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.