Mud truck gearing

Does a faster front gear actually keep you straight? How much faster? Maybe 5%? Less? All three runs this past weekend I was from wall to wall. A straight shot could have probably saved a second or so.

yes, its called overdrive.

its usually more like 10% and also a smaller tire in the front.


Running skinny swampers in the front and boggers in the rear will help as well. Its almost impossible for me to run straight with wide boggers front and rear.

I've got the 38.5x11 boggers up front. 38.5x15 in the back. I'm thinking about trying 39x18 on the back though.

try 4.56/4.10 or 4.10/3.73 depending on combo with 38.5/39.5

have you tried it with just the skinny tires on all the wheels? in our club i have seen alot of trucks try to run a wide tire setup in the back and allways go side ways.

I haven't yet. I was afraid the skinny in the back wouldn't provide enough bite. Worth a shot though.

its not IMO.

the only benefit Ive seen from skinnys front and rear is on lower horsepower engines in thick bottomless mud.

All other areas I think skinny fronts and wide rears is the way to go.

Since we're talking. How much power and RPM is the wide 39 going to rob. Right now, with the 38.5x15, it turns exactly where I want it. About 5800 to 6000. I'm afraid the 39 may lug it down.

how much power does the truck have now? what kind of mud do you race in?

the 38.5 boggers have the closest lug seperation in the bogger line. The 39.5s have one of the farthest.

what this means?
38.5 boggers will NEVER hook like 39.5s and that will soak up some RPM but the added traction will probably keep 200' times similar. Id go with the lower gears 4.56/4.10s and run the T-case in low. That will keep the RPMs up.

My combo now is a little different than most. I'm running 5.38 F&R. Running in low. Launching in 2nd, shifting to 3rd. I could be a little faster, but I like that it never lugs down now. Chevy guys think I want have any wheel speed, but they forget their transfercase has a lot more reduction than our 205.

^^ thats an interesting way to do it.

r&p ratio x trans gear ratio x t-case ratio

4.56x2.46x1.96 = 21.98

5.38x1.46x1.96 = 15.39

hmmm...5.38s starting in second is very similar to 3.25:1 gears starting in first.

Id rather have a little more gear and turn a little harder than that.

Id rather have a little more gear and turn a little harder than that.

You lost me there. You talking about turning the motor more RPM's?

yes.

My truck would be rather lazy with the equivalent of 3.25:1 gear as the final drive ratio.


Every combo is different and every pit is different so Im not saying YOUR truck doesnt run well like this. I would like to know why you dont start in 1st though.

I would like to change gears to make first usable, just don't have the funds right now.
I almost think I could leave in third. I stall it to about 3k, hammer it and within 10-15 feet I shift to third. I wish I had 4th gear just to see if it would turn it, probably would.

I would try running 1st and "maybe" 2nd on the high side, but I'm afraid the converter is going to stall to close to my max rpm.

cant shift 3 times?

I would imagine your 60' times are rather slow.


I foot brake to 3k, shift to 2nd at 5400 at around 50' and most often 3rd at 5400 at 160-175' and this is a nothing special hyd cam 521 in a 6000lb 79 F250. Sometimes I just hold 2nd and end up bouncing off the 6k limiter and blinding myself with the shift light but it all depends on the track. Id never go to 3rd in a deep or thick mud pit.

Frank Merkl gave me a valve body mod that works like a champ in my truck, put it in D and mash the loud pedal. It hits all three gears on it's own @ 5500. I've been doing quite well this year and running out the big end just starting to bounce on the rev limiter @ 6400 rpm. Most of the guys I'm running against have more hp than me and are running 38-9" tires to my 33"s. When I go to modified class, I put a set of cut 35's on the back and still run out the end bouncing off the limiter.

looks like I need to give Mr Frank a call.

IcallhimGeorge wrote:looks like I need to give Mr Frank a call.

Want his #

yes that would be great!

Thanks Schmitty

403 793 5412

It's really hard to do, and takes some high dollar parts, but it's worth it. LOL
Brake spring and a handfull of pennies. Cost me about $2

IcallhimGeorge wrote:cant shift 3 times?

I would imagine your 60' times are rather slow.


I foot brake to 3k, shift to 2nd at 5400 at around 50' and most often 3rd at 5400 at 160-175' and this is a nothing special hyd cam 521 in a 6000lb 79 F250. Sometimes I just hold 2nd and end up bouncing off the 6k limiter and blinding myself with the shift light but it all depends on the track. Id never go to 3rd in a deep or thick mud pit.

I could shift 3 times, but I don't see the point. Leaving in 2nd, as soon as I come off the brakes its at 6k. Shift to 3rd, within a few feet its doing all it can do. Between 5800-6000.

I suppose my 60' times could be slow. Although, Everyone told me this past weekend, I won off the line. It comes out of the hole pretty fast. I'm going to post the vids as soon as I can.

schmitty wrote:Frank Merkl gave me a valve body mod that works like a champ in my truck, put it in D and mash the loud pedal. It hits all three gears on it's own @ 5500. I've been doing quite well this year and running out the big end just starting to bounce on the rev limiter @ 6400 rpm. Most of the guys I'm running against have more hp than me and are running 38-9" tires to my 33"s. When I go to modified class, I put a set of cut 35's on the back and still run out the end bouncing off the limiter.

I think that would be the way to go, if I had a little more reasonable gear. Right now first is useless.

schmitty wrote:It's really hard to do, and takes some high dollar parts, but it's worth it. LOL
Brake spring and a handfull of pennies. Cost me about $2

really? that is