By introducing many new gears and changing the tire size I am altering the torque delivered to a rear bicycle wheel from an electric motor. This then changes the "power where rubber meets pavement". "Forward thrust?" I don't know what the proper name is!
I have googled around, but find myself just plain confused and unable to sort through how to evaluate this by using the information I have - which consists of the ratios and wheel sizes. This web page seems to explain it all, but for the life of me I can't follow it.
Yeah, I guess I'm a dummy.
I do not have an actual measure of the motor's starting torque, yet. Have yet to figure out how to affix my torque wrench to the motor without hurting the motor or myself. Motor torque will be a variable named in the equation, so a value won't be needed at this point.
I need to determine how much MORE torque I am applying to the wheel with the new gear setup versus the original gear setup. This is so I can decide if I have increased the delivered torque enough to accomplish the goal of moving ~180lbs with relative ease compared to the original gearing. The original gearing and wheel size was insufficient for the task and by looking at the percentage or ratio of the increase I should be able to ballpark whether I have the design right to move the weight.
The current ratios were set up so that the max speed of the wheel in high gear at the motor's preferred speed of 2700RPM will be at the legal limit of 22KPH/15MPH. I thought that that should put my starting power in the lowest gear somewhere good enough to get the bike and the weight rolling along - but I cannot figure out how to verify that.
Original Gearing/Wheel setup:
Motor > 5.81 reduction direct mount on a 11.5" diameter wheel (that's actual rolling diameter, it is nominally a 12") .
New Gearing/Wheel Setup:
Motor > 5.81 reduction > 3-Speed transmission reductions > final-drive 1.5 reduction fixed to 20.5" diameter wheel (that's approximate rolling diameter - it is nominally a 21").
3-Speed gearing ratios are 1.33, 1, and .75 - these are not changeable.
New gearing combined ratios:
1st gear - 11.05,
2nd gear - 6.68,
3rd gear - 8.86
all fixed to the same 20" wheel.
If I should be calling torque 'power' when I talk about it at the wheel instead of the motor, please let me know what the distinction is and if I need to make them distinct in the equation.
I am looking for an equation to use that allows me to vary the 5.81 reduction and the 1.5 final reduction and see the changes in torque/power at the wheel.
At its core the question is:
How much more starting grunt do I get with
XXX ratio and
Xwheel than I did with
AAA ratio and