Difference between 4.30 & 3.55 gears

Depends on the tire size and transmission ratios. They're likely pretty similar. Fuel consumption will be worse not towing. Towing it might be similar. It depends on how fast your going in which gear and what RPM the engine ends up in. You will turn more RPM to go the same speed.
Generally it should pull a lot stronger and accelerate better at the possible expense of some fuel.

KD4UPL wrote:
Depends on the tire size and transmission ratios.

Generally it should pull a lot stronger and accelerate better at the possible expense of some fuel.

Generally ignore answer #2 and see answer #1. ;)

You have to know what the overall drive ratio IS at whatever speed you are interested in and it ALL comes into play......including tire size.

The formula for engine rpm is as follows:

(Axle Ratio x Vehicle Speed(in MPH) x Transmission Ratio of Selected Gear x 336.13) / Tire Diameter = Engine RPM


Just plug in the numbers and you get what rpm each rear gear ratio should be at a certain speed.

The worse fuel consumption depends on many variables, but yes when towing a shorter gear ratio(higher number) will generally have better fuel economy than a taller gear ratio(shorter number) when towing.

On a side note, I've had both. My 2011 F450 had the 4.30 rear with 17" wheels. My 2015 F350 has the 3.55 with 20" wheels.

On the surface, that sounds like the two trucks are world's apart. As crazy as it sounds, I prefer the 3.55, even for large heavy loads. The 4.30 was complete overkill. But we do virtually no mountain travel.

May I inquire what you're pulling?

Unless you are towing really heavy, or changing trailers to really heavy, the 4.30s would be overkill. The new 6.7 is a little stronger than your 2011, so if the 3.55 is working for you, no need to move to 4.30.

Towing in 5th with 3.55, would be close to towing in 6th with 4.30.

Jerry

I'm fairly sure the transmission ratios have not changed in the 6R140 from 2011 to 2017.

It is quite possible that the F450 will have shorter diameter tires on it than an F250/350SRW with 18" or 20" wheels. Anyhow, the difference in diameter is not likely to be more than 2 inches.

KD4UPL wrote:
Depends on the tire size and transmission ratios. They're likely pretty similar. Fuel consumption will be worse not towing. Towing it might be similar. It depends on how fast your going in which gear and what RPM the engine ends up in. You will turn more RPM to go the same speed.
Generally it should pull a lot stronger and accelerate better at the possible expense of some fuel.

X 2

ShinerBock wrote:
The formula for engine rpm is as follows:

(Axle Ratio x Vehicle Speed(in MPH) x Transmission Ratio of Selected Gear x 336.13) / Tire Diameter = Engine RPM


Just plug in the numbers and you get what rpm each rear gear ratio should be at a certain speed.

The worse fuel consumption depends on many variables, but yes when towing a shorter gear ratio(higher number) will generally have better fuel economy than a taller gear ratio(shorter number) when towing.

X 2

The biggest difference between the 350 and 450 is tire circumference. The 450 will have larger diameter tires compared to he 350. Some V-10 powered class A's have 4.88's!

Most of the factory stock tire sizes for American 3/4-ton and 1-ton pickups are within about 2 inches diameter of each other, regardless of the factory wheel size.

225/70-19.5's are ~32" diameter
245/70-19.5's are ~33" diameter

215/85-16's are ~30.5" diameter
235/85-16's are ~31.5" diameter
245/75-16's are ~30.5" diameter
265/75-16's are ~31.5" diameter
285/75-16's are ~33" diameter

225/80-17's are ~31" diameter
235/80-17's are ~31.5" diameter
245/70-17's are ~30.5" diameter
265/70-17's are ~31.5" diameter

265/65-18's are ~31.5" diameter
275/65-18's are ~32" diameter
285/65-18's are ~32.5" diameter

I don't know offhand the tire sizes for 20" wheels, or I would post those too.