How do you figure out the crawl ratio with an automatic transmission. I know what the formula is with a manual. I know that if I took my C4xD20x4.10 it would be a pretty low number. Is there a differnt set of numbers to compare it against when you have an auto? I just bought this EB and haven't had a chance to wheel it yet so I have know idea how well this combo will work offroad.

Multiply first gear in transmission, by your low range gear in your t-case by your diff gears. For example a Rover has a 2.48 first gear trans x 3.32 t-case x say 4.10 gears = 33.75.

Make sure you factor out tire increase. If you go from 33" tires (stock size??) to 37" tires you lower your effective ratio by 27.6%. Make sure that you lower your diff gears or t-case gears by the same amount or you will be unhappy.

Way

That doesn't take the torque converter in to account though...

Whats the formula to do that?

most people I've talked to double the first gear to compensate for torque converter slippage.
C4(2.46*2)*D20(2.46)*rear gears(4:10)=49.6 Crawl Ratio
Which should be rightish cause a C6+NP205+3:50=17:1 Crawl ratio, but it works WAY better than that.
I don't think any formula is accurate for an auto cause you can stomp the brakes, hammer the gas, and still go nowhere without stalling (depending on engine:D ).

All torque converters are not created equal. The actual torque multiplier is dependant on many factors. In general a single stator stock torque converter will be around a 2 times torque multiplier. A dual stator will be around 4 times.

so take your mechanical crawl ratio and multiply by 2 or 4.

BTW dual stator torque converters are very rare. I've heard that some of the GM 4L80E's came with them but I haven't confirmed this yet.

Thanks for the input guys. I thought there was another factor involved. I forgot about the torque converter.

Originally posted by lt1yj
All torque converters are not created equal. The actual torque multiplier is dependant on many factors. In general a single stator stock torque converter will be around a 2 times torque multiplier. A dual stator will be around 4 times.

so take your mechanical crawl ratio and multiply by 2 or 4.

BTW dual stator torque converters are very rare. I've heard that some of the GM 4L80E's came with them but I haven't confirmed this yet.

I've heard similar info; only one more data point here: according to I believe it was Jim Manning at Dynatrac, the ratio for a dual-stator converter such as the 4L80e is 3.5-to-1. Pretty close to the 4-to-1 you mentioned but just thought I'd put in the additional 2 cents!

Originally posted by Rogue Bronco
most people I've talked to double the first gear to compensate for torque converter slippage.
C4(2.46*2)*D20(2.46)*rear gears(4:10)=49.6 Crawl Ratio
Which should be rightish cause a C6+NP205+3:50=17:1 Crawl ratio, but it works WAY better than that.
I don't think any formula is accurate for an auto cause you can stomp the brakes, hammer the gas, and still go nowhere without stalling (depending on engine:D ).

So then all auto tranny guys actually have a lower ratio if they dont multiply the first ratio ratio by 2 due to the convertor?

So instead of my combo, 700r4(3.06)*208(2.62)*4.56=36.56
It would actually be 73.12?

Hmm... Interesting!

One thing to remember about the converter multiplication though is the fact that as ground speed increases, this factor drops. Torque multiplication is greatest at zero ground speed and rapidly diminishes. That said, I still love my slushbox! :D

and my 70.58=141.165 with an auto at stall :flipoff2:

Yes, the 4L80E torque convertor is a dual stator design, which is why it weighs 85lbs, no wonder my K3500 was such a slug with a small block.

Auto tranny crawl ratio can be multiplied by 2 for crawling UP, but for crawling down, shouldn't you DIVIDE by 2?!

Originally posted by tiessen
Auto tranny crawl ratio can be multiplied by 2 for crawling UP, but for crawling down, shouldn't you DIVIDE by 2?!

autos crawl better down than people give credit for. a LOT better.

Hint: put it in 1st, instead of Drive. ;)