This is a rough guide on how much lift you will need to fit relative to original clearance. There are of course exceptions, but this guide should maximise your articulation.
Radius of original tire package:
carcass width/percent sidewall/rim size
take the carcass width, multiply by sidewall percent, divide by two, convert quantity to inches, and
add to rim size divided by two.
Here's a working example:
185(.70) = 129.5mm
This is how much of the tire is sidewall, because the sidewall exists on both sides, divide by two.
(129.5)/2 = 64.75mm
This is how much your sidewall lifts the rim above the ground, also how much your tire projects above the rim, under the fenderwell.
Convert this quantity to inches:
(64.75mm)/(25.4(mm/in)) = 2.55 inches
Add this quantity to the rim diameter divided by two
13/2 = 6.5in
Total projection of tire and wheel package above axle towards fender is:
**This is the initial value**
Do the same calculations for the larger tire you would like to equip, and take the difference (new package vs. stock package).
This will tell you how much more radius the new package takes up. You will need to lift your chassis by this much to retain the stock suspension articulation.
Edited by Mantis_Toboggan, 12 June 2010 - 01:49 AM.