My mother has an 07 Tahoe with Stock 17 wheels and 265/75R17 Tires. My father recently found a good price on a set of the OEM 20 inch wheels. He wants to know if the dealer needs to reprogram the speedometer to account for the difference in size. I use this calculator here. http://www.miata.net/garage/tirecalc.html and it shows that the stocks are a little taller than the 20s with 275/55R20. The stock size is 32.6 inches tall and the 20s are 31.9. So we're talking 7 tenths of an inch. It shows that the speedo will read 2.3% too fast. A difference this minor shouldn't have an affect on the transmission or anything should it? I told him I think it'll be alright without the programming.
Upgraded 17 stock wheels to OEM 20s.
- Thread starter trnsfmr
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
73shark
Full Access Member
It will run your odometer faster also which, if still in warranty, means it'll expire quicker. Also the 20" package is heavier which I read somewhere has an effect on the ABS.
When I replaced mt stock 17 wiht the stock size 20 I put the two side by side and they were exactly the same size. In that case there is no need to reprogram anything. My truck drives exactly the same no abs issues and when I checked against mile markesrs on the road it was dead on
73shark
Full Access Member
So are you saying that the ABS algorithm doesn't take the rotating mass into consideration?
My abs works exactly the same as it did before. Abs uses a sensor at each wheel that reads the bearing on these trucks and the axles on some cars. It dectects how fast they are turning and looks a difference between them. As long as all tires are the same size all the sensors read the same so no issues. No way for them to tell how heavy the wheels are.
73shark
Full Access Member
I just thought that I remembered someone from GM posting that the computer used the wheel/tire weight in its calculations for activating the ABS. Could have misremembered.
Stargazer
Full Access Member
I thought the stock tires were 265/70R17. Well, it is according to Tire Rack. That what I bought for winter tires to replace my 20". There is no noticeable difference in the overall diameter between the two.
While I agree there is no affect of heavier wheels on ABS specifically, more unsprung weight will affect handling and heavy wheels may reduce overall braking performance.
However, that being said, since the 20" rim is an OEM option, I'm sure that GM designed their vehicles to handle it without any problems. It's not like those of us with 20" rims from the factory get larger brakes when we order that option.
So you'll be fine.
You're right Stargazer. I entered the wrong information. They are 70 series instead of 75. With that being said the information from the tire Calculator I posted before is wrong. The new tires and wheels are 31.9" tall while the stock 17s are 31.6" which makes it only .3 tenths of an inch off for a 1% change.
Similar threads
