opinion on 315/70R70 with 3.21s

desertrunner

desertrunner

Hooked
looking into either a set of Coopers and torn between the 295/70R17 or the 315/70R17. They would be going into a 12' Sport 6 speed that only has 3.21s in it. Im not going to have the money to re-gear for a little while and its not going to be my DD but wondering if in the opinion of hopefully someone that has done it if i am going to be pulling my hair out with the lack of power with the 315s and 3.21s

I ran the stock 4.10s on 37" KM2s on my 08 Rubi in Colorado, and yeah i wanted to re gear it but it really wasnt that bad i didnt mind it too much. (the 4:1 Tcase helped though)
 
desertrunner said:
looking into either a set of Coopers and torn between the 295/70R17 or the 315/70R17. They would be going into a 12' Sport 6 speed that only has 3.21s in it. Im not going to have the money to re-gear for a little while and its not going to be my DD but wondering if in the opinion of hopefully someone that has done it if i am going to be pulling my hair out with the lack of power with the 315s and 3.21s

I ran the stock 4.10s on 37" KM2s on my 08 Rubi in Colorado, and yeah i wanted to re gear it but it really wasnt that bad i didnt mind it too much. (the 4:1 Tcase helped though)
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The power loss between either size will be virtually the same.
Either one is going to be sluggish.
3:21 is undergeared for even stock tires lol
Pretty sure the difference between 315 - 295 in actual height is only .25 - .5 of a inch.
 
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I'm running the 295 Coopers on my WJ with 4.56 and it is just about perfect. With that being said, we are running 285 duratracs on the wife's jk with the stock gears (whatever the 2011 sport has) and have no complaints even in the mountains here. So I would think the 295s would be OK assuming we have 3.21s as well. Jake (boardsurfer) is running 35 Coopers with stock gears and I think he's pretty happy with it. I don't know what gears he has though.
 
JKDream said:
The power loss between either size will be virtually the same.
315 or 295 is the tread width, not height.
Height/radius change is what causes power loss.
It's going to be very sluggish regardless, and you'll likely see transmission temperatures run warm/hot during hill climbs etc.
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the little tire size calculator i was using was showing the 315s being about an inch taller like a 34.4 :thinking:
now im confused haha
 
WJCO said:
I'm running the 295 Coopers on my WJ with 4.56 and it is just about perfect. With that being said, we are running 285 duratracs on the wife's jk with the stock gears (whatever the 2011 sport has) and have no complaints even in the mountains here. So I would think the 295s would be OK assuming we have 3.21s as well. Jake (boardsurfer) is running 35 Coopers with stock gears and I think he's pretty happy with it. I don't know what gears he has though.
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I wanna say the 11's came with 3.73s but when the 3.6L engine came out they put 3.21s in it unless you got the option for 3.73s I could be wrong though
 
WJCO said:
The 295 is roughly 33.25 diameter and the 315 is roughly 34.4.
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ok so i did see that right cool haha.

of course everyone wants a bigger tire and i would love the 315s i just think it might be a bit much for the 3.21s and the sport T case im gonna be on the clutch like crazy when wheeling.

the 315s are also about 1 inch wider so more weight and resistance...
 
desertrunner said:
the little tire size calculator i was using was showing the 315s being about an inch taller like a 34.4 :thinking:
now im confused haha
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** Just noticed you have the six speed.
In that case it might not be too bad.
3:21 and 35s in my 13 auto was aids. Transmission was always running hot.
 
JKDream said:
** Just noticed you have the six speed.
In that case it might not be too bad.
3:21 and 35s in my 13 auto was aids. Transmission was always running hot.
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My biggest worry is burning out a clutch while wheeling with the 3.21s and the sport T case.

Its not going to be my DD so other than driving to and from the trail its hopefully going to see dirt most the time haha.
 
if i can get away with the 315s on the 3.21s for a while to save up for a PR44 front and regear the rear at the same time that would be sweet but if I am going to shoot myself driving it that way then ill just go 295.

But like was said earlier the difference in the 295 vs 315 on 3.21s might not really be all that different so F it go bigger haha
 
desertrunner said:
I wanna say the 11's came with 3.73s but when the 3.6L engine came out they put 3.21s in it unless you got the option for 3.73s I could be wrong though
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Just checked. We have 3.73. Sorry for the confusion. Yeah you would probably struggle a little with 315s on 3.21.
 
With the 6 speed and the 3.6L you will probably be ok on 315s. I run them with the 6 speed/3.8L and 3.73 gears. It is sluggish, but not too bad to handle. You will need to keep your limits in mind on steep off-road though.


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desertrunner said:
My biggest worry is burning out a clutch while wheeling with the 3.21s and the sport T case.

Its not going to be my DD so other than driving to and from the trail its hopefully going to see dirt most the time haha.
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desertrunner said:
if i can get away with the 315s on the 3.21s for a while to save up for a PR44 front and regear the rear at the same time that would be sweet but if I am going to shoot myself driving it that way then ill just go 295.

But like was said earlier the difference in the 295 vs 315 on 3.21s might not really be all that different so F it go bigger haha
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That's what I did, granted I built a Rubi 44 but same idea.
The 4low with 3:21's wasn't bad, I could still spin tires; but I didn't have a clutch to worry about.
I'd go with the 315's personally. When you swap axles/re-gear you'll probably want to go bigger anyway.
 
I guess I'll roll into a few more questions with this. The rims it has on it now are the old rubi style 17s. I know I would need spacers for sure on the 315s and I'm guessing I may need them as well with the 295s but not sure?

Also if I do just say F it go with the 315s and the gears drive me nuts has anyone swapped gears out their selves that would save a shit ton of money?!

I had a buddy who did a re gear on his XJ it took him 3 days and I was there for 1 of those days to help and it just looked like a miserable game of guess and check that I'm not sure I want to play.
I would have access to a lift and bearing press and everything but after his experience it doesn't seem worth it to try it myself.

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desertrunner said:
I guess I'll roll into a few more questions with this. The rims it has on it now are the old rubi style 17s. I know I would need spacers for sure on the 315s and I'm guessing I may need them as well with the 295s but not sure?

Also if I do just say F it go with the 315s and the gears drive me nuts has anyone swapped gears out their selves that would save a shit ton of money?!

I had a buddy who did a re gear on his XJ it took him 3 days and I was there for 1 of those days to help and it just looked like a miserable game of guess and check that I'm not sure I want to play.
I would have access to a lift and bearing press and everything but after his experience it doesn't seem worth it to try it myself.

Sent from my SAMSUNG-SM-G890A using WAYALIFE mobile app
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Can't comment on the spacers as I bought wheels before tires.
I'm all for working on your own Jeep, but gears aren't something I would attempt.
There's too much margin for error, and if you make a mistake you break a R&P and it ends up costing more money in the end.
Shop around for a while, you'll find some good deals. I got my 5:13 R&P's for $50 per set new.
D44 was $400 with e-locker.
**FYI, pretty much every gear set is made in the same factory in Korea. Find whatever is on sale and roll with it.
 
JKDream said:
Can't comment on the spacers as I bought wheels before tires.
I'm all for working on your own Jeep, but gears aren't something I would attempt.
There's too much margin for error, and if you make a mistake you break a R&P and it ends up costing more money in the end.
Shop around for a while, you'll find some good deals. I got my 5:13 R&P's for $50 per set new.
D44 was $400 with e-locker.
**FYI, pretty much every gear set is made in the same factory in Korea. Find whatever is on sale and roll with it.
Click to expand...
I'm hoping here in a few months I'll find a rubi take off with gears and a locker in it then only have to do a rear set. That would be nice haha
Then again takes money out of the pot for a PR

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desertrunner said:
I'm hoping here in a few months I'll find a rubi take off with gears and a locker in it then only have to do a rear set. That would be nice haha
Then again takes money out of the pot for a PR

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Depending on which prorock you go with it might be worth buying for a good price.
The $400 I paid was for the full assembly minus brakes, so I didn't have to buy shafts etc.
Then when you prorock you just swap the housing
 
JKDream said:
Depending on which prorock you go with it might be worth buying for a good price.
The $400 I paid was for the full assembly minus brakes, so I didn't have to buy shafts etc.
Then when you prorock you just swap the housing
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Id prefer to buy the PR with an ARB locker and not use the stock rubi E locker which i believe the Rubi internal housing is different than the standard housing for an ARB so either way id be out the money.

Maybe ill just suck it up buy the 315s and if its really terrible regear to 4.88s and then buy a PR to match down the road.

Re gearing is just not cheap i would rather just do it once.
 
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