jan/feb 2012

Understanding Crawl Ratios

by Tony Konovaloff

You may hear a lot about rigs having a really low crawl ratio and while this sounds great, there is more to it than just numbers. So just how do you determine the crawl ratio in your rig? Multiply 1st gear x low range x differential gears. This gives you a crawl or final drive ratio.

What exactly does this mean? It will tell you how slow or fast you can go at a given engine rpm. You can do the math yourself or use a gear ratio calculator. To save you some time though, I have compiled the most common ratios you might end up with in a mostly stock rig, plus those of a couple of trucks I know well. Then threw in a couple of possibilities as well just for comparison.

H42: 2.27 low, 3.70 differential gears, 30:1

Without a doubt, the most common wagon gearing on the road. Works well but could use some improvement.

H41: 2.27 low, 3.70 differential gears, 40:1

Here is a great idea for a cheap way to get a good ratio while still keeping your road manners. A 25% improvement just by swapping out the transmission.

H41: 2.27 low, 4.11 differential gears, 46:1

Currently the set up in my friend Eric Burch's rig but I do believe he wants more (or should I say less). This setup worked great all the way through the Rubicon trail—while pulling a trailer. Need I say more?

H55: 2.29 low, 4.88 differential gears, 54:1

This is my diesel rig setup, which works great. I cannot say I have ever felt the need for lower gearing to get over something. Do I frequently wish for more on the highway? Absolutely.

H42: 4.0 low, 3.70 differential gears, 52:1

New gears for the transfer case just might be an option to consider. Plenty of low range grunt while maintaining good highway manners.

H55: 4.0 low, 4.88 differential gears, 95:1

If you really feel the need, you can get carried away….

What does it all mean? There is a lot to think about and more options than you might have known when it comes to improving the crawl ratio of your rig. Everything is a compromise. Improving one area will generally affect another.

Transmission
The key thing that I have learned by messing with all these numbers is that the most important factor for crawling is first gear in the transmission. Lowering this gear has the biggest effect on your crawl ratio for the lowest amount of dollars and the least amount of modifications. And if you think about it, on Land Cruisers it is the easiest and cheapest thing to change. There are some good options for reasonable prices.

Differential Gears
Traditionally thought of first when it comes to lowering a crawl ratio but not always the best option. A low gear set in the differentials handicaps you on the highway when it's time to get home—at least for a non-trailered rig. This isn't to say it isn't a good thing to change the gears but never as the first option. It should be tied to other changes. Not cheap to do either.

Tire Choice
Not really thought of very often when it comes to changing the crawl ratio but tire size can have a drastic effect on the final drive ratio (that the numbers don't show). This additional number is important and is the last part of the equation. While taller tires have long been considered "rubber overdrive," people tend to forget that the reverse is also true. A smaller tire will work as an "underdrive" by improving your crawl ratio. Consider running the smallest tire possible that will still get you over obstacles (33's are the shortest I would consider).

And here is some food for thought. If you have the same transmission and transfer case gears in two rigs but put 37's and 4.88 differential gears in one, you can almost match the final numbers with 31's and 3.70 differential gears….

Transfer Case Gear Swap
For years, the mini truck guys have had the option of lowering the ratio in the transfer case just by swapping out a gear. This is also an option for a split transfer case that just may make sense on your rig but there are a few things to consider. It's expensive on a wagon as you have to change multiple gears and the transfer case may have to be modified to clear the gears. And from what I am starting to hear, the 4.0 low gears are loud—lots of noise coming from the transfer case when you are on the road.

Doubling Up The Transfer Case
This is another choice that presents all kinds of options. Lots of gears to select from but I think in reality, it's like a 24-speed mountain bike: you will only use a few chosen gears and lots of them will never be used. This is also probably the most expensive option as it also involves modifications to the driveshafts and additional mounts for all the extra weight. But hey, you can get gearing so low even your brakes couldn't slow it down in low range.

Marlin Crawler ToyBox
Yet another option for super low gears. ToyBox's are reduction boxes design to double the number of gears available in your transfer case. It fits between your transmission and transfer case and requires a few modifications that make me a bit hesitant. Driveshafts have to be cut and the one that makes me nervous would be needing to cut off the output shaft of my transmission. Not something I would be eager to do but there are plenty of them on the trails.
How low is too low and what is a good all-around ratio for wheeling and the road? I don't know if there is such a thing as too low and in reality, it all comes down to how you want to wheel your rig. Maybe think in terms of low enough to get you where you want to go. For the type of wheeling I do, a crawl ratio somewhere between 45:1 and 54:1 works great, doesn't have too much effect on the highway manners and is easily within reach financially (for most people). I've been to some amazing places and haven't found the need for lower gears so far.

A simple swap of the transmission may give you all you need and is the least expensive option. For myself, a combination of transmission swap and differential gear change worked out quite well. But I have to admit the possibility of a transfer case gear change or a ToyBox sounds like they would be a lot of fun….

Finally, don't forget to factor in the other variables. Tires, including size, pressure and tread pattern. And lockers, which will all affect how well that drivetrain puts your crawl ratio to use.

The transmission combination in my wagon gets me where I want to go with minimal breakage.
Photo by Caleb Konovaloff

 

 

A properly set up transmission and transfer case combination will lead you and your Land Cruiser to beautiful destinations. Photo by Jeremiah Konovaloff