Crawl Ratio

[1Bad4Runner]

Is there a such thing as a 'to low' crawl ratio? I was just wondering what the lowest crawl ratio some people have seen in action? Let me know please.

I am thinking of maybe building a 1 seater that will be inexpencive to build and I want to go as low as possible.

Thanks

[Rocksurfer]

Marlin once put 2 crawler boxes in his truck, it was just stupid low. I asked him why he did it and he said, "becasue I can."

[1Bad4Runner]

So it was to low? What should I try to get to? running maybe 38.5" tires

[Rocksurfer]

You could say it was, just the fact that at an event we put it in the lowest gears, let it crawl for about five minutes next to the booth and it only moved about 10 car/truck lenths. Then we measured how far it would move overnight and detirmined that if we put it in a football field and let it crawl it would not reach the other side by morning. Then some smart-ass (me) noted that it would run out of gas before it reach the other side.

I hate 5.29's (pinion gear to small) but running 38.5's you need to be as low as you can the dual crawler kit from Marlin would do you right.

[1Bad4Runner]

Do you know what his crawl ratio was? 1000 or something?

By the way, I'm not using Toyota Gear. I don't have a front axle. So I might use D60/D70 combo.

[Rocksurfer]

I think it was like 1200 or some silly # close to that, I have some footage of him crawling it in triple low with the trans in 4th and it still wouldn't move.

If you get away from a yota drivetrain I could not help you, some of the others around here have done similar conversions so you might want thier advise. The closest I would have to that would be the original axles under my 48 Willys, a d41/25 combo and I have never modified them. I have thought about changing them but with a spicer 18 tcase my options are limited. I did pick up a 20 to put in someday and that would center my rear diff and would open a world of options to me.

[1Bad4Runner]

Well, I would be using a toy t-case and tranny, just not the motor and axles.

So i should aim for like 500-600 for a ratio?

[Hyena]

Marlin has in his truck triple tranfer cases.  The back two cases both have 4.7gears in them.  His crawl ratio is either 1037 to 1 or 1047 to 1.  I can't remember.  Iheard he did have a third 4.7 gearset in it but it was incredibly too slow and he took it out.  Marlin only uses it in triple low to show people how slow ot can go. He rearly ever uses it off road.

[Makman]

I've generally heard that anything in excess of 200:1 is basically overkill for most offroad obstacles but the 400:1 range is easily attained with a couple of 4.7 gear sets.  Besides, never hurts to be prepared for the rare instance it might be useful.  I don't have a doubler (yet) but when I do it'll probably be a 2.23/4.7 combination for versatility but I typically see more mud/slime than boulder fields.

Keep this in mind:
  - A 38.5" tire has roughly a 120" or 10 ft circumference.
  - A typical truck motor will turn upwards of 4000 to 6000 RPM, maybe higher depending on what it is and how it's been built.
  - A 400:1 reduction ratio would allow you to go 6000/400*120 = 1800 in/min...150 ft/min...1.72 mph

If 1.72 mph is too fast with your engine held against the redline, you're one sick puppy and I admire that! 
At close to idle, maybe 1000 RPM, you would only be going 1/4 mph.  Very cool.

[germ]

The only reason I would hesitate to go that low is that you'll probably start to break parts quickly and easily. Your talking about a HUGE amount of torque on your drivelines. and I would think you'll start finding a bunch of weak links (i.e. U-joints, axle shafts, hubs etc.)  . It would be exceptionally cool however. You could probably do OK as long as you kept your foot hovering just above the skinny pedal.

Erik 

[blackdiamond]

I have heard/read that anything lower than 200-250 isn't really useable.  Some people enjoy the  of having dual 4.70s.  If cost is an issue, you only need a 21 spline shaft with a 2.28 in front of a 4.70, but would need to upgrade to a 23 spline shaft for dual 4.70s.  I don't think you need to worry too much about breakage with a 400:1 due to the lack of impact.  I have read somewhere, maybe BigMike can provide more information, about how the super low gears handle the torque.  Usually breakage is the result of impact, spinning wheel contacts the ground (gets traction) and stops spinning.  If you wheels are only turning 1/4 mph, how much of an impact can that be?  Obvously it is possible to simply twist the axles etc.. until they snap.  The marlin dual ultimate is king!  I think Marlin calculated his Low Low Low idle speed to be about 23 hours per mile.

[1Bad4Runner]

Makman, I am planning on using a motor that redlines at 9000rpm and I maybe think about 400:1-500:1 just for fun.

Thanks for all the advice, I'm not to worried about breaking axles because I am using 1 tons.

[Prismo]

With a turbo tranny, dual cases, one 4.7 & 529 gears you end up with 244:1. What kind of horsepower will the engine put out?

[1Bad4Runner]

not to much... only like 110hp. If I tell you what it is you guys will think I'm crazy or something.

[synwars]

not to much... only like 110hp. If I tell you what it is you guys will think I'm crazy or something.

At 110 hp & 9000 rpm that sounds like a way over revved 22r. Or a bike engine.

[1Bad4Runner]

Yes, you are correct, it is a bike engine... a 22r would explode at that kinda rpm I would think.

I haven't completely decided to use it yet, I just think it would be a fun idea.

[Makman]

Waaay too cool!  Definitely going to need some pics on this one.  I don't even know where to begin 

The power to weight should be awesome and think of all the extra room in the engine compartment.  You're probably right to be looking at the deeper reduction since a bike engine will be down on torque...makes up for it with RPM.  Assuming a Toyota tranny and Marlin dual or triple T-case, does anybody out there know if it'll hold up to 9000 RPM use?

Now you have me thinking...there was a Honda Aquatrax turbo-charged 4-cyl on Ebay a while back...
  - Engine Type 1235cc liquid-cooled dry-sump inline four-cylinder with intercooled turbocharger, ~165 hp
  - Bore and Stroke 79.0mm x 63.0mm
  - Compression Ratio 8.5:1
  - Valve Train DOHC; four valves per cylinder
  - Carburetion PGM-FI with automatic enricher circuit
  - Ignition Computer-controlled digital with three-dimensional mapping
...and it'd probably be about as water-proof as it gets straight out of the box. 

[1Bad4Runner]

Lol, Thanks for the interest... The motor weighs about 150lb compared to the like 400-500lb of the stock toy engine. I can't take pictures yet, I'm just designing it right now... I need some stuff machined and I'm not sure if that will be expencive or not, since I am on a very tight budget and am not working right now because of a broken collar bone.

[914Runner]

Lol, Thanks for the interest... The motor weighs about 150lb compared to the like 400-500lb of the stock toy engine. I can't take pictures yet, I'm just designing it right now... I need some stuff machined and I'm not sure if that will be expencive or not, since I am on a very tight budget and am not working right now because of a broken collar bone.

Perfect time to build a nice truck! Errrr buggy.

[Hyena]

I think about 200-230:1 is perfect.

[1Bad4Runner]

Thanks 914runner.. But I need a garage first.

Then I'll try for 300:1 just in case.

[blackdiamond]

I don't think that you have to worry about the gears in the transmission or transfer case at 9000 rpm, the clutch would be the only possible concern.  You might consider a marlin ceramic clutch because the handle high rpm better.  Gears only care about torque.

It is also possible that you might have problems gearing the 9000 rpm powerband into a street useable range since I doubt it will like low to mid rpm with the weight of a truck/buggy.  You might need marlins low first gear, 5.29 gears and 2.28 low range.

My truck runs about 3000 rpm on the highway at 60-65 mph in 5th so your 9000 rpm engine would be doing the same.  You would essentially be making 4th & 5th gears useless unless you wanted to go 150 mph (probably not even possible).  Also, your truck would have problems off the line because 1st gear would be good for 50 or 60 mph.

Gearing is designed to match the engine power curve so this could be a difficult thing to get right.  I would use the online calculators to check rpm and mph for different gear combinations.

[1Bad4Runner]

I don't think that you have to worry about the gears in the transmission or transfer case at 9000 rpm, the clutch would be the only possible concern. You might consider a marlin ceramic clutch because the handle high rpm better. Gears only care about torque.

It is also possible that you might have problems gearing the 9000 rpm powerband into a street useable range since I doubt it will like low to mid rpm with the weight of a truck/buggy. You might need marlins low first gear, 5.29 gears and 2.28 low range.

My truck runs about 3000 rpm on the highway at 60-65 mph in 5th so your 9000 rpm engine would be doing the same. You would essentially be making 4th & 5th gears useless unless you wanted to go 150 mph (probably not even possible). Also, your truck would have problems off the line because 1st gear would be good for 50 or 60 mph.

Gearing is designed to match the engine power curve so this could be a difficult thing to get right. I would use the online calculators to check rpm and mph for different gear combinations.

You are thinking right, but remember, the bike engine has a tansmission. I plan on using the bike transmission and the toyota transmission and t-case.
The toyota tranny will have no clutch, only the bike engine... which I know can handle the 9000rpm.

Let me know if I lost you guys.

[Makman]

(5-speed bike tranny) * (5 speed Toyota tranny) * (3-speed dual T-case setup ) = 75 forward gears and 15 reverse gears.

SWEEET!  Keeping track of what gear you're in could keep you busy   

Blackdiamond does bring up a good point, looking at your torque and speed throughout the range you intend to drive it will be important to make sure it'll have something both on the bottom and at the top.  Sounds like you have considered this and if road bikes are anything like dirt bikes, the magazine and online info should probably have dyno results for the motor you're looking at.  If the motor does 9000 RPM, and it's top gear is an overdrive...the transmission will potentially have more than 9000 RPM input speed which is twirling pretty quick

[1Bad4Runner]

Lol, that is correct... I have thought off all these possiblilities. The first gear of the bike is 2.64, which is all right, but when multiplied by the 3.93 of the toy tranny that gives me a 10.38 first gear. Even with the stock T-case it will give me 125:1 with 5.29 gears.

I plan on doing a few things that probobly have never been done... or maybe have but I've never seen. I know it is probobly a horrible idea, but I think it may work well. I will have to double the street bike chain, because I know they take lots of tourque.
I'm trying to keep the breaking point down though and I know this isn't helping.

Let me know if there is anything I should know about this, is it bad or good to do?

[1Bad4Runner]

Also I have some picture of the gear I may be using... I haven't decided on the tranny because it doesn't have the detachable bellhousing.

Heres a couple pictures of the motor (22.5" wide x 20" tall x 16.5" long)




This is the output shaft, I think it is 12 spline, that is why I don't want to put a whole lot of stress on it.



Here is the tranny... like I said, I'm not sure yet, but it is the 4 speed... the 5 speed is behind the motor, but I see no need to have a 5 speed.



This is the T-case, not sure I'f I'm going to use this one or the other one... But I'll have to see what one is in better shape.



Don't mind the mess in my basement 

My dad thinks I'm crazy with this idea... but I think its all go, If I have to time and money... I figure I should try it at least.

[Makman]

I can't see the pics...just me?

[1Bad4Runner]

Hmm, strange.. I can see them. I dunno what I did wrong.

Anyone else can't see them?