obieredjk

New to the forum, not to jeeps... hello all, I recently bought 2 new bfg ko2's 35x12.50, I was planning in buying the next 2 in a months time. I have 2 315/70/R17 bfg ko's sitting in my garage, I see the tires and I'm really tempted to put them on but I am afraid to have problems in my JK, will running 2 used (20-25%) in front and the new ko2's in rear cause any problems? I ask because I put them side by side and the ko's look to be about 1/2"-1" smaller than the ko2's. thank you all in advance!!

Albino Lizard

I rotated in a spare that was 3/4" larger and have had no issues. (Same size just no wear). I'm not the authority, this is just my experience.

gordhunt

As long as you don't use 4x4 you will be fine but if you do then you have a good chance of breaking something due to the fact that the front & rear won't be turning at the same speed

obieredjk

That is what I am afraid of, I haven't wheeled much lately but I am planning in more often. I guess is back to putting pennies in the piggy bank till I get all new same size tires. Will this apply with used same size tires?

obieredjk

Even while in 4x4? Im just afraid to damage anything over something so small

jedg

From what I can tell, these would be within 3/4" of each other in diameter. But that's only superficial. If you're worried about what it'll do to traction control and such, you set the tire pressures accordingly so that you have the same effective diameter. Measure from the center of the wheel to the ground and then double that. That's what the wheel speed sensor is really seeing for wheel diameter, not whatever the label on the tire says. SO, maybe you have one tire pressure for the 315's and another tire pressure for the 35s so that they both end up with the same effective diameter.

obieredjk

I am very curious about this, this morning I stopped at a discount tire store and was told that I needed to replace all 4 tires at the same time to avoid problems, another tech told me I could run the 2 new tires in rear and the 20-25% used tires in front (assuming that all tires are 35x12.50) That I would def have problems if I engaged 4wd with the 35s and 315.

Albino Lizard

I have run several trails this summer with the one odd tire. Locked both axles. No problems.

I have a solution to the front rear axle size issue. Run one front and one rear on the opposite corners. An open diff will allow for slippage to occur and not create a situation where one complete axle has a different rotating radius.

My disclaimer-I believe this info should be used for temporary solutions like getting home. It probably isn't best to run two tires of one size and two of another unless you really must. My situation is with a spare that is the exact same size as the other tires, just has much less wear.

jedg

eh... I'm skeptical of that. If the distance from the center of the wheel (hence the axis where the axle shaft is) is the same, it wouldn't matter.

someone else chime in if I'm wrong.

EDIT - 3/4" divided by 2 would be 3/8" inch... not sure how much tire pressure difference that would be, could mean that you run around with one set under inflated and one set over inflated... that could cause problems with the tires...

Albino Lizard

I believe circumference will hurt you on your theory. Running a tire low will not change the distance of rubber required for a single revolution. That is why I suggested the tires be on different axles. An open carrier will easily handle the variation without causing problems.