Do I need to re-gear?

[Tommyd]

OK, so I have a 3.73 Axle ratio on my Jeep beach Gladiator which is based on the Willys and I only have put 285/70/17 bfg ko3 tires and a 1.5" Terraflex front stabilizing lift. Nothing in the back, no overlanding gear or nothing extra weighing the truck down.

Now My question is like at times, the truck seems to struggle to maintain speed, not so much on regular driving, but really noticeable with the Cruise Control on (like when it needs to catch back to the set speed it would go as low as 3rd or 4th gear like going really hard rpms) and at times it feels kinda sluggish at regular driving.

Now, I don't know if it is a normal thing with these trucks and engines, or if indeed is due to the tires, or maybe its the gear ratio?? Is anyone having a similar issue with the cruise control like I'm having or think its due to the Gear Ratio on my truck?

Any ideas or recommendations?

I went to 37s a couple years ago with 5:13s. My wife has a bone stock gladiator sport on the horrible skinny street tires in like a 31” diameter.
my gladiator feels way peppier and pull gears better.
if you ever rehear you won’t regret it.
the 3.73s are pretty horrible on anything bigger than stock. Kinda even on stock tires too.

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[Ed Dell]

I've been running 285/70R17 on my 3.73 gears for two or three years now, and I have no complaints. It holds 75mph on the interstate just fine. Did you use a programmer (JScan, Tazer, whatever) to tell your computer about the larger tire size?

Yes, I did updated the tire size with the JScan once I changed tire sizes,

 

[Zachanadandy]

I went to 37s a couple years ago with 5:13s. My wife has a bone stock gladiator sport on the horrible skinny street tires in like a 31” diameter.
my gladiator feels way peppier and pull gears better.
if you ever rehear you won’t regret it.
the 3.73s are pretty horrible on anything bigger than stock. Kinda even on stock tires too.

Feelings are meaningless. Myself and several others measured actual 0-60 before and after gears and gained nothing to 1/10th of a second. Being on 37s I don't care if you run 6.72 gears in the axles the stock sport will drag you if you line up next to each other as it's so much lighter with so much less rolling resistance. A JLU sport with 3.45s and 32s has the same 0-60 as a Rubicon with 4.10s and 33s. Gears only make it feel quicker as it's running through the gears at lower speeds. If it isn't measurable it isn't quicker period.

 

[Ed Dell]

Sidetrack: I wouldn't doubt the proper calibration of tire size would/could hav

Since 33s are standard on Rubi and Mojave, with 4.10s, there's likely little difference with 33s and 3.73 gears.

Sidetrack: I wouldn't doubt the proper calibration of tire size would/could have an effect. Before I changed my tire size, I downloaded a GPS-speedometer to compare. I also used Waze to compare speeds between the three sources. The truck was off, the other two matched. Changed the tire size until speed matched. 36.5" or something like that. Comparing to the radar trailers, my speeds match those.

TBH I thought about that too... I had wondering around in my mind that probably the tire size input I put with the Jscan was not accurate...

I did the whole setup to get the proper size and input for the tire into the scan but to be hones didnt feel too confident. Not sure if that might be the issue?

Also, Care to share the GPS Speedometer app you used?

 

[629]

Ask yourself two questions. 1. Does my final drive work for my driving conditions? IE can you still use top gear how you drive the Jeep. 2. Is my first gear low enough for my usage? IE towing (getting a load moving) or offroading (is 1st low enough for how you wheel without using low range). Really all the gears in between make no difference.

Example…I run 4.88s in my TJ with 31s…sounds low but I live in the mountains, frequently offroad in steep conditions and the max posted speed in my county is 55. So for my use I can use 5th and 1st just fine with that gearing.

 

[RHINO79]

I think a 32 inch tire is maximum for 3.73 the willys come with 255 75 17 =32.1 inch tire.

 

[D_JT]

Since you plan on going to a 35 later on, I would plan on regearing to 4.56 for the 35's.

 

[SamJ3]

Sharing what I've learned on this subject, then my personal experience....

Tire size - yes, you need to 'tell the Jeep' what size the tires are. You can use JSCAN, Tazer, or pay your Jeep dealer to reprogram.

Transmission - Assuming you have an automatic transmission, your 850RE transmission has 8 gears to choose, two of which are over drive. The transmission 'learns' its shift program while driving. When you change the tire size, the transmission needs to 'relearn' the shift points. This happens over time, but there are ways to force/accelerate the process.

Axle ratio - JTs come with ratios as low as 3.73:1, but options like MaxTow, Rubicon, etc. increase this (e.g., 4.10:1). On top of that, transfer case has low ration (4L) of 2.72:1 with the Select-Trac as standard, or 4:1 on Rock-Trac in Rubicon.

Total low gear ratio is the derived from the combined effect of the differential and transmission low gear.

Changing gears will affect both extremes - high speed driving, and low speed off roading.

Larger tires reduce the effective axle ratio, hence the consideration to regear.

Here's my experience: I upgraded the tires from the stock 31.5 inch to 34.6 inch all-terrain tires, and immediately reset the tire height setting (using a Tazer). Initially, the shift points where way too high under light accelleration. Over the course of several days of city driving, the transmission programming imrpoved. Eventually, it settled into a very normal behavior. Most highway cruising would sit on 7th gear (lower of two overdrive gears). Sometimes it would find 8th gear, and sometimes it would stick to 6th (1:1) for a while, especially on hilly highways. The point of this is that the transmission has plenty of gear choices to optimize the shift points, and will adapt to the conditions and drivetrain available.

In stop and go driving, I feel no noticable change in accelleration under normal driving, or perhaps I got used to the slight change, or perhaps the transmission reprogrammed itself to yield similar performance. Outright full throttle launches from a standstill are affected. My 0-30 times are 0.2 seconds slower. In practice, full throttle launches aren't a regular thing.

My vehicle does about 4 weeks of off-road per year, so I rely on 4L. While I can't move as aggressively on the trails as a lower geared double locker set ups, it is still performs respectably. On the road, MPG are generally unaffected - driving habits are the biggest factor in actual fuel economy.

Thus, for me and my Jeep, the factory 3.73 gears work just fine with 35"" Mickeys.

My recommendation is drive it for a while (to allow the transmission to relearn) after changing the tire height before deciding that you need to replace the gears.

 

[GI Grandpa]

OK, so I have a 3.73 Axle ratio on my Jeep beach Gladiator which is based on the Willys and I only have put 285/70/17 bfg ko3 tires and a 1.5" Terraflex front stabilizing lift. Nothing in the back, no overlanding gear or nothing extra weighing the truck down.

Now My question is like at times, the truck seems to struggle to maintain speed, not so much on regular driving, but really noticeable with the Cruise Control on (like when it needs to catch back to the set speed it would go as low as 3rd or 4th gear like going really hard rpms) and at times it feels kinda sluggish at regular driving.

Now, I don't know if it is a normal thing with these trucks and engines, or if indeed is due to the tires, or maybe its the gear ratio?? Is anyone having a similar issue with the cruise control like I'm having or think its due to the Gear Ratio on my truck?

Any ideas or recommendations?

EDIT** SInce I forgot to mention it originally , I did change the tire size with the Jscan in the truck.

Also, I might be thinking of going into 35's next tire change (not soon tho) so that might also influence my decision into re-gearing down the road if it indeed affects performance.

Do you need too, no. In my case, I went from 33s to 35s and I waited about a year before regearing my Mojave from 4.10 to 4.88s. After regearing I gained 8th gear back, picked up 2 mpg on road trips and a solid mpg around town and I have improved acceleration and throttle response. Also, I live in Colorado, so going a little deeper in the gears helps compensate for the altitude.

 

[Tommyd]

Feelings are meaningless. Myself and several others measured actual 0-60 before and after gears and gained nothing to 1/10th of a second. Being on 37s I don't care if you run 6.72 gears in the axles the stock sport will drag you if you line up next to each other as it's so much lighter with so much less rolling resistance. A JLU sport with 3.45s and 32s has the same 0-60 as a Rubicon with 4.10s and 33s. Gears only make it feel quicker as it's running through the gears at lower speeds. If it isn't measurable it isn't quicker period.

Wow that makes no sense. I’m not talking about 0-60. I never floor it every time I drive. You get your tourqe back from goi g up in tire size. Like I said I had both and still do. I pull trailers loaded with mounded green red oak that I split. 3:73s would be absolutely horrible. 2nd gear is to tall on some trails so you have to leave it in first and rev it or put it in 4 low. A lot more pros too. I don’t care to list them.
best money I spent.

 

[Zachanadandy]

Wow that makes no sense. I’m not talking about 0-60. I never floor it every time I drive. You get your tourqe back from goi g up in tire size. Like I said I had both and still do. I pull trailers loaded with mounded green red oak that I split. 3:73s would be absolutely horrible. 2nd gear is to tall on some trails so you have to leave it in first and rev it or put it in 4 low. A lot more pros too. I don’t care to list them.
best money I spent.

You said "peppier" and I pointed out it's not measurablly quicker which means your peppier is placebo, myth, emotion, or confirmation bias justifying the money spent and nothing more. 4.10s and 37s and even hauling an overloaded 8200lb trailer 600 miles there was no lack of gearing. Maintained 65mph even up a major grade that gains 4k feet in 20 miles. Outside of 1st gear there's no advantage gained by axle gears that can't be had with a simple downshift. Final drive ratio is all the engine sees. It doesn't know the difference been 5.13s in 8th, 4.10s in 7th or 3 45s in 6th a they are the same final drive ratio. Glad you're happy with your gears but they don't do near as much as some think they do.

 

[Tommyd]

You said "peppier" and I pointed out it's not measurablly quicker which means your peppier is placebo, myth, emotion, or confirmation bias justifying the money spent and nothing more. 4.10s and 37s and even hauling an overloaded 8200lb trailer 600 miles there was no lack of gearing. Maintained 65mph even up a major grade that gains 4k feet in 20 miles. Outside of 1st gear there's no advantage gained by axle gears that can't be had with a simple downshift. Final drive ratio is all the engine sees. It doesn't know the difference been 5.13s in 8th, 4.10s in 7th or 3 45s in 6th a they are the same final drive ratio. Glad you're happy with your gears but they don't do near as much as some think they do.

Yes as in it pull the gears way better. It has more tourqe. Who cares about 0-60. Just drive one with deeper gears and you will understand. If you’re fine with your stock gears then whatever who cares.

 

[Zachanadandy]

Yes as in it pull the gears way better. It has more tourqe. Who cares about 0-60. Just drive one with deeper gears and you will understand. If you’re fine with your stock gears then whatever who cares.

We've run both stock and regeared and I can tell you for a fact it was a waste of $3k period. Gained 1 mpg around town, lost 2-3 at freeway speeds. We roadtrip and wheel our Jeeps all over the country so I need the top end as much as the bottom. Like I said, technically you have more torque in a given gear, but outside of 1st gear the auto will run whatever gear you need for the load. Who cares if I'm pulling a trailer up a steep grade in 4th gear with stock gears or 5th gear with deeper gears? The torque is the same at that point and the engine doesn't know the difference of where the final drive ratio is coming from.

 

[Gladiatorx2]

I have had 3.73 gears with 275/70
R17 which I think is about a 32" tire. I also had 4.10 gears on a Max Tow with light 315/70R17 and they performed virtually the same.

I am on my 2nd Rubicon with 4.10 and 37's. The first one had a camper shell and a 2.5 lift and with me in it weighed 5,670 lbs. The performance around town and off road was fine. It was only lacking at elevation while climbing a grade.

This Rubicon only has a tonneau cover and weighs 5,400 with me in it. It is lifted 3.5" and while still on the stock Falken MT's I averaged around 19 mpg. After adding heavier 37's I have averaged around 17 mpg. In the around town and off road case the performance difference is negligible, but at elevation and climbing grades it is noticeable.

I agree with the members that post an improvement with a gear change. I do see that acceleration, towing and economy would be improved.

I also agree with the post that shows minimum improvement in acceleration, especially for the cost of doing so. I would guess that the value of the gear swap would be in the overall drivability.

If I had a friend that would furnish the labor for beer and barbecue I would make the change myself. But, considering the total cost of installation in my area w/parts and labor exceeds $3000, I will continue to view my 4.10 gears as "adequate ".

Based on owning 4 Gladiators, to me the 4.10 with 35's has been my best combo. But, with my lift, they would look kind of silly.

 

[Zachanadandy]

I have had 3.73 gears with 275/70
R17 which I think is about a 32" tire. I also had 4.10 gears on a Max Tow with light 315/70R17 and they performed virtually the same.

I am on my 2nd Rubicon with 4.10 and 37's. The first one had a camper shell and a 2.5 lift and with me in it weighed 5,670 lbs. The performance around town and off road was fine. It was only lacking at elevation while climbing a grade.

This Rubicon only has a tonneau cover and weighs 5,400 with me in it. It is lifted 3.5" and while still on the stock Falken MT's I averaged around 19 mpg. After adding heavier 37's I have averaged around 17 mpg. In the around town and off road case the performance difference is negligible, but at elevation and climbing grades it is noticeable.

I agree with the members that post an improvement with a gear change. I do see that acceleration, towing and economy would be improved.

I also agree with the post that shows minimum improvement in acceleration, especially for the cost of doing so. I would guess that the value of the gear swap would be in the overall drivability.

If I had a friend that would furnish the labor for beer and barbecue I would make the change myself. But, considering the total cost of installation in my area w/parts and labor exceeds $3000, I will continue to view my 4.10 gears as "adequate ".

Based on owning 4 Gladiators, to me the 4.10 with 35's has been my best combo. But, with my lift, they would look kind of silly.

Unfortunately the drop in power at elevation wasn't helped by gears either. The only solution for that is v8 swap or forced induction in my experience. Unless it's lacking torque in 1st gear, no amount of axle gearing is going to help. If that worked we could just drive around in LO range and get all this magical power and mpg and what not.

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