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[frodus]

I wanted to post some gear ratio and torque I calculated for the Zero SR.

Zero SR:
Peak torque: 144Nm
Rear tire: 140/70-17 0.32 meter (1.03ft) radius
Final Drive: 4.4:1
Torque at rear axle: 633.6 N-m or 467.32 ft-lbs

As a fun little exercise, I wondered how much force is that on the road from the rear tire? I did this wrong the first time by using ftlbs and newton-meters interchangably, thanks to Protomech for questioning me, I was rushing

We know Torque = radius * force * sin(90). We have torque, so the equation becomes Force = torque* 1/r
The angle is 90 degrees since the road is tangential to the tire, so its just 1. So one newton-meter of rotational force would equal one newton of force at 1 meter away. My "rear tire ratio" is 1/r, or 3.13. If calculating using feet, the ratio is 0.97.

Rear Tire ratio: meters: 3.13:1 (feet 0.97:1)

Rear tire peak force at rubber: 1983 N or 445.80 lbf


Here's some tools to convert from N-m to ft-lbs and from Newtons to lbf (pound force):
http://www.unitconversion.org/energy/newton-meters-to-foot-pounds-conversion.html
and
http://www.unitconversion.org/force/newtons-to-pound-forces-conversion.html

[NoiseBoy]

What about some comparisons to gas bikes?

[Doug S]

Fantastic info, frodus. I always get a lot out of your posts! It's interesting that the Empulse has very similar torque at the rear wheel with their gearbox.

[RickSteeb]

What's that work out to in lbs of thrust at the pavement?

[Doug S]

What's that work out to in lbs of thrust at the pavement?

Rick, torque is in foot-pounds in English measurements, or Newton-Meters in metric. Since frodus gave us the radius of the rear tire, 12.3 inches or 0.315 meters, thrust in Newtons would be 615 N-m / 0.315 m, or 1950 Newtons. That's equivalent to 438 pounds of force. That's why the front wheel doesn't always like to stay on the ground so much.

[RickSteeb]

What's that work out to in lbs of thrust at the pavement?

Rick, torque is in foot-pounds in English measurements, or Newton-Meters in metric. Since frodus gave us the radius of the rear tire, 12.3 inches or 0.315 meters, thrust in Newtons would be 615 N-m / 0.315 m, or 1950 Newtons. That's equivalent to 438 pounds of force. That's why the front wheel doesn't always like to stay on the ground so much.

Ah-hah, that much force would accelerate a 438 lb bike at 1G without a rider [given sufficient traction...].  Wheee!

[frodus]

I had my rear tire torque on the road wrong, its a force, and I was calculating it incorrectly. Edited my original post with correct info, and how I calculated it. I used Newtons because I like metric. I posted links to a couple conversion calculators.

[frodus]

Zero S:
Peak torque: 92Nm
Rear tire: 140/70-17 0.32 meter (1.03ft) radius
Final Drive: 4.7:1
Torque at rear axle: 432.4 N-m or 318.92 ft-lbs

Rear Tire ratio: meters: 3.13:1 (feet 0.97:1)

Rear tire peak force at rubber: 1353 N or 309 lbf