JamesDowning wrote:Just trying to understand the numbers you're reporting. A number without comprehension is just a number.
My truck has a off-road maxion ratio of 520:1 - great, but what does it mean exactly!
Nothing...
It will still carry a tire over any off-road sized rock.
If you check out the calculators on the grim jeeper site (
http://www.grimmjeeper.com/gears.html ) you will find that all your rpms and miles per hour are also calculated as you input numbers. That, and you can compare side-by-side two different builds, change tire size, gearing, add a doubler, etc., and see what changes in overall performance.
Some of you may be wondering why crawl ratios as low as 100:1 or lower are needed for off-road work. The reason is primarily technical trail or rock work. There are basically two ways to get up an obstacle, blast it and bounce over the top (if you don't first bounce back down or break something in the process) or apply your choice of correct wheel speed to slowly, with max power, place a tire on an obstacle and crawl it.
A T-case doubler (or a 3-speed case like a Stak) offers multiple choices of gearing, similar to a 10-speed bike. You can get higher or lower gearing with a selection, and in the case of a rock or step or other technical trail where side-slipping, spinning, etc., will eventually hurt something or someone, you select a gear that barely turns over the tires. At that extreme slow speed, it is possible to place a tire right against an obstacle and walk it directly up instead of bouncing off repeatedly until something bends or breaks. I've watched this process so many times it hurts... Also, when you get a tire on a big obstacle, you may be able to crawl up and over that obstacle if gearing is low enough. Tires grab best when you barely turn them over (spinning negates all forward motion). We commonly place a lug on a ridge of rock and let the tire go thump ... thump ...thump, until it grabs and pulls you up and over. We then watch the guys that didn't think that gearing and tire size mattered get on the same rock and spin and spin and spin and spin until, "Snap" and their day is over.
Most guys don't end up with doublers or crawl boxes, so they gear for the lowest possible wheel speed, but that eventually hinders some other aspect of the rig, like the time when you are on a clay hill when wheel speed is needed to clean the lugs, or a mud bog area where wheel speed is needed to get through the mud quicky before bogging down. One of my trucks built where mud and sand hills were the norm featured 38" tires with 3.73 gears. That gear ratio (crawl ratio) was stupid, except that in low range, with over 500hp on tap, I could cut loose and literally float on top of whatever I was trying to get through. I had an 85 mph top speed in low range and could "easily" outrun my brother's new 350 IROK Camaro. In my case, I geared the low range for the tallest possible ratio to have maximum tire speed. My max crawl ratio calculates to about 24:1. My Ranger truggy with a doubler (crawl box) calculates to 85:1 low-low, 31:1 in low, and 12:1 in high range. My maximum ground speed with the doubled Ranger will be 335 feet per minute @3000 rpm versus 1200fpm at the same speed from my mud truck.
