Author Topic: Computing MPH  (Read 7133 times)

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Offline RoMow

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Computing MPH
« on: November 03, 2020, 01:41:36 pm »

   I thought I'd seen this Posted somewhere on this site, but I couldn't find it, so I'm Posting it here.  A customer recently asked me how to figure the MPH of his mower in each gear, so to do this, you will need to know the following information: 
1. Transaxle or Transmission Input Shaft RPM -- This can be determined by dividing the transaxle/transmission pulley diameter by the engine pulley diameter; 
2. Drive-tire diameter; and
3. Gear ratios -- These can be found in other Driveline Posts for the 700 transmissions and the MST 200 and 820 transaxles.  For an unknown-model transmission/transaxle, you'll have to count the gear teeth.  Always divide the gear-tooth count of the gear on the shift-key shaft by the gear-tooth count on the countershaft (the shaft with the driven input bevel gear) to get the individual ratio.   
   For the overall gear ratio in any given gear, multiply the bevel-gear input ratio x the individual gear ratio x the final-drive ratio.  When using the 700 transmission, the final-drive ratio will be the number of teeth on the axle sprocket divided by the number of teeth on the transmission output-shaft sprocket. 

   When you have this information, use the Formula: 
Input RPM x Gear Reduction x Tire Circumference (Tire Diameter x 3.1416) x 0.000947 = MPH.   

Rodney Rom 
Rom's Reworks 
Butler, MO 
"No matter how many material possessions or awards you may acquire in your lifetime, the only thing you will ever truly own is your reputation." (Age 73)