RamblerRyGuy
New Member
- Joined
- Sep 9, 2019
- Messages
- 19
- Reaction score
- 4
- Points
- 3
- Location
- Ohio
- Vehicle Year
- 1995
- Make / Model
- Ford Ranger
- Engine Size
- 1.9 TDI
- Transmission
- Manual
- 2WD / 4WD
- 4WD
- Total Lift
- 3 inch
- Tire Size
- 33’s
- My credo
- Graduated one of the top in my class for automotive technology at Sinclair College, Ohio.
There are a few charts out there showing the RPM’s that you run with certain axle gears with certain tires at a given speed. I used one of these such charts from one of the posts I stumbled across on this website a long while back. Sorry, I don’t remember where I found it on here. I got tired of referencing it during my diesel Ranger build, since the ideal RPM range highlighted for the stock Ranger gas engines is not at all the ideal economy and power RPM ranges of the VW TDI I’m installing. So I determined that I was going to make formula for calculating what RPM’s your engine will turn with any setting of tires, axle gear ratio, and/or transmission gear ratio (also including low or high range if you want).
Sure you can collect anecdotes from other people with certain combinations, but isn’t it better to be self sufficient? Plus, if you have an off-road rig, you can figure out your crawling RPM’s as long as you plug in the MPH number.
This calculation turned out much easier than I originally thought.
So here it is.
Pi • Diameter of tire / 12 = X
5280 / X = Revs of tire per mi.
Revolutions of tire per mile • Speed \ 60 • Axle ratio • Trans gear ratio (multiply by low range ratio if desired for final number)
Feel free to post your numbers from your particular setup at highway speeds or any other speed you want to specify.
Sure you can collect anecdotes from other people with certain combinations, but isn’t it better to be self sufficient? Plus, if you have an off-road rig, you can figure out your crawling RPM’s as long as you plug in the MPH number.
This calculation turned out much easier than I originally thought.
So here it is.
Pi • Diameter of tire / 12 = X
5280 / X = Revs of tire per mi.
Revolutions of tire per mile • Speed \ 60 • Axle ratio • Trans gear ratio (multiply by low range ratio if desired for final number)
Feel free to post your numbers from your particular setup at highway speeds or any other speed you want to specify.