I have a 1990 2500 with the 5spd, standard tires,no guages though and I wanna know what my rpms are at 100kms in 5th gear ?

 

i have the same. 1990 CTD 250 with a Getrag 5 speed and 235 tires, 2WD though. It depends on rear end gear ratio. My truck wide open and fueled out @ 2500 rpm with stock spring (and with pump turned up) is 75-80 mph. So my guess is with my truck 1800-2100 rpm @ 60 mph, but im not sure. I have a tach on the way.

 

If you can tell us what gears you have,
there's a formula that you can use to tell
what rpm's your running.

 

Definatley need to know your rear ratio to tell.

 

I'l check the VIN and find out gears thanks

 

Take a look at the rear axle. There should be a tag on one of the rear cover bolts telling you what gears you have unless it has disintegrated.

 

https://www.dieselbombers.com/calculators.php

 

I have getrag 5spd, 3:55 gears and 265/75/16's I don't know the formula but...
You can do it!!!!

 

whats the gear ratio for the 5th gear

if its 1:1 the speed should be:

2000rpm = 50.4mph
2500rpm = 63.0mph
3000rpm = 75.6mph
3500rpm = 88.2mph

 

THANKYOU 2500HD for that calculator I couldn't find her for fools gold when I searched