El_Topo said:
Thank you for the explanation, I was asking because I am trying to understand this whole suspension business a bit better because it is so frustrating to not be able to buy an off-the-shelf full suspension fat ebike because all of them have high q-factors, see
this thread if you are interested, maybe you can comment on general frame design and why nobody builds such bikes?
Well as others posted, I don't think you can find a good solution off the shelf. Every motor has its width, making it especially small is possible, but needs extra small bearings, extra small gears etc. so that would lower its reliability and lifetime. Who would pay extra money for a motor that needs new bearings and gears every season?
Additionally, I personally see a problem with a too narrow width of the swingarm-frame connecting axle. Riding precision though chassis construction comes from several factors and an as-wide-as-possible base for the swingarm front axle is one of them. Have you seen Daxxies video about his shudder problem? See the motor pulling the titanium hardtail to the right when torque is applied? Imagine a swingarm with small bearings being pulled to the side, where every bearing adds play to the system. The bike will wiggle so much you would think the frame is from plastic. This isn't a big problem when riding on heavy forest ground or with lower speeds, I assume most riders in mountainous terrain don't notice it. But on the street, while cornering fast, you will feel veeerrrry insecure.
Long story short: I think a good mid-motor driven fully has to have a wider Q-factor.
I have no experience with systems like the cyclone
http://cyclone-tw.com/3chkit.html or similar constructions, but maybe you could build something with such a motor and well chosen cranks that would work for your problem?
I changed my cranks from stock bafang ultra to FSA Metropolis parts which decreased the overall Q-factor for maybe 8mm, but they come quite near to the motor on the left.
You could build something with the motor in the rear wheel. But the weight of the engine in that wheel will foil the use of your rear suspension for being too heavy to react to bumps. Unsprung weight has to be kept as low as possible.
At least that's my understanding what a full suspension is for. After reading lots of other threads where that topic is discussed, I understand that my (minority) view on this comes from the motorbike riding experience. I don't ride my e-bike in heavy country terrain where I suppose you want the suspension travel for jumps and a better tractional contact of the rear wheel to the ground and where lateral movements of the wheel line (let's say it clear: a bending frame) is tolerable. And of course it gives you a much more comfortable ride in the forest.
If you corner fast on the street (lets say 50 km/h) and on your line is a big hole in the tarmac, the difference is
a. going straight over it with a stable chassis where the rear wheel stays on the tarmac all the time or
b. find yourself one meter to the outer side of the curve with your bending chassis and your jumping rear wheel,
which means if you cornered left and cars overtook all the time you are now in the gutter. Let's better not think about cornering right and a truck overtook...
btw. I never understood the hype about fat wheels. Besides the looks which is of course in the eye of the beholder, they have only disadvantages. Ask automotive tire producers what they think about fat wheels like they had in the 60ies on the cars. They give you more comfort if you have a poor suspension and chassis design, but they have the big disadvantage of handling verrry imprecise. Thats why with all the engineering knowledge of our days, the comfort comes from chassis set up and modern suspension parts and the tires are as thin as possible. The thinner the tire(side-view of course, my english comes to its borders here), the better the precision in steering, the better the control in curves. Car engineers favor a tire pressure of 6 bar or more, because that makes the tire even more stiff, but their sales guys tell them to go lower - the customer loves comfort, they are told...
So fatties could be useful for a hardtail in the forest or on the beach, but a fully with fatties is simply wrong. The suspension does the comfort job...
It was a process of fitting in the jig. It does work perfectly, which I cannot say about the front fork from DNM. After some hundreds of km I have to withdraw my first impressions. It distorts and it is not very sensitive for little bumps, so it is not so precise as needed and uncomfortable.