Someone posted how you find the new gear ratio on the rear axel as changing tire size affects it. I went from a 235-55-17 to a 285-40-18.

Thanks

 

there's an excel spreadsheet floating around... rpm vs. speed or something like that...

 

235-55-17 = 27.18" dia

285-40-18 = 26.98" dia.

Pretty close.
At 70 MPH in 5th gear there will only be about a 15 RPM difference.

Your odometer & speedometer will read slightly higher, only 1%.

 

Try this:

http://www.corral.net/tech/gearcalc.html

For example, by using the above link, there is about a 200rpm difference between running a 275/40/17 vs a 275/50/17

 

This is the best calculator I've ever come accross. It can help you make sure the tire heights for front and back are close, if you have a staggered set up.

Plus it calculates just about anyhting else you'd want to know.

http://gs.tolan-hoechst.com/tirecalc.htm

 

maybe I was not clear. someone said that changing your tires/rims affected your rear end gearing like changing your gears, ie more performance? tire change makes the gears from a 3.55 to a 3.73 or so.

 

<div class='quotetop'>QUOTE(traffic142 @ April 14, 2006, 2:58 AM) Quoted post</div><div class='quotemain'>
maybe I was not clear. someone said that changing your tires/rims affected your rear end gearing like changing your gears, ie more performance? tire change makes the gears from a 3.55 to a 3.73 or so.
[/b][/quote]

Thats if you go with a shorter tire, which is easier to spin. Use the website links above to see how different tire sizes effect your rpm at (lets say) 60 mph. But basically, a shorter tire raises your gear ratio (for ex 3.55 to 3.73) and a taller tire reduces it (3.73 to 3.55). Question is, how much? It depends on the difference in tire sizes, in which you can use the links above to see the difference.