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Mix and match gear ratios, what is the limit?

Lil'John

Former #278
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May 20, 2020
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Title kind of states it. Short: how far out of matched gears can one go and still be usable?

Examples:
4.30 front and 4.56 rear. Too much difference?

5.29 front and 5.38 rear. Too much difference?

This will be on/offroad rigs that will use 4wd on road(rain/snow) as well as rock crawling. No mud. Maybe some snow wheeling.
 
Hardcore trail-only rig, I would consider up to 5-6% difference.

Street rig, 1-2% at most especially with modern tires that don't slip easily on wet asphalt.

4.56 and 4.30 are about 6% difference.

5.38 and 5.29 are about 1.7% difference.
 
But running slightly taller gears in the front axle gives some interesting benefits. Climbing will have the front axle pulling a little harder and keeping the front end stuck a bit better, and turning will be a bit tighter.

Turning in reverse will be worse, and backing up anything steep will be unstable.

I've seen this done on a couple trucks, and I have ran different gears in RC crawlers for years. :grinpimp:
 
Last edited:
5.13 vs 5.29? Obviously 5.38 would be better but whats your thoughts?
 
Hardcore trail-only rig, I would consider up to 5-6% difference.

Street rig, 1-2% at most especially with modern tires that don't slip easily on wet asphalt.

4.56 and 4.30 are about 6% difference.

5.38 and 5.29 are about 1.7% difference.

Thanks for the math. I was afraid the 4.56 and 4.30 were going to be a bit too far apart... kind of my luck:rolleyes:
 
Building a truck that came from GM/CHEVROLET M1031 CUCV with 4:56 gears in front and putting a 1985 D70 dually axle in the rear in place of the 14 Bolt w Detroit locker that came stock.

The D70 has 4:10 so keeping the front driveline out of it before I forget and slip it into 4wd and wreck the brand new NP205.

Have everything gathered but the pesky unobtainable bellhousing.
 
Every time this comes up it's always a bunch of people speculating. "omg, you can't drive on the street with 4.10s and 4.11s!?"

Tons and tons of people run 5.29/5.38, it's not enough to even ever ever notice.

My buddy ran 4.56/4.37 in a short wheelbase isuzu amigo. When we first put the Toyota axle in, we put it in 4 hi and pushed it back and forth on dry concrete by hand just as easy as 2hi.

Years ago, I blew my 5.29 rear diff and swapped to 4.10s since I needed the rig to drive for work. We went up to the hills and ran into more snow than I expected. 5.29/4.10s is definitely too much :laughing:

My tow rig had 4.10s and I swapped the whole rear axle to 3.54s. The r&p I had in the front burned up in my garage, so 2 years later it's still mismatched :homer: I've had to use 4wd a hand full of times to back up my steep gravel driveway. It's definitely noticeable, you can hear the rear tires slipping since there is almost no weight on them compared to the front. So yes, 15% is definitely too much.

As far as street driving, I don't see why that matters. Who's driving around on pavement in 4hi?

As far as the tcase being bound up, if you're rock crawling, it's always bound up.
 
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