I'm trying to figure something out to get in the ballpark with overall low range. So here's what I'm thinking:
I'm at 62:1 with the auto, so figure about 124:1 with the converter. With a 42" tire, circumference is 130" or so. So I go about 1" for every revolution of the motor. I do have a 468 so I have some good torque available but this works for me.
Previously I was running 55:1 (110:1 with t/c) with a 37" tire, circumference = 116". so the 1" per engine revolution theory holds up for that configuration also (it worked for me too).
With a manual, I know a buddy was at 6.55x2x4.10 = 53.7 with 35's and it didn't work so well. So he did the Doubler and went to about 107:1 and with 35's it seems like it worked nicely. So once again we have 110:1 gears with a 110" tire circumference and a v-8.
So this seems to hold up so far. I know displacement, vehicle weight, personal preference, etc all figure in but this seems good so far. I bet it doesn't hold up real well with small displacement motors and heavy rigs. A really heavy 4cyl toyota might have problems with the same gearing. And a really light rig with major beans could probably stand "shallower" gears.
What do you think? Where does everyone stand as far as inches traveled per motor revolution? Is 1" of travel per revolution of the motor a good guideline?

I personally like it a little lower. I have 465-205-Rockwells. That yields about 86:1 crawl. with 33" boggers i move about .8 inches for every Rev, and i want it lower still. Obviously the 33's aren't sttaying, so i am going to need alot more gearing. I think about .5 inches per rev is the lowest i would ever need. But with a klune added into the mix eventually, i will have a lot of options depending on what obstacle i am at...

Laters-

OK come on, we all have gears and we all have opinions, let's hear them.
Figure it like this:
final drive ratio = trans gear x t-case gearing x diff gears
distance traveled with each tire revolution = tire diameter x 3.14 (pi x d)

Distance travelled per revolution of the motor = tire circumference divided by final gearing ratio.

example: 6.55 transmission, 4:1 transfer case, 4.56 diff gears = 122.5:1 final gear ratio

37" tire circumference = 37 x 3.14 = 116"

Distance traveled/revolution = 116/122.5 = .95 inches

For the above post with 33's and 86:1, you would have 1.2" per motor rev, not .8" per rev. Going to 44's you would have 138"/86=1.6"/rev.
You have to do the distance divided by ratio. So that means that if you're closer to 1:1 you would be happier.

Originally posted by Stephen
example: 6.55 transmission, 4:1 transfer case, 4.56 diff gears = 122.5:1 final gear ratio

37" tire circumference = 37 x 3.14 = 116"

Distance traveled/revolution = 116/122.5 = .95 inches You tell me my head hurts from lack of sleep.

370:1
38.5" tire



Answer:0.32672972972972972972972972972973

mine is 1.51 inches. It's a little too high for my liking. 1 to 1 would be pretty good imo.

38.5 x 3.14 = 120.89"

120.89 / 370 = .33"per motor rev. That's really slow

sorry, i was thinking backwards, it happens sometimes. I still think that a 1:1 ratio is not slow enough for every situation. I will still buy a 4:1 klune, instead of the 2.72. that will give.4 inches for every rev But that's just me.

anyone else?

I'm at 61:1 (6.5x1.92x4.88) running 39" boggers with a 454, so I'm at 2:1 and it's been working great in Tellico/attica type places, I can't think of a time when I needed less tire speed in low gear...there have been hundreds of times I wish I had less tire speed in the higher gears tho. :)

I will be at 24:1 with an auto ( :( ) and 37's :eek: Oh well will just have to get a tranny temp gauge. The 1:1 thing seems pretty damn good. I've driven a few rigs with around 65-70:1 and 33's and they did very well. I think if you have a good motor and moderate rate 1"/rev is more then enough gearing for almost all situations.

Current setup:
-------------------------------
3.06(700R)*2.92(NP241)*4.88(diff) = 43.60
With converter 43.60*2 = 87.2

37(td)*3.14(pie) = 116 116/87.2 = 1.33 inches


This summers setup (I hope)
--------------------------------
2.48(TH400)*7.2(doubler/203 low set)*4.88(diff) = 87.13
With converter 87.13*2 = 174.26

39.5(td)*3.14(pie) = 124.03 124.03/174.26 = .711 inches

Side note: With the Wagoneer 203 low gears I would also have 3.6:1 and that works out to 1.42 inches


My math sucks but me thinks it's right, still not sure on how the converter part works in due to RPM's etc..

Anyone have the gear ratios of the following parts or can calculate my crawl ratio?
T98a trans x d18 tsfr x 5 . 38 gears with 33" tires
Thanks in advance:beer:

just wondering, why is there an 2:1 reduction in the torque converter? my friend and i were arguing it, and i know there is, i just dont know how it works to argue it.

Jeff

With the auto trannie the torque converter has built in slip at lower rpms. This varies with the stall point of the converter. A higher stall means more slip at low speeds. The generally held thought is that a rig with an auto and a higher stall point 'feels' like a manual trans but with a 1.9x to 2.3x multiplication of torque. Feels like. This is why folks with auto trannies can get away with higher overall gear ratios for off roading. My bro who has a all-out rock crawler with an C4auto with an 800rpm stall, AA 4.3 and 7.5:1 axle gear reduction has decided the 4.3:1 AA is too low and he's just now swapping it out for the 3.0:1 AA t.case, and going to a higher stall converter. He came in 9th at the most recent Warn National Rock Crawling Championship in Las Cruces.
I've gotten to a fairly low 130:1 [6.69x4x4.88]with my trail rig and feel it's about right, off-road, with 36" Swamper Radial TSL's. The lowest of low ranges has kind of gone out of style the last year or so. I still like around 136:1 to 150:1 as an adequate creeper gear. The 'Beater Boys' I jeep with all have lower low ranges than me, but my MPI/4.4L/H.O. I -6 will pull like the devil at 500 rpm and not stall, so it's o.k. Frank has 136:1 in his Jeep [6.32x4x5.38], Mark has 274:1 crawl in his CJ8 [6.4x2.62x4x4.10], and Cal has 335:1 with a Th700R4, a couple of Marlin Crawlers, and 4.56's, and that doesn't account for the torque converter slippage. All I can say is that no one on the trail likes to get behind our group.
regards, as always, jefe

So jefe's at 130:1 with a 36" tire. Assuming it's a true 36" tire which it isn't but we have to start somewhere....
You're at 113 / 130 = .87" per motor rev.
Don't know about the tires for the rest of the guys, but they're all lower than .87.
Maybe with auto trans 1:1 works and a manual might want a little lower?