37s on xtreme recon package?

[Steph1]

Yeah, I don't know anything "Marty". I've just driven across country and wheeled 2 Rubicons on 37s. all over the place. If you want to use all your gears, they need to be taller.

You meant ‘’lower’’ thus numerically higher. And you are absolutely right. I dont get it either why people would buy an optimum jeep with proper gearing….and then modify it to become a lesser Jeep than optimum Jeep. I have 4.56 with my 315/70 and it’s just perfect. 37s would definitely require 4.88s to be as awesome to drive as it is now.

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[Zandcwhite]

You meant ‘’lower’’ thus numerically higher. And you are absolutely right. I dont get it either why people would buy an optimum jeep with proper gearing….and then modify it to become a lesser Jeep than optimum Jeep. I have 4.56 with my 315/70 and it’s just perfect. 37s would definitely require 4.88s to be as awesome to drive as it is now.

You’re assuming stock rubicons are geared “optimally“. A stock sport has a 31.5” tire and 3.45 gears. Mathematically that’s the exact same drive ratio as 37’s and 4.10 gears. If you prefer the way a sport drives, you’ll be more than happy with 4.56’s and 37’s.

 

[J0E]

4.10 - Rarely saw 8th. Dropped to 4th and 5th all the time. Crawl was OK. This is the ratio for the 'I'm too cheap to do a non-flashy upgrade' crowd. Justify it however you want. 4.10 is not the right ratio for 37s.

That entire thread is Optimize for DD on the highway, not crawling. With the 4:1 xfer case, 37's are fine with the stock 4:10 differentials, as long as you know how to do M1.

Crawling is where these low gears shine, but with the 4-1 low range even the 4.10's were excellent there. The only place I'd say the deep gears are truly better is 4 hi situations like mud and deep snow where you want wheel speed but still need torque at times.

Exactly

You’re assuming stock rubicons are geared “optimally“. A stock sport has a 31.5” tire and 3.45 gears. Mathematically that’s the exact same drive ratio as 37’s and 4.10 gears. If you prefer the way a sport drives, you’ll be more than happy with 4.56’s and 37’s.

Use my https://bt39.com/GearWheelSpeed to compare.

 

[roaniecowpony]

I was doing the math on my JLUR with 4.10s/33s vs 37s (36.4) and found that 4.56 is numerically going to provide the same rpm/mph. However, that doesn't consider any loss of performance due to the longer moment arm of the taller tire. The power required to turn the larger tires against the wind resistance and rolling resistance is higher. That says nothing about the amount of wind resistance and rolling resistance that is increased by the higher body and larger tire/wider tread/coarser tread.

So, for the reasons above, an equal rpm/mph calculation will surely not equal the same performance. That's why those that have gone to 37s have felt in the seat of the pants, a better outcome with 4.88s.

 

[TxJeepers]

That entire thread is Optimize for DD on the highway, not crawling. With the 4:1 xfer case, 37's are fine with the stock 4:10 differentials, as long as you know how to do M1.



Exactly



Use my https://bt39.com/GearWheelSpeed to compare.

Optimize is Jeep engineers putting 456 with 35s.

 

[Zandcwhite]

Optimize is Jeep engineers putting 456 with 35s.

Or is optimized Jeep engineers putting 3.45's on 32's? The fact of the matter is the 8 speeds 1st gear is so much lower than any other wrangler before it you can run tall gears with big tires and it's better than a stock tj or jk. Conversely with our double over drive you can gear as low as you want and still maintain freeway speeds with ease. Having run 4.10's with 37's and 38's for tens of thousands of miles and 5.38's with 38's for tens of thousands of miles, I preferred 4.10's on the street, especially at freeway speed. You absolutely can gear too low. If you live out west we're most people cruise 85mph on the freeway I'd choose 4.56 for 37's and keep my freeway rpm down if I had it to do again.

 

[J_Winslow]

You will probably need a new lift, new shocks, new wheels (or wheel spacers), new tires, and a new gate support. Pretty much replacing most of what the XR included...haha.

All of that is wrong.

With the bumpstops on the XR being overkill you can fit 37s on it. You MIGHT rub a hair at full flex but the XR suspension has garbage flex.

The XR wheels take 37x12.50r17 just fine and no mods needed to the tailgate. Might want to raise the tail light a bit though.

 

[Jtphoto]

The XR is well suited for 37s just the way it is. Jeeps plan all along so don’t be surprised if Ford keeps pushing with the Bronco the next Gen XR will have the 4.88 gears and 37s.

 

[kah.mun.rah]

All of that is wrong.

With the bumpstops on the XR being overkill you can fit 37s on it. You MIGHT rub a hair at full flex but the XR suspension has garbage flex.

The XR wheels take 37x12.50r17 just fine and no mods needed to the tailgate. Might want to raise the tail light a bit though.

It wouldn't be the 1st or last time I have been wrong; however, with the Mopar lift raising my JLUR 3" and using one of the smallest 37s on the market (BFG) I was rubbing when off-roading. If you limit yourself to no passengers, no gear, and only flat pavement runs to the mall you will probably be ok with 37s on the XR lift.

 

[J_Winslow]

It wouldn't be the 1st or last time I have been wrong; however, with the Mopar lift raising my JLUR 3" and using one of the smallest 37s on the market (BFG) I was rubbing when off-roading. If you limit yourself to no passengers, no gear, and only flat pavement runs to the mall you will probably be ok with 37s on the XR lift.

So your saying you did not use the proper bump stops...

 

[kah.mun.rah]

So your saying you did not use the proper bump stops...

I used the right stops. If you are adding extra bump stop to prevent tire rub, it is just going to limit your flex and rattle your teeth on the bumps.

 

[J_Winslow]

I used the right stops. If you are adding extra bump stop to prevent tire rub, it is just going to limit your flex and rattle your teeth on the bumps.

Hitting the body is doing the same thing but causing damage to the body/fenders.

 

[Jtphoto]

It wouldn't be the 1st or last time I have been wrong; however, with the Mopar lift raising my JLUR 3" and using one of the smallest 37s on the market (BFG) I was rubbing when off-roading. If you limit yourself to no passengers, no gear, and only flat pavement runs to the mall you will probably be ok with 37s on the XR lift.

You need appropriate bumpstops for that lift and tire combo and the same backspace as the Mopar XR wheels. As mentioned it’s the longer bumpstops on the XR that stops the rub, not the lift or the shocks.

 

[Jtphoto]

I used the right stops. If you are adding extra bump stop to prevent tire rub, it is just going to limit your flex and rattle your teeth on the bumps.

Bumpstops is the only way To stop rub. You have to reduce the up travel and make up for it in droop. If you want more uptravel for bigger tires without bumpstops you need to go with flat fenders or no fenders.

 

[kah.mun.rah]

Bumpstops is the only way To stop rub. You have to reduce the up travel and make up for it in droop. If you want more uptravel for bigger tires without bumpstops you need to go with flat fenders or no fenders.

All I am saying is that if you don't have enough lift in the coils for a larger tire, increasing the bump stop (reducing the bump stop gap) is not the right solution.

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