Manual JTR with 37" Tires--Comments?

[guntrust]

My 2020 JT Rubicon (4:10 gearing standard) with manual transmission is stock now but i'll soon be getting 2" Mopar lift.

37's are a popular choice but i've heard the experience is not so great with manual transmission.

I do not want to have to regear. Also concerned about strain on axles although the offroading i have in mind is moderate. Also have heard larger tires can lead to braking issues.

So i'm leaning toward putting 35's on my stock 17" wheels. [My understanding is that most 37's are really closer to 36 inches and if i go for something larger it will be 36 inches max in order to fit in spare tire well.]

If anyone is actually running 37's on a manual, please tell us how it's going. Thanks.

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[yngvepau]

I have 37" tires with the molar 2" lift with no re-gearing. I will say that you do notice the difference and loss of power. That being said however, the Jeep does everything you want it to do. Does fine off road, haven't done Moab yet, but does all I need it to do. You will see that 6th gear isn't used a lot, unless on straight and level or downhill. I have decided to NOT re-gear

 

[Micky]

I have a manual Mojave on 35x11.50 Toto at3 and 4.88 gears. Since I will be going to 37s this year, I wish I got 5.13s. I wouldn’t put the tires on without the gears.

 

[hjdca]

I have a manual JTR with big 37s (Goodyear MTRs and Method 703 - light rims) and I went with Dana Spicer 5:13 gears. What a huge difference in performance. It even gets better gas mileage now. The torque and performance with the 5:13s is impressive. Much, much faster 1/4 mile time. It really moves with those huge 37s - everybody that sees me row through the gears with purpose is impressed.

Off-road, the 5:13s are great. The granny gear if perfect for rock crawling - ie. you can practically stop without clutching. In addition, you can stay in 4wheel High longer, instead of always going into 4Low.

Also, because of the torque multiplication, all gears except for 5th and 6th really have a good surge in the high rpm, and you can easily go from 4th to 6th, skipping 5th. 6th will also pull small hills on the hwy.

Really, it feels like there is a different motor in there. Lots of low end grunt, and the high end pulls in every gear.

For me, it was well worth the money spent. I do not even think about the Hemi Wrangler anymore. You cannot get it with a stick anyway, and now my motor moves my Gladiator great with big tires. --- and I am getting really great gas mileage !

PS. I think you can count on 1.5 to 2 mpg increase with the right gears and your 37s... So, that also could be a good justification.

 

[guntrust]

I have a manual JTR with big 37s (Goodyear MTRs and Method 703 - light rims) and I went with Dana Spicer 5:13 gears. What a huge difference in performance. It even gets better gas mileage now. The torque and performance with the 5:13s is impressive. Much, much faster 1/4 mile time. It really moves with those huge 37s - everybody that sees me row through the gears with purpose is impressed.

Off-road, the 5:13s are great. The granny gear if perfect for rock crawling - ie. you can practically stop without clutching. In addition, you can stay in 4wheel High longer, instead of always going into 4Low.

Also, because of the torque multiplication, all gears except for 5th and 6th really have a good surge in the high rpm, and you can easily go from 4th to 6th, skipping 5th. 6th will also pull small hills on the hwy.

Really, it feels like there is a different motor in there. Lots of low end grunt, and the high end pulls in every gear.

For me, it was well worth the money spent. I do not even think about the Hemi Wrangler anymore. You cannot get it with a stick anyway, and now my motor moves my Gladiator great with big tires. --- and I am getting really great gas mileage !

PS. I think you can count on 1.5 to 2 mpg increase with the right gears and your 37s... So, that also could be a good justification.

Interesting, so it sounds like you are getting better mileage with 37's than you did with stock 33's? Wow! Didn't expect that. I guess regearing is necessary according to most of what i hear. Sounds like it may be a plus on mileage and power as well. Dealer is hesitant to regear now because of some issue with differential parts not being available, so may have to hold off on that. What kind of lift do you have?

 

[Deleted member 30519]

I've been running 38s on 3.73 6spd manual for a few weeks now and I'm looking for someone in my area to do 5:13s. I noticed a big loss in power going from 35s to 38s.

 

[Deleted member 30519]

I have a manual JTR with big 37s (Goodyear MTRs and Method 703 - light rims) and I went with Dana Spicer 5:13 gears. What a huge difference in performance. It even gets better gas mileage now. The torque and performance with the 5:13s is impressive. Much, much faster 1/4 mile time. It really moves with those huge 37s - everybody that sees me row through the gears with purpose is impressed.

Off-road, the 5:13s are great. The granny gear if perfect for rock crawling - ie. you can practically stop without clutching. In addition, you can stay in 4wheel High longer, instead of always going into 4Low.

Also, because of the torque multiplication, all gears except for 5th and 6th really have a good surge in the high rpm, and you can easily go from 4th to 6th, skipping 5th. 6th will also pull small hills on the hwy.

Really, it feels like there is a different motor in there. Lots of low end grunt, and the high end pulls in every gear.

For me, it was well worth the money spent. I do not even think about the Hemi Wrangler anymore. You cannot get it with a stick anyway, and now my motor moves my Gladiator great with big tires. --- and I am getting really great gas mileage !

PS. I think you can count on 1.5 to 2 mpg increase with the right gears and your 37s... So, that also could be a good justification.

I'm sold ! Now I just gotta find a reputable place to do it. I wonder how close in size our tires are. I'm running the 38" patagonias that I think measure to 37.8".

 

[hjdca]

Interesting, so it sounds like you are getting better mileage with 37's than you did with stock 33's? Wow! Didn't expect that. I guess regearing is necessary according to most of what i hear. Sounds like it may be a plus on mileage and power as well. Dealer is hesitant to regear now because of some issue with differential parts not being available, so may have to hold off on that. What kind of lift do you have?

Clayton 3.5", you can click on my build thread in my profile and see it all, and 4wheeling videos in excruciating detail... lol.

Here is the story on my gas mileage. On my manual JTR stock, my gas mileage was always low, like 13, 14, sometimes even 12. I live in a very hilly area, so, it seemed right... GPS always showed my 1 or 2 mph low at 70 mph or 80 mph, but, the tire setting was 33.08, which is actually higher than the true tire size. I think the computer is setup for the 8th gear auto tranny instead of the 6th gear manual tranny which has a lower 6th gear than the auto 8th gear. So, even though I did not change it, to fix the speedometer, I would have had to go up from 33.08.
So, when I did my lift and tires, I decided to go with my Escort radar detector with GPS and for 2 or 3 days, I played with the tire size to get the mph perfect. Again, it turned out that the size is higher than 37". It is something like 37.15, but, I do not remember exactly. Now, I am getting my true mpg, and I am over 14 mpg in the city and over 15 mpg on the hwy, and I am running the soft top with it open at 70 mph and lots of hills in the mountains here in California.

I think what helps the gas mileage is that I am always in 6th gear early and at much lower speeds. 6th gear will pull now at lower speeds because of the torque multiplication. In the city, I also go from 4th to 6th and skip 5th a lot.

I am actually amazed at the torque, power, and gas mileage of this "so called" van motor with the 5:13s and a light set of 37" tires and rims. It really is a great motor when geared right.

 

[Happycoop]

Glad to see this thread as I just ordered my wheels and I'm deciding between 35s for now or jump straight to 37s and a potential re-gear. I live in the Appalachian mountains (so not as tall as midwest), and the stock 4.10s w 33s is a good combo. I could live with 35s and no re-gear, but I have a feeling 37s would push it. My thought is to put in 4.88 or 5.13 once I go 37.
On a separate note, the Hemi is actually available with a 6 speed if you go through AEV (I almost bought one before deciding against it). They don't make many of them, but they do make it.

 

[JTRUBI]

JTR, Mopar 2” and 37” K02s 6 Speed

it needs a regear, I do about 100kms a day on the highway and any incline I have to drop a gear or two to keep the RPMs up enough to accelerate.

while you can get away with the not regearing, I’d recommend it. I do plan to regear, but haven’t decided on the gearing yet as I might go bigger lift and tire.

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