jedg

So doing some research and have found one source (P4x4) that talks to what the optimum overall crawl ratio is for rock crawling. I currently have an 6.0L with 6L80e, 2.72:1 TC, 4.88 gears, 35.5" (measured) tires and 5800lb overall weight (very close to even balance front to rear) so a current 53.36:1 crawl ratio right now. I feel like my overall crawl ratio (while close to what my ratio was as a stock Rubicon) is still too high. By that, there are occasions where I'm balancing between crawling and then give it just a slight bit of throttle and now I've overpowered the traction. I think that if I had deeper crawl ratio, I wouldn't need the throttle so much. Now, my experience is low compared to some of you veterans of the rocks so maybe I'm just not seeing it right.

I will move to Dana 60 axles and an Atlas TC in the next year. I'll keep 4.88 gears in the axle and I'm considering 4.3:1 for the TC. That gives me an overall of 84.5:1 with that combination in first gear.

What's your opinion (based on experience) as to what is an optimum overall crawl ratio for a JKU with the above specs? I've read that optimum for an automatic is 80-100:1 ratios but it's pretty sparse on the reading for this topic. Below is just the numbers run for the above.




Tire diameter - 35.5

Transmission ratios (6L80e)
1 - 4.027
2 - 2.364
3 - 1.532
4 - 1.152
5 - 0.852
6 - 0.6673
R - 3.064

Axle ratio - 4.88

Current Crawl Ratio - 53.36:1 with the current TC (2.72:1 LO)

Atlas 2 Speed
3.8 - 74.68:1 (43.76 in 2nd gear)
4.3 - 84.5:1 (49.61:1 in 2nd gear) --- Probably this one??
5.0 - 98.26:1 (57.68:1 in 2nd gear)

zstairlessone

My Rubicon (6-speed) is 73:1 with factory tires in first. Something to consider when going past this, in an automatic, is the ability to stop what I call torque creep. When you get to this or higher it becomes harder to keep the tires from moving with the stock brakes, if you go with the 5.0 Atlas you should think about a brake upgrade as part of the job.

jedg

Yup. That would be part of the axle upgrade.

TheDirtman

Some throttle is just part of wheeling momentum is your friend most of the time. Any of the ratio's you mentioned will be better but they are close enough that you are not going to eliminate the need for throttle. That is more to do with the weight of your jeep and the tire traction. If you do a lot of technical stuff where you are climbing big boulders and trying to avoid body damage then go as low as you can go with the ratio so you have slow control. Just realize you will be going slower when wheeling with others. With the 5:1 you can always run in second gear and be closer to what a stock jeep is going to be in 1st gear. If you like going fast off road then you may want the 3.8:1 so you can get more speed in low range.

When I am in 10:1 if the wheels have traction I can crawl at idle even with the 6 speed it won't stall but if my tires don't hook up I can't get any momentum to bump over the obstacle. I have to shift into second gear which is close to a 5:1 to get that momentum and wheel speed to climb real steep stuff.

jedg

Thanks. I felt like 5:1 is where I should be but could commit. The idea of using 2nd gear is why I put that info there as well. I thought that gives me the option for momentum when needed. Thanks. !!