What's the performance difference between 15 inch, 16 inch and 17 inch tires (all else equal)?
 

On Fri, 21 Jul 2017 16:47:43 -0000 (UTC), Mad Roger
wrote:

On Fri, 21 Jul 2017 08:35:10 -0600,
rbowman wrote:

For starters, I am not talking about a dashboard display provided by the
manufacturer. As I've said repeatedly I use a ScanGauge II plugged into
the OBD II bus. How accurate and repeatable is the ECU? Tach? That would
depend on the smoothing algorithm for the display. Counting the ignition
pulses is a no brainer. Distance? The unit can be calibrated for the
rolling circumference of the tire. Variability on tire temperature and
pressure? Sure. Injector timing? Temperature? How good is the sensor?

I think you're answering a different question than is meaningful to most
people simply because most people don't have a ScanGauge II to plug into
the OBDII port.

Most people have a tripmeter reading and a gas pumpmeter reading.
Where they fill the tank and reset the tripmeter before driving away.

I can't find any reliable source that says what the accuracy or
repeatability of that mom-and-pop tripmeter/pumpmeter calculation, but
basic logic dictates that the errors compound such that there is likely
(IMHO) no way to get anywhere near decimal-point accuracy, and worse,
probably plus or minus 1 mpg is the closest anyone can get in terms of
repeatability and precision.

So, someone's 20 mpg is really somewhere in between 19 mpg and 21 mpg.
For a lot of dufii out there it's closer to between 15 and 19

What's the performance difference between 15 inch, 16 inch and 17inch tires (all else equal)?
 

On 07/21/2017 10:58 AM, Mad Roger wrote:
It is amazing that even a faired motorcycle has the Cd of a semi truck!

They (bikes) are pretty dirty. Over the years trucks have improved. You
still see old school squared off tractors with no roof mounted fairings
but I would guess many of those are O/O's who chose based on what a
'real' truck looks. The fleet operators go for the more efficient models
and watch the fleet averages like a hawk. I've wondered how much affect
the belly panels on dry vans have. I've seen a few attempts to smooth
out the rear of the box too but that adds more work before you can back
into a dock.


The only thing that saves them is a low frontal area.
I would hope full fairings would help.

I assume they do. There are two problems. First is the bling factor
again. Naked and retro bikes are in currently even with the metric
riders. A really effective fairing would also be really awkward. Craig
Vetter has been at it for ages and some of the stuff he inspired is
sci-fi material;

http://craigvetter.com/

That plastic gets pricey too when you drop the bike. For a completely
unscientific comparison, I have two bikes that are only similar in that
they have 650 cc engines. The DR650 is a carbureted single, enduro
styled bike with DOT knobbies and a minimal windshield. The DL650
(V-Strom) is a FI twin with a fairing and street tires. My mileage
calculations make mom and pop look like EPA scientists -- rough division
in my head of an inaccurate odometer by the pump gallons. I did go up a
tooth on the DR's front sprocket to keep the highway rpm down.

Given apples and pomegranates, both can get around 50 mpg. The DR does
it screwing around on dirt roads and reasonable highway speeds and the
Strom tends to do it consistently. The difference is the DR at 80 mph is
down in the low 30's and the Strom is still happily up in the '50s. More
variables than a dog has fleas but the complete lack of aerodynamic
finesse on the one really seems to hurt as the speeds climb.

I
replaced the OEM tank on one bike because a potential 120-150 mile range
wasn't going to make it.
That's a lot more than I ever got on a tankful of fuel, at least in the
olden days.

The Sportster has a 3.2 gallon tank, runs in the 40's and I generally
fuel at 110-120 miles. The stock DR tank was also 3.2 iirc so averaging
out someplace in the 40's would put in a similar range. The aftermarket
tank is 4.9, which gives me some insurance. There is a dirt road that
goes over the divide into Idaho. I would pass the point of no return a
little ways into ID and would have to ride out to civilization in ID to
get back. This way I can screw around put on about 200 miles without
getting nervous. The V-Strom has a 5.8 gallon tank but I generally fuel
a little over 200 miles. It also has a relatively accurate gas gauge
which helps. Of course, there's no petcock to turn to reserve when it
starts to sputter so you damn well better be watching it.

Some of the Sportsters had a 'peanut tank' that was a little over two
gallons. More bling, looked kewl, but I ride a little longer distance
than bar hopping around town. Another gallon is good.