RHO gears… for trx

[Fifty]

Any of the dealership folk on here know if the RHO gears are available for purchase yet?

I’d love to put a set of 3.90 or what ever it is in my trx

Don’t need the whole rear axle, just the gear sets. If the front gear set is available seperate of the front differential too that would be great.

But I have a feeling this gear swap will become very very popular

 

[Quietpeen]

to have more low end grunt out of this truck would be fun. Not interested in top speed, but the people averting 7 or 8 mpg’s might not like the hit

 

[Fifty]

Oddly enough, having two overdrive gears, when you step up in gearing you actually get better mpg…
But when you go to far in gearing that’s where the mpg take a hit.

I’d bet we would gain a mpg or two until we pass 4.5x gears

 

[TCAT]

I would be interested.

 

[TRX-TK]

Would be interested as well!

 

[trxmanusa]

maybe with 37's it would be good but the factory gear ratio seems perfect to me. . .

 

[FULLTHROTTLERICK]

If we did gain 1-2mpgs, why wouldnt the dealer have just put them in from the factory? My understanding would be they’d want a better EPA rating if it was that easy/cheap!

 

[Fifty]

EPA ratings are computer simulations. It’s why on paper the 5.3 gm motor gets better mileage than the 6.2 but in reality it’s opposite.

3.55 gets better mileage in a no wind, low friction 55 mph computer simulation but in reality a 3.90-4.xx will keep the engine in the sweet spot at a different mph and rpm with wind and friction

OEMs build to keep the epa happy

 

[FULLTHROTTLERICK]

EPA ratings are computer simulations. It’s why on paper the 5.3 gm motor gets better mileage than the 6.2 but in reality it’s opposite.

3.55 gets better mileage in a no wind, low friction 55 mph computer simulation but in reality a 3.90-4.xx will keep the engine in the sweet spot at a different mph and rpm with wind and friction

OEMs build to keep the epa happy

Yea that 5.3L GM is definitely not better than the 6.2. Had a few of them myself. Good motor though

 

[DirtMcGirt8732]

Any of the dealership folk on here know if the RHO gears are available for purchase yet?

I’d love to put a set of 3.90 or what ever it is in my trx

Don’t need the whole rear axle, just the gear sets. If the front gear set is available seperate of the front differential too that would be great.

But I have a feeling this gear swap will become very very popular

I’ve been checking Mopar OEM parts sites pretty regularly. They really just started showing parts for the RHO, but nothing for the differentials yet.

 

[Fifty]

Usually the techs get access to the individual parts before the general public.

I wonder if @PotterTRX knows of anything

 

[GP4L]

I’d love to put a set of 3.90 or what ever it is in my trx

3.92 according to Ram. And agreed. Even on OEM tires, the weight/drag of the TRX.. A 3.92 would probably work very well overall. Seems like the 3.55 was really only ideal for the EPA's CO2 testing parameters - the thing they care the most about - which is hilarious as the TRX sill only got a 1/10 rating from them for greenhouse/smog lmao

 

[Fifty]

I’d love a 3.92 on my 35’s let alone 37’s.

When I did my s/c v6 from 3.42 to 4.56 on 31’s and 35’s it was awesome.

6,7 and 8th gear were actually functional, no more down shifting or gear hunting in 7th and 8th on the freeway.

My trans temps stayed happy offroad.

So aside from the acceleration help on the trx, I bet the trans temps will be happier offroad.

 

[Jimmy07]

2025 parts catalogs have been up for a while now. But 3.92’s have been available on Ram 1500’s since 2019, so all the same parts.

Rear Axle: Housing, Differential and Vent for 2025 Ram 1500 | All Mopar Parts

parts.allmoparparts.com

 

[Fifty]

Front yes, rear no.
The d60 rear is a new to trx and now RHO axle

 

[Teedger]

Curious if upgrading to the 3.92s would require a tune or not necessarily?

 

[Fifty]

Yes

If there is a way for the Tazer to reprogram the speedo…. Or if a local dealer would be willing to do it.
Or alpha obd (I need someone to Barney style teach my dumb ass how to use alpha obd)

But really it will just be for speedo correction. Even if you don’t care that the speedo is off, the speed limiter will be lower with the new gears.
I’d have to do the math to figure out how much. What ever the ratio difference is, it will be that much lower.


The guys running 37’s will be effected less but still be effected

 

[Fifty]

New speed limiter would be 107 mph if you don’t correct the “speedo”

It’s not just the speedo, it’s also the abs/traction control signal which commands the speed limiter.

 

[Fifty]

Gear Ratio Calculator

First Gear Ratio 1)
4.71
Second Gear Ratio 1)
3.14
Third Gear Ratio 1)
2.11
Fourth Gear Ratio 1)
1.67
Fifth Gear Ratio 1)
1.29
Sixth Gear Ratio 1)
1.00
Seventh Gear Ratio 1)
0.84
Eighth Gear Ratio 1)
0.67
Reverse Ratio 1)
3.30

 

[Fifty]

It looks like 3.92 gears and 37’s have the same overall ratio as 3.55 and 35’s

So looks like no speedo correction needed with 3.92 and 37’s