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Are there magic numbers......

wasted wages

wasted wages

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that I should be shooting for in my final drive ratios ??


I have always built rigs with mudding in mind...
large diameter tires,, deep gearing,,,big horsepower....

but I've noticed with the little bit of crawling experience I have,,,,many rigs out there run 42's...doublers...and mild gearing..and mediocre horsepower.

I understand crawling is more about precision and proper lines,,,
what I don't understand is, is there a proven "magic" set of numbers that I should target for my tire size, transmission gearing and axle ratios ? why aren't 44's used more than they are on crawlers ? Is it a center of gravity thing ?

what about final crawl ratios ?

can someone explain what works best on rocks and why ?

Discuss......
 
I don't know about the numbers part of your question but, IMO, the tire selection has more to do with climate and terrain. Out west is more rocky but dry so a smaller tire with great traction, more gear ad less hp is all you need to crawl an obstacle. Down here in the southeast there is some rock but it's usually damp from year round rain and here's always mud in the mix so most folks around here run a much bigger tire and more hp because more wheel speed can be necessary.
 
No real magic numbers, I've always heard having a crawl ratio of 3 times your tire size is good in the rocks but it's all personal preference.

My crawl ratio with (465/241/205) is PLENTY deep, I don't even really use double low first gear (161:1 crawl ratio).

As for why you don't see 44's, I chose 42's because I didn't want the extra width that a 44 has.
 
I've always heard that the "magic" number was to match the crawl ratio with the tire's circumference.

Damn Chris, you beat me to it.
 
Most people I know with 42's chose them because the 44's are a lot wider and heavier and they didn't want to deal with that.

On the comment about having a doubler and mild axle gearing vs. normal transfer case and deep axle gearing. You get a LOT more gear reduction through a doubler, or other low geared t-case option, then axle gears. A doubler, well, doubles the gear ratio (100% reduction) while even going to "deep" axle gears (5.13 or 5.38 since it's the lowest for the common 14FF) is only a 20-30% reduction over 4.10's. On a trail rig if you get the crawl ratio down by using t-case options then there is no reason to spend money regearing the diffs. If it's a vehicle that sees regular street duty than a different story because obviously the t-case low range doesn't come into play and lower axle gears are the only way to optimize road performance.
 
One of the awesome things about lower transfer case gearing is that you can run highway friendly gears in the axles and still have low gears when you're 4 wheeling. You don't have to compromise any of that anymore :pimp:
 
For a full size Chevy or something similar, I would shoot for around 45:1 (pure ratio not multiplying by 2 for the torque converter) to 50:1. Not much reason to go deeper unless your motor is really lacking in power.

With a manual about twice that. 90-100:1

That is pretty much with any tire size, if you are going to run 44s I would stick to the deeper ends of those.

I don't run 44s because of the extra width mostly. I did run 44s for a while and went back down to 42s

You don't need a big powerplant to crawl because its all in the gears. Dependability is key, which is why you may not see a ton of heavily modified motors in crawling. In addition to that we spend a ton of time at idle.

The numbers really boil down to what you plan to do with your rig. My rig will do mud pretty good in just low range not double low. Alot of people have asked me what I did to the motor, its dead bone stock.

If you are going pure off road and crawling will be your main thing then as low as possible.
 
Well,,, my rig IS strictly off-road...on 44" TSL's

So with a T-400 /203/205 doubler and 4.56 gears
puts me right at 45.23 to 1 correct ?

(2.48 x 4 x4.56 ) = 45.23

and with the T/Converter at 2 to 1, I'm at 90.47 final crawl ?



I've always heard having a crawl ratio of 3 times your tire size is good in the rocks
Click to expand...

with 44's x 3 = 132
and 42's x 3 = 126

does the extra width really hurt you on the trails ???? :dunno:
 
Last edited:
wasted wages said:
does the extra width really hurt you on the trails ???? :dunno:
Click to expand...


In technical boulder crawling yes. Although I have run both and the main reason I went back down to 42s is reliability.

When I get chro mos and links I will more than likely step back up to 44s. Even though they are super wide its just a different line you have to take and your rig has to be built to take the extra stresses. I hit alot of small undercuts with the 44s that I never hit with the 42s

I LOVED the clearance of the 44s though, if you already have em run em
 
cegusman said:
http://www.grimmjeeper.com/gears.html
Click to expand...

here is a few of my #'s to play with. first is my end product when complete. .

4l80-e/203/205/5.13/38" tires = 49.87 crawl ratio / 65mph = 2211 rpm

4l80-e/203/205/4.10/31.5" tires = 39.86 crawl ratio / 65mph = 2132 rpm

looks like i will gain about 100 rmp to keep my motor in the sweetspot for the bigger tires down the road.

if i wanted to go grazy 6.0/6l80-e/203/lowmax 205/5.13/38" tires = 124.04 crawl ratio / 65mph = 1975 rpm

and if i understand this all correct with auto tranny you x2 the crawl ratio you get right ? so 49.87 x 2 = 99.74 ?

and if true then thr 6l80-e/203/lowmax 205/5.13/38" tires = 124.04 x 2 = 248.08
 
wasted wages said:
So with a T-400 /203/205 doubler and 4.56 gears
puts me right at 45.23 to 1 correct ?

(2.48 x 4 x4.56 ) = 45.23

and with the T/Converter at 2 to 1, I'm at 90.47 final crawl ?

with 44's x 3 = 132
and 42's x 3 = 126
Click to expand...

That 3 to 1 is a general rule I heard a long time ago that applies more to the Suzuki and Toyota crowd that need super low gears to turn big tires over big obstacles.

After about 80:1 you will probably have all the low speed control you would want, I generally only run in single low (which is ~80:1 at the lowest).
 
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