Re: ahlmans formula
Ok...I tried the math for myself and you're right, it doesn't work. I suspect the problem is the "88" in the denominator (not sure where that came from?).
The top of the equation seems to work. I'll use 5000rpm because I know that means about 75mph on my bike. Also, you have the ratios calculated backwards in your first post...
Primary reduction 48/73 = .657
6th gear 21/25 = .84
Final drive 16/43 = .372
Circumference = 78"
so: 5000rpm x .657 x .84 x .372 x 78in = 80,067inches/minute
There are 63,360inches in a mile, so: 80,067/63,360 = 1.26miles/minute
Multiply by 60 to convert to hours= 75.6miles/hour Which seems right.
I'm sure the 88 is a factor to do the inches-miles and minutes-hours conversion, but I think it is wrong.
edit: By my math, the correct denominator should be 1056
1 / ((60min/hr) / (63360in/mile))
Last edited by dB; 02-18-2004 at 2:59 PM.