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30" Tires On Stock Height?


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Unless you really NEED 31s, go with the 30s. Yes, in diameter they are only a hair larger than a 235/75-15, but they are wider, both in cross section and at the tread. You can run 31s on OEM Jeep rims with a stock suspension, but the rubbing on the lower control arms will be worse, and you don't really gain anything. Especially with a 4-banger, you will NOT be happy trying to spin 31" tires through stock gearing.

 

The 30s, IMHO, look just about perfect on a stock-height MJ.

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dadinator: I did look at your thread and thats why I am looking at 31's.

 

eagle: part of my reason for 31's is the fact that my daily drive is about 80% highway or more one way so the lower rpm's of the tire would be nice and won't hurt me to much for the 3 stoplights I have to go through which are normaly green anyway.

 

automan: I've never heard of that company before. all of their products are re-treads?

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automan: I've never heard of that company before. all of their products are re-treads?

 

Yes, and a fantastic value at that. Look at the prices. JP has done testing on them including airing them down past what treadwright recommends and wheeled it with no problems what so ever. I think a few people on the board here have them, with no complaints. They take an old tire, skin it, and apply their own tread. The all terrain is so close to the BFG AT I am surprised they haven't gotten in trouble. When you order, you can ask to have matched casings, so you get all matching sidewalls.

 

A guy I work with asked for matching carcasses and got the A/T's. When they showed up, they had put the A/T tread on 4 old BFG A/T carcasses. Unless you knew they were retreads, and looked for the parting line, you wouldn't have known any better.

 

I've only ever heard of one problem. Someone had told me that a buddy of his had one separate, and went to them on facebook. They immediately bought all the tires back and gave him new ones. Now that is customer service.

 

Rob

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Yes, and a fantastic value at that. Look at the prices. JP has done testing on them including airing them down past what treadwright recommends and wheeled it with no problems what so ever. I think a few people on the board here have them, with no complaints. They take an old tire, skin it, and apply their own tread. The all terrain is so close to the BFG AT I am surprised they haven't gotten in trouble. When you order, you can ask to have matched casings, so you get all matching sidewalls.

 

A guy I work with asked for matching carcasses and got the A/T's. When they showed up, they had put the A/T tread on 4 old BFG A/T carcasses. Unless you knew they were retreads, and looked for the parting line, you wouldn't have known any better.

 

I've only ever heard of one problem. Someone had told me that a buddy of his had one separate, and went to them on facebook. They immediately bought all the tires back and gave him new ones. Now that is customer service.

 

Rob

 

A friend of mine got a set of 4 MTs (looks like the old Goodyear MT/R), and one had a small defect that would not affect the performance. He emailed them with a picture and they sent him a new tire free of charge, told him to keep the old one for a spare if he wanted.

 

Former coworker of mine ran a set of MTs in 31x10.50 on his Dakota. Had them on for 2 years before I lost contact with him.

 

I put a set of ATs in 265/75R16 (~32x10.50) on my daughter's Cherokee using stock Liberty rims. They are on BFG AT T/A KO carcasses, so unless you know what to look for you won't know they are retreads. Been on there for about 6 months now and have performed great on dry pavement, wet pavements, and surprisingly well off road (a large part of that might have been driver skill, she puts me to shame out there). Don't know about snow yet.

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lower rpms do NOT directly relate to better fuel economy. otherwise we'd all have 2.00 gears in our axles. peak efficiency comes at the peak torque. which is not all that low for the 2.5L. :thumbsup: you might find 5th gear pretty worthless.

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lower rpms do NOT directly relate to better fuel economy. otherwise we'd all have 2.00 gears in our axles. peak efficiency comes at the peak torque. which is not all that low for the 2.5L. :thumbsup: you might find 5th gear pretty worthless.

 

what 5th gear :thumbsup:

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eagle: part of my reason for 31's is the fact that my daily drive is about 80% highway or more one way so the lower rpm's of the tire would be nice and won't hurt me to much for the 3 stoplights I have to go through which are normaly green anyway.

 

You won't be running even in 4th gear -- except for downhill with a tailwind you'll be in third gear most of the time. If you have a 4-cylinder with the 4-speed manual, you will NOT be happy with 31s.

 

Don't think that lower RPMs are always better. Pete already said it, but I'll repeat it. I have history on my side, being old enough to have grown up before most cars had overdrive. When I graduated from college, my first new car was a 1966 Rambler American with a 3-speed manual transmission (and no overdrive). The engine was a 199 cubic inch version of what later became the 4.0L Jeep engine -- and the 2.5L Jeep engine. The gearing and tire size worked out exactly to 25 MPH per 1000 RPM, so 60 MPH was exactly 2500 RPM. This was verified -- I ran a tachometer in it, and verified the speedometer. I got 28 MPG for gas mileage.

 

Your 4-speed, 4-cylinder Jeep on 30x9.50-15 tires will be turning 2496 RPM at 60 MPH. You won't be hurting anything at that engine speed. It's just over a fast idle (sort of ...).

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You won't be running even in 4th gear -- except for downhill with a tailwind you'll be in third gear most of the time. If you have a 4-cylinder with the 4-speed manual, you will NOT be happy with 31s.

 

Don't think that lower RPMs are always better. Pete already said it, but I'll repeat it. I have history on my side, being old enough to have grown up before most cars had overdrive. When I graduated from college, my first new car was a 1966 Rambler American with a 3-speed manual transmission (and no overdrive). The engine was a 199 cubic inch version of what later became the 4.0L Jeep engine -- and the 2.5L Jeep engine. The gearing and tire size worked out exactly to 25 MPH per 1000 RPM, so 60 MPH was exactly 2500 RPM. This was verified -- I ran a tachometer in it, and verified the speedometer. I got 28 MPG for gas mileage.

 

Your 4-speed, 4-cylinder Jeep on 30x9.50-15 tires will be turning 2496 RPM at 60 MPH. You won't be hurting anything at that engine speed. It's just over a fast idle (sort of ...).

 

point well taken. 2496 rpm would be nice. I wish I had a gauge cluster with a tachmeter but nooooo, I have the dummy version with dummy lights and no tach. although I do like to big fuel gauge.

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even worse. :( that means you have 3.55 gears. :(

 

Doesn't matter much. 4th gear with 3.55 and 5th gear with 4.10 both give the exact same final drive ratio. So basically the factory 5 speed setup gives you a lower 1st gear, but the top gear is the same.

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Fuel economy's a little more difficult to box in than that. When accelerating, it's more efficient to do so at peak torque (thus minimizing the time when you're doing more than making up for rolling resistance, drag, &c) but at a constant speed, you only need enough torque to fight those loses, so there's a balance point where everything's minimized.

Case in point, the LS7 in the Corvette Z06. Peak torque is at 4800 rpm, but there's really no need to make 470 lb-ft just to cruise down the highway at 75. It would be stupidly wasteful to have the engine revving that high, when with much less fuel you could be doing 1500 rpm in 6th instead of 5000 in 2nd.

This is why CVT's don't keep the engine at peak torque. There's a point of peak efficiency which is usually lower than that of peak torque, but it moves around a lot because it's dependent on engine load.

So yes, below that point, your fuel economy does go up with engine speed. But once you've hit that point, it starts dropping again, regardless of where peak torque is.

 

But I understand where you're coming from with that. My Dad still can't figure out why I get better mpg's in his van than he does, since I accelerate harder and drive faster than he does, but I'm definitely not at peak torque engine speeds (~4k) down the highway. Much faster than 70mph and the mpg's go back down again.

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Doesn't matter much. 4th gear with 3.55 and 5th gear with 4.10 both give the exact same final drive ratio. So basically the factory 5 speed setup gives you a lower 1st gear, but the top gear is the same.

 

true. first gear is going to suck. :(

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so what your saying is that I wouldnt see any benifit from am ax5 swap either? well besides the fact that my ax4 is a 2wd trans and I want 4wd.

 

If you don't change the axle gearing from 3.55 to 4.10 the 5th gear will be completely wasted.

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After I found I only got 19 mpg running 75mph (but 27mpg at 60) on flat ground with my AX4 I swapped in an AX5 and kept the 3.55 gears. Now I get 24mpg at 75 and still 27 at 60. But I am running almost stock sized tires and 5th gear is useless on any sort of incline.

 

For larger tires I would suggest 3.73 or 4.10. With the stock 3.55 and larger tires you can swap in an AX5, but you won't be using 5th very much if at all.

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Would running over size tires cause excessive wear on a clutch/transmission in the long run?

 

Perhaps to a point, but it would be negligible I would think

 

For example, I have been running 31's on a 4 cyl TJ since 1998 and it still has the original clutch at 180K.

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