SPLIT from altierior's tire thread: : "Gearing the Trail Rig"

Quote from altierior

They don't last long as it is. I broke one last time out, replaced it on-the-spot with my spare, then promptly broke the spare.

I'm planning on swapping in alloys next week. ;D

Thats the gearing, but you probably already know that.

Hey john I would look to see if anyone shimmed the turnstops. I broke axle shafts a lot on my old beater until I shimmed it up to keep me from overdoing it. Then my only problem was driveshafts but yes gearing has alot to do with it.

we need to get whitelightning out on the trail more

Quote from altierior

Oh, yeah, I haven't checked that. Makes sense. Checking that has now moved to the top of my list.

after thinking about it also could of been the fact I was more aware that every time they broke my wheels were cut all the way, and I just quite doing it so much

Quote from altierior

OK, I know this is a newb question, and I feel a little silly asking, and I know that my nomenclature is probably off, but here goes:

It seems to me that lower gearing converts more torque toward the axle shafts and wheels and hence be more likely to cause breakage there. (Ian suggested this to me when I expressed reservations about the gearing before I bought the rig.) Higher gearing (as the rig stands now) would cause the engine and transmission to bear the brunt of the effort in a climb, obstacle, etc. (or simply denial), and be more likely to cause overheating issues or breakage of driveshafts, since the torque is higher BEFORE the diff.

I know this is a very fundamental topic, but can someone please elucidate as to how my logic is flawed.

I think its because basically you just cant craw. your always forcing and therefore breaking.

Quote from J-Man

I think its because basically you just cant craw. your always forcing and therefore breaking.

You are dead on John. I don't see a flaw.

It's where you are placing the greatest amount of force through gearing. The purpose of gear reduction is to get the RPM's of your engine to correctly match the RPM's of your tires. That is it.

This is done through the transmission, transfer case, and axle differentials. Any combination of those three ratio's must reduce the tire rotation to the proper speed.

Ideally you want to place the least amount of stress throughout the drive line so that the ratios aren't stressing the drive shaft or axle shafts more than they should. For example if you run a slight reduction in the T-Case such as a 2:1 and a large reduction in the differentials such as 5.13 to 1, you are placing most of the load on the axle shafts and not as much on the drive shaft. Likewise, as J-man knows all too well, if you run 3.07:1 axles, you are placing a huge load on the drive shafts which can also cause problems.

Balance to match strength though out the drive line is the ultimate goal.

With the higher gearing(numerically), your forced to used the skinny pedal a bit more to get momentum, causing everything to spin a bit faster. When the drivetrain is spinning and those tires finally bite your putting a huge shock load on those axles/driveshafts etc.. Ive also found that with skinny pedal comes bouncing. Instead of crawling over crap your kinda taking running starts at things and causing the drivetrain to bounce and bit with much more force that usual. Thats my .02 Ive never really had my rig geared "right" for rock crawling. This is why you often see me on the skinny pedal Contrary to popular belief, its not just because I like tire smoke.

Ed
(Thats my story and im sticking to it).

Quote from altierior

Ed, I agree with all of that, except I think you probably mean higher gearing (which is lower numerically).

Lower gearing (higher numerically) allows a slower crawl vs. engine rpm.

Yeah thats what i ment....My bad.

Quote from 2000sahara

your forced to used the skinny pedal a bit more to get momentum, causing everything to spin a bit faster. When the drivetrain is spinning and those tires finally bite your putting a huge shock load on those axles/driveshafts etc..

I agree with this but at the same time, even someone with proper gears/t-case reduction can get their tires spinning pretty fast. It's just that they now have a shit ton more torque because of the reduction.

EDIT: John...you are part of this thread jacking so I left it alone. LOL. If you need me to move anything, let me know.

Quote from altierior

Seriously though, I know there is an opposing point of view to this, so I invite Andy's respected rebuttal.

Who Me?

Sorry, the intent was not to cause a hijack... but we have had long discussions about this John... I'll try to explain my opinion as best as possible. Feel free to punch it full of holes.
As has already been stated, it takes more rpms to spin 35" tires when rock crawling with 3.55 gears. RPM causes torque load on the drivetrain. Torque load, when stopped abruptly (finds grip, tire binds... any number of reasons), can break the weakest link. With 4.56 gears, this is not as big of a problem since it takes less rpms to turn the 35's (because the torque is transferred to the tires), which means less torque load on the drivetrain. 4.56 gears puts more torque to the tires, reducing the potential for torque load in the drivetrain.
If you have a driving style that involves a heavy foot, especially with 35's and 3.55 gears, then you are exposing your drivetrain to more torque load. I agree with Knox Rents that the gearing needs to be balanced. If you consider that the auto XJ came with 3.55's and a 225 or 235 size tire, then to get it back to a "close to stock" ("close to stock"= balanced... yeah I know, but lets just go there for the sake of argument) rpm/mph level with 35" tires, 4.56 gears are needed.

With My CJ, (4speed) 4:10s and 35s actually worked out very nice. I do admit that on the trail , I would like a 4:56's but I think my top end would suffer .. 4:10s roll 35s about 65-70mph at 3k rpm. As my daily driver its right for me.