Originally Posted by Jackrabbit379 (Post 484621)

A friend of mine has a 359 with 3.55 rears. 475 CAT, with a 15 behind it. It's cool driving about 72 and the motor is running about 1600.
Feels like you are going down a country road in a Cadillac. :p

Originally Posted by Mackman (Post 484604)

Get real trucks with 3.90s or 4.10s :thumbsup:

I know you guys are talking OTR

Originally Posted by Shnerdly (Post 484584)

Actually, it's the opposite. The larger the number, the higher the RPMs of the engine will be.

Copperhead has it right. The way it is usually talked about makes it kind of an odd concept.

When people say they are lowering their gear ration, the are actually going to a gear set that has a higher number but the reference to a lower gear ratio means a lower top speed.

If you have 3.42 gear ratio, your drive shaft will turn 3.42 revolutions to one revolution of the wheel. If you have a 3.58 gear ratio your drive shaft will turn 3.58 revolutions for one revolution of the wheel giving you a lower top speed and slightly higher RPM if all other factors are the same.

The other factors are tire size being 22.5 or 24.5 and low profile or not. Also the transmission matters. Some are direct drive meaning the output to the drive shaft is equal to engine RPM's in high gear. Some are overdrive meaning the drive shaft is going slightly faster then engine RPM's in high gear. There are even some underdrive transmissions out there though they are not very common.

Originally Posted by Mackman (Post 484604)

Get real trucks with 3.90s or 4.10s :thumbsup:

I know you guys are talking OTR but if it makes you feel any better I got 3.90s with a 13speed. Turn around 1550-1600 rpm at 60

Originally Posted by Aufgeblassen (Post 484901)

Yeah, real dumb trucks!

No, I run regional/Southeast only, and am home EVERY weekend. Pretty much just Florida & Georgia.

Originally Posted by Steel Horse Cowboy (Post 485100)

My 99 FLD has 3.90's, a direct 10 speed, and 22.5LP's and at 1550 im going 65mph ???

Guess your final drive must be higher than mine.

Anyways, I keep it about 1400 and go 60mph in the right lane and have avg'd 8.2mpg for the last 2 years (pulling light dry bulk)

Originally Posted by terrylamar (Post 485104)

You don't have a direct drive with those numbers.