On 7/19/2017 2:00 AM, Mad Roger wrote:
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.


The main reason is appearance. In the late 50's auto makers went to 14"
wheels to make cars lower. Decades later, that is not as important as
big flashy wheels.

The average driver will notice little difference in everyday driving,
most cars are designed with the wheel size in mind. Larger diameter
tires will last a but longer as there is more distance per rotation.

Tire profile will also affect performance. The low profile look
sleeker, but the balloons are better on the bumps.

You will find some actual test results here
https://www.carthrottle.com/post/how...t-performance/

On Wednesday, July 19, 2017 at 8:17:31 AM UTC-5, Ed Pawlowski wrote:
On 7/19/2017 2:00 AM, Mad Roger wrote:
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.


The main reason is appearance. In the late 50's auto makers went to 14"
wheels to make cars lower. Decades later, that is not as important as
big flashy wheels.

The average driver will notice little difference in everyday driving,
most cars are designed with the wheel size in mind. Larger diameter
tires will last a but longer as there is more distance per rotation.

Tire profile will also affect performance. The low profile look
sleeker, but the balloons are better on the bumps.

You will find some actual test results here
https://www.carthrottle.com/post/how...t-performance/


My old Dodge van has 15" wheels and the last time I was looking for some used tires for it I was having trouble finding them. The used tire shop owner told me they were hard to come by because all the new vehicles had 16" and 17" wheels and all he was getting in were the larger sized tires. ヽ(ヅ)ノ

[8~{} Uncle Wheeled Monster

On Wed, 19 Jul 2017 09:17:21 -0400,
Ed Pawlowski wrote:

You will find some actual test results here
https://www.carthrottle.com/post/how...t-performance/

Thank you for that performance-related test article,
https://www.carthrottle.com/post/how...t-performance/

Where the 3 main performance-related takeaways are...
"the force can be calculated to be around 460 Newtons. Now, increase that
wheel diameter to a set of 19-inch ... Run the calculation through again
and that driving force will decrease to 360 Newtons... which will culminate
in a decrease in acceleration of said wheels."

"Fuel economy will inevitably suffer as well due to the engine having to
work harder to rotate the wheels"

"Smaller diameter wheels will make for more concise handling as each
rotation of the wheel covers a shorter distance, meaning more acute
adjustments can be made during cornering compared to a larger diameter
tyre"

To summarize what the article said for moving to larger-diameter wheels...
+ The engine delivers 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 (all else being equal)

On 7/19/2017 8:27 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 09:17:21 -0400,
Ed Pawlowski wrote:

You will find some actual test results here
https://www.carthrottle.com/post/how...t-performance/

Thank you for that performance-related test article,
https://www.carthrottle.com/post/how...t-performance/

Where the 3 main performance-related takeaways are...
"the force can be calculated to be around 460 Newtons. Now, increase that
wheel diameter to a set of 19-inch ... Run the calculation through again
and that driving force will decrease to 360 Newtons... which will culminate
in a decrease in acceleration of said wheels."

"Fuel economy will inevitably suffer as well due to the engine having to
work harder to rotate the wheels"

Only if you try to maintain the same acceleration level. Engine and
transmission parts will be moving slower, reducing losses. Only if the
engine ends up at the bad end of it's power curve will the mileage go
down. Some transmissions can be selected for efficiency modes, where
they shift into higher gears earlier. It's the same kind of change.


"Smaller diameter wheels will make for more concise handling as each
rotation of the wheel covers a shorter distance, meaning more acute
adjustments can be made during cornering compared to a larger diameter
tyre"

Really?? The part of the tire that makes ground contact will hardly
change if the width of the tire stays the same. This statement just does
not make sense. What does the rotation distance of the tire have to do
with anything. The smaller tire putting the center of gravity closer to
the ground would make more difference.


To summarize what the article said for moving to larger-diameter wheels...
+ The engine delivers 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 (all else being equal)

On Wed, 19 Jul 2017 11:17:25 -0700,
Bob F wrote:

Only if you try to maintain the same acceleration level.

At cruising speed, say 60mph, the main component of force is the drag
coefficient, isn't it?

So you need torque at the wheels sufficient to overcome the wind
resistance, even if you maintain a set speed of 60mph.

If the needed torque to maintain that speed of 60mph is 100 Newtons
(plucking a number out of thin air), and your engine has to work harder to
generate a torque of 100 Newtons, then we may not get the fuel economy that
we thought we'd get.

Rest assured that my intuition is the same as your intuition, which is that
we "should" get better fuel economy by gaining an inch on every rotation of
the tires, but intuition isn't always correct.

It would be nice to see a reliable article that backs up our intuition.

Engine and transmission parts will be moving slower, reducing losses.

It will be nice to find a reliable article that backs up our intuition.

"Smaller diameter wheels will make for more concise handling as each
rotation of the wheel covers a shorter distance, meaning more acute
adjustments can be made during cornering compared to a larger diameter
tyre"

Really?? The part of the tire that makes ground contact will hardly
change if the width of the tire stays the same. This statement just does
not make sense. What does the rotation distance of the tire have to do
with anything. The smaller tire putting the center of gravity closer to
the ground would make more difference.

It's a direct quote from the article so I can't argue it better than the
authors did themselves.

On Wednesday, July 19, 2017 at 2:39:02 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 11:17:25 -0700,
Bob F wrote:

Only if you try to maintain the same acceleration level.

At cruising speed, say 60mph, the main component of force is the drag
coefficient, isn't it?

So you need torque at the wheels sufficient to overcome the wind
resistance, even if you maintain a set speed of 60mph.

If the needed torque to maintain that speed of 60mph is 100 Newtons
(plucking a number out of thin air), and your engine has to work harder to
generate a torque of 100 Newtons, then we may not get the fuel economy that
we thought we'd get.


And there is where your physics goes wrong. Torque is not measured
in Newtons, it's in Newton Meters. You're completely neglecting the
distance part. Sure, the engine applies less torque to the wheels
with a smaller diameter tire, but it also has to apply the force
through a longer distance. With a large tire, it's more force
but through a smaller distance around the tire. With a small tire,
it's less force but you have to go more than the one revolution you
did with the large tire to move the car the same distance. The
*energy"* is the same.

Now there could be other difference between those tires that affect
the rolling resistance, etc, but the basic torque physics are as
above.

What you're arguing is like saying that the energy required to move
a bicycle up a hill is different, that you can do it with less
energy input, based on the gear ratio. There is no free lunch.

On 7/19/2017 11:38 AM, Mad Roger wrote:
On Wed, 19 Jul 2017 11:17:25 -0700,
Bob F wrote:

Only if you try to maintain the same acceleration level.

At cruising speed, say 60mph, the main component of force is the drag
coefficient, isn't it?

So you need torque at the wheels sufficient to overcome the wind
resistance, even if you maintain a set speed of 60mph.

If the needed torque to maintain that speed of 60mph is 100 Newtons
(plucking a number out of thin air), and your engine has to work harder to
generate a torque of 100 Newtons, then we may not get the fuel economy that
we thought we'd get.

Rest assured that my intuition is the same as your intuition, which is that
we "should" get better fuel economy by gaining an inch on every rotation of
the tires, but intuition isn't always correct.

It would be nice to see a reliable article that backs up our intuition.

Engine and transmission parts will be moving slower, reducing losses.

It will be nice to find a reliable article that backs up our intuition.

"Smaller diameter wheels will make for more concise handling as each
rotation of the wheel covers a shorter distance, meaning more acute
adjustments can be made during cornering compared to a larger diameter
tyre"

Really?? The part of the tire that makes ground contact will hardly
change if the width of the tire stays the same. This statement just does
not make sense. What does the rotation distance of the tire have to do
with anything. The smaller tire putting the center of gravity closer to
the ground would make more difference.

It's a direct quote from the article so I can't argue it better than the
authors did themselves.

But you state it as fact. Use a little common sense. That article is
written by an idiot.

On Wed, 19 Jul 2017 11:58:50 -0700 (PDT),
trader_4 wrote:

What you're arguing is like saying that the energy required to move
a bicycle up a hill is different, that you can do it with less
energy input, based on the gear ratio. There is no free lunch.

We both agree that our intuition tells us that the larger diameter results
in better gas mileage.

Yet neither one of us can find a reliable reference that backs up that
claim.

Here's an article on "Tire Size Vs. Gas Mileage"
https://itstillruns.com/tire-size-vs...e-5587784.html

"The most popular notion about how tire size affects fuel economy is that a
tire with a larger diameter will cover more ground per revolution, thus
reducing overall gearing and causing the engine to run at lower revolutions
per minute (RPM). Some assume lower RPM equates with less fuel used to
travel the same distance. Though this idea does have its merits and is true
in some cases, the effect is hardly universal and varies greatly depending
upon the vehicle and the increase or decrease in diameter."

That article concludes the same thing that the Cooper Tire article did,
which is "The only vehicles which stand to benefit from a larger diameter
tire are those produce more torque than they need to in order to maintain
speed."

Both articles mentioned that wider & taller tires reduce fuel economy but
let's keep the wider and taller part out of this discussion because it's
already too complex with just the one change in diameter since most of us
are running on pure intuition.

On Wed, 19 Jul 2017 12:03:58 -0700,
Bob F wrote:

But you state it as fact. Use a little common sense. That article is
written by an idiot.

It seems that Ed Pawlowski, Frank, and I are the only ones who are trying
to quote from real articles.

Here's a quote from the LA Times on the subject which backs up the Cooper
Tire assertion that there are too many variables involved but in most
instances of larger tires, you lose fuel economy.
http://www.latimes.com/business/la-f...y03-story.html

"all else being equal, bigger rims and wider tires are heavier, are less
aerodynamic and create more rolling resistance."

But notice they talk about wider tires, which I was trying to keep out of
the equation.

They do say that every tire in and of itself has a different fuel economy,
which backs up what Cooper Tire said, which is that most cars won't get
better gas mileage mainly because of the complexities involved (including
the torque curve and resistance of each tire itself).
"Others who upgrade to oversize rims and low-profile tires -- which are
known to increase fuel consumption -- may not realize what a price they're
paying".

On Wednesday, July 19, 2017 at 3:43:51 PM UTC-4, Mad Roger wrote:
On Wed, 19 Jul 2017 12:03:58 -0700,
Bob F wrote:

But you state it as fact. Use a little common sense. That article is
written by an idiot.

It seems that Ed Pawlowski, Frank, and I are the only ones who are trying
to quote from real articles.

Here's a quote from the LA Times on the subject which backs up the Cooper
Tire assertion that there are too many variables involved but in most
instances of larger tires, you lose fuel economy.
http://www.latimes.com/business/la-f...y03-story.html

"all else being equal, bigger rims and wider tires are heavier, are less
aerodynamic and create more rolling resistance."

But notice they talk about wider tires, which I was trying to keep out of
the equation.

They do say that every tire in and of itself has a different fuel economy,
which backs up what Cooper Tire said, which is that most cars won't get
better gas mileage mainly because of the complexities involved (including
the torque curve and resistance of each tire itself).
"Others who upgrade to oversize rims and low-profile tires -- which are
known to increase fuel consumption -- may not realize what a price they're
paying".

You really think a reporter at the LA Times is an authority on tires
and their effect on fuel economy?

On Wed, 19 Jul 2017 13:27:10 -0700 (PDT),
trader_4 wrote:

You really think a reporter at the LA Times is an authority on tires
and their effect on fuel economy?

Shooting down one reference that says what the others said (particularly
the tire manufacturers' article and consumer reports and the cartalk guys),
doesn't shoot down them all.

I referenced in this thread all the reasonably reliable articles I can
find.

Every one said essentially the same thing.

If you want to say the opposite of what the quoted references said, that's
fine - all you need to do is find a reliable reference that supports the
alternative view that you intimate is "more better".