Donnymac

Does the 7 speed transmission in a 222 need to know wheel diameter to work correctly?

if so, is that info supplied by a sensor or manually programmed?

i want to go from 20RF to 19Sports.

Thanks.

obwielnls

it doesn't.. As long as all four tires have the same diameter you should be good. .

Donnymac

I'll measure the OEM staggard set diameter manana. Wheels are the same diameter but are staggered tires?

Mitch Alsup

Tires are designated in such a way that one can determine the rolling radius (or diameter) and lots of other useful data.........
[Width]-[aspect]/{rim}<letter>R means
Width of the tire footprint on the road in millimeters
Aspect ratio between width and height of time on rim
rim is the diameter of the rim in inches
R is for radial.

So 275/40-19 will have a rolling diameter of:: 2*(275*0.40)/25.4 + 19 = 27.66 inches
A 275/40-20 will have a rolling diameter of:: 2*(275*.4)/25.4 + 20 = 28.66 inches

Given that tires wear over their lifetimes, the car should put up with any tire with a rolling diameter between 27" and 29"

Donnymac

I never thought about calculating rolling diameter.

Excellent point! Bullseye!

Thanks.

Donnymac

2x post sorry.

seamus2154

Go on tirerack.com and look at the specs on any tire being considered. It will tell you the revs per mile. I am in the same boat going to non run flats HATING these runcraps. I am considering only Michelins. In the stock 20" size the fronts are 27.7 inches in diameter and rears 27.6 with 750/755 revs per mile respectively. In 19" stock sizes they are 27.7 in diameter and 751 revs per mile. So there will be no consequences going to 19" rims as long as you buy the correct size sidewall as not to effect the revs per mile. The revs is what the car calculates for abs, active handling and speedometer.

Donnymac

I am running the same exercise and building a spreadsheet comparing 20/19/18. PM me your email and I'll send you a copy if you want one maņana.

I too am a Michelin fan but the Continentals seem to have a big MB following also. I have zero Continental experience.