Just got a completely stock 89 sidekick. Havin to do a few things to get it in good running condition first. Already love taking in out. Bald radials and outdoing my buddies jeeps already. Lookin at puttin tires on asap. How much lift do i need to get 31s under it? And will they fit on the stock rims?

they fit on stock rims. they also fit on a stock truck somewhat. they will rub when turning.

a 2 inch spacer lift helps with the rubbing and either 2 inches of body lift or some trimming will get them to fit better.

i have grand vitara coils under my 2 dr and its 3 inches of lift, im throwing some 31's on next weekend for loaners at my local zuki meet, going to see how they fit with only the suspension lift.

True 31's are about 14% oversize (diameter) and that will affect your overall gearing. 31's are also mostly 10.5" wide, while stock tires are about 8". Tire manufacturers specify the width rim their tires are approved for. Visit:  http://www.yokohamatire.com/customer_service/customizing _width.aspx 
to get an idea. For my tire, the BFG TA/KO, 31's call for a 7-9" rim. Stock rim is only 5.5".  Unless you use rims with reduced backspacing (i.e. negative offset), you may (likely) rub with 31's.  Wider rims are also heavier, so it's not just the added weight of the larger tire. This is a very popular subject.  There's been a lot posted over the years. The needs of a daily driver (DD) differ greatly from the trailer queen. Everyone has an opinion, but not everyone has the same wants and needs as you do. A good tire and wheel info site is at: http://www.rsracing.com/tech-wheel.html

Before you take the leap for 31's, take a look at the 235 size. It should fit a Sidekick without needing a lift, and is almost a match for the stock rim width. And it'll raise your gearing by only half as much (7%).

Idodge- I have an older 3" suspension lift and run with 235's which are right at 29".  I do get a rub on the inside of the stock bumper at full turn or near it when I flex the suspension.  The back side of the sock bumper can be easily ground off to correct it.  I think if I were to do it from the start I would go with a coil spacer lift 1 1/2" then 2" body lift to try and maintain as close as possible front end geometry.  Both of these lifts are fairly cheep and do not need to be done at the same time. Mine is a DD, so road characteristics are important to me.  If it were a weekend toy, then I would look at going a bit more radical.  There is a guy named Jeff on here that build the coil lift at a great price and I believe several people here are satisfied customers.  I however can not speak from experience on that lift, but would take a hard look at it if I were in your shoes.

I run 31 mud terrians on ford 15x8 rims with 3.5 back space.  I trimed the back of the fender, only the inside not the outer skin of the fender and massaged the firewall with a 3lb hammer and hammered the rear lip on the quarters.  I get very very little rub at full flex.  I am running them on a 95 2door 16valve 3speed auto with stock 4.30 gears.  Accelleration is still ok, but you can tell the heavier stuff up at freeways speeds especially going up hill.  Offroad does great and has plenty of power to climb fairly steep long hills in 4 low.  I just leave it in drive while offroading.  I say skip over 235's cause you know you will just want bigger.  Ground clearance is about the only downfall on these little things.  And body lifts do help with tire clearance but it still leaves the frame hanging down....

Guess i should have told everyone im not worried about what it looks like or drives like on the road. Got this thing cheap and just for a toy. Think im gonna cut my fenders this week.