Desireable crawl ratio info, please.

[colbystephens]

So I'm looking at the grimjeeper gear ratio calculator and I'm playing with the numbers if I were to use a STaK 3 speed case. I like my combination of 4.10's w/ the 38" tires because it gives me really streetable gearing and great HWY fuel economy. However, off road I could use some more gearing. Not that I'm going to be able to get a STaK case any time soon... but I'm just playing.

So, what sort of crawl ratio should I be looking for? Right now, I've got a 205 behind the 465, so I have an overall low crawl ratio of 52.72. This is pretty good for most crawling I've done, but I'd like to have something much lower every now and again - particularly snow and technical rocks.

With the STaK 3 speed cases, you get some options which is cool. Their highest ratio option would give me 55.14 and 100.86 ratios for the low ranges. That sounds like all the gearing I'd ever need. I'm attracted to that set up also, because it doesn't make the first low range too low for general trail riding.

The other two give me 65/116 and 82/146. Ofcourse, the crazy low second low ranges sound cool, but I don't think the first low ranges would be particularly trail friendly because I'd have to be in my highest gear to go what would still be too slow for the easy parts of the trail... I think.

So, if you were in my position (and if my position were actually one that could buy a STaK ) what would you think of all this jibberish?

 

[kylo28]

Get the STak! Those sound like two nice ratio's and there ain't nothin like crawlin on snow

 

[Greg72]

I know you are just playing around with numbers, but if you get serious about an aftermarket box spend some time reading about STaK over on Pirate first. There were some significant design issues and I'm not sure that everyone who bought one is satisifed.

As for crawl ratio, one of the common "rules of thumb" is 1 inch of forward travel per engine RPM.... the easiest way to apply that rule is to try to match the crawl ratio to your tire circumference.

38" = 119" circumference -> 119:1 crawl
40" = 125" circumference -> 125:1 crawl
44" = 138" circumference -> 138:1 crawl

Obviously it will be almost impossible to hit the number exactly, and it's not entirely necessary. The main thing is to understand that the tire size does affect your speed across the ground, so even though a crawl ratio is calculated without regard to tire size, you should make sure that the number you get is reasonable based on what you intend to run for tires.

 

[colbystephens]

As for crawl ratio, one of the common "rules of thumb" is 1 inch of forward travel per engine RPM.... the easiest way to apply that rule is to try to match the crawl ratio to your tire circumference.

Thanks! That's exactly the type of info I'm looking for!

 

[6.2Blazer]

I think if you are happy with your current low range most of the time then try to keep that ratio (or as close as possible) available for normal riding, then have a second low-low range for crawling.

Also keep in mind the use of all of the gears in the transmission....meaning there is nothing wrong with using 3rd and 4th regularly instead of shifting the t-case. The only problem is you only have 1 reverse gear.

 

[Hogback Fabrication]

I think if you are happy with your current low range most of the time then try to keep that ratio (or as close as possible) available for normal riding, then have a second low-low range for crawling.

Also keep in mind the use of all of the gears in the transmission....meaning there is nothing wrong with using 3rd and 4th regularly instead of shifting the t-case. The only problem is you only have 1 reverse gear.

Yeah but how often do you need to move quickly in reverse?


Crawl ratio is largely personal preference but the info others have posted is around what I prefer.

 

[colbystephens]

Also keep in mind the use of all of the gears in the transmission....meaning there is nothing wrong with using 3rd and 4th regularly instead of shifting the t-case. The only problem is you only have 1 reverse gear.

this is what i regularly do.

Yeah but how often do you need to move quickly in reverse?

Well, sometimes it can get a bit annoying to have to back out of a snow covered trail at super slow speeds... but then again, that's what 4high is for.

 

[6.2Blazer]

Yeah but how often do you need to move quickly in reverse?

Probably depends on your area, but quite frequently on the trails I run. We don't do true mud-bogging, but there are always mud holes and slick ruts to contend with so it's nice to be able to get wheel speed in reverse. High range can be an option depending on the gearing (i.e...sometimes high range is too high).

 

[howdiy]

I seem to remember hearing one of the Watson's say 50:1 or 60:1 was fine for a full size.

Ciuld be wrong though.

 

[Hogback Fabrication]

I seem to remember hearing one of the Watson's say 50:1 or 60:1 was fine for a full size.

Ciuld be wrong though.

All they run are autos and I bet they aren't counting the 2:1 reduction that is usually assumed with the torque converter in the auto.

Last I checked all three of their rigs are running autos and doublers.

 

[blazinzuk]

I would say 50 or 60 to 1 for an auto is fine and dandy, I am right close to 50:1

For a manual its hard to speak as far as chevys go but for every other truck I have wheeled with a manual above 80:1 seems alright. Closer to 100 to 1 is what I would prefer for a manual trans, once again this is spoken from crawling 6 and 4 cyl, never a v-8 or a diesel for that matter

 

[howdiy]

All they run are autos and I bet they aren't counting the 2:1 reduction that is usually assumed with the torque converter in the auto.

Last I checked all three of their rigs are running autos and doublers.

I missed the manual part

 

[Vee]

All they run are autos and I bet they aren't counting the 2:1 reduction that is usually assumed with the torque converter in the auto.

so when is this torque converter reduction applied to the crawl ratio formula? is it multiplied by the 1st gear ratio of the tranny?

 

[Hogback Fabrication]

so when is this tc reduction applied to the formula? is it multiplied by my 1st gear ratio? my th350 has a 1st gear ratio of 2.52:1 x 2.0:1 = 5.04:1 adjusted 1st gear ratio? is that correct?

With algebra, you can multiply by two wherever you want and it doesn't matter.

By the same right, I've never seen any proof of why everyone assumes 2:1 for torque converters. Torque converters certainly are capable of gear reduction per se but the ratio is a guess that someone probably made up and everyone now assumes, IMO.

And it's another thing altogether to bring up the slip in a clutch because torque multiplication isn't the idea of low gears, it's speed and control. If you can count the torque converter as 2:1 for the final drive why can't you slip the clutch a little and count it as 2:1 as far as speed/control go (yes, I know it doesn't double the torque applied but again, when crawling with a V8 you almost never even need to touch the throttle anyway)?

 

[colbystephens]

That's always why I am troubled by the assumption of 2:1 for the torque converter. Well said.

 

[blazinzuk]

That's always why I am troubled by the assumption of 2:1 for the torque converter. Well said.

The reason most assume a 2:1 ratio is that is the average used currently, there have been torque converters in the past that have achieved as much as 5:1.

I also think the reason most assume a 2:1 is when you are crawling with an auto you are at "stall" alot, i.e. the truck is not moving forward but the engine is still running and you are in drive or 1st. The torque converter applies maximum torque multiplication right at stall speed. The amount of torque multiplication drops rapidly as impeller speed and input speed become closer to each other, i.e. the vehicle is accelerating.

So they just assume the maximum possible torque multiplication, the fact that you are at stall or just right above it often while crawling.

You cannot discount the torque multiplication of an auto because it is variable, it still occurs. Also there are ways to figure out what exact torque multiplication exists but it is dependent on so many sources that an accurate figure of what your torque converter is multiplying torque is a very complicated process.

 

[6.2Blazer]

The reason most assume a 2:1 ratio is that is the average used currently, there have been torque converters in the past that have achieved as much as 5:1.

I also think the reason most assume a 2:1 is when you are crawling with an auto you are at "stall" alot, i.e. the truck is not moving forward but the engine is still running and you are in drive or 1st. The torque converter applies maximum torque multiplication right at stall speed. The amount of torque multiplication drops rapidly as impeller speed and input speed become closer to each other, i.e. the vehicle is accelerating.

So they just assume the maximum possible torque multiplication, the fact that you are at stall or just right above it often while crawling.

You cannot discount the torque multiplication of an auto because it is variable, it still occurs. Also there are ways to figure out what exact torque multiplication exists but it is dependent on so many sources that an accurate figure of what your torque converter is multiplying torque is a very complicated process.

Well said as I was going to say the same thing. 2:1 is just an average that seems to work well for most factory style torque converters. It also seems to equate well when comparing a manual to automatic equipped vehicle when crawling down a rocky trail. In my auto rig I have almost 70:1 if you factor in the 2:1 TC, and manual rigs with similar power and tire size appear to need at least 70:1 or lower to be able to crawl with the same type of control and not slipping the clutch.

 

[blazinzuk]

And it's another thing altogether to bring up the slip in a clutch because torque multiplication isn't the idea of low gears, it's speed and control. If you can count the torque converter as 2:1 for the final drive why can't you slip the clutch a little and count it as 2:1 as far as speed/control go (yes, I know it doesn't double the torque applied but again, when crawling with a V8 you almost never even need to touch the throttle anyway)?

A clutch is incapable of increasing torque, thats why you can't count it as a 2:1, A torque converters job is to increase torque. Well one of its jobs, its other job is of course a coupler. This is strictly speaking. A slipping clutch can help you mantain engine speed and effectively do a similar job to a torque converter. I.E. maintain forward motion

The best way to understand how a torque converter actually increases torque is to get in a Jeep with an AX 15 or T4, or a mustang with a t-5 or any other close ratio trans. Start in 2nd gear, is it an easy as a turbo 350? The gear ratios are very similar between the transmissions.

 

[Hogback Fabrication]

A clutch is incapable of increasing torque, thats why you can't count it as a 2:1, A torque converters job is to increase torque. Well one of its jobs, its other job is of course a coupler. This is strictly speaking. A slipping clutch can help you mantain engine speed and effectively do a similar job to a torque converter. I.E. maintain forward motion

I know that and mentioned it

The best way to understand how a torque converter actually increases torque is to get in a Jeep with an AX 15 or T4, or a mustang with a t-5 or any other close ratio trans. Start in 2nd gear, is it an easy as a turbo 350? The gear ratios are very similar between the transmissions.

I'm not doubting that torque converters multiply torque, I was only saying that I feel that no one really knows if its 1.5:1 or 3:1 or what. I understand that the 2:1 conclusion probably came from comparisons to manual transmission setups.

Good job explaining how torque converters work a few posts back BTW

 

[blazinzuk]

I know that and mentioned it



I'm not doubting that torque converters multiply torque, I was only saying that I feel that no one really knows if its 1.5:1 or 3:1 or what. I understand that the 2:1 conclusion probably came from comparisons to manual transmission setups.

Good job explaining how torque converters work a few posts back BTW

Yah reading is not my strong suit!

I have found some manufactures that actually know what their torque multiplication is, the 2:1 is actually pretty much a standard in that most modern torque converters were rated at about 1:8 to 2:3. And by moderns I mean like turbo 350s C4s C6s 727s etc.

I think that is where the 2:1 assumption comes from, its a fairly safe assumption.

Where people get it wrong is a torque converters ability to increase torque drops off rapidly the further it gets away from its stall speed. A manual trans retains reduction throughout its rpm range.