Wheel/Tire Change

I'm thinking about replacing the stock wheel/tire combo on my 2001 Supercharged Suburban, however I don't want the performance to be affected too badly. The car has a supercharger and I know the change will be similar to a lower numberical rear gear, I just don't know how much the change will affect the speedometer and performance. Currently the car has P265 70R16s. I'm thinking of going with P285 50R20s or possibly P305 50R20s. Can anyone tell me how much the tire change will affect the performance (or effective ratio)?

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2001 Suburban - Magnason Supercharged 0-60 in 5.74 secs.

Burk,
The largest tire you can fit under a '01 suburban without a lift is a 295/75/R16, anything above that your tires are going to rub, and you might have to do some minor fender trimmin wtih the 295's. Also, If you are going to go taller you also want to go wider. a 50 means that the tires height is only 50% of it's width. The general rule for getting larger tires is for every inch you go up you want to go out 2 inches. I have a bunch of mathematical solutions to figures out how much your speed, and gear ratios are effected. I'll post it as soon as I find it.

Depending on whether you're looking to go taller overall, that's tire and rim, then you may have to put a lift kit into it. Going this route your speedo and performance will change.

Or you may be looking at changing to a larger rim size but staying with the same tire height of what your tires are now. If you're wanting to keep the truck at the same ride height as it is now, then you're on the right track, lower profile tires, big rims. Staying with the same overall wheel height using larger rims and lower profile, nothing will change with regards to speedo or performance.

Best thing to do is go to your tire / wheel dealer and explain to them what you're after. They can and should set you up with some different combinations to look at until you get the look you're after.