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Old July 17th, 2013, 03:53 PM   #1
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Default Will I need to regear? Tire Size Upgrade

02 TJ 4.0L
3" Suspension Lift
D30 Front/D44 Rear 3:73

I currently have 31" BFG A/T tires on the Jeep, I am looking at getting some bigger tires soon. I was thinking 33-12.50R15 size, possible BFG KM2 or Kevlars.

Question is, will I need to do any regearing or anything else or should I be good to go?

Thanks
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Old July 17th, 2013, 03:55 PM   #2
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Need to? Not likely.

But you will probably have more fun with 456's. Check out our rpm calculator and run some numbers.

http://completeoffroad.com/p-3351-rp...ator-page.html
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Old July 17th, 2013, 03:55 PM   #3
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You should be okay but nor optimum with 3.73's.
It will struggle in a headwind or larger hills.
4.10's would be better.
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Old July 17th, 2013, 04:04 PM   #4
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Need to? Not likely.

But you will probably have more fun with 456's. Check out our rpm calculator and run some numbers.

http://completeoffroad.com/p-3351-rp...ator-page.html
Hmm okay this might sound like a dumb question but I am still on my way on learning about Jeeps/Cars and the like.

So what I getting out of this calculator, is the lower gear ratio I have, the higher the rpms? I thought it was the other way around?
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Old July 17th, 2013, 04:14 PM   #5
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a numerically higher ratio will raise your rpms if you are staying with the same tire size.

You can offset the loss of power that occurs when going to a larger tire by going to a numerically higher ratio.

Ideally, you want to move to a ratio that delivers the same rpms at a given speed as the vehicle was stock.

Like Dale said, 410's would be a good fit, but the % change from 373 to 410 is pretty low. It makes it a matter of whether or not its really worth it.

456's would give you great power, but you have to be careful not to limit your highway speed. If you go to too high of a ratio, you'll be screaming on the interstate trying to do 65 mph.

If it were me, I'd move to the moderately larger tire without the gear change. If you find that it is underpowered or not performing the way you want, then its time to investigate the gear change.
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Old July 17th, 2013, 04:20 PM   #6
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Originally Posted by Complete Off Road View Post
a numerically higher ratio will raise your rpms if you are staying with the same tire size.

You can offset the loss of power that occurs when going to a larger tire by going to a numerically higher ratio.

Ideally, you want to move to a ratio that delivers the same rpms at a given speed as the vehicle was stock.

Like Dale said, 410's would be a good fit, but the % change from 373 to 410 is pretty low. It makes it a matter of whether or not its really worth it.

456's would give you great power, but you have to be careful not to limit your highway speed. If you go to too high of a ratio, you'll be screaming on the interstate trying to do 65 mph.

If it were me, I'd move to the moderately larger tire without the gear change. If you find that it is underpowered or not performing the way you want, then its time to investigate the gear change.
Okay thank you very much, I will have to see how it is with the tires on and decide if I like it or not. If I do decide to upgrade the gears, will I need a RP Set for both the front and rear axle? And is that all I will need is the RP, or will I need something else?
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Old July 17th, 2013, 04:55 PM   #7
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try a 10.5 x 33 x 15, its a thinner, lighter combo, and will hurt u less.
a 4.56 ratio is about perfect for ya, though 4.10 would work.
it would give u a little more rpm at the same speed, but not alot.
your mpg would go up, or be about the same.
it will struggle on hills with 33's and 3.73's.
the mpg will suffer, cause the engine is lugging.
more or less rpm will not always hurt or help the mpg's.
u need to be in the power band at highway speed.
at lower rpm you wont make enough power, so the engine will work harder.
2500 to 2800 rpm should net u about the best mpg on the highway.

good luck
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Old July 17th, 2013, 05:42 PM   #8
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Originally Posted by joe_jeep View Post
try a 10.5 x 33 x 15, its a thinner, lighter combo, and will hurt u less.
a 4.56 ratio is about perfect for ya, though 4.10 would work.
it would give u a little more rpm at the same speed, but not alot.
your mpg would go up, or be about the same.
it will struggle on hills with 33's and 3.73's.
the mpg will suffer, cause the engine is lugging.
more or less rpm will not always hurt or help the mpg's.
u need to be in the power band at highway speed.
at lower rpm you wont make enough power, so the engine will work harder.
2500 to 2800 rpm should net u about the best mpg on the highway.

good luck
Intresting..How easy is it to regear? Will I just need the Ring and Pinion Set (2 of them, one for front one for rear axle) or will I need more?
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Old July 17th, 2013, 05:52 PM   #9
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you would need install kits and new carriers to gear your axles that high. So you would need full lockers or open carriers able to use the ratios you want. Because a ring gear on a 4.56 is substantially bigger diameter than your 3.73 ring gear. In all honesty it would cost you about $600-$1000 to do the gear swaps in both axles with new carriers. More or less depending on locker choice and all that mess.
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Old July 17th, 2013, 06:04 PM   #10
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you would need install kits and new carriers to gear your axles that high. So you would need full lockers or open carriers able to use the ratios you want. Because a ring gear on a 4.56 is substantially bigger diameter than your 3.73 ring gear. In all honesty it would cost you about $600-$1000 to do the gear swaps in both axles with new carriers. More or less depending on locker choice and all that mess.
Hm yes and I would probably have a professional do it as well, so tack that on. I'll have to do some thinking, but I do see a lot of guys with 33"s with stock gears on the road and they are fine. But mine is also a DD
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Old July 17th, 2013, 08:35 PM   #11
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Hm yes and I would probably have a professional do it as well, so tack that on. I'll have to do some thinking, but I do see a lot of guys with 33"s with stock gears on the road and they are fine. But mine is also a DD
I ran 3.07s & 33x12.50 s for about a year. 3.73s will be fine. Save the gear swap for when u get 35s
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Old July 17th, 2013, 08:39 PM   #12
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I have a 4.0 yj with 4.10 gear, and 35s, and can cruise 70 with no problem.

If I were you, I'd Pull axles from a 4cycl to get you to 4:10s, and call it a day.
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Old July 17th, 2013, 08:53 PM   #13
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Is it a manual or automatic? I've got a manual 2000 TJ with D30/D44 and 3:73 gears. I didn't have any real problems running 33x12.50 on 10" wide rims. Yes, I did have to occasionally downshift on some uphills on the highway but it didn't bother me (stroker fixed that problem). On the other hand I have a friend that has a 3 speed automatic 99 TJ with D30/Ford 8.8 and 4:10 gears. He is running 35x12.50 and hates the RPM's at highway speed. If you are going to regear get ahold of BigBChevy
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Old July 17th, 2013, 09:15 PM   #14
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Stay with the 3.73's till you decide if you like wheeling enough to consider upgrading to stronger axles. I've seen guys wheel 36" tires with 3.54 gears and have a great time. (not as a daily driver)
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Old July 18th, 2013, 12:05 AM   #15
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Stay with the 3.73's till you decide if you like wheeling enough to consider upgrading to stronger axles. I've seen guys wheel 36" tires with 3.54 gears and have a great time. (not as a daily driver)
That is what I am thinking. Like I said, she is my DD and I only wheel her about 2-3 times a year. My real goal is to eventually get a CJ-7 someday, that I would probably do a lot more work to. But since this is my DD first and offroader second I may just stick with the 3.73. I was just curious if it was a good idea or not, and if I should be fine.
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Old July 18th, 2013, 03:27 PM   #16
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i daily drove a 91 xj with 250-287k miles first with 33x12.5 on 10" wide wheels then with 32x11.5 on the same wheels. 3.73 gears. got around just fine down the road, wasn't lacking power at all, it'd do donuts on wet pavement.
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Old July 21st, 2013, 02:26 PM   #17
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I have a 4.0 yj with 4.10 gear, and 35s, and can cruise 70 with no problem.

If I were you, I'd Pull axles from a 4cycl to get you to 4:10s, and call it a day.
This is what I have, its perfect on the road. It would be nice to have 4.56s when wheeling but definatly not necessary.
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