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post #1 of 40 Old 11-02-2011, 07:37 AM Thread Starter
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Crawl ratio

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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post #2 of 40 Old 11-02-2011, 07:46 AM
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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


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post #3 of 40 Old 11-02-2011, 08:19 AM
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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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post #4 of 40 Old 11-02-2011, 02:02 PM
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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.

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post #5 of 40 Old 11-02-2011, 02:19 PM
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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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Quote:
Originally Posted by jester116th View Post
Confucius say "If you no want break axle, Drive with BIG head not LITTLE head"
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post #6 of 40 Old 11-02-2011, 02:29 PM Thread Starter
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Originally Posted by Suffolk JK View Post
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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post #7 of 40 Old 11-02-2011, 02:43 PM
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Enough for what?

You'll be fine on 35s with 3.73s and a six speed offroad. I've done it myself...it's fine for 99% of us. You aren't competition rock crawling, so don't worry with the figures. Just go out there and have some fun!

Marcus


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post #8 of 40 Old 11-02-2011, 02:56 PM
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Whats fun? Lol. I agree with Marcus


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post #9 of 40 Old 11-02-2011, 03:14 PM
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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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Quote:
Originally Posted by jester116th View Post
Confucius say "If you no want break axle, Drive with BIG head not LITTLE head"
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post #10 of 40 Old 11-02-2011, 03:19 PM
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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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post #11 of 40 Old 11-02-2011, 03:32 PM
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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.

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Quote:
Originally Posted by jester116th View Post
Confucius say "If you no want break axle, Drive with BIG head not LITTLE head"
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post #12 of 40 Old 11-02-2011, 04:16 PM
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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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post #13 of 40 Old 11-02-2011, 06:58 PM Thread Starter
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Quote:
Originally Posted by Suffolk JK View Post
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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post #14 of 40 Old 11-04-2011, 06:43 AM
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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-

JIMBO


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post #15 of 40 Old 11-04-2011, 09:07 AM
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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.

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post #16 of 40 Old 11-04-2011, 12:25 PM Thread Starter
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Originally Posted by JPK View Post
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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post #17 of 40 Old 11-07-2011, 07:55 AM
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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?

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post #18 of 40 Old 11-07-2011, 08:15 AM
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Quote:
Originally Posted by JPK View Post
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 !

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post #19 of 40 Old 11-07-2011, 09:33 AM
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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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post #20 of 40 Old 11-07-2011, 10:16 AM
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Quote:
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I'm a fan of an auto and two footed driving. How about you?

JPK
Totally
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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post #21 of 40 Old 11-07-2011, 10:34 AM
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As others have clearly stated, how and where you wheel has a huge impact on your 'perfect' ratio. Personally, I think Rubicons should offer both transfer cases. 4-1 is great for some but bad for others. A stick usually needs more gear (off road) than an AT. For loose hills, sand or snow 4-1 is too low. What motor you have also plays a big part. The torque of a Hemi will change the gearing you will need.

I wheeled for 16 years with what is widely considered one of the best (although old school) trans and t cases ever built- 6.32 T-18 with a 300 t-case. I swore I'd NEVER go to an auto trans. After 1 week in an AT rig in multiple areas, I was hooked. No manual for me. The torque convertor of the AT and a 2.72 t-case is great for everything but the full time rock guy. Part time rocks ok, full time rocks I'd go to a deeper t-case. A 4 sp Atlas is the perfect combination. I'd give it the nod over a Rubi Crawler because being able to do front digs with a twin stick is the BEST.
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post #22 of 40 Old 11-07-2011, 10:47 AM
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One thing I forgot to mention, if you're running triple digit crawl rates, with an auto you will not be able to stop without shifting into neutral because it will power through your brakes. That's when having a standard is nice, because all you have to do is push the clutch.


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post #23 of 40 Old 11-07-2011, 11:31 AM
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One thing I forgot to mention, if you're running triple digit crawl rates, with an auto you will not be able to stop without shifting into neutral because it will power through your brakes. That's when having a standard is nice, because all you have to do is push the clutch.
Yep, my Rubicrawler overcomes the brakes. But things are happening so sloooow that there is plenty of time to shift into neutral and stop or kick the doubler out. I takes a few trips to get used to it, but once you do its no longer an issue. We are talking slow enough to get out of the damn jeep and get back in with only a couple feet of movement! Thats the great thing about the auto with a doubler; you just take your feet off the pedals and slowly pick your way through stuff. And to put it in perspective, its something that won't even be used 99% of the time, so the braking issue doesn't get annoying.
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post #24 of 40 Old 11-07-2011, 12:34 PM
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It would be nice to bump up the idle just a bit with the Rubicrawler then I'd have no complaints.
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post #25 of 40 Old 11-07-2011, 01:21 PM
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Yep, my Rubicrawler overcomes the brakes. But things are happening so sloooow that there is plenty of time to shift into neutral and stop or kick the doubler out. I takes a few trips to get used to it, but once you do its no longer an issue. We are talking slow enough to get out of the damn jeep and get back in with only a couple feet of movement! Thats the great thing about the auto with a doubler; you just take your feet off the pedals and slowly pick your way through stuff. And to put it in perspective, its something that won't even be used 99% of the time, so the braking issue doesn't get annoying.
True but you haven't gotten in a jam where you're in lo-Lo and straight vertical about to drop a rear tire off a ledge and you can't shift or stop because you're bound up. Not normal but its happened. Like you said though, that doesn't happen often. And besides you can't even run a rubicrawler with a standard as far as I know.


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