BURPLE00@aol.com wrote:
: OK guys, I need to know how to figure out what MPH im going, since my speedo is not working correctly. I know there are calculators out there for this stuff , I just dont know where to find them.
This should get you close:
(RPM * tire height * .00297) / (rearend ratio * tranny ratio)
For example, a truck with 28" tall tires and 3.55s in 4th gear at 3,000 RPM
(3000 * 28 * .00297) / (3.55 * 1) = 70.3mph
Tranny ratios can be found in the FSM, or I think they are in the DML
FAQ also. Just use the number to the left of the colon. For example,
an overdrive ratio of 0.80:1 is just .8, a ratio of 3.42:1 is just 3.42)
I simplified the formula a bit, so there's some rounding in there. If
you want to go through the whole process, here's the thoery:
- Engine RPM divided by tranny RPM gives you driveshaft RPM.
- Driveshaft RPM divided by rearend ratio gives you wheel RPM.
Now that we know the rate at which the wheel is turning, we need to
figure out how much distance the truck moves per every revolution.
That's the circumference of the tire.
- PI (3.14159...) times tire height gives you the distance traveled
per revolution, in inches.
- Distance in inches divided by 12 is distance in feet
- Distance in feet divided by 5280 is distance in miles
Putting it all together:
- Distance in miles times wheel RPM equals miles traveled per minute
- Miles traveled per minute times 60 equals miles traveled per hour
(Also known as miles per hour) :-)
---Jon-
.---- Jon Steiger ------ jon@dakota-truck.net or jon@jonsteiger.com -----. | I'm the: AOPA, DoD, EAA, NMA, NRA, SPA, USUA. Rec & UL Pilot - SEL | | '70 Barracuda, '92 Ram 4x4, '96 Dakota, '96 Intruder 1400, '96 FireFly | `----------------------------------------- http://www.jonsteiger.com ----'
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