knee pain
SHORT CRANKS.. 130MM creates a deficiency in the ‘swipe threw pull back’ factor. u could save a lot of money by drilling and tapping the cranks at 150mm.
I had some pain relief because my knees are not bent as much as when pushing threw the dead zone that pushes up the kneecaps, but still hurt my self by pushing too hard. It’s a bit harder to climb hills with because there is less leverage and uses slightly different muscle sets. It’s like cranking in a higher gear, so you need lower gearing for hill climbing.
I am sure that elliptical chain rings can help also, as they help get your feet threw the dead zones. But I hear that Biopace should be rotated for them to work. The use of shorter cranks would be possible with out the swipe threw pull back problem and may not need a lower gear to compensate for the lack of leverage, don’t count on it. Also climbing with a faster cadence is easier because it helps you threw the dead zone at the top of the crank circle.
GEAR INCH FORMULAS. Obviously every one is different, even at different times. So you can use this only to for estimation with 170mm cranks. If an average healthy man can sustain a power output of about 0.33 hp, or 10890 ft-lbs per minute, up to 45 minutes. Or .2hp = 6600ft.-lbs/min. for 1.5 to 2 hours for climbing those long mountain roads. If you're trying to climb a 14% grade with a combined weight of 390 pounds with a power output of 10890 ft-lbs/min, divide by (.14 grade x 390 lbs) = 199.4505 feet per minute. Now, if your cadence is 80 rpm at the crank, and you're moving at 199.4505 ft/min x 12”= 2393.406 inches per minute, divide by (80rpm x pi)= 9.52gi. [70rpm= 10.88gi and 60rpm= 12.69gi]. It is best to calculate at 80rpm cadence to give yourself room for error in your strength level. If you’re forced to slow down to 60rpm you’re pushing too hard. Over 80rpm your wasting too much energy just heating your legs. An approximate 14% grade is the maximum that I can pedal aprox. 390lb at 12.5gi. (slower than 60rpm) resting my legs every 20ft or so. Don’t worry most hills are never more than 9%. To move a quarter ton up a 10% grade 10.4 gear inches would be needed.
The best way to measure the road grade is to hold a level, one end to the road surface and measure the other ends height when level. The grade is the vertical distance divided by the horizontal.
Gear inch: driving sprockets divided by driven gear sprockets, multiplied by measured diameter of drive wheel and tire. A set of gears equaling a 20” is like pedaling a 20” wheel with out gears. See bikeatwork.com for more info.
POWER ASSISTANCE. The most efficient motor for an HPV is a hub motor. The only place to put one is at eh end of the left side axle, and you would need a new axle made at a machine shop. I don’t know if they make one that fits. It maybe better to strap a motor on the side of the axle and connect it to a single freewheel with a BMX chain.