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inquiring_mind2 08-16-2005 01:02 AM

tire size and gear ratio
I am in the process of building a new toy. I am building a jeep for a mud bogger. My question is I want to make the front wheels turn faster than the rear ones. I have no clue on how to do this. I am running a 350 turbo for the transmission. a 208 for the transfer case. I would like to know about how to match the gear ratio and tire size to make everything to work properly. Right know I have 4:10 gears front and back. I am also running 35 boggers front and back. I am not wanting to go any bigger than a 35 inch tire. I know I will have to run a smaller one in the front but thats where I need some help. on how to pick the correct gear ratio and the correct tire size. any help would be greatly appreciated



bracketeer 08-16-2005 01:15 AM

Rear end and tire heighth calculators.

johnsongrass1 08-16-2005 08:02 AM

SO you want the front turning More rpm than the back tires?

You have 4:10's now.

Just put 3:73's in front. Or change the front to a 33" tire.

inquiring_mind2 08-16-2005 08:04 AM

that won't tear up the tranny or the transfer case

inquiring_mind2 08-16-2005 08:04 AM

yes that is what I am wanting to do

johnsongrass1 08-16-2005 12:29 PM

Yes, it hard on the driveline anytime you aren't in the dirt. But you are going to have to suffer those consequences with a faster moving tire. Even if you gear the front to a 3.73 with smaller tire in front the rpm will remain the same This is defeating the purpose. Or am I not getting what your are asking?

inquiring_mind2 08-16-2005 11:12 PM

I have seen other people do it. What I am wanting to do is have the front tires pull me through the mud and have the back one push me. I want my front tires to be turning more revolutions than the back ones. at the same time I don't want to hurt my tranny or transfer case either. Am I making sense so everyone knows what i am wanting to do or do I need to try and describe it another way? let me know



IanRiordan 08-17-2005 03:30 AM

If you use a3:73 and 35's, you will run around 27.5 mph per 1000 rpm in high range top.4;10 and 35's equal 25mph, so you have a10% step up. This will stretch the chain in your 208, and if you are still running a dana 30 in the front it could be an issue. Who cares? blow it up then put a 60 in the front and a14 bolt GM in the rear. By the way, to work out gearing easily, multipy tyre height(loaded) by 2.94, then divide by overall gear ratio (my formula) it will get you within 2%.

M&M CUSTOM 08-17-2005 05:45 AM

I've seen this done before, and it works.
You are aiming to go as straight and as fast as possible in MUD, the easiest way to acheive this is to have the front tires spin faster than the rear.

I agree with just switching to 3.73's, or the tire size to acheive the same result.

I have only seen one truck owner match the gearing correctly and have the guts to run 40 inch tires in the rear and 33 inch tires in the front, and he deliberately ran a stock NP-203 transfer case to allow the internal differential take care of any gearing differences he might have.
The truck was mostly for show but he wasn't afraid of hosing off a few hundred pounds of mud if the occasion popped up, and someone called the truck a trailer queen.

Poopy 62 08-17-2005 07:38 AM


Originally Posted by inquiring_mind2
I want my front tires to be turning more revolutions than the back ones. at the same time I don't want to hurt my tranny or transfer case either. Am

LOL, I've been into rockcrawling for years, what you want is impossible unless you are ONLY driving in gooey mud, If you have any traction, your T-case is not going to last.

inquiring_mind2 08-17-2005 08:35 AM

that is all I am using it for is in the mud. I want to go as straight and as fast as I can in the mud.

inquiring_mind2 08-17-2005 08:41 AM

right now I am using a gm corp 10 bolt with dana axles in the front and a gm 14 bolt in the back. I would like to have a dana 60 but dam those bad boys are not to CHEAP. So for know I will have to stick with the 10 bolt with the dana axles I also got to looking at the transfer case and it is a np 203 not a 208. to much grime on the numbers. lol

I run in low range so will that make a difference? I also run around 6500 to 7000 rpms also

johnsongrass1 08-17-2005 09:57 AM

I've got a mud toy based from a 79 jimmy 3/4 ton. All stock driveline cept for welded lockouts. I've got siped 40" gumbo's and run 300 rpm faster in front to stay on top of the mud. Most times I find, you lose wheel spin and momentum by hitting the wall of mud left from the previous guy who got stuck. This will bury the front.

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