hillary this, Hillary that. Tell the truth,
have you ever gotten laid without paying for it? Don't respond, I
know the answer......


Go **** yourself hypocrite. How's that?

I am crushed, your opinion matters so much to me.