Grin all-axle hub on a front suspension

[taiwwa]

So generally the advice is to not install a hub motor on a suspension fork but grin on their product page specifically mentions suspension forks as good for the front hub.

Maybe a cheaper design is heavier and more durable? It seems that a lot of bicycle expense comes in weight reduction designs and that cheaper designs are actually more durable and stronger. I’m guessing there are some suspension forks which are just a spring and air pressure and without any oil or gaskets that can leak.

Suspension forks being perfectly round are better for the clamps of the torque arm.

Heavy direct drive motors in my experience transmit a lot of vibration and so a suspension fork would be a good addition if viable.

 

[RunForTheHills]

I think that the integrated torque arm on the All-Axle might make it less likely to break your dropouts. Increasing the unsprung weight of the wheel will make the ride worse.

 

[neptronix]

Here's what's good about that.

- we don't have axle flats to destroy
- some motor torque is transmitted higher on the fork arm, like a disc brake

The thicker the fork stanchions, the stronger and less twisting force.

Here's a rockshox with 38mm stanchions. Look at that super thick bridge. Looks like it belongs on a motorcycle. I would feel pretty confident putting at least 1000w into this. I would feel way different about a 28mm stanchion BSO fork.

 

[99t4]

Heavy direct drive motors in my experience transmit a lot of vibration and so a suspension fork would be a good addition if viable.

Depends what you mean by "transmit a lot of vibration" but a heavy DD motor is unsprung weight, disadvantageous to suspension performance.

 

[taiwwa]

Depends what you mean by "transmit a lot of vibration" but a heavy DD motor is unsprung weight, disadvantageous to suspension performance.

Unsprung weight is bad and yeah what I describe as my experience is from the unsprung weight. The weight of the wheel prevents shock from just skipping and instead all of it transmits through the bike.

But the issue is whether or not suspension systems make unsprung weight more tolerable.

Particularly, I am curious about inverted suspension forks. Theoretically that would absorb a large amount of vibration from a heavy hub.

 

[amberwolf]

If you don't have suspension, then you have no sprung weight at all. The entire bike moves as a unit, regardless of what type of motor you have. ***

If you have suspension, then any part that is not "above" the spring is unsprung weight, and causes the suspension to react more slowly.

If your suspension is designed around that, it'll still do the job it needs to--but generally bicycle suspensions are designed around a very light wheel, so a motor (even a small one) affects the performance compared to just a bicycle wheel.

There are at least a few threads about this whole thing with more details, most of them findable simply using "unsprung" as a search term.

Inverted suspension (with the uppers on the outside and the lowers on the inside) doesn't do anything different about the unsprung mass problem (other than potentially slightly reducing it's *own* unsprung weight). All it does is change which part slides into which for telescoping-suspension type forks.**** Depending on how they're made they can be stronger or stiffer (less wiggle) than non-inverted forks with lowers being on the outside, and the uppers on the inside.

The wiggle problem is really more up to the bushings / etc used, and the design of that interface between the two sliding tubes.


But if there is vibration coming thru your fork because the suspension can't damp it out, it'll happen regardless of type. The thing that changes the damping is whether the suspension is designed to do that, for the mass of the wheel and any other unsprung weight.



***Note that a middrive aroudn the center of mass of the no-suspension bike makes it easier for the bike to move around that center of mass more quickly, where a heavy hub on either end of the bike slows the response of the bike pivoting around the center of mass. Whether that makes a ride better or worse probably depends on the conditions and the bike itself. Some frames are more flexible than others, especially if they're longer or if they have the "classic" thin somewhat flexible type of nonsuspension fork, and that can absorb some road vibration, but not all that much.


****Note that inverted forks do make fork-mounted racks and whatnot "better" in that now they're sprung weight (where they're attached to the moving uppers), where they're unsprung weight on non-inverted forks (whey're they're attached to the unmoving lowers).

 

[99t4]

You will have to experiment with this to find out if it works to you satisfaction in your specific case. How heavy is the motor? The bike? What power? What speeds to you travel? What are the road conditions? What is the bike's geometry?

Particularly, I am curious about inverted suspension forks. Theoretically that would absorb a large amount of vibration from a heavy hub.

Why do you think in inverted fork would work better than a common non-inverted one?

 

[taiwwa]

You will have to experiment with this to find out if it works to you satisfaction in your specific case. How heavy is the motor? The bike? What power? What speeds to you travel? What are the road conditions? What is the bike's geometry?


Why do you think in inverted fork would work better than a common non-inverted one?

Because the piston joint is closer to the wheel weight.

 

[taiwwa]

If you don't have suspension, then you have no sprung weight at all. The entire bike moves as a unit, regardless of what type of motor you have. ***

If you have suspension, then any part that is not "above" the spring is unsprung weight, and causes the suspension to react more slowly.

If your suspension is designed around that, it'll still do the job it needs to--but generally bicycle suspensions are designed around a very light wheel, so a motor (even a small one) affects the performance compared to just a bicycle wheel.

There are at least a few threads about this whole thing with more details, most of them findable simply using "unsprung" as a search term.

Inverted suspension (with the uppers on the outside and the lowers on the inside) doesn't do anything different about the unsprung mass problem. All it does is change which part slides into which for telescoping-suspension type forks.**** Depending on how they're made they can be stronger or stiffer (less wiggle) than non-inverted forks with lowers being on the outside, and the uppers on the inside.

The wiggle problem is really more up to the bushings / etc used, and the design of that interface between the two sliding tubes.


But if there is vibration coming thru your fork because the suspension can't damp it out, it'll happen regardless of type. The thing that changes the damping is whether the suspension is designed to do that, for the mass of the wheel and any other unsprung weight.



***Note that a middrive aroudn the center of mass of the no-suspension bike makes it easier for the bike to move around that center of mass more quickly, where a heavy hub on either end of the bike slows the response of the bike pivoting around the center of mass. Whether that makes a ride better or worse probably depends on the conditions and the bike itself. Some frames are more flexible than others, especially if they're longer or if they have the "classic" thin somewhat flexible type of nonsuspension fork, and that can absorb some road vibration, but not all that much.


****Note that inverted forks do make fork-mounted racks and whatnot "better" in that now they're sprung weight (where they're attached to the moving uppers), where they're unsprung weight on non-inverted forks (whey're they're attached to the unmoving lowers).

How about spring forks like this?

What exactly makes a fork tuned for lower or heavier wheel weights?

 

[99t4]

That's an old-school springer fork. As a kid I had one on a Schwinn. In my experience, modern telescoping forks offer much better shock absorption and handling qualities. The old springer fork also lacks torsional rigidity-- too easy to twist from one end to the other.

I agree with you that tuning is key. There's plenty of tutorials out there explaining how to tune for common MTB scenarios, however, not much is available for tuning for a hubmotor installation.

Have you tried searching for front suspension hubmotor builds?

 

[LewTwo]

Have you tried searching for front suspension hubmotor builds?

I did and didn't find much with or without a hub-motor. Most of the stuff I did find relative to MTB had to do with individuals tuning for various scenarios that were generally associated with trail riding ... not riding on pavement where they judged "suspension" was wasted. I finally started a thread on the subject here: Suspension Forks, Talk to me

Note my opening words: "The length, width and depth of my ignorance has no bounds.".

That has not changed.