Figuring RPMs....

[Jeffrey.Deaver@domain.elided]

Hi All,

Since my '58 A-102 does not have a Tachometer, I thought I could figure the
engine RPM's from the speed & gear ratios and make myself a little chart.
But after doing so, the RPMs seem sort of low.  Can you all check my math....

Thanks! - Jeffrey Deaver
'58 A-102  Grandpa's Farm Truck  (got the cattle gates too!)

THE MATH....

Wheel Diameter = 27.5 inches
Wheel Circumference = 3.1416 * 27.5 = 86.394 inches

1 Mile = 5280 ft = 63,360 in

63,360 in per mile  /  86.394 in wheel circumference  =  733.38 wheel
rotations per mile

T1 Gear Ratios 1st 3.039
  2nd 1.641
  3rd 1.000
  R 3.682
(which, to me, means in 1st, 3.039 turns of the crankshart (ie 3.039RPM) = 1
turn of the power train.)

Rear Axle Single Reduction ratio is 3.73 : 1, which means 3.73 turns of the
power train = 1 turn of the wheel axles.

Over all Engine to Axle ratios obtained by multiplying Transmission Ratio and
Rear axle ratio...
    1st 1:1  x  3.73:1  =  3.73:1
    2nd 1.641:1  x  3.73:1  =  6:1
    3rd 3.039:1  x  3.73:1  =  11:1

Speed conversions & wheel rotations per minute
10 MPH / 60 min = .16 MPM (mile/min) x 733.38 wheel rotations/mile = 117.34
wheel rotations/min
20 MPH  / 60 min = .33 MPM x 733.38 = 242.01 wheel rotations/min
30 MPH  / 60 min = .50 MPM x 733.38 = 366.69 wheel rotations/min
40 MPH  / 60 min = .66 MPM x 733.38 = 484.03 wheel rotations/min
50 MPH  / 60 min = .83 MPM x 733.38 = 608.70 wheel rotations/min
60 MPH /  60 min = 1 MPM x 733.38 = 733.38 wheel rotations/min

RPM calculation..

10MPH / 1st Gear
  117.34 wheel rotations per minute  x  (11):1 engine to axle ratio  =
1290.74 RPM

60MPH / 3rd Gear
  1 MPM  x  733.38 wheel rotations per mile  =  733.38 wheel rotations per
minute
  733.38 wheel rotations per minute  x  (3.73):1  =  2735.5 RPM


The final chart looks like this... (with RPMs rounded).... (hope the tabs
work)

MPH/Gear 1 2 3 R
10 1291 704 438 1611
20 2662 1452 903 3323
30 4034 2200 1368 5035
40 5324 2904 1805 6646
50 6696 3652 2270 8358
60 8067 4400 2736 10069