RAGBRAI LI Route Announced on Jan. 27!

Reply To: Can I do it on a BMX Bike?

“Bicycle Bill”, April 16, 2017 at 12:22 pm

Short answer is sure it could be done, but you’d never catch me doing it.

Because distance traveled per pedal revolution is a function of 1) front sprocket size (number of teeth), 2) rear cog size (again, number of teeth), and 3) wheel diameter, doing this ride on a BMX bike would be comparable to driving a car but only using first gear.

The equation goes like this — number of teeth on front sprocket divided by the number of teeth on the rear cog, then multiply that number by the wheel diameter; now multiply that number by ‘pi’ (the mathematical constant — π; not pie as in what you eat with ice cream).

So, take that bike you showed us.  The specs say it has a 25-tooth front sprocket, and a 9-tooth “driver” (which I assume is the rear sprocket).  25 divided by 9 gives us 2.77; multiply that the wheel diameter (20 inches); this give us a 55.6-inch gear.  Now multiply 55.6 by π — 3.14 — to get 174.58 inches (or about 14½ feet) traveled per pedal revolution.

Compare that to the road bike I used when I rode on RAGBRAI.  It had 12 possible gear combinations and I generally was able to cruise comfortably with a 50-tooth front gear and a 17-tooth rear sprocket; 50 ÷ 17 = 2.94, and because I had a larger wheel (27-inch), 2.94 x 27 = a 79.4 inch gear.  Now multiply 79.4 by π and you can see that I am moving forward 249 inches (more than 20 feet) per pedal revolution.  And I will freely admit that I was already coming up on 50 years old and was not the strongest rider on the road; there were people pushing gears that moved them as far as 30 feet down the road per crank revolution — twice as far per pedal revolution as your bike can take you.

So to repeat; sure it could be done, but like a couple of other people have said you’ll have a lot more fun if you’re not pedaling twice as hard as the guy alongside of you.

-“BB”-

#1260160 |

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