Correct me if I'm wrong

JPTHING · Mar 31, 2010

Help me with my math

I want to figure out how many times the drive shaft needs to turn to go 30 miles an hour? here are the specs:

47" tire = (12.25' Circumference)
5.13 axle ratio

30(mph)x5,280(feet in a mile)=158,400 (feet per hour)

158,400/ 12.25'(tire circumference)= 12,930.61 tire rotations to go 30 miles(158,400 feet)

12,930/ 5.13(axle ratio)= 2520.46 Driveshaft RPMs = 30 mph??? Correct?

Ty. · Mar 31, 2010

http://www.offroaders.com/info/tech-corner/reading/calculators.htm#FindMPH

There's a few of these sites out there that I use.

Binder · Mar 31, 2010

JPTHING said:
12,930/ 5.13(axle ratio)= 2520.46 Driveshaft RPMs = 30 mph??? Correct?

I think you have it right up to this point but the 12,930 should be mutiplied to the axle ratio not divided to get rotations per hour of 66330.9. The driveshaft turns 5.13 times as fast as the axle shaft.
Divide this by 60 to get rotations per minute and I think the correct answer is 1105.515......
Then again I could have screwed it up too.:redneck:

JPTHING · Mar 31, 2010

Binder said:
I think you have it right up to this point but the 12,930 should be mutiplied to the axle ratio not divided to get rotations per hour of 66330.9. The driveshaft turns 5.13 times as fast as the axle shaft.
Divide this by 60 to get rotations per minute and I think the correct answer is 1105.515......
Then again I could have screwed it up too.:redneck:

You are correct! Awesome, I couldn't figure out how it was soo many rpms to go 30mph.

Thanks

JPTHING · Mar 31, 2010

So here is another one for ya, 11479 inch pounds = 956.583e Ft pounds correct???

Maverick26 · Mar 31, 2010

Binder said:
I think you have it right up to this point but the 12,930 should be mutiplied to the axle ratio not divided to get rotations per hour of 66330.9. The driveshaft turns 5.13 times as fast as the axle shaft.
Divide this by 60 to get rotations per minute and I think the correct answer is 1105.515......
Then again I could have screwed it up too.:redneck:

Nope, Binder you are right. One way to find out if this is true is put your rig in 1.1 and 1.1 (high rang and 5th gear) and go 30mph down the road. Your tach should read around 1100rpm. :awesomework: