What is the difference between a 35/12.5/18 and a 325/65/18. If my math is correct they both appear to be 35". So why would you go with one over the other. I read somewhere that the 35's are 8 ply and the 325/65 are 10 ply. All things being equal, which is better?

 

While diameter might be relatively the same and width is likely within a quarter inch, there could be large differences in the amount of weight they will support. Bigger or more weight isn't always better, and you can create some issues with having a tire designed for heavier service than your vehicle. Ideally you probably want a tire with a service description of between 115 and 125. Not that you can't make a heavier or lighter tire work, but one will give you sidewall sway and the other will give you a harsher ride.

As for ply ratings they don't mean anything these days. They are leftover from the bias ply days and todays tires may just have a couple with varying strengths and rigidity. Again, they aren't going to tell the whole story.

So with the little bit of data available, I'll assume the 35x12.5x18 is the right direction. The 325/65/18 would seemingly be a heavier service tire and likely beyond the needs of your JK. If you have a really heavy JK, bumpers, armor, winch and a regular larger payload you might want to go the other way, but we're talking about a seriously heavy rig.

I hope that helps.

 

After I posted this I started noticing the weight differences between the two. For gas consumption reasons I'd rather go with a lighter tire. I'm surprised however that the 35"s are the lighter tire. I would have thought the opposite would have been true. I also noticed the speed ratings are generally different. 325's are about 110mph whereas the 35's are only 100.

I will be changing the bumpers and adding a winch. Other than that, I'm not going to have much additional weight.

Thanks for explaning the difference!

 

You're welcome!

Again, really look at the Service Description. Going with the lighter tire is likely the right decision unless the SD# is under 115. Not something I thought about much until I got stung with my Goodyear MTR I purchased being too light of a tire for my JK. Unfortunately I could have got roughly the same size tire with a more appropriate Service Description which would have led to my JK handling better.

 

Is there anything wrong with going with a very high load rating? Is there an optimal load rating if you are trying to target handling?

 

I didn't have problems with my Toyos with a Service Description of 125 I believe. They were the outer bounds of sidewall strength for my JK which is similar to your ambitions. Ideally, I would like to be in the upper hundred teens, but could make anything work from 115-125.

If you get too high of a service description you can't let enough air out for on road performance. The contact patch starts deflecting, tire wear is is compromised and you can start scalloping the outer tread blocks. That can lead to otheer issues along with the need for more frequent rotations and a rough ride. Just want to avoid that if possible, although doesn't make much of a difference off road.

 

Awesome info man thanks!!

 

JPop, I have a question for you. I am switching from heavy 33s 12.5 17 (DC Mud Countrys 64lbs) to MTZs 35 12.5 17 (68lbs), should I expect minimal difference in the way my rig drives/handles mpg and pick-up? Or am I in for a big change that I may be over looking? I will be running the 35s with auto and 3.73 gears.
Thx

 

Take a look at the Service Description. If I have the right tire, LT315/70R17 (35x12.5x17), they have a Service Description of 121 which would be right in your wheelhouse for an appropriate tire. Your inflation rate will probably end up being in the high 20s for appropriate wear and will have enough inflation so the tire can perform as designed.

 

Thx for the quick response, that is the correct SD of 121. I plan to run them at 28psi and rotate every 2500miles, hopefully getting 45k on these. My Mud Countrys were rock hard and really heavy for a 33 ( i did like them alot but the 35 MC weighed in at 80lbs!) figured I give the MTZs a try. The only thing Im not really fond of it they run a little thin for width and small for height as the Mud Countrys were more true with the height/width. (which is prob the reason they weighed as much as 35s). Lol