Heymow - Lawnmower Racing Forum

Mower Building / Setup Help => Driveline => Topic started by: RoMow on November 03, 2020, 01:41:36 pm

Title: Computing MPH
Post by: RoMow on November 03, 2020, 01:41:36 pm
Heymowers, 

   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.   

Respectfully, 
Rodney Rom 
Rom's Reworks 
Butler, MO