Quote:
Originally Posted by travislambert
Your example is backwards, but your point is valid. (When you increase the circumference of your tire, the speedometer reads slower than your actual speed.)
Here's another good calculator:
https://tiresize.com/comparison/
An example of particular interest to me:
ZL1 front: 285/30ZR20 Goodyear Eagle F1 Supercar 3
ZL1 rear: 305/30ZR20 Goodyear Eagle F1 Supercar 3
ZL1 1LE front: 305/30R19 Goodyear Eagle F1 Supercar 3R
ZL1 1LE rear: 325/30R19 Goodyear Eagle F1 Supercar 3R
There is about -2% difference between the ZL1 and ZL1 1LE tire sizes. So not only will the speedometer be off, for every 1,000 miles there's going to be an extra 20 miles on the odometer due to the error. It's not a lot, but I think it's enough to annoy me.
Also, the ratio front to rear is changed ever so slightly.
Zl1 Front vs Rear: 1.85529% difference
Zl1 1LE Front vs Rear: 1.89036% difference
Most likely it isn't going to make a lot of difference, but I'm still interested in knowing exactly what might be impacted. |
Changes to the circumference of the drive wheels can definitely affect mileage on the odometer. Since warranty is based on odometer readings, it would seem prudent to have a means of re-calibrating the speedometer/odometer. This would prevent extending or shortening the warranty and may also prevent owners from getting speeding tickets in strict enforcement areas.
As for your question on potential effect of tire size on automated systems, I can attest that neither my 27.8" tall Mickey Thompsons (345/35R18 ET Street S/S) nor the 25.9" Hoosiers (335/30R18 DR2 D.O.T. Slick) have triggered any warnings or intervention from Performance Traction Management, ABS, Stabilitrak, or any other systems.
When I first starting looking for replacement DRs I too was worried about intervention, having heard stories implying that some of our automated systems might complain and interfere. After comparing front to rear size difference between stock, MT's, and Hoosiers; and doing simple calculations and other research, I felt the risk was minimal. I was relieved after my road test when
there were no negative effects whatsoever.
You can read about my initial search in "
Help selecting replacement DRs" and my final selection and testing in "
Hoosier DOT Slicks vs MT ET Street SS".
Individual posts from these threads with details and test results:
Rear wheel diameter comparison of stock to previous and prospective DRs
Wheel diameter front-to-rear comparison of stock to previous and prospective DRs
New Hoosiers Mounted, Balanced, Installed, and Tested
--Cal