Change gear ratio on 454 class C

jrbelk wrote:
I've got 98 coachman class C 454 with 4:11 rears. I want to improve mileage by going to 3:23 gears. Will this work? Thanks

IMO, it will work, but you will not save much of anything overall as far as fuel mileage. IMO, here's why. Going from 4.11 to 3.23 is a BIG jump. The engineers pick the axle ratio in an attempt to run the engine close to the max torque point (this is a curve) while at cruising speed (this is a range) while in top gear. Dropping the ratio to 3.23 will cause the transmission to run in lower gears (higher RPM's) while at cruising speed a lot of the time. Even while at cruise speed when you are on level ground. The transmission prefers to be in top gear while cruising which is what most motorhomes do most of the time. If you are like most Class C motorhomes, you will be at or close to max gross weight most of the time. So, the engine needs to spin fast enough to generate enough torque. (horsepower too) If you want to improve fuel economy, slow down, lighten the load, and travel with the wind if you can

Chum lee

As an afterthought and in agreement with what Phil says below:

For example: If you are now running P225x70 R16 tires and change to P245x70 R16 tires this will have the effect of dropping your current 4.11 gears about 5% or down to 4.11 x .95 = 3.90. The corresponding RPM drop will occur in cruise as long as the engine/transmission can handle it.

Provided there is clearance in the wheel wells for larger tires, IMO this is a much more conservative, safer approach.