Optimum crawl ratio?

[dieselcruiserhead]

Speaking of diesels, I know a few guys who actually use the big Dodge and Ford diesels hard for hunting. In both cases they tell me the torque is there, but the extremely heavy front end is a major problem in any type of soft terrain. They are both running 285/75-16's with no lift and don't want to lift the rigs since they are also used as tow rigs. The one gentleman is a professional lion guide/hunter/tracker, so he's usually got a four mule/ten dog trailer in tow...

I wish our locals had this common sense, there are massively lifted Fords and Dodges and with 37's all over the place, rear end all slumped down, towing 15K Bobcat and backhoe loads all over the place here....

 

[dieselcruiserhead]

Started typing and this long-*** post is what happened. Sorry...



A lot of good info here. It does vary a lot of vehicle, tire size, terrian, engine torque specifically, and transmission type and gearing.

With mine, I ran a larger tire (35") but felt I was just perfect at 63:1 with my diesel! (This would be considered quite low, for example, by Scott's standards). But that is here in Utah, lots of dry terrain but I ran everything, mud, you name it, and the ratio challenged me to enjoy wheeling realy hard stuff but also did very well day to day and all terrain. This is what you should be after. No compromising gear ratios.

The beauty of the standard is the diverse range of gearing. You can be fast and slow with a shift... (I'm sure this is fine too with an auto but you always start in the lowest gear). My setup was: 5.61 first (granny) with NV4500. 2.72 Low Range with a NP241 transfer case. 4.1 factory Toyota diffs = 63:1. I am going with almost identical gearing again this time, but I have a choice of going lower with a 4:1 kit. I agree this is probably too low in reverse in particular, and it is cheaper to stay stock.

With the diesel at super low RPMs... My off road style since I've owned diesels, is idling over everything. Left foot brake in gear to slow down to even 400rpms (it chugs over anything, it is like a wall of unstallable torque), then if I need fuel I bump it or throttle it accordingly. It can go from low RPMs with tons of torque to upto the 2500 rpms governed limit. It is like a V8 at 1000-1300 RPMs going to 3500 rpms. It is a "common complaint" with American rock crawlers that diesels will not have high RPMs for throttle up things. The diesel is a little less top end than a V8 but works well and is comparable to a gas engine it you run it this way. I never found it to be an issue. Also this low chugging is easy on parts, very little breakage. But crawling in this style only works in high traction situations like dry high traction terrain and all over hte Southwest for example.

But this ratio for me was literally perfect and was universally great. There is only one place at one time that I particularly wish my ratio was lower, on dump-n-bump on the Pritchett Canyon trail in Moab. I had to brake my way as slow as possible (but still nailed it fine). And also if I get into some really really hairy large boulder wheeling like Montrose or something similar, which has happened a few times... My only complaint about the whole combo was a wide spread between 3rd and 4th gear (and generally awkward gear spreads of the overly-wide NV4500) so I solved this by purchasing a NV5600 this time which adds an extra gear between the 5.63 low and .73 overdrive.

I have played and messed around a lot with gearing ratios. I also drove stockish trucks for years with manuals and very fast low ranges, 28:1 and 30:1 and such. A gain, IMO learned how to drive, how to get up and over stuff, and for years with stock rigs I did fine. You learn how to slip the clutch, bump over things etc. It is not the prettiest method but you learn. The biggest issue with these is the lack of a decent crawl ratio. Trucks designed for off roading in Mud and needing speed, rather than grace... The only appropriately geared truck I've even owned out of the package was a Series III Rover (never owned an automatic).

My last built Cruiser (the sprung over FJ55 on 35's) I was very comfortable and easily hung in there with way more built rigs and always got over most things with this 63:1. I was also frequently told that my combo felt like it was 100:1 or deeper on a built rig with large tires, so it was the best of both worlds. You could get out out and walk along side it as it idled up a hill.

I also did some massive mud trips (one night the truck spent the night in a bog near town, 2 feet deep in a bottomless pit, the other two trucks were stuck too, nothing to winch to (why I now own a Pull Pal!). And Kurt and Dave Connors and I did a La Sal trip out of Moab one night with me and Kurt with our 35's taking turns breaking trail up maybe 3' deep snow way up there... The diesel let out a lot of smoke at higher RPMs with the wheels spinning away and high RPMs only (no traction) but did great. It was an awesome setup..

For a gasser, the issue is torque (or lack of it in certain applications). This is why manuals are less comfortable with gas engines, because they stall easily (stalling = lack of torque). As they say (Ferrari), horsepower sells cars, torque wins races. Some engines have a lot less torque than others and stall out easily. If this is the case you want a high gear ratio, this increases the torque (torque x gear ratio = actual torque at wheel) and lets you get over more. This, the gas engines they run, and the massive tire sizes the guys on Pirate4x4.com run, and high traction, means most of them want deep t case ranges.

Automatic gearing is less important but is important too, in my opinion. I have heard excellent comments about different first gear ratios in autos and it does matter. The beauty of autos is the torque converter and slipping. I consider automatic gearing to be more of an issue of "balance" rather than "capability." So basically any gear ratio works to an extent, but different t-case and axle combos combined with different tire sizes makes them happier and perform stock-like. My philosophy, at least with Toyotas with autos but probably any other truck too, is to modify gear ratios accordingly to tire size. So with FZJ80 Land Cruisers, 35's with 4.88 axles, no other changes. Stock tires with stock 4.10s. There is a big difference between FZJ80s with 35's and stock 4.1 axles and 4.88. The 4.88 is much happier with 35's. So the crawl ratio goes "deeper" so it might seem more competent, but is really just trying to get back to stock or just a hair below it.

I hope this all helps and is what I have learned over the years...

 

[rusty_tlc]

There are way too many variables to have one "best" crawl ratio for any type of off-road travel.

For instance, diesel may have low end torque, but without deep gear reduction, even idling in low range over the Rubicon is still way too fast.

SWB can tolerate a faster crawl than LWB, and the torque converter of an automatic also lets you tolerate a slightly faster crawl as well, though as noted, at the price of more heat in the tranny.

In the US, the "expedition" type places are still mostly graded dirt roads, where a low range is occasionally needed, but true crawling ability is not. What ever comes stock is just fine for that. It still makes sense to match the differential gearing to the tire size.

For me, I have about 80:1 in my FJ40. In places like the Rubicon, I would still on occasion like to go slower. If I were doing Rubicon in a LWB wagon, I think 150:1 would be nice. For my other trucks out in open desert or even the other low intensity trips we take, 35:1 is just fine.

In all cases, matching the diff gears to the tires is the place to start.

I agree stock gearing is fine for 95% of the roads most of us see.

Dual cases on trails like the Rubicon are the way to go IMHO. 150:1 for obstacles is great but to slow for most of the trail. I switch between the 4:1 Orion and the 2.48:1 toy box. Once in a while I'll leave the toy box engaged and shift in the Orion because it's easier, thats about 144:1 I think. But stupid low is a PITA, you have to be in third or fourth to even feel like your moving. I prefer to stay in a reduction range where I can control my speed by shifting between 2nd and 3rd. For me that is the sweet spot in the FJ40 tranny.

 

[lowenbrau]

I agree with Scott's point about backing out of a mudhole with low gears. That can be a problem. I think the nicest setups are ones which add an intermediate gearbox such as Marlin, Ashcroft, Mark's, 203 etc. That generally allows something like a stock 2:1 low range, an auxillary range, anywhere from 2:1 to 6:1 depending on the manufacurer, and finally an ultra low range multiplying both. I have the 203 between the 465 and my splitcase in my FJ45 and I plan to have Marlin's Toybox in my BJ74 very soon.

The downside to these setups is you are adding driveline components that will eventially fail. The upside is that with lower gears you will work your clutch less hard and not lose it days from civilization as was my expereience this summer.

I had about 65:1 in my previous BJ70 and found it to be very practical.

 

[Redline]

'96 F350 Power Stroke, crew-cab, long-bed, stock gearing:

5.08 - 1st gear Manual 5-sp
4.11 - ring & pinion
2.64 - stock Borg-Warner T-case

Equals 55:1

This has worked very well for 11-years, even in Moab.

Though I used to 4wheel my F350 all the time, a couple years ago I started using smaller rigs. I still use it for hunting, towing, and back country travel. Like your example, I don't have a lift and usually run 33-inch 255/85R16 tires. I have a custom high clearance T-case skid plate.

I agree about the heavy front end. It leads to awesome traction when the ground is firm but it sinks in the soft.

With my ‘05 Rubicon I also found the 4:1 T-case great for crawling, but a little low for general 4x4 stuff. Would really have liked a 3-speed T-case. Maybe 1:1, 2.5:1, and 5:1.

My current primary rig, V8 4Runner with a very low first gear in the A/T:

3.52:1 - first
2.566:1 - T-case
3.73 - gears

33.6:1 seems to work pretty well.

I might go lower in the diffs for on-highway and reap the benefits in crawl ratio, not sure yet.

Speaking of diesels, I know a few guys who actually use the big Dodge and Ford diesels hard for hunting. In both cases they tell me the torque is there, but the extremely heavy front end is a major problem in any type of soft terrain. They are both running 285/75-16's with no lift and don't want to lift the rigs since they are also used as tow rigs. The one gentleman is a professional lion guide/hunter/tracker, so he's usually got a four mule/ten dog trailer in tow...

 

[dieselcruiserhead]

I think you mean 2.56 transfer? That 5.5 transfer sure would be low

 

[Redline]

Yep, typo fixed, thanks

I think you mean 2.56 transfer? That 5.5 transfer sure would be low

 

[rusty_tlc]

I agree with Scott's point about backing out of a mudhole with low gears. That can be a problem. I think the nicest setups are ones which add an intermediate gearbox such as Marlin, Ashcroft, Mark's, 203 etc. That generally allows something like a stock 2:1 low range, an auxillary range, anywhere from 2:1 to 6:1 depending on the manufacurer, and finally an ultra low range multiplying both. I have the 203 between the 465 and my splitcase in my FJ45 and I plan to have Marlin's Toybox in my BJ74 very soon.

The downside to these setups is you are adding driveline components that will eventially fail. The upside is that with lower gears you will work your clutch less hard and not lose it days from civilization as was my expereience this summer.

I had about 65:1 in my previous BJ70 and found it to be very practical.

Not just the clutch, with lower gears you have a lot more control and are less likely to break something like leak pack, birfield, driveline etc. The skinny pedal has broken a lot of parts.

 

[lowenbrau]

Not just the clutch, with lower gears you have a lot more control and are less likely to break something like leak pack, birfield, driveline etc. The skinny pedal has broken a lot of parts.

Yep, the club mantra around here is... "As slow as possible. As fast as necessary"

 

[Scott Brady]

Yep, the club mantra around here is... "As slow as possible. As fast as necessary"

That is nice to hear. An old Rover motto

 

[TeriAnn]

There are way too many variables to have one "best" crawl ratio for any type of off-road travel.

I agree with this statement. But for most expedition type travel that can include moderate rock crawling I've found that somewhere around 55:1 at the axle seems to be a very handy gear with 33 inch dia tyres. Much lower than that seems like overkill unless you are doing technical rock work. Much higher than that and you can be moving too fast for the terrain even it idle (assuming you have enough bottom end torque to push the gear at idle. Sorry but I only have experience with tyres in the 31-33 inch dia range.

My low range first is 70:1 and I almost never use it as I seldom go into rocks that require that slow of movement. My vehicle came from the factory with a low first of 40.7:1 at the axle. I found that I was slipping the clutch in the more technical obstacles. I frequently wished for a lower ratio so I could take obstacles more slowly. So I regeared.