Outer Limits 4x4 Board

Rock crawler ratios!

rover

mog...

Lada Niva(joke), Is this just a general knowledge question?, or are you getting at something?

Best as in what? just lowest reduction?.

Diesel hilux on stock tyres is pretty low..

Hummer H3 68.9:1 (Manual)
JK Wrangler Rubicon 73.14 (Manual)

The auto wrangler is 46:1 numerical, but with converter that's going to be well over 90:1- could be over 100:1 - depends on converter ratio.

Mogs run about 650:1 with ag gearing, but over 2000:1 is possible with the right combinations.

Nothing form nissan or toyota is even close - they're all in the 30-40:1 range.

the party starts at around 60:1 with a manual and 40:1 in an auto IMHO.

Steve.

Gwagensteve wrote:the party starts at around 60:1 with a manual and 40:1 in an auto IMHO.

Steve.

I would guess the auto figure is not taking hill descent into consideration. Given that I'm looking at purchasing a diesel auto 4by, I'd be interested in your thoughts on ratios for decent engine braking.

Perhaps you could advise me on the correct length for my string, too?

-Scott- wrote:
I would guess the auto figure is not taking hill descent into consideration. Given that I'm looking at purchasing a diesel auto 4by, I'd be interested in your thoughts on ratios for decent engine braking.

Perhaps you could advise me on the correct length for my string, too?

I guess the real issue is whether you can change the gearing of what ever you plan to buy. It's one thing to want more gears, it's quite another thing to need them and not be able to do anything about it.

You're right about the string length though - tyre diameter, vehicle weight, and torque converter characteristics all play a large part.

My Gwagen has quite low gearing for an auto - around 42:1, a very low stall converter (around 1200rpm hard stall - the car pulls from about 800rpm) and the ability to knock the idle speed down to about 300rpm. That's a "mod" - I have the idle speed set too low and the hand throttle "on" a little bit constantly to bring idle speed up to "normal" - so when I descend, I knock the idle down to 300rpm to assist.

Even with 36" tyres, it descends quite well up to a point, but it has TERRIBLE brakes, so it's nothing for me to have BOTH feet on the pedals on stop it on a steep hill offroad.

Modern autos all have quite "tight" converters and low 1st gears, and some can be modded to lock the converter in 1st gear. Along with decent brakes, It's not really a problem once the car is properly geared to climb, it's properly geared to descend- and that's regardless of petrol or diesel.

Cj's old vitara ran 64:1 and 31's with a 1.6 litre petrol. It rarely ever needed 1st low on descents, let alone brakes- 2nd low felt plenty low enough- 1st was silly.

Personally, I'd look at your gearing options and desired tyre size and build it to climb properly. It'll go downhill fine then - so I'd be shooting for anything over 40:1 crawl. Bigger tyres/ less HP - add crawl. Smaller tyres/more power, less crawl. I don't think a trail driven auto needs more than about 60:1.

I know this isn't an answer but at least you get the idea.

Steve.