Best gear swap

[dogbones]

Opinions on the best gear swap for a diesel running 35’s vs 37’s........ Thanks in advance.

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[Schreconjeep]

Hoping some 4:10 take offs should do it for 37s on the EcoDiesel

 

[dogbones]

Hoping some 4:10 take offs should do it for 37s on the EcoDiesel

We might need to start a thread looking to buy 4.10 take offs......

 

[Schreconjeep]

Shhhhhhh! Wait till we get ours first.
good info on the topic...

Skip forward to 7:50

 

[WXman]

For 37s I'd stick with 3.73.

For 35s 3.73s are still OK but 3.55 would be ideal.

I know everybody has been on the "don't fear the gear" kick for the last 30 years, but this diesel + 8HP75 trans is a totally new ball game and the best axle gearing for this is also a totally new ballgame. With the gas engine, you're trying to increase RPM to stay in the power band. On the diesel, you need lower RPM because that's where the power band peaks.

I'm running Patagonia M/Ts that are virtually a 35" tire (they measure out 34" mounted on wheels which is where my 35x12.50s usually fall as well) and 3.92 axle gears and it's overkill. 1st gear is almost useless and rarely ever used, and the trans shifts way too often. The standard axles are 3.21s and that would have been a better match.

 

[RedTRex]

I agree. Torque peak is around 2000 rpm. This engine (well running GEN 2 at the moment) prefers to stay between 1.5-3K

 

[BrightWhiteGladiator]

For 37s I'd stick with 3.73.

For 35s 3.73s are still OK but 3.55 would be ideal.

I know everybody has been on the "don't fear the gear" kick for the last 30 years, but this diesel + 8HP75 trans is a totally new ball game and the best axle gearing for this is also a totally new ballgame. With the gas engine, you're trying to increase RPM to stay in the power band. On the diesel, you need lower RPM because that's where the power band peaks.

I'm running Patagonia M/Ts that are virtually a 35" tire (they measure out 34" mounted on wheels which is where my 35x12.50s usually fall as well) and 3.92 axle gears and it's overkill. 1st gear is almost useless and rarely ever used, and the trans shifts way too often. The standard axles are 3.21s and that would have been a better match.

So axle gearing is admittedly an area I know very little about. I have a gas 3.6L Overland with 35” tires. Would I benefit from different gearing? My wheels and tires are over 70lbs each of that makes a difference.

The only time I have messed with this in the past was on a 6 speed STi... changing 6th gear to get better gas mileage on highways (since I rarely got to 6th gear on AutoX courses)

 

[WXman]

So axle gearing is admittedly an area I know very little about. I have a gas 3.6L Overland with 35” tires. Would I benefit from different gearing? My wheels and tires are over 70lbs each of that makes a difference.

The only time I have messed with this in the past was on a 6 speed STi... changing 6th gear to get better gas mileage on highways (since I rarely got to 6th gear on AutoX courses)

What are you trying to achieve? My JLU Wrangler with 3.45 gears and 35" tires would smoke the tires from a stop and run to 60 MPH in 7 seconds. To me that was perfectly acceptable. I put the same tires on the JT Gladiator and the truck was a little slower because it's heavier, but performance with the 4.10 gears was still great.

I think the new 8, 9, and 10 speed transmissions these days are eliminating the need for axle regearing for everybody except the guys running 38-40" tires.

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