Mine is 103:1 so yours is another 50% lower! You might go through a few sets of pads trying to pull that up!
IMO 2.72: on top of 4:1 is way too low.
I would stick with another 2.72.
Thats what Im doing with my build.
Ian, eurosonic: Yea, I know the commonly agreed upon max for an A/T is usually a crawl ratio of 130:1. A lot recommend no more than 100:1.V5MT1 M/T
5.38 axle (crawl ratio):
This is what I wheel now in my big Sport. KIM, it weighs in @ almost 6K lbs w/driver just doing DD service. If I pack it for Moab, its pushing into the high side of 6K lbs. The new one will still sit between 20-25" off the ground (ground to bottom of frame) so its still going to be top heavy like my current Sport. And, I live @ 5500 feet and have to deal with a minimum of one (usually two) 12/13K ft highway mountain pass to get anywhere west, and most of my wheeling is at 8K ft+. Big, loose crap, steep and off camber. I also still need to be able to do 70 MPH on the highway and put 3000 miles on it a trip without issues.
So, I need to make some concessions. This build will still lean more towards an Expedition vehicle rather than a true rock crawler. Just a little less Expedition and a little more crawler than my big Sport now. V4AW3 A/T
(please let me know if these ratios are incorrect)
So, I did some math and this is what I came up with. My existing build works pretty dang well on the mountain lower speed highways and great back and froth to Moab on the long stretches where I don't have 12% grades - it BARELY will get me over the passes without ending up in 3RD doing 40 MPH for 15 miles.
Existing build (3.5L)/
5.38 Axle, 34.4 diameter tire:
70 MPH, OD: 3049 RPM
70 MPH, 4TH: 3678 RPM
I have 4.90s in my '03 3.5L (with the Montero 5-speed A/T) so I think I can make some educated assumptions on the 5.13s. 4.90s in the new build I'm almost certain won't work here in CO (definitely didn't in my M/T build!). If I load the '03 up with gear and take it over the passes I'm in 3rd and 4th all the way up - probably 1/2 the time in 3rd. I can't see adding 1500 lbs and 37"s having a positive impact.
5.38s I THINK are too deep for an A/T although that puts me at about 2600 RPM in OD and 3500 RPM in 3RD @ 70 MPH. Better for OD but not great. I'd prefer OD to be about 2800 RPM. <img src="/forums/images/graemlins/frown.gif" alt="" /> Anyway, maybe just a tad deep in 3RD for an A/T.
So, 5.13s I guess. These should be a reasonable compromise. If I were lower in altitude (and stayed there) - even 4K ft - I think I'd consider the 4.90s, but my travel range is 10K vertical feet with a speed range of 75 MPH. A 4-speed A/T w/OD limits what you can do in the axles.
New build (3.5L)/
5.13 Axle, 36.6 diameter tire:
70 MPH, OD: 2486 RPM
70 MPH, 3RD: 3297 RPM
So, this is where I think I'm pretty well stuck at with axle gears even taking into account torque multiplication if I want to have a functional (useful) OD and TC lockup.
These are the projected crawl ratios for the new build.
I don't wheel A/Ts (except my stock '03) so I'm kinda in the dark here but that is way, WAY lower than my M/T build. CoSport had a '98 Sport w/35"s so I'm going by what I remember when we were wheeling together. The stock crawl ratio was 22.4 which was amazingly pathetic. That was like 52"/sec on 35"s - insanely fast. <img src="/forums/images/graemlins/frown.gif" alt="" />
New build (in/sec):
Existing build (in/sec):
I HOPE that an A/T will compensate for the difference. Lo-Lo-Lo could go up and that would be fine. 8" or even 10" /sec is no big deal. 31"? That's not so good - I'm not sure that converter slippage will change that number a lot.
2-speed rather than a 3-speed setup? No. 2.72 isn't deep enough by itself to handle any meaningful amount of my wheeling. I'd end up spending 99% of my time in Lo-Lo ( 2.72x2) - might as well just put in a single NP231 with 4:1 and call it a day.
Ian, I don't know. You all are running the Mitsu brakes I presume. I just don't have enough A/T experience to make a good judgement on stopping. What I DO know is my current brake setup can stall it in Lo-Lo-Lo, so .... The ProRocks will be the same as what I have now. Exploder rears w/ 1/2 ton fronts. PowerSlot rotors and Hawk 'green' pads. Enough? Don't know.
Anyway, I don't think I have much of a choice. Need deeper axle gears because of where I live and wanna keep the 3-speed t-case setup. If anyone has a better idea(s)/opinion(s), let me know.