Is this motor suitable ?

[Chalo]

Now of course a wheel isn't a perfect circle, and it deforms as it rolls.

Yes.

So the contact patch(es) provide rolling resistance from friction, and with a larger wheel (larger diameter but same width and type), more of a contact patch will mean an increase in resistance from friction.

I think you misunderstand what causes rolling resistance. Surface contact isn't the problem; it's hysteresis in the rubber. For the same reason a rubber band heats up when you repeatedly stretch and release it, the rubber in a tire never returns all the energy used to distort it when it rebounds. The difference is lost as heat. On a smooth surface, this is the main source of rolling resistance. The more rubber is distorted, and the greater a degree to which it's distorted, the more energy is lost to hysteresis. The resistive force from hysteresis is a fixed value independent of speed, but the energy lost rises with speed.

There's a second significant source of rolling resistance that can become the dominant one as surface roughness and speed increase. When vibrations and shocks are transmitted to the bike, rider, luggage, etc., the energy of those forces also isn't restored to the bike's kinetic energy and is almost entirely lost. Energy lost to bumps and vibration increases asymptotically with speed.

The area of a tire in contact with the ground is always proportional to the weight on the ground, divided by the pressure in the tire. A larger diameter wheel doesn't have a larger contact patch area (for the same thickness and hardness of rubber); instead it's longer and narrower. The rubber in a larger diameter tire doesn't flex nearly as much to establish enough contact patch to hold up the load as the rubber in a small diameter tire. So the big one has less hysteresis and less energy loss.

Furthermore, the larger diameter wheel bridges asperities better and surmounts bumps more gradually, giving a smoother ride that loses less kinetic energy to shaking the bike and rider.

Road racing cyclists use the largest diameter wheels that still fit neatly on a smallish adult's bike with good nimble geometry. That's to balance rolling resistance on one hand against aerodynamic resistance and wheel mass on the other. But in recent decades, racers have progressed from 20mm wide tires, to 23mm, then 25mm, and now often 28mm. As bikes have become lighter overall, and wheel aerodynamics have improved, tires have enlarged to reduce rolling losses.

Unrelated to wheel diameter, but related to rolling resistance: It comes as a surprise to many people when they learn that given equal tire construction, a wider tire has less rolling resistance than a narrower one. It doesn't have to flex as much to establish its contact patch, and at the same time it does a better job of smoothing out surface irregularities and preventing bumps from being transferred to the rider. The reason road racers use comparatively narrow tires is to save weight and minimize aerodynamic cross-section, not to minimize rolling resistance.

 

[Ebike rider]

Alright, I like to think of myself as a relatively smart cookie, but I have to admit that this isn't making any sense to me (and very little bothers me more than not understanding things, for better or worse). Maybe if I just ramble for a paragraph, somebody will be able to notice what I'm not getting and point it out or something.

So I'm trying to draw a force diagram in my head, and it's not saying what you're saying (like from physics 101, where you break down every force acting on an object in a given situation). On a flat stretch, gravity is doing nothing except increasing the force of friction on the tires because it's pulling them down onto the concrete. At low speeds or starting from a dead stop, the inertia seems to be the only thing resisting moving the bike. Now when it's going up a hill, gravity becomes the largest factor, and it's going to take something like the displacement distance multiplied by the cosine of the angle of the slope (or whatever it really is, it's been nearly 20 years).

Now of course a wheel isn't a perfect circle, and it deforms as it rolls. So the contact patch(es) provide rolling resistance from friction, and with a larger wheel (larger diameter but same width and type), more of a contact patch will mean an increase in resistance from friction. But it seems like that would be negligible, since the wheel doesn't slide across the pavement, it rolls across it.

I'm just totally not seeing how less torque could be required to move a bike with small wheels, but then require more force to keep it moving once it's in motion. Maybe I'm not understanding what you mean by "bigger is always easier?"

As for their mommas dressing them funny, that part I definitely get: I'd feel pretty silly cycling on 6" wheels like a Jetson has.

Thanks sir for your information ..
I see that a small tire needs less torque , but it travels less distance also ! So the large wheel needs more torque because it will travel a long distanse after one revolution ...

 

[glennb]

So the contact patch(es) provide rolling resistance from friction, and with a larger wheel (larger diameter but same width and type), more of a contact patch will mean an increase in resistance from friction.

Sorry, I haven’t read the rest of this thread, just your post in isolation, so lack context. The above comment stood out though.

Rolling resistance is a function of tire deformation, and surprisingly is inversely proportional to wheel diameter. Despite that, wheel diameter’s of little significance, the only parameter worth concerning yourself with is carcass suppleness/stiffness.

Chalo covered it.

 

[riding_on]

I think you misunderstand what causes rolling resistance.

You're absolutely right; thanks for taking the time, Chalo.

 

[HANDSOME-TOM]

my viewpoint is to install a gearbox for your ebike .it will get a big torque and low the rotate speed