What is the best gear ratio for 37" tires (2020 Gladiator Overland)

[Pmpirn99]

I just purchased a 2020 Gladiator with 37" tires but the gear ratio doesn't seem right. The jeep struggles to stay in 8th gear (automatic transmission). I've read a lot that I should be at either 4:88 or 5:13 but not sure what is preferred. I'm not overly familiar with gear ratios' etc. but was wondering if there is any sort of suggestion on a place I can take it in the Mechanicsville, VA area that someone would recommend.

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[Zachanadandy]

4.88s are more like stock, if you want it to have a little more grunt you could go 5.13s. I drive on the faster side so I'd go 4.88.

 

[ChiefsJT]

What you will be using your JT for will also change what ratio you should run. I have a Sport S on 37s, and will be running 5.13s because we have a small camper we will be pulling with it. The extra little torque from the 5.13s, especially when we head up into the mountains, seems like a good tradeoff for MPG loss or top speed loss.

 

[Teqsand]

Assuming you're a gasser not diesel?

 

[Volt0]

Depending on what you’re planning to, you might also consider downsizing to 35s, or dare I say 33s. I’m sure those 37s look cool, but you’re at some increased risk for breaking axles ( especially if those weren’t upgraded as well, and you plan to wheel/tow with it ). If you plan to drive in winter conditions, depending on the kind of snow you’re in, you could get better traction with narrower tires. Regearing will also increase the risk of breakage in the differentials. To fit those 37s, I’m guessing there’s a lift, and either some wheel spacers or offset rims, which can also make a challenge for your steering components.

I’m calling all of this out, b/c someone has started opening Pandora’s box with those bigger tires, and it’s not clear how far down that path your gladiator is. It could be less expensive in the longer term, and more inline with your needs, to downsize the tires.

 

[Dickster]

Here is another chart.

 

[Warped]

The charts posted are great and affirm my automatic JL running on 37s with 4:56 and is near perfect for on or off-road situations.

 

[Pmpirn99]

What you will be using your JT for will also change what ratio you should run. I have a Sport S on 37s, and will be running 5.13s because we have a small camper we will be pulling with it. The extra little torque from the 5.13s, especially when we head up into the mountains, seems like a good tradeoff for MPG loss or top speed loss.

I have a small Gradywhite that I’ll be pulling with the truck. My concern is that I can’t stay in 7th or 8th gear for my transmission when driving normally. Wasn’t sure if this would hurt or shorten the life in my transmission.

 

[Pmpirn99]

Assuming you're a gasser not diesel?

Yes gas

 

[JTGuy]

With the 8 speed auto the 6th gear is 1:1. Very strong with possibly less heat buildup. Towing a trailer at 55 in 6th is not a bad thing. With lower diff gears like 5.13 the pinion starts to get small with less teeth and is really spinning fast.

 

[Gizmo]

Something else to consider with some vehicles OE driveshafts may not be balanced well enough for higher rpms that you get with lower axle ratios and can end up with a vibration then ya have another thing to work on . Seen that with TJs which isnt to bad being you only have 1 DS instead of two in the rear

 

[CrazyCooter]

That chart is for JKs with the NAG1 5speed trans. Our 8 speed trans has taller OD gears.

 

[Pmpirn99]

Something else to consider with some vehicles OE driveshafts may not be balanced well enough for higher rpms that you get with lower axle ratios and can end up with a vibration then ya have another thing to work on . Seen that with TJs which isnt to bad being you only have 1 DS instead of two in the rear

Thanks Gizmo.

 

[Dickster]

That chart is for JKs with the NAG1 5speed trans. Our 8 speed trans has taller OD gears.

I posted the 8speed gear ratio as well.

 

[Scott L]

There's a few good shops in Manasas. But I'm thinking Mechanicsville is pretty far south in Va?

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