Originally Posted by
elcruxio
Well this is interesting. If I use our e-bike and my road bike as an example:
E-bike has 20" wheels and 57mm tires so the braking torque radius is 260mm (or 0,26 for the calculation)
Weight: bike, me and kids is 200kg
Front wheel rotor diameter is 180mm (or radius 0,09 for the calculation)
road bike has 28" wheels and 28mm tires so the braking torque radius is 345mm (or 0,345 for the calculation)
Weight. bike, me, two water bottles, tools etc. is 125kg
Front wheel rotor diameter is 160mm (or radius 0,08 for the calculation)
Initial speed is 10 m/s (36 km/h or 22mph) and stopping happens in 10 meter distance (that's a fairly hard stop now that I think of it)
E-bike
braking force = 1000 N (F=ma ie. F=200kg*5)
Torque at wheel hub = 260 Nm (1000*0,26)
Force at brake caliper = 2 889 N (260/0,09)
Road bike
Braking force = 625 N
Torque at wheel hub = 216 Nm
Force at brake caliper = 2 695 N
Huh. I'm kinda surprised how close those two figures are. Unfortunately I have no idea what any of that means. I really should have done more physics at school...
You're doing good, better than most. The two values are close because you are using different value for braking force (thrust at ground), when they should be the same. I didn't verify the force based on your decelleration, but regardless, plug that same braking force for the e-bike into the road bike calculations and then look at the result. EDIT: OH, I see, your braking force is proportional to the mass. So yes, less force at caliper for less mass. Your e-bike brakes are more stout, designed for higher bike mass and higher speeds. But you'll see big difference if you assume same braking force. Look at one thing at a time, in this case, difference in wheel diameter. Then factor in disc size difference.
Your e-bike brake force at caliper is not much different, but the smaller wheel is spinning faster, so that adds heat, which is not evident from looking at caliper force alone.