OK guys, this has been bugging me for a while. It's one of those things that CAN be done, but SHOULD it be done?

What if you put 4.11 gears up front with 37" tires and 4.88 gears out back with 44" tires? The gear ratio and tire sizes offset each other, so ground speed will be the same front and rear. Or vice versa, swap the gears and put the bigger tires up front.
(there are many different gear ratio and tire size combos that will get the same idea)


I'm sure I'm not the first one to think it up. Can anybody tell me why you might want to go to all the trouble?

-tom

Yep, been done.
We saw two buggies last July at Tellico running like that. They had what looked like 35's up front and 40's or 42's in the rear. Didn't get a chance to talk to them, so I can't tell you much else. They did climb pretty well from what I saw.

Originally posted by ryankopecki
Maybe so your 44 front lives while you have extra traction and ground clearance with the bigger tires on your 14 bolt rear.

That's how it started with my group... d44 and 11x38 boggers w/ a d60 and 39.5x18 rears. I still use the same combo for tellico and mudbogs. The skinny tires steer real well and can pick finer lines, plus they don't weigh as much. I have a shaved 35sp. front now and I bought the same tires again. Deep mud is the only bad side I have found.
I'm running the same gears ft and rear (4.88), I used to have 4.88vs4.56 , I don't notice any difference with the minor height difference of the tires.
Works for me...

Originally posted by LandCroozer

I'm sure I'm not the first one to think it up.

Not even close ;)

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TEX

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TEX

It works, but I think it looks stupid :p

Hey Tex, I thought for mud it was common to run smaller tires in the front with the same gears so that the front had more wheel speed and stayed up on top. Is this right or am I brain farting again?


Off topic, I bet ya dont remember, but we've met a few times. I joined MidMo back in about 95 or 96, was only in the area for a couple years. Wheeled with Blain alot, black YJ.

Ken

Originally posted by kwrangln
Hey Tex, I thought for mud it was common to run smaller tires in the front with the same gears so that the front had more wheel speed and stayed up on top. Is this right or am I brain farting again?


If they ran smaller tires with the same gears, the front would spin SLOWER. So, actually they run smaller fronts, with higher gears - enough to keep the front spinning at least as fast (if not faster than) the rears.

This the Ken who moved to Texas? You were in the Coast Guard, right?

TEX

That would be me, stayed in Texas till late 99, been in Jersey ever since. I saw Blaine last year when I went to a school at Ft Leonardwood. Last time I talked to him he was in Utah. Just wished I had the time to hit some of the trails while I was there.

Ken

I figured I had brain farted on the gearing.

Well, good to hear from ya again. Always wondered where you ended up. Club's still around, still doing lots of mud, getting back into the trails more & more these days.

TEX

Originally posted by kwrangln
Hey Tex, I thought for mud it was common to run smaller tires in the front with the same gears so that the front had more wheel speed and stayed up on top. Is this right or am I brain farting again?

Ken

I've definitely heard of this.. But like was said you run a taller gear up front to keep them spinning faster in the mud.

But anybody do this on the rocks?

Here's what I'm thinking; bigger tires up front. This will let you float on top of rocks and crawl over obstacles. Smaller tires will get down in the rocks and ruts and give you traction for climbing power.

-tom

Check out this rock rod (http://www.4wheeloffroad.com/featuredvehicles/99638/).

Originally posted by LandCroozer
Here's what I'm thinking; bigger tires up front.

Ummmmmmmmm, I don't think so.


TEX

I'm pretty sure most guys I've seen around Tellico do it so their 10 bolt fronts won't explode :D

all i can say is......:rainbow: !!!!! Just disregard the hill billie thoughts as soon as they enter your head. Yes it can be done and NOOOOO please don't do it. i think it would be cooler to see a 10 bolt explode then to see the 10 bolt being compensated for!:flipoff2:

Originally posted by TEX


If they ran smaller tires with the same gears, the front would spin SLOWER. So, actually they run smaller fronts, with higher gears - enough to keep the front spinning at least as fast (if not faster than) the rears.

TEX

Please xplain this as it makes no sense to me. So if I have 5.13's in both diffs with 44's on the rear and 38's on the front, the front will be spinning slower than the rear?????

Originally posted by clc900


Please xplain this as it makes no sense to me. So if I have 5.13's in both diffs with 44's on the rear and 38's on the front, the front will be spinning slower than the rear?????

Despite my earlier brain fart, I think I can explain it for ya. Set a 38 and a 44 side by side. Roll them both forward one revolution, the 44 goes farther due to its larger circumfrence. Now spin them the same speed, and the 38's are continuallly trying to cover less distance than the 44's, so in effect they are slower.

Got it?

Originally posted by kwrangln


Despite my earlier brain fart, I think I can explain it for ya. Set a 38 and a 44 side by side. Roll them both forward one revolution, the 44 goes farther due to its larger circumfrence. Now spin them the same speed, and the 38's are continuallly trying to cover less distance than the 44's, so in effect they are slower.

Got it?


He is correct, some people run shorter gears in the front to make the front tires spin faster than the rear, helps alot w/ steering in the muck.:rolleyes:

No mud expert but I think the front turning slightly faster
in the mud goes a long way in keepin the rig in a straight
line :)

There's no reason why you couldn't compensate for differences in tire size with differences in the gearing. I read an interview with the guy that built the rock rod and he said that he did it to be different and a hot rod just didn't look right to him with the tires the same size.

I could definitely see how putting higher (numerically lower) gears on the front and overcompensating for the smaller tire size would help to keep a mud rig straight as well. It would effectively drag the front of the rig foreward and if it got out of line, the slower rear would act like an anchor holding the rear back until the front could get straight again. Ever seen a front drive car in the snow? Similar thing.

Just make sure the gears compensate for the tires as close as possible if you're going to run the thing on high traction stuff like road or the granite bowl, otherwise :nuke:

-John

Originally posted by suspect



He is correct, some people run shorter gears in the front to make the front tires spin faster than the rear, helps alot w/ steering in the muck.:rolleyes:

Actually, I believe a higher ratio is referred to as a "tall" gear. In other words, a 5.13 would be a "short" ratio & a 3.08 would be "tall".

Think of it this way, to run TALL tires, you have to compensate with a SHORT gear.

BTW, the formula for tire speed is as follows:

FD*MPH*336/TD = RPM

FD = Final Drive, MPH is Miles Per Hour, TD is Tire Diameter, RPM is RPM :p

Using what they taught us in Algebra back in 8th grade, you can twist the formula around as follows:

(RPM*TD)/(FD*336) = MPH

So, let's say we have 2,000 RPM's, 5.13 gears, 1:1 top gear (for a 5.13 FD), and 44" tires in back with 38.5's up front. We'll also assume true diameters for this.

The rear tires would spin as follows:

(2000RPM*44" tires)/(5.13*336) = 51 MPH

The front tires would spin as follows:

(2000RPM*38.5" tires)/(5.13*336) = 44.7 MPH

So, the fronts would spin slower due to the reduced circumference of the tires. As Ken explained earlier, the # of tire revolutions would be the same front & rear. But, because the rears are larger, they'd travel more distance per revolution. In other words, they'd move faster.

To find a ratio to correct this, you take (38.5/44)*5.13 = 4.49.

Dropping down to a 4.27 would make the fronts spin just slightly faster than the rears.


TEX

I thought 'tall' gears were numerically low...:confused:

Originally posted by bigdude
I'm pretty sure most guys I've seen around Tellico do it so their 10 bolt fronts won't explode :D

BINGO

Either that or they are running 44s on the front for the small tires and run some big agricultural tire on the back in a 50"+ size.

Originally posted by TEX


Ummmmmmmmm, I don't think so.


TEX


Ummmmmmmmm, why not?

-tom

Originally posted by LandCroozer



Ummmmmmmmm, why not?

-tom

For all the reasons mentioned above, not the least of which is that the frontend is typically a weak link in the drivetrain.


TEX