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Tire replacement

i have 245/70-16 tires on a 2004 gmc c1500 sierra and would like to install 235/75-16 tires. will this cause great harm in the overall performance of the truck?

You will not even notice the difference…The diameter is probably almost identical…

Your first step ought to be to look for the vehicle tire placard - which on GMC trucks is located on the driver’s door or doorpost. That will tell you the original tire size and the proper pressure for that size.

You are looking at a narrower and taller tire as the replacement. If they fit on the wheels OK, and I think they will, then you should be fine. You can expect your speedometer to have some error in the reading vs actual speed. This is easy to check with a GPS unit. Otherwise the narrower tire might have a bit less grip, but I’d bet hardly noticeable. In snow the new tires might do better, but tread design is a big part of snow traction so you’ll just have to see how they do when the snow flies.

I agree…there is Powerdog.com to check the overall diameter of the two. I go from 265/65-17 to 265/70-16 in the winter. Though not a direct comparison to yours, like Caddyman said, the differences are insignificant if the ratios and treadwidth result in the same outside diameter; which yours look like they do.

245/70-16 6.8" 14.8" 29.5" 92.7" 684/mi 60MPH 10000mi N/A
235/75-16 6.9" 14.9" 29.9" 93.9" 675/mi 59MPH 9875mi 1.3%

As you can see…the difference is .1 inches radius, and less than 1.3 % circumferance rolling distance …don’t worry as long as all are matched.