hey just want to ask about tires. when you guys put these bigger tires on, how does it perform with the stock gears??. would the tires not be to much for the motor? 

31's are all my 4dr. wants with stock gearing.

Right now in riding on 225/75R16's (29.4") with a turbo exhaust , cone air filter and stock gears.  Personally I wouldn't go much bigger with a four banger without switching to higher gears... it takes a bit of skill to judge when to correctly pull out in front of traffic with 29ers.. but with no one riding my ass I can happily cruise up to 75-80mph!
That is my 2 cents! 

I agree with what they are saying. I went from 225/75/16 (29.5")to 215/85/16 (30.5") and it was a noticable difference, especially in the wind here in WY.

Here's how I see it:

My sidekick 1.6 16valve with 95 horsepower and 0 lb-ft of low-end torque is barely adequate with 31's and stock gears.

My Vitara 2.0 with 127 hp and 134 lb-ft of lower-end torque is fairly decent. I think with 31's and 5.13 gears out of a Sidekick you could run 31's with EASE, and 33's if you want to really push those hamsterpower out of the 2.0L. The 33's are probably a bit much for the stock front diff though so make sure when you do your gearing swap you get a steel one from a GV or XL7.

i run 31x9.5 swampers on my 2003 2.0L 2dr, no problems around town but can be sluggish into strong winds and up big hills.  gearing is stock at 4.62.  the tires are getting really worn and i plan to put 32inch swampers on it next season and am not worried about gearing/power.  it's a tracker, it's never gonna be quick anyway!  however i do plan on changing the gearing at some point in the future but a big part of my reasoning for that is to install a locker in the rear 3rd because it there are none that are confirmed to work with my 2003 model year.  i run skinny tires to save weight; rotational mass will affect power, so if you go wider you are going heavier..