Soooooo. I have confirmed via GPS that honda's 245 rear tire on the ap2 is actually causing the speedo to read about 1.5-2 mph faster than actual speed.

And i found that installing 255 width tires will correct the speedo

This is evident due to the difference in the rolling diameter between your typical 255 and 245. In each case the 255 tire netted a correct speedo reading.



245 re50 vs 255 re50
245 re50 vs 255 kumho
245 re50 vs 255 bgf

I base my results on data collected in my 04 s2k and my 06 s2k both of which resulting in the same difference of 1.5-2mph and a correct speedo reading when running 255 width tires.


of course we all know that Honda did make the mistake on ALL hondas with the milage calculations. But it seems the easy fix is to step up to a 255 series tire in the rear (and maybe match with a 225 in the front)

The 08 CR already has 255 in the rear.

Just thought i would share my finding with you all.

kenneth

 

the mph thing wasn't a "mistake", most OEMs calculate some sort of fudge factor so people think they're going faster than they really are, to slow down for safety.

 

if that was true my GPS would show similar results on other cars as well. But only the S2000 is off by this margin.

 

And to run up higher mileage on the odometer, thus ending the warranty sooner.

 

my 350z was off, as was my accord, my sentra, and of course my motorcycles are all off.

 

my motorcycle's off by like 10% but that's cuz i have a sprocket change :-)

And 1.5-2mph isn't bad at all, most cars do have some variance to the real speed.

 

glad i just upgraded the rears! never even look @ my speed on gps. thanx

~tina~

 

ive done the same with TWO GPS units at once and even with 255/40's the speedo is still too high.

 

255, 245, 240 without any other info doesn't really mean anything.

What was the hight of the tire?
Wheel diameter?

IOW circumference.

Or even more precise: revs per mile per manufacturer's spec.
I don't know for sure but that's most likely determined with weight on the wheel&tire.

 

different companies make different size 255 series anyway. it's like buying shoes a 10 in Nike isn't a 10 in Reeboks, they put the tire they felt made the car handle the best on there.. no speedo is perfect either, not until they make car speedos GPS controlled anyway. that would actually be pretty sweet.