I have read the many, many posts about gearing here on this site, but I still need some advice. (Mostly I think because my highway max speed is 60mph where I drive, and most posters here are talking about 70-75mph max).

I need to get more trailer pulling ability for my occasional trailering. I currently have the following:
31.6 inch tires. 4.6 5 speed manual trans. 3.55 diff.
which runs about 2000 rpm in OD at 60 mph, in 4th it runs at about 2500.
I cannot decide between 4.10, 4.30 or 4.56 gears. I am leaning towards the 4.56. If I use 4.56 gears I will be running 2500 rpm in OD on the highway and 3000 in 4th when pulling the trailer, if I pull at 60 mph which so far I don't (or can't) do.

I drove on the highway in 4th on one trip, (no trailer), And I did not find the 2500 rpm to be any problem. It was too short a trip do get any real mileage results, but I wasn't shocked at the pumps. This test would replicate what will be happening when I am in OD with the 4.56 gears.

One of the main reasons I was thinking of the 4.56, with the resulting increase of 500 rpms, is that you can REALLY feel a surge in power when the engine hits 2900 rpm, so I figured I should try to get the rpms closer to that.

What has me doubting this decision though, is that most of the posters here that have put in the 4.56 gears are running larger tires than I am. I know that for many it is to get back to "stock" rpms, (and running at higher highway speeds) but I am looking for more pulling power.

I would appreciate any thoughts on this subject. Thanks.

 

i really think a 4.10 will make you more than happy unless you plan on upping the tire size at a later date. that is a fairly large jump from 3.55.

4.56 is too low a gear for your uses, at least in my opinion.

 

I agree. How heavy is the trailer your towing?

 

Well, fully loaded it's about 5500 lbs, but right now with no wind I can keep it at 60 mph only if it is floored. With a head wind I have trouble keeping it at 50 mph. I generally drive it at 50 if there is no wind just to keep the throttle pedal off the floor.

 

You DO realize that your rated max towing capacity with the 5 speed manual is 3500# or less, right? This is due to a weak input shaft in the M5OD.