Towing on Highway with 4:10 differential

[rockinreel]

I have an '86 CJ7 (AMC 258 i6 / 4.2l ) with a 2:73 gear ratio, which is an open differential. Will be upgrading to a traction enhancing diff soon. I often tow a small trailer with a ATV on it and additional weight and can't use 5th gear while towing on the Interstate. So, I tow in fourth gear. I can use 5th without towing, as some people say they can't.

If I switch from a 2:73 diff to a 4:10, I'm concerned I may not be able to tow in 4th gear at 65 - 70 mph anymore and maybe not even in 5th with a 4:10. Will I end up towing in 4th at 55mph to keep the RPM's down, or will I be able to tow in 5th with a 4:10?

thanks

 

[tarry99]

I have an '86 CJ7 (AMC 258 i6 / 4.2l ) with a 2:73 gear ratio, which is an open differential. Will be upgrading to a traction enhancing diff soon. I often tow a small trailer with a ATV on it and additional weight and can't use 5th gear while towing on the Interstate. So, I tow in fourth gear. I can use 5th without towing, as some people say they can't.

If I switch from a 2:73 diff to a 4:10, I'm concerned I may not be able to tow in 4th gear at 65 - 70 mph anymore and maybe not even in 5th with a 4:10. Will I end up towing in 4th at 55mph to keep the RPM's down, or will I be able to tow in 5th with a 4:10?

thanks

You need to look at a Standard Gear & Tire ratio RPM chart like the one attached........that will tell you all you need to know

 

[rockinreel]

That chart says for my 32" tires, I need a 3:73, 4:11, or a 4:27. Would be nice to test drive the different gear ratios first.

I also found this chart:

Tire & Gear Ratio Chart at Morris 4x4 Center

 

[csuengr]

Screw gear ratio charts.

32" tires, 2.73 gears, and Jeep T-5 tranny at 70 mph:

4th gear = 2071 rpm, 5th gear = 1781 rpm

32" tires, 4.10 gears and Jeep T-5 tranny at 70 mph:

4th gear = 3110 rpm, 5th gear = 2675 rpm

32" tires, 3.54 gears and Jeep T-5 tranny at 70 mph:

4th gear = 2686 rpm, 5th gear = 2310 rpm

3.54 gears would be appear to be a better choice.

 

[rlitavecz]

I assume that 5th gear is an OD? If that is true, 4:10 gears should be fine to about 70 mph with the 32" tires. I have 31" tires, 3.73 gears and high gear in my Transmission is 1:1 ratio engine to tranny output. At 70 mph my engine is wound out.

 

[007]

I've used this site a lot in the past...

Gear Ratio Calculator

 

[rockinreel]

I assume that 5th gear is an OD? If that is true, 4:10 gears should be fine to about 70 mph with the 32" tires. I have 31" tires, 3.73 gears and high gear in my Transmission is 1:1 ratio engine to tranny output. At 70 mph my engine is wound out.

Thanks, rlitavecz, nothing like raw experience on the highway. With yours and csuengr' input, you've answered my question.

thanks