backspacing/gear ratio needed?

[mpslaney]

I'm thinking of getting a set of 33x12.5 dayton timberline mt tires with a new set of 15x8 rims and was wondering if i will need a wheel spacer if to what size. Also will i have to change the gear ratio for a tire this size?
98 jeep tj with 4" lift

[jps4jeep]

no and no

If your getting new wheels, just buy ones with the proper backspacing, IMHO, spacers should be avoided when ever possible.

4" of back spacing or less will be fine. I ran 4.5" backspacing for years, similar set up, but on a YJ and rubber on the leafs at full lock.

As for gearing, while it won't be Ideal, you can keep your stock gearing. If you do change your gears, I am a firm believer in Going as deep as you can.

For example, with a 4.0 5 speed and 33's on stock 30/35 combo, I would put in 4.10's for a Daily driver (look to swap stock 4cyl axles) and at least 4.88's for a trail rig.

[Bounty__Hunter]

Do you have a 4cyl or 6cyl engine?

Regearing is recommended but not always necrssary.

[mpslaney]

it's a 4 banger

[jps4jeep]

it's definatly doable, but a regear would be ideal. another thing to think about is, you have a 4.10 or 4.11 gear set stock,95-98 Ford 8.8's with LSD diffs and 4.10 gears can be found dirt cheap and could be swapped in simply by cutting off the stock bracketry and welding it onto the 8.8 this would be a great upgrade from the D35 you currently have

[mpslaney]

well in that case i'm going to stick them on like it is now and that'll be something to look at in the near future.

[David]

Here's a link to a gear calculator which I found on the web: Gear Calculator.

It can tell you where (approximately) you'll need to re-gear to with a change in tire sizes.

[Bounty__Hunter]

If it's a 4banger 5spd, you already have 4.10 gears. Lowest you can go on stock axles is 4.88 and would really help move the 33" tires. Consider the 33"x10.5" to help out the 2.5L engine.