I have an auto 4 door Rubi with 35's and 4.88 gears.

At 65mph in the mountains I drop to second gear and a high 5,000 RPM to maintain speed.

With lower gears (5.13-5.38) I understand that at the same engine RPM's in second gear would result in a lower speed- probably around 55 MPH.

***Would the lower gears produce more torque at the rear wheels with less RPM in 3rd gear?***

Is it possible to maintain 65MPH in the Colorado mountains without topping out the 3.8L?


Thanks for any info!

 

Your torque is going to be rpm dependent and has nothing to do with what gear set you have. To start getting into the meat of the torque curve you want to be at 2500 rpms or higher.

Living in Colorado you are a definite candidate for 5.38s with an automatic, and if there was a steeper gear set available it would also be worth consideration.

 

I have the 4 auto door in Colorado with 35s/5.13s. I still kick down into second summiting some of our mountain highways. I have never had 4.88s so I cant say it happens any less. But I can that 5.13s will not completely solve this problem. 5.38s might work. I have just conceded that I will be going 45 mph, in second gear, near some of the summits.

 

Only a HEMI will help that issue!

 

No real comparison to Colorado but I drive from 2K to 4K elavation to work daily. Prior to installing 5.38 the auto would continue to hunt shifting from 4-3 and at times down to 2 for me to keep up with traffic or god forbid try to pass someone. Now with 5.38 and 35" tires it will stay in 4th no problem 2500 rpm 72 mph.
Yes, if you have the funds a Hemi would truly solve the problem.

 

Pls correct my thinking if Im off base:

Gears offer you a mechanical advantage and are a multiplier of torque.

With a lower gear (numerically higher) you are multiplying the torque by a greater amount increasing your mechanical advantage.

Your rpm migjt be higher but the engine will be working less to maintain speed.

 

How 'bout oxygen injection!
The air is thin as hell up there.

Get a tank and strap it on.

 

Yes, your drive line ratio delivers torque to the wheels at the given amount for a single revolution of the axle. What they don't do is change the amount of torque the engine produces, just the delivery. Also I think horsepower is better for determining the OP query, as HP just adds the element of rotational speed to torque. Torque being the hammer and HP being the come-along.

At the 5,000 rpm that was mentioned, there is no where to go for additional power. So the question becomes will the increase in driveline to a steeper gear set precluded the vehicle from making the downshift to 2nd? I have no idea if the 10-15 more hp would be enough to keep it from downshifting, but I do have some confidence that Chrysler isn't going to throw the vehicle into "blowd up" mode.

Perhaps the better thing is that the higher gear set won't unlock your converter as often also keeping your rpms a little more under control.

 

Thanks for all your replies!

I think I'll try temporarily swapping my 35's with some stock 31's to mimic a lower gear ratio.

As I'm currently at an Army school, I'll be able to do this in a couple weeks.

 

That's a really good idea!


I'd then get the weight differences from the tires, double that as a payload and you should have it nailed.