about 180:1 on 38.5's with a manual here. Crawl ratio is useless without tire size, IMHO. There's a big difference between 100:1 on 33's, or 100:1 on 44's.

I have no opinion on the rest.

 

I think that the whole thing with automatics needing only half of the crawl ratio is total bullshit. Automatics can get away with less because they have essentially unlimited crawl ratio--you can be in gear and not moving at all. That doesn't mean that frying your torque converter/fluid to try to move is an ideal situation.

I think that the crawl ratio number is essentially meaningless. 180:1 in a Nissan with 100 ft lbs of torque is not really comparable to 100:1 in my Chevy with a stroker V8.

The number is convenient for comparing similar vehicles but essentially meaningless without the other specs.

 

I think that the whole thing with automatics needing only half of the crawl ratio is total bullshit. Automatics can get away with less because they have essentially unlimited crawl ratio.

excuse my french, but the BS is what you just said.

the reason that auto trannies do indeed need less numerical crawl ratio, is because of the torque multiplication factor of the torque converter.

a T/C will actually increase the output torqe by apprx. two times, and therefore make the actual crawl ratio almost double than the nominal one.

in fact, this multiplication factor is a variable one, and it changes as the RPM moves up. anyway, it is acceptable to regard this factor as almost 2.

if you need a proof of this simple and well known fact, check out the gear ratios of any manual versus any auto tranny. you will find out that an auto tranny has, as a general rule, much higer gears than the manual ones. the difference will always be around 1.5-2, which is, in fact, the a.m. multiplication factor.

for example, TH-400 has a 2.48 first gear; a TH-700 will have a 3.06 first gear, etc., etc.
an AX-15 manual will have almost 4:1 first gear, and the older manual trannies will have between 5:1 up to even 7:1.

therefore, when you wish to calculate your crawl ratio with an auto tranny, alway multiple the nominal result by 1.5 up to 2. i think that a factor of 1.8 is more acuurate, since crawling is done at relatively low RPM usually, and that is when the torque multiplication is quite high.

indeed, the wheel size means alot and will have to be known when you want to calculate speeds, distances, etc., but the rule is that for a GIVEN tire size, an auto tranny's crawl ratio should be multipled by close to 2, in order to get real results and predict vehicle behaviour.

 

as stated, crawl ratio is a wortless state unless tire size is calcualted as well.
The only way to calculated a true crawl ratio would be the # of engine rotations per 1 circumfrence of a tire.

 

I think in order to make the best comparison you need to know the engine revolutions per foot, and combine that with engine torque at say 800 rpms. The 2F (inline six) in my landcruiser will make decent torque at 500rpms, where as the v6 in my 4runner would make very little at that rpm. As for the auto, there is definately a difference, but I'm not sure you can give a definate figure on reduction. Maybe 2-1, but that puts them back roughly equal. For example if you have an auto with a 3:1 first and a torque converter compared to a sm465 with around 6:1, it all evens out. You could take into account the ability to slip the clutch for more gearing too. Anyway, I don't think there is a definate answer.

 

FWIW, I have about 50:1 with an auto tranny and 37" tires. I find that to be about right but sometimes my toyota friends do neat things with their manuals and 200:1 ratios. If I was much more than 50:1 I'd have to lay on the brakes pretty hard just to keep it still.

BTW, the thing about needed less with an auto is absolutely true. I've wheeled both and it's undeniable.

 

beating dead horse

 

I have to agree with you on that one.

 

bla bla bla......

facts are needed, not deep inner thoughts with not even a shread of proof.

i wish to remind you that the earth circles the sun, and not the other way around.

moreover - whoever had experience with both manual & auto, knows those facts.

read some and then load us with your reflections, which so far are clearly empty.

by the way, there's a nice saying which seems to suit you well. it says something like "do'nt try to confuse me with facts".....:shaking:

 

And once the stall speed is reached, it's essentially meaningless anyway.

Autos can get away with less crawl ratio because they're "slipping the clutch" by frying the fluid.

I would argue that there is absolutely no torque multiplication going on. Energy is being lost to heat...which means less of it reaches the input shaft, not more.

 

You obviously don't grasp the concept of the torque converter.

A) Yes, there is torque multiplication.
B) Sure it creates heat as you shear the fluid, however a well designed system will have an adequately sized cooler to vent the created heat away and keep the system temperature in spec. Some power is lost through this action, it does not negate the torque multiplication
C) It's not like slipping the clutch as your not burning away a non-renewable material. Your heating a fluid that can just as easily be cooled and used again and again.

 

remember when a man drove a truck with a 4speed. damn those were the good ole days.

 

Yup. When those autos suck up some water or crack the case the torque multiplication matters not.

There is a reason they call it a MANual. :flipoff2:

 

I not sure where to argue on this but I can tell you that my Ranger had 40:1 with a manual and i similar torque peak to my 27:1 auto Dodge (less power but also less weight) and the Ford was hard to drive slow enough (on 33"s, Dodge was on 35"s). Now i am at 50:1 with the Dodge. It was perfect for 37"s but with 42"s, I sometime could use just a tad more. Auto never heats up wheelin though, only blasting up dirt roads. Also top speed in low range is frustrating. Could certainly use a STaK so I could have a mid range, and have 68:1 crawl.

In comparison, a friend has been wheelin a chevy with 44"s and 20:1 crawl ratio (stock TH400/454/NP203) and it needs way more gear. However, it still gets the job done, much better then trying to drive rig with a manual and too tall of gears. I wheel with a lot of rigs with too tall of manual gears, and it gets old. 63:1 with an DOHC engine and 35+ tires ends up with a lot of smoked clutches and bouncing.

 

Your crawl ratio is 55.6:1 not 48:1. Big difference in an auto. I have had many combinations and ratios, 50:1 is the minimum for an auto rockcrawler unless you have big block torque.

 

http://en.wikipedia.org/wiki/Torque_converter

 

for those of you who had'nt had the time to click the link Kieth gave, here is a short paragraph from Wikipedia which gives the facts, not the "educated" reflections of fryiong oil and all that kind of pure & genuine BS. =



Torque converter
From Wikipedia, the free encyclopedia
• Ten things you didn't know about images on Wikipedia •
Jump to: navigation, search

A torque converter is a modified form of a hydrodynamic fluid coupling, and like the fluid coupling, is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load. As with the fluid coupling, the torque converter takes the place of a mechanical clutch. Unlike a fluid coupling, however, a torque converter is able to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction gear.

 

facts,

Thats great. When can I expect the results from anyone on this board of driving/wheeling a 78/79 bronco for a year with a stock engined, stock geared C6 drivetrain (upgraded rear axle allowed, as long as it is stock geared) and 44 boggers. I'll make it easy for ya. Don't even have to wheel it, just drive around on the street for a year. I'll save ya the trouble though, it ain't happening. :flipoff2:

 

Last time I checked Wikipedia was not a quotable source for any research or anything requiring documentation, I wouldn't go basing your facts on it. I don't know much about autos and CR, but I could probably find a "fact" somewhere on the web that would rebuke your Wiki article.

Point is, get your info from a real source.

 

Last time I checked, all my shop manuals say the same thing as Wikipedia :shaking: Go back to your day jobs..... Or do I need to scan all of my manuals? ps.... my day job fursure is not scanning

 

I don't know about the exact numbers, or hard data or any of the rest of the crap, but some seat-of-the-pants data from my last wheeling trip.

My normal wheeling rig (Scout = pig) - 392 V8, wide ratio, 4:1 D300, 4.10 gears, 33" tires - so 101:1 crawl. Good over all, sometime I wish it was lower, just because I still have to ride the clutch sometimes, even at 500 rpm. But that might also just be me and the way I want to crawl.

Last trips rig (Scout, but stripped = lighter pig) - 304 V8, slush box(2.45 1st x 2 as per above convention), 2:1 D20, 4.56's, same 33's - so 44.5:1. For wheeling the trails, adequate. Little lower (or more options) would have been nice to be a little easier on the tranny, and make up a little more for the weaker engine, and with some tranny-building options (more compression braking) lower for slower down hills would have been nice. But the auto made up the 'crawl' difference pretty well. I even got used to it and [shudder] might switch some day. They definitely have their advantages. Did miss the stick sometimes though, but the auto I was using is pretty much a junk-yard units with no work over or goodies, which may make a difference.


So I guess I'd have to agree possibly that the 100:1 vs 50:1 is probably pretty close to accurate.


BTW, I went to manual brakes the auto as well.... VERY nice when you loose the engine on a hill or something... recommended.

 

By slipping, just like a clutch.

 

no, not like a clutch. like a vortex. conservation of angular momentum. as the outside of the vortex spins at speed x the inside of the vortex spins at a ratio varying directly as the difference in diameters. the force of the vortex then varies inversely.

secondly, just because a fact comes from wikipedia does in no way make it less of a fact. once upon a time (1958 c.e.) the roman catholic church, in their ever vigilant efforts against open source, maintained that the earth was indeed the center of the universe. wikipedia i am certain does not agree. :shaking:

the heat is built up in the tc due to fluid sheer which has less to do with "slipping" than it does to the separation of the van der waals forces between the molecules of said fluid.

 

Ok, drive your manual around for a day and keep your foot on the clutch pedal to keep the disk partially disengaged and tell me if it works just like a clutch.

 

and in case no one notice, i just made all of that shit up.

i have no friggin idea what i am talking about.:flipoff2:


and now back to the existential debate at hand...bring on the horse...

 

hahaha it was too smart for me anyways


Auto w/ a minimal crawl is all well and good if you have good brakes otherwise you end up rolling faster down the backside of whatever you just climbed slowly until the t/c hooks on to the e/c

Auto w/ uber crawl = t/c has less work to do(if you stay off the brakes), if it's a higher stall speed t/c then you're brakes aren't working too hard either. In addition you get excellent comp braking and an overall excellent wheelin experience.

Personally if I can't have uber gearing I'd rather have the 4 speed. Because I suck at making good brakes

 

i am 3.06 x 2.72 x 2.61 x 4.10

which equals 90-1 with an auto and 42's


its perfect. my brakes can hold it back with no problems, and the ratio is awesome

 

I have been stuck on gentle slopes in 1 ton chevys with autos that will not move
the motor didnt have enough power to overcome the losses in the convertor
engines makes noise but tires do not move
didnt feel like torque multiplication to me

 

And I'm sure that a 5:1 gear in a manual would move the same load no problem...but there is no convincing them.

Torque converters allow you to stop when in gear and create a lot of heat. Other than that, their function is basically useless for our application.

If I ever go back to an auto, I will make sure that I have at least the crawl ratio that I have now, or more...and for good reason.

 

i love my manual T18 with the 6.7:1 crawl ration. It works as easy as an auto and is very forgiving and will idle over rocks.

 

those were new for their day chevy 1 tons with 350 and autos.
but I have seen it many times since then
the stall speed is too low and the motor doesnt have enough power at that rpm to move the vehicle.
the torque multiplication thing is total bullshit.
you can post all the bullshit you want but it doesnt prove a thing.
you lose power through a fluid coupling and there is no getting around it.
the stator trys to minimize the loss but you certainly arent gaining a damn thing.

 

torque converter does increase torque. 2x is probably a good number for a high quality converter at peak efficiency.

It doesn't matter in a modern rock buggy though. we have plenty of torque to spin tires and break axles. The important part is to be able to control wheel speed smoothly and acurately.

There is a lot to torque convertor design to make that happen, but the tricks they do usually actually decrease that torque multiplication number. basicly a good crawling convertor is like a "Soft hit" drag race convertor where the stall speed is very load dependant. Right now these convertors are pretty expensive, but that may change soon.

 

Anyway, back on topic. I am running an Auto with 47-1 with 37s and I could stand to be a little lower. Maybe more like 57-1. The same Jeep with an 86-1 manual worked well also.

Ryan