Understood. I guess my experience with variable pots is that they tend to drift due to temperature and vibration etc. That being said, there very well may be a potentiometer inside the speedohealer that you cant even see.
4.56 or 4.88 gears?
- Thread starter CHAWK
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The pcm uses the speed signal for other things, and then communicates it to the cluster digitally, so there's not really a good way to intercept and change it there. It's gotta be between the sensor and the pcm.
Fair enough. Then at the PCM instead of at the transfer case. Same principle.
Stock rubi lockers to something aftermarket that doesn’t require thick gears since as far as I’m aware, there is no thick cut 44 5.89 R&P….for the TJ anyways.
Exactly. That's what both of the mentioned solutions do. Sounds like Blaine prefers to turn a knob until the speedometer reads correctly, the speedo healer does some math in between to adjust it by a percentage.
I don't know what the signal format is; I always figured it was some sort of frequency or pulse width modulation but if a simple potentiometer works then it would have to be a scaled voltage. Unless the potentiometer solutions Blaine mentions are not literally just a potentiometer but an adjustment knob that shifts the modulation.
The Jeep engineers (with all their high level math and engineering) also used the same axle gears for the 6 speed manual and the 4 speed auto. 0.84 OD vs .69 OD.I've spent the last two hours trying to wrap my mind around some of the concepts discussed in this thread. Somehow this has turned into some high level math and engineering. It certainly has my brain feeling like it needs a nap. Probably because of my "calculations" the convo has taken a turn into the weeds of engineering, physics, and math that I for one can't figure out and has me feeling dumb too.Which brings up another point, the educated and experienced engineers did a lot of calculations and work to design a jeep a certain way, I don't think that even they had all the "right" answers. Interestingly though if you run the numbers on gearing vs tire size for a stock tj (I think it is 30" tires and 4.10 gears?) and then for 33s and 4.56, it is almost exactly the same ratio as stock. Meaning it would get drive shaft, transmission, and motor speeds, relative to vehicle speed, right where the eggheads at Jeep put them. But loads of people like their jeep better geared lower and the entire aftermarket industry is there to "improve" stock designs. So who knows?!
42rle / 29.5" /3.73 = 2052rpm @ 70mph
NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)
AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)
NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)
32rh / 29.5" / 3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)
The only 5.89 gears for a Dana 44 I have ever seen are from Dana. And the last time I asked about them, they didn't work on an ARB rd116 which uses regular cut gears. I forget the reason.
Not sure why that would be. Revolution has a listing for “Dana 44” from 3.55-5.89 and lists a ton of vehicles. XJ/TJ are on there.
So as long as you go to an Eaton or other standard locker (I guess not ARB unless that info was incorrect), then I can’t possibly think of why you couldn’t gear a TJ Rubi to 5.89 after ditching the stock lockers since they use the same LP gearset f/r. Unless I’m missing something but I don’t see what I’d be missing here since Revolution lists the TJ.
5.89 Revolution Dana 44 Gears
A tire will vary in revs/mile depending on the psi.
Measuring the hub center height x2 is more accurate to your Jeep and your tire pressure. The more accurate (but nearly identical method) is to determine your speed via GPS at a certain engine rpm and use a calculator like GrimmJeeper to adjust the tire size until the engine rpm and gps speed match. That number will be the hub center height x2.
I've used many of the turn to adjust types starting with the Superlift version, then Dakota Digital until they messed that all up and now the Jet Accuspeed. None of them have drifted or changed correction value. Maybe I don't know what is being turned to correct the signal but whatever it is, it appears to be fairly steady.
Unless I've missed something in the documentation and the install videos, the speedohealer only attaches at the transfer case, not at the PCM.
No other specific brand was discussed other than a generic reference to one that had a knob you turn. I have no idea where that one attaches, probably anywhere you want since I believe you have to cut into the harness to install it. But as my objective is plug and play that's not really what I'm after.
I did find another brand called SpeedoDRD which might be plug and play but theres little to no information out there about it and I wasn't able to find any install documentation to see which end it attached to.
I've noticed some ratios use different tooth counts between thick vs standard...the thick uses the smaller tooth counts. Gear design is outside my wheelhouse so the only thing I could infer from that was that they'd prefer the larger tooth cross section afforded by the smaller tooth count but are forced by the thinner gear into the more numerous, shallower teeth. Following that logic, maybe they just don't think they can get enough tooth area into the thickness of the standard ring gear.
Yes, though I have a theory I've been wanting to test out:
1. A significant determiner of a tires load capacity is the heat generated by sidewall and contact patch deflection at speed.
2. The tire is designed to have a specific contact patch to achieve its intended treadwear characteristics.
Which leads me to theorize that the ideal pressure for any vehicle may be the one that results in the same sidewall deflection as the manufacturer designed it for at max load rating and max inflation pressure. It's a variation on the chalk test, but instead of using my opinion of what the contact patch should look like, it uses the one developed by the multimillion dollar R&D budget of the tire manufacturer.
To test it I plan to adjust the pressure until my hub height matches what I calculate from the revs/mile and see if it results in a reasonably comfortable ride. If it returns a pressure I that sucks to ride on or is too low for me to be confident in, then I'll consider the theory disproven and start using my hub height at 25psi in my calculations.
It intercepts the signal at the transfer case and transmits a new one to the pcm. It just does it at the transfer case because there's a connector there that you can unplug, then plug one into the sensor and one into the harness.
ok, I had assumed that the other end of the cable at the PCM also had a connector.
Appreciate the insight. I don't plan to trailer at any point, so I'm often driving a good distance to trails. With the 4.88 am I just looking at spending more time in 4th gear while climbing? I'm concerned that with the 5.13 I'll be winding out RPM's if I spend a good amount of time on the freeway to reach destinations.... with the significant $$$ associated with regearing, I want to give myself the best chance of being happy with it! I guess worst case I could always make the tires bigger or smaller!
It's all relative. I'm running 35s with 5.13s and (6 speed which has a .84 overdrive) at 70mph I'm turning ~3,000rpm comfortably. If you consider 2,800 rpm at 70 mph winding it out, then I'd stick with 4.88s. As Jerry pointed out increased weight and rolling resistance should be factored into gear selection. Check out grimmjeeper.com for more info on the effect different gears will have on your set up.
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