No. The bcm, pcm, and abs don’t care what the gears are. Speed is taken from the wheel speed sensors only, so the only thing that matters is that the bcm is broadcasting the correct tire size.
RHO gears… for trx
- Thread starter Fifty
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I believe The speed limiter uses a signal from the tcm not the wheel speed sensor (abs/tcm)
So it will likely trigger the speed limiter at 107 mph if you are running 35’s.
37’s , the speed limiter and everything else should be fine.
So it will likely trigger the speed limiter at 107 mph if you are running 35’s.
37’s , the speed limiter and everything else should be fine.
Nope. The speed limiter is a specific number set in the PCM (in the TRX case, it’s set at 117mph). The wheel speed sensors report the vehicle speed to the cluster speedometer (via the ABS module) based on what the tire size is set to in the BCM.
From the factory, the tire size in the BCM is set to 2680mm circumference (33.6” diameter tires). If you put 37’s on the truck (and assuming the ACTUAL diameter is 37), and you don’t adjust the tire size accordingly in the BCM, then the top speed that will display on the speedometer will still be 117mph, but you’ll actually be traveling about 128mph.
This is why you can trick the TRX into going 140+ mph by adjusting the tire size in the bcm down to about 28” diameter (when factory sized tires are on the vehicle). This is also why shift points are corrected when you change the tire size in the BCM for when bigger tires are installed.
Changing the gears won’t have any effect on the top speed either. If all else remains the same (factory tires, bcm settings, etc), and all you do is swap out the 3.55’s for 3.92’s, the top speed is still going to be 117mph, but obviously the shift points will be different.
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Pardon me if I missed something in this thread, but I don't think a front "gear swap" is possible without replacing a lot more in the front. Since about 2013 or 2014, Ram has welded the gears to the carrier in the front axles. Unless for some reason the TRX front axle is done differently than all the other Ram 1500s, despite it being the same axle.
When the RHO axle specs were first announced, I brought this idea up, but as a complete axle swap with a partly wrecked RHO.
When the RHO axle specs were first announced, I brought this idea up, but as a complete axle swap with a partly wrecked RHO.
Then ram is doing it different than everyone else. Which is good for us.
That will make things a lot easier. I am sticking with 35’s for a bit since I have two sets.
Commenting on this thread because I want to see this done, hopefully @Fifty will do a video or pictures to guide us in this journey
I’ll let everyone know. But when it comes to install, I’ll be hitting up one of the trx experts.
There is a guy here who is a ram mechanic I want to say in Michigan or Kansas or something.
I’ll likely see if he will do the install for me and I’ll drive out and back from Cali.
There is a guy here who is a ram mechanic I want to say in Michigan or Kansas or something.
I’ll likely see if he will do the install for me and I’ll drive out and back from Cali.
Not sure the RHO gears would be a big enough jump for me to wanna drop the $$ and have everything pulled apart. 410s maybe.
If the RHO crowd reach out to the gear companies then they will bite. But until….
3.92 would be a nice jump.
3.92 would be a nice jump.
Playing with the gear ratio calculator, the 3.92 gears would be quite perfect for a stock tire size drag application for most with an upper pulley + tune (in that +150-300whp range) since almost all will need to trap well above 110ish mph. Getting into 5th like 10mph earlier vs just barely getting into 5th, and still not needing 6th unless the power is there to trap above 130ish mph. Not to mention a significant 0-60 improvement in general.. Yeah, where do I sign up? lol
I hate you drag guys, but since you are on my side I’ll make an exception
Lolz
Lolz
Thr front diff assembly is pretty reasonable for the trx. If the front axle assembly in the photo has all the internals installed, it will probably be easiest to just buy a new front RHO diff. The question will be availability for a while. Then we can just re-gear the rear axle.
Attachments
Wow, that price seems WAY too low. Cheaper than a ring and pinion in most cases.
My best, somewhat educated guesses on the RHO parts based on the catalog notes and the fact that neither of these part existed before the 2025 model year. Front:
Rear:
The actual catalog for the RHO specifically isn’t up on the dealer sites yet. Have to select a different trim level and do some workarounds to even get this far. Doesn’t really matter since the parts are currently unavailable anyway.
Rear:
The actual catalog for the RHO specifically isn’t up on the dealer sites yet. Have to select a different trim level and do some workarounds to even get this far. Doesn’t really matter since the parts are currently unavailable anyway.
I thought the same thing. Gear setup alone would cost that much. I will happily install a new stub axle assembly but I don't mess with gears.
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