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Discussion Starter #1
Im trying to figure out what my crawl ratio will be. My set up wil be 35 inch MTRs with a command trac 2.7:2 ratio xcase on 3.73 gears and a NSG370 manual transmission. I added the numbers that I thought were correct into a crawl ratio calculator, but I am not sure if they were indeed correct or not. For the transmission gear ratio, you want to put in the ratio of first gear correct? Or is than an overall gear ratio for transmissions that needs to be computed? Either way i got a 44:1 ratio, does that sound about right? I am a lil confused about all this honestly...I couldnt find anything that explained how the numbers are computed in laymans terminology.
 

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There is a calculator that gives you an "adjusted" axle ratio to input for different tire heights. It's not entirely accurate, but is a good estimation.

For starters your transfer case is 2.72:1, not 2.7:2. Yes you use first gear which is 4.46:1.

...is this going to be your third regear thread?! Lol


Sent via paper airplane
 

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That sounds about right if you have a manual trans. With the auto (2007-2011), first gear is only 2.84:1 - so the crawl ratio is MUCH lower.

I have an auto, but am also running 5.38s in the axles with a RubiCrawler, giving me a 113 crawl ratio.

The numbers are confusing, often irrelevant, and usually slightly inaccurate due to other variables.

For rock crawling, most agree that 100 is about perfect. Most folks who run the mud like around 50-60. So your terrain will have a lot to do with it. MANY people (especially the Toyota guys) run WAYYYYY too low for what is actually usable.

The versatility of an Atlas 4 or Rubicrawler lets you have it all: Very low crawl gears and good intermediate gears for normal use.
 

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Transmission 1st gear ratio X transfer case ratio X rear axle ratio = Crawl Ratio

For your Jeep using Goodysgotacuda's ratio for 1st gear:
4.46 X 2.72 X 3.73 = 45.249376 or ~ 45:1

A note on auto transmissions, the calculated crawl ratio understates the effective ratio since the torque converter doesn't lock up at idle or just off idle, and so provides what is effectivey a lower first gear ration.

JPK
 

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You need to multiply 1st gear, by low range t-case ratio, by r&p.

45:1 is garbage. I can't wait to source a used 4:1 case or save the $ for an Atlas. Need 95:1+
 

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Discussion Starter #6
You need to multiply 1st gear, by low range t-case ratio, by r&p.

45:1 is garbage. I can't wait to source a used 4:1 case or save the $ for an Atlas. Need 95:1+
Yeah it does. And from what I understand a re-gear to 4.88 will only increase it to about 65:1. Still not enough.
 

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We're not competitive rock crawlers either, but especially with a manual tranny the minute you hit a big boulder and it bogs down, sometimes enough to stall, lower crawl would be nice. A few rigs in the club are at 100:1+ and I've test driven them... you can't COMPARE idling vs. throttling just to get on a rock face.

I did 33s and 35s with 3.21s and the 2.72 tcase. It was complete SHIT. When I went to 4.88s, it was a WORLD of difference, but still not enough. I find the engine bogging down a lot more, especially when you start doing harder and harder obstacles.
 

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Enough for what?
Kind of the point is was politely trying to get at. For 90% of wheeling out there, even a 4:1 case is too low.

Look at you average KOH style buggy with 4L80E and Atlas 3.8: They are running crawl ratios in the 60-70s. Because they know the rig has to be able to run a little bit of everything.

I have actually used my 7.4:1 low in the Rubicrawler maybe 10 times since I got it a year ago - and thats with rock crawling almost every weekend. It is totally useless for anything except a couple of very technical spots in Johnson Valley and Ridgecrest - but it is nice to have when I do need it. And those 4:1 Rubi cases, those are even too damn low for most trails - and actually hurt your performance in the mud and sand.

I wouldn't pay "Crawl Ratios" any attention. Totally meaningless. If you are having problems on the trail, its for other reasons.
 

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If you're going to be playing in mud, sand and faster environments, you don't want a super low range. If all you have is tight technical rock gardens, I beg to differ. My 2 cents.:beer:
 

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I have an auto 5:13s and a Rubicrawler. The low/low is not used much but sure is nice on steep hills, either going up or coming down. 108 crawl ratio as is.
 

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Discussion Starter #13
We're not competitive rock crawlers either, but especially with a manual tranny the minute you hit a big boulder and it bogs down, sometimes enough to stall, lower crawl would be nice. A few rigs in the club are at 100:1+ and I've test driven them... you can't COMPARE idling vs. throttling just to get on a rock face.

I did 33s and 35s with 3.21s and the 2.72 tcase. It was complete SHIT. When I went to 4.88s, it was a WORLD of difference, but still not enough. I find the engine bogging down a lot more, especially when you start doing harder and harder obstacles.
agreed. but im done complaining about my crappy crawl ratio. marcus is right!
 

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:smokin: I'm really happy with my '08-JKUR auto and 61/1 crawl-

Really helps when towing my trailer up a steep dirt/rock hill-

:grinpimp::grinpimp: JIMBO
 

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Over looked throughout this thread is that crawl ratio alone does not tell the whole story. Crawl ratio only deals with the gearing, but performance is also significantly effected by tire size.

Stepping up from 33's to 35's and then 37's decreases effective crawl ratio slightly more than 5% for each 2" incremental increase in tire size. (the decrease is not linear.)

Performance is also effected by the auto's almost infinite first gear vs. the manual's fixed first gear and by engine torque and engine rpm range.

JPK
 

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Discussion Starter #16
Over looked throughout this thread is that crawl ratio alone does not tell the whole story. Crawl ratio only deals with the gearing, but performance is also significantly effected by tire size.

Stepping up from 33's to 35's and then 37's decreases effective crawl ratio slightly more than 5% for each 2" incremental increase in tire size. (the decrease is not linear.)

Performance is also effected by the auto's almost infinite first gear vs. the manual's fixed first gear and by engine torque and engine rpm range.

JPK
So your saying a manual has better or worse performance?
 

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Well, that wouuld be a personal opinion.

An auto won't stall when it crawls to an obstacle it can't surmount without more torque like a manual would, but because of the torque converter it won't just crawl smaller obstacles either, you would need to apply some skinny pedal more frequently, but at slower speeds.

You can go slower over an obstacle with an auto, or alternatively you can slip a manual's clutch. That can be problematic.

I'm a fan of an auto and two footed driving. How about you?

JPK
 

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:smokin::---BINGO--


Well, that wouuld be a personal opinion.

An auto won't stall when it crawls to an obstacle it can't surmount without more torque like a manual would, but because of the torque converter it won't just crawl smaller obstacles either, you would need to apply some skinny pedal more frequently, but at slower speeds.

You can go slower over an obstacle with an auto, or alternatively you can slip a manual's clutch. That can be problematic.

I'm a fan of an auto and two footed driving. How about you?

JPK
Can't beat a Rubi xfer case/4lo/auto and 5.38 gears-

Where's lunch gonna be, I'll be there !

:grinpimp: JIMBO
 

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Umm. How many people have actually wheeled with 200+:1crawl? My yota had 236:1 in low low and was the shit!! I could crawl an extreme off camber vertical route and the suspension would smoothly and slowly cycle without unloading when everybody else was rolling as soon as the shocks unloaded. Did I use it constantly? No but it was damn nice to have available.
 

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I'm a fan of an auto and two footed driving. How about you?

JPK
Totally:beer:
I really like the crawl of my ruby TC with 35's and 5.38 gears, it works well for me. When it's too low, I just pop it to 4hi.
 
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