Brick

As the 02 uses the larger tire and there is a ~2% change in diameter does the o2 use a different speedometer gear? Can you change something in the 01 to make it more accurate?

I am thinking to change the rears to the 285/30 as I have 10" wheels and the larger tire would fill out the rim nicer. The front looks like the side wall is perpendicular to the ground while the rear with the 265/35 appears that the rim is wider than the tire, thus it sort of slopes. It is the recommended size for a 10" 01 model according the list in Christophorous. But the 02 recommends the larger tire.

It would seem to me 2% is enough of a difference for Porsche to address.

Bill

fahren affair

i have an '00 and switched the rears from 265/35s to 285/30s. i can't tell if there's any significant speedometer error. the car read 3 mph faster, even before the switch. i've also noticed one mfr's 285s are have a diferent rolling diameter than the next. the swing could easily be 2%.

lexpilot

Borrow a friends GPS to get your actual speed versus indicated now. It is possible your speedo reads 70 when you are going an actual 67. Then do your math on the diameter differential. It's possible with the big tires your speedo will read 70 and you will be going 71. Then compensate.

Brick

My 2% figure is based on the called out size of the tires, nothing to do with the manufacturer. I think that the speedometer may very well read fast now and this is another reason I wonder if it can be adjusted. But I don't know if Porsche makes any parts. I guess I'll call a dealer and see what they say.

Bill

Paul Marangoni

I asked at Beverly Hills Porsche service and they told me that they don't make any adjustments to the speedometer for changes in wheel size. I am running 285-30-18 in back too, and as far as I can tell, this not only causes the speedometer to read faster than reality, but the odometer will show higher mileage too (albeit, slightly).

eternal

Call me crazy, but wouldn't a larger tire make your speeder read slower then reality not faster, and wouldn't the mileage be lower not higher??

fahren affair

the rolling dia. of a 285/30 is less than a 265/35. that's why.

chitownbob

I thought I remember someone talkigna bout a software glitch causing the odo to read slightly higher than it should. Is there any truth to this statement????

Bobby

JohnM

Post deleted as probably wrong

Dudley

Just wondering how closely you try to match diameters of front and rear wheel. There is quite a difference between the 285/30/18 at a diameter of 24.7" and 265/35/18 at a diameter of 25.3".

dave

Torags

Doesn't have an effect on the understeer?

Gnome

Dealer told me the speedo reads approx 5 mph fast at speeds above 30 mph or so. He said this was programmed by Porsche on purpose, but does not affect the odometer. I haven't been able to test and find out exactly, but my car seems to read AT LEAST 5 mph fast, if not more.

Anyone have better info?