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Crawl Ratio


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13 replies to this topic

#1 Scott in Bellingham

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Posted 05 December 2005 - 07:25 PM

I keep seeing this term, "Crawl Ratio" now how is it figured out ?

is it the low dual range gear x 1st gear x diff ratio ?

what are the stock Soobs?

what is like the ideal ratio for offroad?

#2 Qman

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Posted 05 December 2005 - 08:34 PM

Rooinater had some stuff on his site somewhere.

#3 Mike W

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Posted 05 December 2005 - 11:01 PM

Or if Jared's web address isn't handy, you can Google the words "crawl ratio." First hit seems to work. Crawl ratio expained

#4 NoahDL88

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Posted 05 December 2005 - 11:22 PM

A stock EA-82 tranny's crawl ratio is about 22, most "real" offroaders have a crawl ratio of somewhere between 40-70.

#5 zyewdall

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Posted 06 December 2005 - 12:28 AM

A stock EA-82 tranny's crawl ratio is about 22, most "real" offroaders have a crawl ratio of somewhere between 40-70.


It'll also depend on how big of tires you have. If you've got 44" monster tires on a jeep, you'll obviously need a higher crawl ratio for a given land speed than a suby with 28" tires.

#6 Rollie715

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Posted 06 December 2005 - 12:52 AM

Right you are Zyewdall!

Tire diameter is a huge factor

It is true that a typical Subaru has a crawl ratio of about 22
or 3.545 (1st gear) x 1.59 (lo range) x 3.9 (differentials) = 21.98

That equates to 3.11 mph at 1000 rpm with a 23" diameter tire

To fairly compare that to a Jeep or Pickup with say 38" tires, you would have to factor in the difference in tire sizes.

38 (Jeep tire) / 23 (Soob tire) x 21.98 (Soob crawl ratio) = 36.32 (equivalent crawl ratio)

What I'm saying is that a Soob with 23" tires and a crawl ratio of 22 is equivalent to a vehicle with 38" tires and a crawl ratio of 36.32.

I hope I didn't lose too many people in the math :)

That is why if you put too large of tires on your Soob even tho your calculated crawl ratio hasn't changed, your 'effective' crawl ratio has got worse and you have trouble when it comes to pulling those hard hills or getting out of those gumbo mud holes.

Just my 2 cents worth

Rollie

#7 Scott in Bellingham

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Posted 06 December 2005 - 09:01 AM


It is true that a typical Subaru has a crawl ratio of about 22
or 3.545 (1st gear) x 1.59 (lo range) x 3.9 (differentials) = 21.98

That equates to 3.11 mph at 1000 rpm with a 23" diameter tire

Rollie


so if you add a nissan transfercase with a 2:1 ratio your final crawl ratio would be 44

#8 Numbchux

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Posted 06 December 2005 - 09:18 AM

so if you add a nissan transfercase with a 2:1 ratio your final crawl ratio would be 44


correct

#9 Sweet82

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Posted 06 December 2005 - 11:11 AM

A crawl ratio is somewhat misleading when you apply tires.

I have always been of the opinion that a new ratio must be calculated that accounts for tire size.

Something like a Creep Ratio.

In other words a ratio that matches engine rotation to not only wheel rotation but distance traveled.

Just a thought?
Glenn
82 SubaruHummer with a lousey crawl ratio compounded by a even worse creep ratio.
84 GL Mad Max
01 Forester

#10 Scott in Bellingham

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Posted 06 December 2005 - 11:31 AM

A crawl ratio is somewhat misleading when you apply tires.

I have always been of the opinion that a new ratio must be calculated that accounts for tire size.

Something like a Creep Ratio.

In other words a ratio that matches engine rotation to not only wheel rotation but distance traveled.


maybe it could be a Creepie Crawler :brow:

#11 Shadyirishmen

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Posted 06 December 2005 - 11:41 AM

Classic Scott! (creepy crawler)... I love it

#12 soobme

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Posted 06 December 2005 - 01:04 PM

A CR of 44 is good with like 30"-33" tires. I have a CR of 66:1 on my 'Burb with 35"s and it's nice! I'm not sure how to compair that to the 44:1 with say 29" or 30" tires, but I know that it's close.

#13 Rooinater

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Posted 09 December 2005 - 07:40 AM

the formula is just that
1st gear X low range X axle ratio

if dual cases
1st X LR1 X LR2 X AR

with 4.11 gears in the diffs, the math came out to some where between 55:1 and 60:1. the nissan tcase is 2 point something, not just a straight 2.0 if my memory is serving me correct, at this moment.

as for the new toy a 223:1 will be it's crawl ratio... anything is better than the stock 20:1 to 22:1 depending on tranny.

#14 Scott in Bellingham

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Posted 17 December 2005 - 12:10 AM

as for the new toy a 223:1 will be it's crawl ratio.



yes tell us about this NEW toy 223CR




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