Changing Tire Size

bradpell8 · August 10, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

redvett · August 10, 2007

Unless you correct for tire size engine performance,fuel economy, transmission shifting,ABS & SDM will be compromised along with speedo/ODO being incorrect.

There are several tire calculators on the web just do a search.

bradpell8 · August 10, 2007

What could i do to correct the speedo and other issues

Puggy · August 10, 2007

Here is a nifty tire size calculator. Just plug in the original tire size and the one you want to change to and it will tell you all you need to know.

kdogg · August 10, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

If you change from 265/70R-17 to 285/70R-17 it only changes the width. The radius is the same and does not effect the speedometer, but does effect mileage, brakes, power, and handling(for the better).

kdogg · August 10, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

If you change from 265/70R-17 to 285/70R-17 it only changes the width. The radius is the same and does not effect the speedometer, but does effect mileage, brakes, power, and handling(for the better).

I take that back, it does change to 2.3 miles an hour more thn speedo shows at 60 mph. You can get an adapter at the dealer.

redvett · August 10, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

If you change from 265/70R-17 to 285/70R-17 it only changes the width. The radius is the same and does not effect the speedometer, but does effect mileage, brakes, power, and handling(for the better).

I take that back, it does change to 2.3 miles an hour more thn speedo shows at 60 mph. You can get an adapter at the dealer.

There is no adapter since the speedo is electronic since 1988. Its all done by the PCM on the GMT800 & 900's.

hotwheels57 · August 10, 2007

A tuner could change that % discrepancy possibly...

svensk · August 10, 2007

You would have to do a 285/65/17 to keep the speedo right and that might be a tougher tire to find.

Paul58 · August 10, 2007

If you don't want to mess with the engine tuning there is always the SuperChips Tire Paq:

Tire Paq

It's supposed to correct the speedometer, odometer and shift point.

callmekurt · August 11, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

If you change from 265/70R-17 to 285/70R-17 it only changes the width. The radius is the same and does not effect the speedometer, but does effect mileage, brakes, power, and handling(for the better).

Wait, since the width is more (by a factor of 20 mm), wouldn't the diameter change since the wheel diameter and aspect ratio are constant? 33" (285) vs. 31" (265)

I was thinking about doing this change too. And I assume it can be done with a crank or two of the t-bars (on a 4x4). right?

But my question is about doing it on a lease...anyone mod a lease? (I know why mod a lease that you're going to give up in 3 years). Well, I've modded car/truck I've owned (even matchbox as a kid). And 2 years has been my longest ownship of a vehicle (this Sierra is #16). So having it for 3 years is long....<breath> sooo...thoughts about cranking the t-bars and throwing on 285's (I'd keep the stock 265's to throw on when I turn it in).

Thoughts?

callmekurt · August 11, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

If you change from 265/70R-17 to 285/70R-17 it only changes the width. The radius is the same and does not effect the speedometer, but does effect mileage, brakes, power, and handling(for the better).

Wait, since the width is more (by a factor of 20 mm), wouldn't the diameter change since the wheel diameter and aspect ratio are constant? 33" (285) vs. 31" (265)

I was thinking about doing this change too. And I assume it can be done with a crank or two of the t-bars (on a 4x4). right?

But my question is about doing it on a lease...anyone mod a lease? (I know why mod a lease that you're going to give up in 3 years). Well, I've modded car/truck I've owned (even matchbox as a kid). And 2 years has been my longest ownship of a vehicle (this Sierra is #16). So having it for 3 years is long....<breath> sooo...thoughts about cranking the t-bars and throwing on 285's (I'd keep the stock 265's to throw on when I turn it in).

Thoughts?

Also, can I use stock rims or will I need different backspacing?

BigJayDogg3 · August 11, 2007

I was told for my 245/75/16s I could keep the stock wheel when I asked about 285/75/16. I was told to just monitor tire pressure, because from what I can understand there will be a bulge at the sides, so you have to compensate. Good luck on your purchase!

By the way, for my size wheels, I was told the tire manufacturers suggest a wider wheel, but a friend of mine is running 285s on a stock wheel, so with me looking into only 265s it shouldn't be a problem.

svensk · August 11, 2007

I was told for my 245/75/16s I could keep the stock wheel when I asked about 285/75/16. I was told to just monitor tire pressure, because from what I can understand there will be a bulge at the sides, so you have to compensate. Good luck on your purchase!

By the way, for my size wheels, I was told the tire manufacturers suggest a wider wheel, but a friend of mine is running 285s on a stock wheel, so with me looking into only 265s it shouldn't be a problem.

Yeah just watch for cupping. Keep your pressure up.

zozmanGMC · August 11, 2007

I was wondering what i would have to do if i went from 265/17 to lt 285/70r-17. How off would my speedo be. And also would this be cause to void warranty. I have extended till 5/75.

The non-stock tire is 3.5% too slow. When your speedometer shows 60 mph, the actual speed is 62.1 mph. Changing your tire size does not void your warranty.

zoz