Axle Ratio

[Kevin1]

Hello,

I recently purchased a 2003 Thomas FS65 on a Freightliner chassis. It has a cummins 5.9 engine and an Allison 2000 series transmission with 5th gear being overdrive.
My sticker on the bus says the gear ratio is 5.38. The tires are 10r 22.5.
I cant quite put it together cause when I'm driving down the highway, my rpms are at 2000 while doing 60-63mph.
Other than ripping out the axle is there some kind of math I could do to figure it out?
Thanks for the help anyone. It's just out of curiosity.

[Booyah45828]

What can't you put together?

10r22.5 tires will have an average height of 40.2 inches, an allison 2000 has a 5th gear ratio of .71, your rear axle is a 5.38, and your rpm is 2000.

Put all that data into any one of a hundred online speed to rpm calculators, and you get 2000 rpm = 62.64 mph, which is what you're seeing.

What are you trying to figure out? If it's the rear axle ratio, you could always pull the pumpkin and count the teeth to be 100% certain. But based off of your data, I'm thinking the 5.38 sounds correct.

[Brad_SwiftFur]

I had a 5.38 in my bus, with same size tires. However, I have a 5 speed manual with a 1:1 top gear and I was seeing 2600 RPM at 55 MPH - the overdrive makes a big difference for you. I swapped my ratio to 3.91 and my top speed is now around 78 MPH, though on the freeway I'm averaging around 70 for top speed on any uphill.


I haven't double checked Booyah's math but based on my own calculations and experience, everything sounds about right. The 5.38 is a fine gear ratio for those who have overdrive gears. Not so much for those with 1:1 top gears.

[Kevin1]

Originally Posted by Brad_SwiftFur

I had a 5.38 in my bus, with same size tires. However, I have a 5 speed manual with a 1:1 top gear and I was seeing 2600 RPM at 55 MPH - the overdrive makes a big difference for you. I swapped my ratio to 3.91 and my top speed is now around 78 MPH, though on the freeway I'm averaging around 70 for top speed on any uphill.


I haven't double checked Booyah's math but based on my own calculations and experience, everything sounds about right. The 5.38 is a fine gear ratio for those who have overdrive gears. Not so much for those with 1:1 top gears.

Brad_SwiftFur,

Thanks for your reply. I'm new to all of this and not much of a computer guy. I just figured that the axle was swapped out at some point.

Take care!

[cadillackid]

0.74 for 5th gear on the common school bus allison (2500 PTS)

[Booyah45828]

I've seen the 2000 used on the fs65.

[cadillackid]

Originally Posted by Booyah45828

I've seen the 2000 used on the fs65.

Columbus city schools still has a few... FS65's with 2500 PTS

[Cloudy]

Hi, I know this is weird but is there any way you have a picture of the Fuse labels in the panel that's beside the driver's chair? I really need some pics of the fuses' labels there and the ones behind the floor heater next to the door.