Rear suspension and rear hub question.

[Chalo]

The axle and flange see higher stresses in an unsuspended bike, sure. But they are designed to withstand those forces.

The magnets, wire connections, sensors, etc., see much higher accelerations in a suspended setup, and they are not necessarily designed to withstand such forces.

 

[John in CR]

What Chalo, these tires aren't fat enough for you? The rear tire is 5" wide.


BTW, the huge diameter tires on that Surly are a terrible choice for a hubmotor due to the diameter. I'm sure the axle and bearings would appreciate it, but the extra heat of running at lower efficiency will more than offset it.

 

[Samd]

I say it is ALWAYS reduced on a shocker bike compared to the hardtail.

When you go over a bump, the shock is applied to the mass on board (ie You and the weight of the bike). The rate of this shock and it's derivatives is faster, so the derivative of it (rate of change) of the change in velocity, acceleration, and jerk will always be higher. As will the reactionary force that is exerted by the bike's mass back on the front and rear axle.

In a calculus sense I cannot see any other valid answer when comparing bikes of equal mass (or similar).

As the rate of velocity and it's derivatives will always be slower with suspension than without, it must be the case.

When Chalo said:" Remember that the mechanical suspension is between the wheel and the seat. The wheel can't benefit from it at all. The suspension provided by a tire benefits everything else on the bike. " I disagree completely. The force and it's derivatives exerted by the rider and bike coming back down onto the rear axle will always be lower. An equal but opposite force.

 

[sn0wchyld]

I say it is ALWAYS reduced on a shocker bike compared to the hardtail.

When you go over a bump, the shock is applied to the mass on board (ie You and the weight of the bike). The rate of this shock and it's derivatives is faster, so the derivative of it (rate of change) of the change in velocity, acceleration, and jerk will always be higher. As will the reactionary force that is exerted by the bike's mass back on the front and rear axle.

In a calculus sense I cannot see any other valid answer when comparing bikes of equal mass (or similar).

As the rate of velocity and it's derivatives will always be slower with suspension than without, it must be the case.

When Chalo said:" Remember that the mechanical suspension is between the wheel and the seat. The wheel can't benefit from it at all. The suspension provided by a tire benefits everything else on the bike. " I disagree completely. The force and it's derivatives exerted by the rider and bike coming back down onto the rear axle will always be lower. An equal but opposite force.

whilst I agree with 99.9% of what your saying, I do admit that chalo and d8veh are have a point in that there could be a decrease in the acceleration of a non suspended wheel due to greater deformation of the tire, resulting in smaller shock loads for the motor internals, though with greater loads on all weight baring components as a result. However I'd say these gains for the internals are probably marginal at best, more likely negligible though, in particular compared to the increases in stress to the weight baring components.

The axle and flange see higher stresses in an unsuspended bike, sure. But they are designed to withstand those forces.

The magnets, wire connections, sensors, etc., see much higher accelerations in a suspended setup, and they are not necessarily designed to withstand such forces.

I'd have to disagree completely. Axles on motors are known to fail (though rarely), or at least distort (not so rarely). They may be designed for commuting, not so much for heavy offroading. and if your only commuting, then these failures are far less likely in either case. The only internals I've heard of failing due to vibration and shock are halls - its FAR easier to fix a hall than it is to fix a snapped axle. and a broken hall isn't exactly likely to cause a crash either, unlike a broken/bent axle. I have also heard of spoke flanges failing too, though thats also pretty uncommon.

The most likely thing to break however is your tire, rim and spokes... all of which are notably worse off with a hardtail. The failure of any of these parts is also considerably more dangerous than the loss of a hall or any other internal component. Even the clutch and gears of a mac will be better off in a suspended bike, as they're most likely to break in a landing while under power. The effect of the suspension will mitigate some (probably small) amount of the shock loading to these components during a landing as the bike rocks back under acceleration.

mine is 5" wide..

mine's bigger :wink: :lol:



Ultimately, trying to answer what the op was asking - if a hub was better off with a suspended bike. its pretty well known that hubs, in particular DD hubs, are pretty robust, and will probably handle most of what can be thrown at it - in particular since there are other components that will probably fail before any hub components do. Unless someone runs a sim or a propper real world test we'll never know 100% for sure, but it seems the general consensus, going on peoples experience and knowledge is that suspension is beneficial - though exactly how much is debatable.

Is it required? absolutely not.
does it offer significant protection to the hub? probably not much under 'normal' conditions.
What should I get? either. other factors should influence your decision to go or not to go rear suspension more than just protecting the hub.
What would I personally get? full sus all the way baby! 8) 8)

 

[GCinDC]

[youtube]UZZQhX1mlXU[/youtube]

 

[sn0wchyld]

[youtube]UZZQhX1mlXU[/youtube]

like I said... 'normal'... :lol:

quite like the music on that one - is it just yt generic stuff or an actual band?


edit
its actually a good vid... it shows the tire's deformation all but maxing out on something as simple as poping up a curb. ergo, a hard tail would be worse off in the same situation.

 

[dogman dan]

Broken hubmotor alxes I recall seeing pictures of, were either weakened by drilling to increase wire size, or just run at much higher power levels than they were designed for.

I just haven't seen evidence that suspension or not had any role in the failures I can recall at the moment. It was other factors. But I'm sure you can huck a jump and land flat enough to break anything.

Despite the rough riding I've been doing, I haven't had a bearing failure yet. Kind of astonishing given the cheap 9c motors reputation for coming with a defective bearing.

Again, the only thing I've shaken loose is phasewire connections on a 9c clone, after they have been heated enough to melt the solder. FWIW, a genuine 9c has the phase wires crimped then soldered. So they won't shake loose evne when melty. Halls with melted solder will shake loose though.

In summary, My opinion is that direct drive hubmotors ARE built to take quite a beating.

 

[GCinDC]

thanks, generic yt.

ps. i ruined first MC rim w/ such low tire pressure (less that 5 psi). i later rebuilt the MC wheel and never let it go below 30psi.

i've ruined lots of rims by taking drops w/ too low tire pressure, and i've always underestimated the amount of pressure needed.

 

[Chalo]

its actually a good vid... it shows the tire's deformation all but maxing out on something as simple as poping up a curb. ergo, a hard tail would be worse off in the same situation.

Hardtails, let alone unsuspended bikes, do not get into the same situation. They require technique and reward finesse. For instance, you don't slam into a curb; you bunny hop up onto it, or you "pick up" the bike as the wheels encounter it.

In the following video of completely rigid MTB riding from 1992, you can see a lot of what I'm talking about between 5:30 and 6:30. You can tell by the way these guys "float" over obstacles and stairs that it is all about technique, and that it's easier on the equipment than larding it up with suspension and smashing into stuff. By the way, these bikes would make great platforms for e-conversion.

[youtube]uyrlEE9AV58[/youtube]

So it's not actually making a direct comparison to say, "if I sit here like a sack o' taters and motor my bike into that square step, is it easier for the hubmotor if I have suspension?" If you do that, the vertical acceleration of the hubbie will be more violent with the suspended bike, and the stress on the rim will be higher on the unsuspended bike, but the more relevant fact is that you just don't do it that way on an unsuspended bike.

The sort of riding in the video posted by GCinDC is an expression of the motor vehicle fetish I was talking about. Motorcycles are better tools for it. But riding a bicycle-- like a bicycle-- is more wholesome fun.

[youtube]JL_ZuBkEmXE[/youtube]

 

[GCinDC]

Hardtails.... don't slam into a curb; you bunny hop up onto it, or you "pick up" the bike as the wheels encounter it.

easier said than done after adding 40lbs to the bike, no?

riding a bicycle-- like a bicycle-- is more wholesome fun.

off topic perhaps? aren't we talking about ebikes w/ hub motor?

The sort of riding in the video posted by GCinDC is an expression of the motor vehicle fetish I was talking about.

as opposed to bicycle fetish?

 

[Chalo]

My e-bikes have ranged all the way up to 120 lbs, but they have all been (unsuspended) bicycles, and I have ridden them like bicycles. No bunny hops, to be fair, but curb climbing? You bet. Just no smashing into things.

Bicycles are virtuous machines; getting on their terms makes you a better person in all sorts of ways. E-bikes become more virtuous to the degree that they emulate bicycles.

There's nothing particularly wrong with motorcycling, especially when compared to driving cars. But there's nothing all that wholesome about them to make you a better person.

 

[sn0wchyld]

honestly chalo, do you ever stop twisting peoples words? or is it because I forgot (or rather, didn't think it was necessary) to add 'all other things equal' to each and every one of my statements?

Clearly, if you bunnyhop/unweight with one bike, and not the other... then all other factors are not equal, and any comparison between the loads a hub takes between different bikes is largely moot. The other thing you dont seem to realise is that unweighting your bike will mean less deformation of your tire, much like... a full susser!! better hope those halls are well glued in!

And if you're suggesting that people ride full sussers because they lack the 'technique' or 'finesse' to ride a rigid frame, or that people don't unweight/bunnyhop their full sussers, then that is just plain stupid. Moreover, it seems you are suggesting that riding like gc in dc, ie popping off curbs, doing stair drops etc and generally messing around is only done by mad motorcyclists riding illegally... are you crazy? You've never seen anyone doing the same stuff as GCinDC and more on a normal non electric bike?

I guess these guys just lack the 'finesse' to 'float' over all those obstacles...
[youtube]56kJ99AvfoI[/youtube]



Quit trolling chalo. And I'll try to quit feeding 'em.

its actually a good vid... it shows the tire's deformation all but maxing out on something as simple as poping up a curb. ergo, a hard tail would be worse off in the same situation.

Hardtails, let alone unsuspended bikes, do not get into the same situation. They require technique and reward finesse. For instance, you don't slam into a curb; you bunny hop up onto it, or you "pick up" the bike as the wheels encounter it.

In the following video of completely rigid MTB riding from 1992, you can see a lot of what I'm talking about between 5:30 and 6:30. You can tell by the way these guys "float" over obstacles and stairs that it is all about technique, and that it's easier on the equipment than larding it up with suspension and smashing into stuff. By the way, these bikes would make great platforms for e-conversion.

..............................

So it's not actually making a direct comparison to say, "if I sit here like a sack o' taters and motor my bike into that square step, is it easier for the hubmotor if I have suspension?" If you do that, the vertical acceleration of the hubbie will be more violent with the suspended bike, and the stress on the rim will be higher on the unsuspended bike, but the more relevant fact is that you just don't do it that way on an unsuspended bike.

The sort of riding in the video posted by GCinDC is an expression of the motor vehicle fetish I was talking about. Motorcycles are better tools for it. But riding a bicycle-- like a bicycle-- is more wholesome fun.
.........................

 

[cal3thousand]

So am I understanding it right that 'technique' now has an effect on physics?

I must be misunderstanding it, but my belief is that 'technique' and 'suspension' are not mutually exclusive.

 

[GrayKard]

Bicycles are virtuous machines; getting on their terms makes you a better person in all sorts of ways. E-bikes become more virtuous to the degree that they emulate bicycles.

Do you really believe this drivel?

 

[shock]

You can usually find Chalo by following the piles of word vomit. Don't RIDE the bicycle, BE the bicycle...

 

[full-throttle]

Back on topic

Depending on the force and speed of the hit a hub (motor or not) will benefit very slightly from hydraulic suspension. The faster the hit is the less the difference, the heavier the hub the less the difference. It's all to do with inertia.

Picture hitting a glass bottle with a spanner - it does not matter if the bottle is resting on hard concrete or a pillow, hit it fast and it will break. The only time the pillow would help is when the speed of the impact is low - replace spanner with a brick and hit it slowly. The bottle on the pillow would most likely survive.

Now, pneumatic tyres are different, because they will see the hit before the force gets transferred further along and attenuate the sharp edge. Imagine the same scenario with the pillow on top of the bottle.

So to answer the OT - suspension helps with 'protecting the hub motor' but not as much as large tyres. In both cases correct suspension setup and tyre pressure are very important.

 

[cal3thousand]

Back on topic

Depending on the force and speed of the hit a hub (motor or not) will benefit very slightly from hydraulic suspension. The faster the hit is the less the difference, the heavier the hub the less the difference. It's all to do with inertia.

Picture hitting a glass bottle with a spanner - it does not matter if the bottle is resting on hard concrete or a pillow, hit it fast and it will break. The only time the pillow would help is when the speed of the impact is low - replace spanner with a brick and hit it slowly. The bottle on the pillow would most likely survive.

Now, pneumatic tyres are different, because they will see the hit before the force gets transferred further along and attenuate the sharp edge. Imagine the same scenario with the pillow on top of the bottle.

So to answer the OT - suspension helps with 'protecting the hub motor' but not as much as large tyres. In both cases correct suspension setup and tyre pressure are very important.

+1

Thanks for putting my point of 'impulse' in a more clear fashion

 

[ions82]

Great thread! I have been mulling over my next e-bike project. I have a rigid steel MTB, a rigid Electra "Townie," and an hardtail frame (aluminum) that is designed to use a long-travel suspension fork. I've been trying to decide if I should use one of those or get a full-suspension rig. I will likely end up using a MAC motor, so I've been considering buying a 29er with suspension and getting a motor that is geared lower. I guess that brings me to another question. Would using a geared motor in a 29-inch wheel provide for more of the "hub protection" that is being discussed? 29ers are known for helping to smooth out bumps. Most of the talk in this thread is in regard to DD hubs. A 14-pound hub in the rear of one of my rigid bikes would definitely affect my ability to "finesse" my way over obstacles.

Anyway, this thread has addressed a few of my concerns, but I still have no idea which one I should build. I'll just have to build them all one at a time!

 

[Chalo]

So am I understanding it right that 'technique' now has an effect on physics?

I must be misunderstanding it, but my belief is that 'technique' and 'suspension' are not mutually exclusive.

Technique can affect not only effective spring rate, suspension travel, and damping rate, but also effective bump length. Really.

 

[Chalo]

le is resting on hard concrete or a pillow, hit it fast and it will break. The only time the pillow would help is when the speed of the impact is low - replace spanner with a brick and hit it slowly. The bottle on the pillow would most likely survive.

Now, pneumatic tyres are different, because they will see the hit before the force gets transferred further along and attenuate the sharp edge. Imagine the same scenario with the pillow on top of the bottle.

You got it. With hydraulic suspension, the hammer hits the hub, which in turn hits the pillow. With pneumatic tires, the hammer hits the pillow, which hits the hub. If you were the hub, which would you prefer?

Chalo

 

[full-throttle]

Technique can affect not only "spring rate" but also "bump length". Really.

Yeah, with the right technique it's possible to use forehead on nails..
Yet we all choose a hammer instead. Why?

Because it's easier, more productive and does not hurt as much.

 

[Chalo]

Exercise hurts more than no exercise. But it makes you better in spite of that.

 

[full-throttle]

Within limits. Overexercise leads to injuries. But otherwise that's true.
A good example
[youtube]7ZmJtYaUTa0[/youtube]

I asked a good rider once why he rides a hardtail and not a dually (full suspension)
"see bike riding is a lot like music" he replied "and hardtail is the equivalent to a virtuoso jazz kind of thing"
Guess I'm into heavy bass then :lol:

PS those stairs remind me of viewtopic.php?f=25&t=33806 (@4:15 i the video)

 

[John in CR]

Awesome video GCinDC with plenty of on topic closeup action of the tire, wheel, and suspension dissipating energy.

 

[cal3thousand]

le is resting on hard concrete or a pillow, hit it fast and it will break. The only time the pillow would help is when the speed of the impact is low - replace spanner with a brick and hit it slowly. The bottle on the pillow would most likely survive.

Now, pneumatic tyres are different, because they will see the hit before the force gets transferred further along and attenuate the sharp edge. Imagine the same scenario with the pillow on top of the bottle.

You got it. With hydraulic suspension, the hammer hits the hub, which in turn hits the pillow. With pneumatic tires, the hammer hits the pillow, which hits the hub. If you were the hub, which would you prefer?

Chalo

Try this without a bike:

Jump from a 7 foot drop landing on your heels and allow compression ONLY at the hips and knees. See how your ankles feel. Painful I bet.

THEN

Jump from 7 foot drop without allowing any compression (pencil dive) . Call someone to help you up after your ankles shatter.