Will I lose much performance going to 31 inch tires?

YooperSkipper

Member
Joined
Jan 31, 2018
Messages
55
Location
Michigan, United States
I am currently running 30x9.5R15's on 8" factory rims on my 02' Sport that are about worn out. I am thinking about up sizing to 31x10.5R15's. My use is primarily a daily driver with some mild weekend off-roading. My dilemma is.....I don't want to loose much, if any, performance in terms of acceleration, ride, etc. I live in the UP of Michigan and have to deal with quite a bit of snow in the winter as well. I don't want an aggressive mud tire either and all terrain or all weather would seem my best choice. Any feedback from those who have faced this same situation would be greatly appreciated....thanks!
 
Are you looking for a good quality tire or a good cheap tire? There is a difference.

Also if you can wait it out until black friday, I can almost promise you a tire site will have buy 3 get the 4th free or a deal very similar, that is what I am doing...
 
Are you looking for a good quality tire or a good cheap tire? There is a difference.

Also if you can wait it out until black friday, I can almost promise you a tire site will have buy 3 get the 4th free or a deal very similar, that is what I am doing...

I hear ya regarding good vs cheap! I am more concerned about going to 31's as opposed to staying with 30's?
 
I hear ya regarding good vs cheap! I am more concerned about going to 31's as opposed to staying with 30's?
Assume you are running 3.73s if it is a Sport with Dana 44 rear. If so there will not be a noticeable difference running 31' tires. I have an X with 3.07s running 31s it ain't great but it will get the job done until I can spend the $ to regear.
 
I can relate to the UP, born and raised there! I have had my 2000 Sport since new, Dana 30/Dana 35 with 3.73 gears, 4L/5 speed. It came with the 30X9.50. I ran a set of 32X11.50-15 BF Goodrich All-Terrain TA’s on stock rims for well over 100,000 miles. I did have install a 2” lift though. I replaced them with 31-10.50-15 Firestone Destination A/T’s and they perform fine on the road and in the snow (still come up to the UP for deer season and flat tow it). You didn’t mention what transmission you had.
 
Do you have any added lift?

They say 31s will fit a stock suspension but it might be snug. If you got some BFG KO2s you would not regret it. They're great tires and mildly aggressive looking. I think if you would probably do fine with 30" KO2s but if you know for sure you want 31s to also go for a small BB too. 30s can look good if the tire is is AT or MT in my opinion. I Have a 2" BB and 31 KO2s and I love them. I ran them with stock rims and they rubbed at full turn but really only when parking.
 
Going from 30" to 31" won't be noticeable. However, you should still be sure you have the proper gear ratio for maximum performance.
 
I can relate to the UP, born and raised there! I have had my 2000 Sport since new, Dana 30/Dana 35 with 3.73 gears, 4L/5 speed. It came with the 30X9.50. I ran a set of 32X11.50-15 BF Goodrich All-Terrain TA’s on stock rims for well over 100,000 miles. I did have install a 2” lift though. I replaced them with 31-10.50-15 Firestone Destination A/T’s and they perform fine on the road and in the snow (still come up to the UP for deer season and flat tow it). You didn’t mention what transmission you had.

My Sport came with the 30" wheel option as well. It also has the 5 speed manual and the Dana 44 rear w/ 3.73 gearing. My Sport appears to be lifted. I'll have to do some measuring to verify just in case....I've been told I could run the 31's without any lift though?
 
Do you have any added lift?

They say 31s will fit a stock suspension but it might be snug. If you got some BFG KO2s you would not regret it. They're great tires and mildly aggressive looking. I think if you would probably do fine with 30" KO2s but if you know for sure you want 31s to also go for a small BB too. 30s can look good if the tire is is AT or MT in my opinion. I Have a 2" BB and 31 KO2s and I love them. I ran them with stock rims and they rubbed at full turn but really only when parking.

Not sure about any lift....it appears there is some just by looking. Will have to measure to verify?
 
Last edited:
If you measure the springs, the stock front is 12” and the rear is 8” I believe. Anything more than that would be added lift.
I’ve got a 2” budget boost spacer and 31” tires on mine. I’ll take a photo of the spacer and spring and post it if it’ll help.
I’ve got a 4 cylinder 2.4l and a 6 speed manual. It does perfectly fine around town and even on the highway. I don’t use 6th gear much though. If I’m driving uphill it can be sluggish but nothing too crazy really.

13CB6514-F517-4315-B027-D22B6E1822C4.jpeg
 
  • Like
Reactions: DrDmoney
I am currently running 30x9.5R15's on 8" factory rims on my 02' Sport that are about worn out. I am thinking about up sizing to 31x10.5R15's. My use is primarily a daily driver with some mild weekend off-roading. My dilemma is.....I don't want to loose much, if any, performance in terms of acceleration, ride, etc. I live in the UP of Michigan and have to deal with quite a bit of snow in the winter as well. I don't want an aggressive mud tire either and all terrain or all weather would seem my best choice. Any feedback from those who have faced this same situation would be greatly appreciated....thanks!

I'm running 31's on 16's, no lift, no issues, fills the wheel wells with a really nice look & stance !
Changes everything !!!


1572904908450.png

1572905009366.png
 
Last edited:
I've always thought about it like this...
a 30" tires is about 95% the diameter of a 31" tire, so expect about a 5% mechanical advantage taken away from your drivetrain. It is not much, and probably not noticeable.
Then there is the weight. A 30" BFG KO2 weighs 39#, and 31" BFG KO2 weights 44#. An increase of about 12%. This is another 12% rotational mass per wheel. It's still not much, but add the two together and you might get a 5-10% total loss of performance.
You might be able to perceive that, but unless you frequently push the limits of your jeep, such as run it to redline on a long mountain climb, you would likely never notice. At the pump, you will probably lose less than 1 mpg.

I know it's not that simple, its just the way I try to simplify and explain it to people
 
hey man, i've been running 31's and 3.73's for a few years and its not bad all around.
My current tire choice which is by far the best i've tried yet are the Cooper ATP's