New crawl ratio.

derherr65 · 07-06-2006, 07:20 PM

I was doing a little theorizing...

"So that we're all on the same page:
Crawl ratio = lowest transmission ratio X transfer case ratio X differential ratio

Crawl ratio is a nice number, but if you have 29" tires instead of 53"(or vice versa) it may not mean much. For example a crawl ratio of 79 is obviously better than a crawl ratio of 43. But if that 79 ratio is on 53" tires and the 43 ratio on 29" tires then they are the same EFFECTIVE ratio! Both trucks at 3000 rpm would be doing 6mph!

This is why you need bigger gears with bigger tires, as most of you know. So, is there a better 'ratio' for crawling prowess? What are good crawling ratios with different size tires?"

And a bright soul offered the obvious solution...

"I've often wondered the same thing. It is a unitless number which doesn't mean much to me. Maybe crawl ratio per inch tire diameter would compare apple to apples. That is often a measure I have used to keep things straight in my mind. For example: 79/53 = 1.49/in or 43/29 = 1.48/in"

So, what are your crawl/inch numbers? (I'm especially interested in stock body vehicles that have done things like Moab.)

Hvy_Chevy · 07-06-2006, 07:23 PM

depends on terrain, engine, auto/manual, driving style, blah, blah, blah

American · 07-06-2006, 07:28 PM

Seriously. If you start messing with things, like tire sizes - well let's just say you'd also have to start figuring in torque, HP, torque convertor, auto/manual, driveline HP loss, etc, etc... do you want to do that? I don't.

But maybe you are on to something. I just odn't think it's as simple as a ratio/tire comparison.

kwrangln · 07-06-2006, 07:30 PM

We've been down a similar road here before, here's the link.

http://www.pirate4x4.com/forum/showt...ht=crawl+ratio

vetteboy79 · 07-06-2006, 07:40 PM

205:1, or 5.18/in by your method.

.84 ft/sec @ 1000 RPM by that other thread.

This has not yet been tested.

derherr65 · 07-06-2006, 07:58 PM

Good link kwrangln.

Yes, there are a ton of other factors. So my thought was if you know the ratios(ratio/inches that is) people are running sucessfully, you know about what's needed for your rig. If you have a wimpy engine, use the top third of the results. A really stout engine and you can use the bottom third.

07-06-2006, 07:20 PM	#1
derherr65 Registered User Join Date: Jul 2006 Member # 75099 Posts: 53	New crawl ratio. I was doing a little theorizing... "So that we're all on the same page: Crawl ratio = lowest transmission ratio X transfer case ratio X differential ratio Crawl ratio is a nice number, but if you have 29" tires instead of 53"(or vice versa) it may not mean much. For example a crawl ratio of 79 is obviously better than a crawl ratio of 43. But if that 79 ratio is on 53" tires and the 43 ratio on 29" tires then they are the same EFFECTIVE ratio! Both trucks at 3000 rpm would be doing 6mph! This is why you need bigger gears with bigger tires, as most of you know. So, is there a better 'ratio' for crawling prowess? What are good crawling ratios with different size tires?" And a bright soul offered the obvious solution... "I've often wondered the same thing. It is a unitless number which doesn't mean much to me. Maybe crawl ratio per inch tire diameter would compare apple to apples. That is often a measure I have used to keep things straight in my mind. For example: 79/53 = 1.49/in or 43/29 = 1.48/in" So, what are your crawl/inch numbers? (I'm especially interested in stock body vehicles that have done things like Moab.)

07-06-2006, 07:23 PM	#2
Hvy_Chevy Zeus of the Sluice Join Date: Oct 2002 Member # 14094 Location: Maine Posts: 2,766	depends on terrain, engine, auto/manual, driving style, blah, blah, blah __________________ Size does matter. Leave the Zukes to those who really understand.

07-06-2006, 07:28 PM	#3
American Registered User Join Date: Jun 2002 Member # 12257 Location: Huntsville, AL Posts: 2,529	Seriously. If you start messing with things, like tire sizes - well let's just say you'd also have to start figuring in torque, HP, torque convertor, auto/manual, driveline HP loss, etc, etc... do you want to do that? I don't. But maybe you are on to something. I just odn't think it's as simple as a ratio/tire comparison. __________________ '74 Scout '00 Ram

07-06-2006, 07:30 PM	#4
kwrangln DOUBLEWIDE ENGINEER Join Date: Sep 2001 Member # 6971 Location: Gulf coast Posts: 4,704	We've been down a similar road here before, here's the link. http://www.pirate4x4.com/forum/showt...ht=crawl+ratio __________________ I'm the "tack tack tack" welding nazi. http://www.pirate4x4.com/forum/showp...&postcount=218 "I didn't mean to kill nobody ... I just meant to shoot the sonofabitch in the head. Him dying was between him and the Lord." R. L. Burnside

07-06-2006, 07:40 PM	#5
vetteboy79 Pigs fly! Join Date: Jun 2004 Member # 31621 Location: Morganville, NJ Posts: 4,646	205:1, or 5.18/in by your method. .84 ft/sec @ 1000 RPM by that other thread. This has not yet been tested. __________________ '94 XJ with 4.6 stroker, NV4500, NP231doubler/D300, D60/14B, 4.56s and Detroits, 38.5 Creepies, 4-link rear & 3-link w/panhard front, dual roll cages. FOA coilovers all around. bacon express TELLICO RALLY POST #18 Last edited by vetteboy79; 07-06-2006 at 07:41 PM.

07-06-2006, 07:58 PM	#6
derherr65 Registered User Join Date: Jul 2006 Member # 75099 Posts: 53	Good link kwrangln. Yes, there are a ton of other factors. So my thought was if you know the ratios(ratio/inches that is) people are running sucessfully, you know about what's needed for your rig. If you have a wimpy engine, use the top third of the results. A really stout engine and you can use the bottom third.

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