Design Geometry of a front hub fork

[taiwwa]

In doing some research on the question of front forks housing hub motors, it appears risky. It can be done but the front fork is generally not engineered for powered applications.

but what if you did engineer a front fork for power applications? What would it look like?

I think that the arms of the fork would be more horizontal. they would also bend upwards, so the fork would look a little like a boomerang. The size of the headset and bearings would also be larger to accommodate the increased weight on the front.

this would require new standards and tooling.

 

[Chalo]

In doing some research on the question of front forks housing hub motors, it appears risky. It can be done but the front fork is generally not engineered for powered applications.

but what if you did engineer a front fork for power applications? What would it look like?

I think that the arms of the fork would be more horizontal. they would also bend upwards, so the fork would look a little like a boomerang. The size of the headset and bearings would also be larger to accommodate the increased weight on the front.

this would require new standards and tooling.

No. Everything about a regular fork works fine for hub motors, except for the tips. Those should be beefed up, preferably with clamping slots. Also the slot should placed so the axle center is correctly located for the disc tabs when a 14x10mm axle is used, so either a 12x10mm or 16x10mm axle would only be off center by a distance of 1mm.

It would be a decent idea in most cases to use slightly more offset than a typical fork, more because typical forks have too little offset for the bike they're on than because it would especially help in a hub motor application. But we're talking like 55mm offset instead of 44mm offset, not "more horizontal" or bent upwards. What would that accomplish anyway, other than ruining the bike's steering?

Consider that regular headsets work great to accommodate braking forces sufficient to stand the bike up on its front wheel. What could a front hub motor do to equal that? Nothing, unless you wheelie in reverse.

 

[docw009]

A blade type drop-out should work. This is the bike from the failed Jump rental ebike venture..I bought a couple of the motors afterwards. 500W Bafang BPM's, I believe.

They included the tires, rotor, fasteners, and Textro caliper. all for about 45 bucks. The fasteners were 12mm thread nuts that screwed in with some type of anti-theft 6mm hex wrench. The doodads on the fork are for locking it into a charge cradle.

 

[lnanek]

Feels like there's other ebikes on the market with motors in front you could look at as well. Ariel Rider Grizzly is all wheel drive, for example. They often advertise using motorcycle fronts too, for extra beefiness.

 

[amberwolf]

There's a thread around here by someone (Avandalen?) designing a fork specifically for hubmotors, to have it manufactured.

EDIT: here it is

First custom carbon fork special made for hub motors

Carbon forks are not suitable for direct mounting of hub motors. That's why I want to have strong carbon forks made especially for hub motors. Because expensive molds have to be made for production, I will sell this fork also to other people, otherwise it will be too expensive for me. If you are...

endless-sphere.com

 

[Chalo]

Now, if we're talking suspension forks, then motor specific design becomes a very different deal. I think a leading link design might make better sense for that than telescopic forks.

 

[lnanek]

Maybe an upsized swing arm front from an escooter would work?

Many scooters are all wheel drive. People even slap chairs on those things and go faster than ebikes. Seems mostly due to fast ebikes being illegal, though.