RPMs

[tractorman21]

I need some help with my math.
I have a 97 Superduty,with a 5.13 rear gear and a E4OD transmission.
It has 235/85/16 tires on the rear.At 60 mph,the engine is turning 3,000 rpm.
Using a gear/rpm/mph calculator,@ 60 mph and using the .71 over-drive transmission,the engine should be turning 2,315 rpm.
Can someone tell me if my math is correct,or do i have a transmission that's not shifting into over-drive?

Thanks,
David

 

[Patrick Feeley]

Just a data point: My 1997 with 4.10 gears, E4OD, and 265/75-16 tires will run about 2800-2900 RPM when not in OD at 60 mph. I think its around 2100-2200 in OD. Cheers!

 

[milspark1]

My '96 does the same with 265/75/16's. I run at 2900 with the tow haul button on and about 2200 in OD. I also have 4.10 gears.

 

[94f450sd]

that is normal speed/rpm for a f450 superduty.

 

[tractorman21]

My '96 does the same with 265/75/16's. I run at 2900 with the tow haul button on and about 2200 in OD. I also have 4.10 gears.

That's pretty close to me....I have 235/85/16's,with a 5.13 gear and at 60 mph,it turns about 2400 rpm in OD.With the tow/haul butto on,it turns about 3000 rpm.

 

[tractorman21]

that is normal speed/rpm for a f450 superduty.

Thanks for the reply...Why would Ford use a 5.13 rear gear with a diesel motor?

I am thinking about replacing the 235/85/16 rear tires with 285/85/16's to help lower the engine RPM's.

 

[94f450sd]

they used 5.13s cuz the f450s were made to work not driven around like a car.they were meant for pulling heavy loads.there is another taller gear set for them but i have yet to find them.supposedly the idi 5 speed trucks had them and supposedly the psd TRUCKS ALL HAD THE HIGHER GEARS.i have a 95 f450 PSD parts truck here with 5.13s in it.i got it cuz it was supposed to have the higher gears in it that i want for my 450.

with the zf5 in mine with 5.13s spins 2500 at 60MPH.