Optimal tire size for 2.5 4 cylinder?

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Kenkolen

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I just picked up a 2001 TJ with a 2.5L motor. It has 31" off road tires, I do not have the exact size handy.
I believe the tires are robbing power, not like there is much to start with.
My use is to pull behind my motorhome mostly. I doubt I will go mudding.
Would changing to a set of change out Michelin Tires on 2018 rims 255/75 17 make any sense?
 
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The 255/75 17 is a ~32" tall tire, so that would be a step in the wrong direction if you don't want rob away more power. Running 30" tires would make it feel peppier.
 
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mots said:
The 255/75 17 is a ~32" tall tire, so that would be a step in the wrong direction if you don't want rob away more power. Running 30" tires would make it feel peppier.
Click to expand...
Correct about the 32" height, I did notice that.
So 30" would make a noticeable difference?
 
With the 2.5, tire size and weight make all the difference in the world with stock gearing. The SE came with
205/75 R15 (27.1')
215/75 R15 (27.7')
225/75 R15 (28.3')
all in a standard load rating 4 ply passenger rated tire.
 
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The optimal size for a 2.5 is no bigger than 31” IMHO.

Make sure you have the proper gearing as well, as life will suck otherwise.
 
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Chris said:
The optimal size for a 2.5 is no bigger than 31” IMHO.

Make sure you have the proper gearing as well, as life will suck otherwise.
Click to expand...
Thank you, not knowing how it ran originally it is hard to say how much worse the 31" rides. I did find out that the spedometer is probably way off so i may be going faster than the speedometer is indicating. I will try using my gps to determine a more accurate speed.
What is your opinion on ride & performance improvement going from 31 to 30?
 
Going from a 31 to a 30" tire wouldn't even be noticeable. You need lower gears in the differential. You can run 33's if you're geared low enough and don't expect to do 80mph on the highway.
 
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Kenkolen said:
Thank you, not knowing how it ran originally it is hard to say how much worse the 31" rides. I did find out that the spedometer is probably way off so i may be going faster than the speedometer is indicating. I will try using my gps to determine a more accurate speed.
What is your opinion on ride & performance improvement going from 31 to 30?
Click to expand...

30 to 31 won't be that big of a deal, but as far as ride quality goes, check out this thread:

https://wranglertjforum.com/threads/how-can-i-fix-a-harsh-ride-on-my-jeep-wrangler-tj.16558/
 
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I would put a tape measure up against the tire and see what your tires actually measure now. I have 31x10.50R15 AT3s and they actually measure in at 29.5 inches. I have the 2.5L, manual trans AX5, but it has been re-geared from 4.11 ring and pinion gears to 4.56. When these tires wear out I will go to a 33" tire.
 
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Kenkolen said:
I just picked up a 2001 TJ with a 2.5L motor. It has 31" off road tires, I do not have the exact size handy.
I believe the tires are robbing power, not like there is much to start with.
My use is to pull behind my motorhome mostly. I doubt I will go mudding.
Would changing to a set of change out Michelin Tires on 2018 rims 255/75 17 make any sense?
Click to expand...
If all you are doing is using the Jeep locally when towing behind the RV with no serious trail use then I would probably go to the stock tires with the 15" rims (probably why your speedo is off) as the stock diameter rims offer a wide selection of reasonably priced tires compared to the larger diameters. BTY it is a simple process to correct the speedo with speedo gear swap if you keep the current tires that cost about $40.

You would definitely improve performance on stock tires with the 2.5
 
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reddvltj said:
With the 2.5, tire size and weight make all the difference in the world with stock gearing. The SE came with
205/75 R15 (27.1')
215/75 R15 (27.7')
225/75 R15 (28.3')
all in a standard load rating 4 ply passenger rated tire
Click to expand...
My question is because I'm also having power loss issues, what is the power gain difference from the 225/75 R15 to the 205/75R15 I had 33X12.50R17 with 3" Spacers and it looked like the most bad ass jeep you would ever see but I cant go up hills period or anything flat. Had to be all down hill or local slow speeds. I downgranded to a 31x10.50R15 and I gained allot of power and top end speed back but perfomance wise it still isnt where I want it to be. I want to go to the 225/75R15 for daily use then use the 33x12.50R17. But if I gain 100 percent power back I want to go to the 205/75R15.
 
chefenfi8 said:
My question is because I'm also having power loss issues. I want to go to the 225/75R15 for daily use then use the 33x12.50R17. But if I gain 100 percent power back I want to go to the 205/75R15.
Click to expand...

Go for it!
p.s. Option #2. Regear it to 4.88 and the 33s and be done.
jeep tiny tires.jpg
 
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I have a 2000 2.5 5-speed and have 265/70/16 (30 1/2”) and won’t go any bigger. I can go 75 on the highway but have to drop down to 4th on steep hills. I had another 2.5 YJ that had 33’s and then 32’s. It wouldn’t go over 65. I put 31’s on it and it would go 70+.

The 2.5 is a decent engine if you use it correctly. Try to go too big and too high and you will regret it. 31’s and below you are alright. Closer to stock size tire and the better performance it has, but it doesn’t look as good to me.
 
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When I bought my 1997 TJ SE it had 33x14x15 TSL Boggers on it with stock gearing. While not super quick or blazing fast IMO it wasn't terrible. I of course couldn't use 5th gear unless I was going downhill. I swapped them out for some 33" A/T tires and it was a little better but still not fast. This was in 2002 and the deepest gears available were 4.88 at the time.

I did 4.88's & a Detroit locker in the rear & a LocRite in the front. Also had Warn small hub kit on the front & a Warn full floater kit with small hubs in the rear.

1997TJnew.jpg


Off-Road it was OK.

firsttrip6.jpg


firsttrip18.jpg



1684791483140.png
 
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reddvltj said:
With the 2.5, tire size and weight make all the difference in the world with stock gearing. The SE came with
205/75 R15 (27.1')
215/75 R15 (27.7')
225/75 R15 (28.3')
all in a standard load rating 4 ply passenger rated tire.
Click to expand...

I want to echo this- point-that you can get a P rated, C rated, and a E rated tire in the same height but dwfinetly different rotational weight trade offs. If you are not doing any serious trail driving consider staying with the p rated tires- you can find decent tread patterns in the P rated that don't have the weight penalty.
 
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chefenfi8 said:
My question is because I'm also having power loss issues, what is the power gain difference from the 225/75 R15 to the 205/75R15 I had 33X12.50R17 with 3" Spacers and it looked like the most bad ass jeep you would ever see but I cant go up hills period or anything flat. Had to be all down hill or local slow speeds. I downgranded to a 31x10.50R15 and I gained allot of power and top end speed back but perfomance wise it still isnt where I want it to be. I want to go to the 225/75R15 for daily use then use the 33x12.50R17. But if I gain 100 percent power back I want to go to the 205/75R15.
Click to expand...

First off, filling out the about you section of your profile, with your Jeep info will help so we're not guessing what you have.
As for the power gains between those 2 tire sizes... Here's the RPM and MPH differences based off GrimmJeeper's calculator
1684802244919.png


1684802271857.png


it's probably the difference of 1 gear climbing an incline... not quite 1000 RPM difference in 5th at 70mph but it could mean the difference between shifting down or staying in 5th depending on how steep the grade.

http://www.grimmjeeper.com/gears.html



JustDandee said:
I want to echo this- point-that you can get a P rated, C rated, and a E rated tire in the same height but dwfinetly different rotational weight trade offs. If you are not doing any serious trail driving consider staying with the p rated tires- you can find decent tread patterns in the P rated that don't have the weight penalty.
Click to expand...

Good luck getting C, D, or E rated tires in those 3 tire sizes....

Now if you go to like a 27x8.50 or 28x8.50 you can get 6 ply but I've never seen 8 or 10 ply in those sizes... except trailer tires...
 
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