Running 37" tires + with stock gearing? experiences???

[jimmyjames82]

Does anyone here have experience running stock gearing while running 37+ inch tires??

Can you tell me what jeep you had even if it was a previous JK. Did it damage anything? What kind of terrain did you drive on? Length of time/miles? Anything and everything you could tell me about the experience is greatly appreciated!!

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[UKCATS]

They will be lots of folks along shortly to tell you it’s just fine. I didn’t like 35’s on the stock 4.10’s, so regeared my JL to 4.88. I recently lifted my wife’s Gladiator Rubicon and installed 37’s. It is terrible. The 8 speed auto is now basically a 6 speed auto. Makes me want crazy driving it on the highway. It is getting regeared in a few weeks. In the end, the decision is yours.

 

[quietpeen]

I won’t say it is just fine, I have basically lost 8th gear on the highway and have to manually put it in 7th so it doesn’t downshift for no reason.

For me city driving the acceleration is still fine, but it holds gears longer. I have not taken it off road yet due to being winter, but I don’t think it will be a problem since I have a Rubicon 3.6 with the 8 speed. 4 door if that matters.

My take is that it is not a deal breaker till you can get it regeared (which I will do when I find a reputable shop near me and have the funds)

 

[ChattVol]

@jimmyjames82 It would help if you would provide better details...are you talking about a JL automatic or 6 speed? Rubicon or non Rubicon?

This has been discussed alot in the axles/transmission/gears section found below. I recommend reading through it first. You'll find your answers + learn alot more.
https://www.jlwranglerforums.com/forum/forums/transmission-axles-and-gears.41/

 

[Toycrusher]

Does anyone here have experience running stock gearing while running 37+ inch tires??

Can you tell me what jeep you had even if it was a previous JK. Did it damage anything? What kind of terrain did you drive on? Length of time/miles? Anything and everything you could tell me about the experience is greatly appreciated!!

How important is fuel economy to you? I'm assuming, based on the fact you upgraded to 37s and drive a Wrangler in the first place, that it's low on your list of priorities.

In the manual, gears 5 & 6 are overdrive gears. In the auto, 6-8 are overdrive gears. On a bone stock Wrangler with street tires, all of those overdrive gears are only worth, MAYBE 1mpg at mild highway speeds.

(I'm assuming you have a Rubicon with 4.10 gears. If you don't, then ignore what I'm saying and regear right away)

When you upsize your tires from 32" to 37", you are basically changing final drive ratios. Your old 6th gear (MT) ratio of engine torque to ground speed is now found in 4th gear. Engine is under roughly the same load for the mph, and ignoring science and assuming your 37s had the same weight and rolling resistance as your stock 32s, you would get the same fuel economy.

With the incredibly deep 1st gear you already have, there's no problem getting moving, and you will row through your other 3 gears at higher ground speeds, but no real tangible difference. Do a 0-60 run and your time will be very similar. Do a 0-100 run and you'll realize the 3.6 still doesn't make enough power to hit 100 either way...

Some people get very hung up on wanting to use EVERY gear in the transmission even though there is virtually no improvement in performance or fuel economy. (For those with an auto, check what engine rpm was at 65mph in 8th and stock tires, for argument sake I'll say 2100 rpm. After upgrade to 37s, check rpm again at 65mph cruise, and you'll find that the transmission decided to stay in 6th gear, but your rpm is still 2100. Same load on engine for mph)

Old transmissions with a narrow gear spread were very sensitive to gearing, my old Dodge Ram on 38s was a dog until I swapped from 3.50s to 4.56. But these modern JL transmissions with such a wide ratio spread negates the need to regear axles, 4.10 ratio is sufficient for 37s and there is basically a transmission gear for any situation that can get the motor back in the powerband it was originally designed to operate in.

Your money, your choice, but there's a lot of other ways to spend that same money you would drop to get your axles regeared

 

[UKCATS]

Re gearing to the proper ratio for tire size actually does increase fuel mileage. After over a dozen Wranglers, I know what I’m talking about. This dudes experience is the same.

 

[SecondTJ]

In the manual, gears 5 & 6 are overdrive gears. In the auto, 6-8 are overdrive gears

The automatic has two overdrive gears not three; 7th (0.84:1) and 8th (0.67:1) as 6th gear is 1:1

 

[Halstem1]

I have a '19 JLUR with 37's on stock 4.10 gears, 3.6L with an auto. Drives almost identical to my '17 JLU Sahara with stock 3.21's and 32 inch tires. I know those are very different but for everyday driving, they feel the same. I have no complaints. I did several trails in Colorado and no issues at all.

Everyone that says they never see 8th gear, I don't fully understand. I'm in Iowa and its flat, so maybe that is why. Mine shifts into 8th quite a bit. Yes it downshifts a little more, but I'm not surprised by that and kind of expected with that 8 speed.

At some point in the future, I'd like to upgrade to 4.88's. There aren't many shops around here so I'd likely have to make an appointment with someone out of state.

 

[TrailTorque]

They will be lots of folks along shortly to tell you it’s just fine. I didn’t like 35’s on the stock 4.10’s, so regeared my JL to 4.88. I recently lifted my wife’s Gladiator Rubicon and installed 37’s. It is terrible. The 8 speed auto is now basically a 6 speed auto. Makes me want crazy driving it on the highway. It is getting regeared in a few weeks. In the end, the decision is yours.

Are you guys going 4.88 on the Gladiator or 5.13’s?

From what I understand (at least on the JLU Wrangler platform) 5.13’s on 37” tires will get your 8th gear back.

It’ll be sluggish on the pass though at highway speed.

4.10’s and maybe even 4.88’s? on 37” tires like you said wont get your 8th gear but will be a lot better for highway passes.

Curious if the above statements hold true on the Gladiator platform.

 

[UKCATS]

Are you guys going 4.88 on the Gladiator or 5.13’s?

From what I understand (at least on the JLU Wrangler platform) 5.13’s on 37” tires will get your 8th gear back.

It’ll be sluggish on the pass though at highway speed.

4.88 on 37” tires won’t get your 8th gear back but will be a lot better for highway passes.

Curious if the above statements hold true on the Gladiator platform.

I am running 37’s and 4.88’s on my 2 door, and I have 8th gear back. Turns about 2200 RPM at 70mph. Stock tires and gears was about 2000 RPM at 70mph. All that said, I am kicking around doing 5.13’s on the Gladiator. Wife is running 37 Trail Grapplers and they are heavy, plus the truck is heavier as well.

 

[TrailTorque]

Yeah...we're on 37s and stock 4.10s in our JLUR....we still use 8th gear from time to time. Pretty sure I've been over 100mph while passing...hard to say for sure since the speedo is off 20%, but based on the vehicle I was travelling with, that # appears to be legit.

So with 4.10’s and possibly even 4.88’s? 8th gear barely gets touched unless you’re on flat highway?

Just trying to gather some information for future reference. I’ll eventually have to deal with this lol

I’m thinking on a Gladiator I’d prefer 5.13’s for the power but I’m not sure with such a heavy vehicle.

Didn’t Brad from TrailRecon throw 5.13’s on his?

Im going to have to go look now lol

 

[TrailTorque]

I am running 37’s and 4.88’s on my 2 door, and I have 8th gear back. Turns about 2200 RPM at 70mph. Stock tires and gears was about 200 RPM at 70mph. All that said, I am kicking around doing 5.13’s on the Gladiator. Wife is running 37 Trail Grapplers and they are heavy, plus the truck is heavier as well.

Yeah I fixed my post up there I meant to say 4.10’s & 4.88’s but is it constant on highway or only flat highway?

 

[UKCATS]

Yeah I fixed my post up there I meant to say 4.10’s & 4.88’s but is it constant on highway or only flat highway?

It is flat here. Can stand on a can of tuna and see into Oklahoma. It stays in 8th mostly. If driving into a headwind and driving up an incline, it will drop to 7th. On 35’s, the 4.88’s were awesome. I am considering making my Jeep “smaller” again.

 

[TrailTorque]

Okay I found it lol

@UKCATS Brad has 38’s on his Gladiator with a bunch of stuff added and he went 5.13’s for reference. His gas mileage is better in the test below. He does speak about why he chose 5.13’s over 4.88’s in the comments section.



Hope this helps ya!

 

[UKCATS]

Re gearing to the proper ratio for tire size actually does increase fuel mileage. After over a dozen Wranglers, I know what I’m talking about. This dudes experience is the same.

Okay I found it lol

@UKCATS Brad has 38’s on his Gladiator with a bunch of stuff added and he went 5.13’s for reference. His gas mileage is better in the test below. He does speak about why he chose 5.13’s over 4.88’s in the comments section.



Hope this helps ya!

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