Switched from 33's to 37's: What gear?

[MOOG5050]

Don’t have the 392 but with the 2.0t on 37s, the 4.56 seem perfect.

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[Zandcwhite]

I would think with the torque of a 392 that 4.10's would be fine (but perhaps not). It would not seem to be worth the cost of a re-gear for 4.56, so 4.88 would be the next iteration.

The 392‘s only come with 3.73s iirc, I'd say 4.88s would be more than low enough. 4.56 would be better if you do a lot of freeway driving and not much crawling. You'll be looking at $2-3k for a regear.

 

[CarbonSteel]

The 392‘s only come with 3.73s iirc, I'd say 4.88s would be more than low enough. 4.56 would be better if you do a lot of freeway driving and not much crawling. You'll be looking at $2-3k for a regear.

Yep, corrected in a later post

 

[AcesandEights]

Weight is a minor factor compared to diameter.

Diameter is the starting calculation. Weight and contact patch together only tell you to round up to the next larger number ratio after doing the calculation.

That should all go without saying; obviously.

 

[mgroeger]

I would go with 4.56 for sure.
If you have a shop do it, I would expect to pay anywhere from $3000 - $4000, when you factor crazy labor costs.

Holy $hit I've never hesard of gears going for that much. Plenty of shops around here and they are all in the $2k ballpark.

 

[word302]

Another way to calculate it:

33" -> 37" = 12%
3.73 * 1.12 = 4.18

The tires aren't just larger, they're heavier too.

That also assumes the original gear/tire combo was perfect.

 

[grimmjeeper]

That should all go without saying; obviously.

You would think. But there are a lot of people who obsess over weight like it's the only thing to factor in a gear change. Not everyone knows how gears and tire diameter relate to each other.

 

[Zandcwhite]

That also assumes the original gear/tire combo was perfect.

The XRs still came with 4.56s and 35s for the 392, which would mean 4.88s would be perfect for 37's.

 

[CarbonSteel]

The XRs still came with 4.56s and 35s for the 392, which would mean 4.88s would be perfect for 37's.

Given the on tap torque of the 392, I would not re-gear from 4.56 to 4.88 to move from 35's to 37's unless a large amount of weight was added and it was operating at altitude.

3.6L = 285 HP and 260 LB-FT
2.0T = 270 HP and 295 LB-FT
3.0TD = 260 HP and 442 LB-FT
3.0TT = 420HP and 468 LB-FT
392 = 470 HP and 470 LB-FT

 

[Zandcwhite]

Given the on tap torque of the 392, I would not re-gear from 4.56 to 4.88 to move from 35's to 37's unless a large amount of weight was added and it was operating at altitude.

Agree completely, I won't even spend that money to regear our 3.6L xr from the 4 56s for 37's. It was more a comment for the OP with 3.73s that even with the 392 4.88s are the right gears for 37's in my opinion.

 

[grimmjeeper]

Agree completely, I won't even spend that money to regear our 3.6L xr from the 4 56s for 37's. It was more a comment for the OP with 3.73s that even with the 392 4.88s are the right gears for 37's in my opinion.

For a 3.6 I'd do 5.13s for 37s any time.

 

[CarbonSteel]

For a 3.6 I'd do 5.13s for 37s any time.

Yep... especially at altitude.

 

[6.2Blazer]

To the OP, you mention downshifting to 7th on most grades. Do you notice a big difference as compared to the stock tires? The reason I mention that is it's not necessarily a horrible thing for the trans to shift from 8th to 7th gear when you put a little extra load on it....that's kinda' the reason they have 8 or more gears in transmissions nowadays were as only 3 gears used to be common. 8th gear is meant to be the optimum for flatland highway driving to give maximum fuel mileage and the lowest RPM's. 7th gear is still an "overdrive" gear meant for high speed low load driving conditions....the fact that a vehicle running 37" tires can maintain OD (7th gear in this case) on the freeway on a grade is pretty impressive. And I would say there is a big difference between saying the trans downshifts on a grade and saying the engine "struggles".

Now with that said I do understand the desire to regear and I'm not opposed to it either. If you currently have 3.73 I would go to at least 4.56 or even 4.88. From my personal experience you probably won't be able to notice the difference between 3.73 and 4.10 and IMO it's a waste of money. On paper going from 3.73 and 33" tires to a 37" tire ONLY considering tire diameter would require 4.18 gears to get back to the exact same cruising RPM. But add in the increased weight and rolling resistance of the tire, and the increased aerodynamic drag of the vehicle with taller tires you would want at least 4.56. You are only talking about 150 RPM at 65 mph between 4.10 and 4.56 and it would still be loping down the freeway at 1,800 rpm. In perspective that is a pretty low cruising RPM in perspective to vehicles from not that long ago.

 

[BDinTX]

3.6L = 285 HP and 260 LB-FT
2.0T = 270 HP and 295 LB-FT
3.0TD = 260 HP and 442 LB-FT
3.0TT = 420HP and 468 LB-FT
392 = 470 HP and 470 LB-FT

I think the 3.0TD is the EcoDiesel. Is the 3.0TT the inline six big brother of the 2.0T?
Also curious about the color coding. The diesel has 3.73 gears, does that change the regear/don't regear question for those?

Edit: I re-read this thread from the beginning and I think the consensus is to regear to 4.56 on ED and 392.

 

[CarbonSteel]

I think the 3.0TD is the EcoDiesel. Is the 3.0TT the inline six big brother of the 2.0T?
Also curious about the color coding. The diesel has 3.73 gears, does that change the regear/don't regear question for those?

Edit: I re-read this thread from the beginning and I think the consensus is to regear to 4.56 on ED and 392.

You are correct; the 3.0TD is the EcoDiesel and I added the 3.0TT as a reference point (new Wagoneer engine). Although you **may** get into a situation that would require a re-gear, with 442 lb-ft of torque and it being a turbocharged diesel, you will notice a tire change without a re-gear far less than say a 3.6L with 260 lb-ft. The same applies to the 2.0T--you hear far less griping about performance after a tire change and no re-gear than a 3.6L owner will.

You will also need less gear for all of them versus what a 3.6L will need to have the same level of performance. I think for the 3.0TD and the 392, the impact (for up to 37" tires) with no re-gear would be enjoyable versus "living with it".

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