Installing smaller rims and smaller sidewall tire on driving wheels (FWD) effectively lowers the final drive ratio as well as introducing speedometer error if speed sensor is based upon transmission and stock rim and stock tire size.

Other side benefits of smaller wheels/tires and lower final drive ratios - lower E.T.s

Anyone tried this?

 

Yes it works in theory. Some have huge benefits from going from factory 17s and 18s to like a lightweight 16, traction becomes an issue though.

 

not only that but you lose out on higher top speed.... just like if you went bigger tires bigger wheels bigger sidewall= lower accel, yet faster high speed... simple physics

 

As long as you don't get more wheel spin off the line. Just a nice chirp can slow you by 2 tenths.....then again, the auto does need lower gears!

Actually this is not always the case....horsepower determines top speed not RPM. Before you think I'm just argueing with you consider this:

I had a Buick that would top out at 110 @ 4500 RPM with 2.78:1 gears. I installed a set of 3.42:1 gears and calculated that I would only do around 90 MPH at 4500 RPM. Makes sense right? Well, when I took the car out it did 110 MPH but the RPMs were now 5400! The engine had a flat horspower curve that went from 4500 to 5400 RPM so the car still would do 110 MPH because it still had the HP to do it. Slightly smaller tires will probably not have as much effect on top speed, but, then again for the dragstrip top speed isn't as important as getting to the finish line faster.

 

Unless you change the speedometer "gear", the speedometer will still show the same speed reading while the actual speed is lower with lower gears/smaller tires or higher speed with higher gears / larger tires....

A measured mile should take exactly 60 seconds at 60 MPH... if its more or less, your speedometer is OFF!

 

there's a reason why slicks are so small :

when i said i wanted to ditch my 18's for 16's or 17's people said i was an idiot. but less rotational mass, less weight (if you do it right) will help.