Rear suspension and rear hub question.

alfantastic

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Does a rear hub motor attached to a frame with rear suspension, get a lot more protection from shocks than a hard-tail?
 
alfantastic said:
Does a rear hub motor attached to a frame with rear suspension, get a lot more protection from shocks than a hard-tail?

No; it's the opposite. Your body weight and the bike's weight serve as an inertial damper for a hardtail, and get the tire working more deeply. The axle might see slightly higher peak loads on a hardtail, but the motor experiences much less shock and vibration.

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.

Chalo
 
Good question.

Regarding the tire acting as suspension for the whole of the bike. In order to get the most out of that, what would be the best inflation pressure? I assume it will have to take into account the weight of bike + rider, tire size, etc, so I am looking for a "best guess" procedure from people with experience.

For info, I have my tires now at 4.5bar (65psi) to reduce resistance. Happy to deflate them to a better "suspension" pressure, but unsure as to how much.
 
Chalo said:
alfantastic said:
Does a rear hub motor attached to a frame with rear suspension, get a lot more protection from shocks than a hard-tail?

No; it's the opposite. Your body weight and the bike's weight serve as an inertial damper for a hardtail, and get the tire working more deeply. The axle might see slightly higher peak loads on a hardtail, but the motor experiences much less shock and vibration.

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.

Chalo

How interesting !
Is there an in-depth analysis somewhere, or a good computer sim ?
I would love to read more !
 
Good question! I also am not sure about motor shocks but on a recumbent you really need at least a rear suspension. On a 2 wheeler your legs and butt absorb a lot of shocks. (Watch Mccaskill jump from walls) On a recumbent that same force is delievere to your back and kidneys as well as your tailbone. Yowch! Ideally you would waht as littlle "unsprung" weight as possible in the hub of ther rear suspension, but to get that ideal 2-3kg minimum you need one of those little teeny geared motors that last about a week and die. Our 9C's weigh about 6-7 kilos in the wheel and the old 5304 C-Lites weighed about 15 kilos in a rear wheel. Somehow Stealth Bombers control that suspension, but I don't know about ride quality and sharp bumps. Sorry to ramble but to me the difference is between having a rear suspension and not riding! Old age sometimes sucks.
otherDoc
 
Well, to me it is just common sense. The shocks are between the rear swingarm and the frame. That means that the rear wheel and swingarm do not benefit from the shock. In a hardtail, there is no shock, therefore all movements are directed towards your body. As your body would move less than the bike, because you flex your legs, arms, and spine, your body is the part that absorbs all shocks.

I do fear for my cromotor-laced rear wheel when going over whatever hurdle. So, if I can get my tires absorb at least small bumps, it would be great.
 
My experience with riding around on softball size or larger boulders is the direct drive hub motors can take the shocks. Rims and spokes though, I firmly believe suspension helps them.

I think the problem is more the other way around. The weight of the hubmotor beats the bike, the bike doesn't beat the hubmotor enough to break it.
 
+1

The way i see it, is that the internals of the hub (stator etc) wont see any difference in the forces it experiences, but the outer weight baring parts will.

Imagine running over a rock, say shaped like an average brick, at tge same pace, on a hardtail and a suspended bike. Both wheels must accelerate up and over the brick at the same rate. Hiwever, the hardtail must move the entire bike around the front axle, where the suspended bike only moves the rear wheel and linkages. Ignoring rider input, this means we effectively have two objects being accelerated at the same rate, but onewith a lower mass than the other. Obviosly this means the forces involved are smaller In the lighter setup. Thus the tension/comression forces are equally, less.

I'm just doing this quickly in my head however, the behavior of the spring/shock of the bike would o doubt have apart to play in the actual figures, but i cant be bothered right now to do the math... My intuition however says that no matter how effective (or not) the rear suspension is, any lowering of the mass being accelerated is going to be beneficial to the components that need to remain intact during that acceleration ie rim, spokes, tires, hub flange, side covers and axle.

All that said, hubs are generally pretty tough. Your spokes, rim and tire are far more likely to give out befor your hub does.

jpgey said:
Chalo said:
alfantastic said:
Does a rear hub motor attached to a frame with rear suspension, get a lot more protection from shocks than a hard-tail?

No; it's the opposite. Your body weight and the bike's weight serve as an inertial damper for a hardtail, and get the tire working more deeply. The axle might see slightly higher peak loads on a hardtail, but the motor experiences much less shock and vibration.

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.

Chalo

How interesting !
Is there an in-depth analysis somewhere, or a good computer sim ?
I would love to read more !
 
sn0wchyld said:
The way i see it, is that the internals of the hub (stator etc) wont see any difference in the forces it experiences, but the outer weight baring parts will.

Imagine running over a rock, say shaped like an average brick, at tge same pace, on a hardtail and a suspended bike. Both wheels must accelerate up and over the brick at the same rate. Hiwever, the hardtail must move the entire bike around the front axle, where the suspended bike only moves the rear wheel and linkages. Ignoring rider input, this means we effectively have two objects being accelerated at the same rate, but one with a lower mass than the other.

The suspended bike's wheel hub will accelerate more abruptly, because the suspension above it, and not the tire below it, is taking up most of the necessary movement. The peak forces at the axle, bearings, etc, are probably similar in both cases-- because of the forces carried into the frame and beyond on the unsuspended bike, and because of the more violent accelerations on the suspended one. The force variations on spokes are certainly higher in the case of the unsuspended bike, because the tire is deflecting more deeply and pushing harder against the rim surrounding the contact patch.

As for tires and maximizing their suspension qualities, try to look at it the same way as you would a mechanical suspension: The tire's inflated height off the rim is the "stroke length", and its inflation pressure is the "spring rate". In both cases the stroke length must be long enough, and the spring rate firm enough, to resist bottoming out. So for more active suspension in a tire, you simply want a wider tire at a lower inflation pressure.

It helps to use a tire that has flexible sidewalls and relatively thin, smooth tread, so that the tire's suspension qualities don't go hand in hand with major rolling resistance. Thus you should use only as much tread roughness as you need, and only as stiff and sturdy a tire as you need, so that its flexibility can work for you.

How low an inflation pressure you can get away with is a compromise involving many values. Pinch flat resistance, rolling resistance, vehicle weight, surface conditions, rim width, and riding style all enter into it. You have to try a range of pressures to see what works best. With fat tires (over 2" or 50mm), usually the tire will display signs of instability in turns before it is soft enough to present a serious risk of pinch flats on the street. But this is highly dependent on rim width, tire stiffness and, of course, how bad your streets are.

Chalo
 
I hear whatbyour saying re tire deformation, though i still think a suspended tire is going to experience lower forces... Even if the hartail was able to halve the acceleration expwrienced by the rest of the bike, (somewhat unlikely id think) that would require that the mass being acellerated to be no more than double that of the suspended bike for the forces to be equal. Again, ignoring how the shock would affect things (a stiff shock obviosly narrowing the gap). And if you did somehow have a setup where the acceleration was halved, i woukd think that this would cause issues with durability of the tire, ie pinch flats etc... And bare in mind, its mot like the suspended bike doesnt benufit from tyre deformation too, so to halve the acceleration is probably unrealistc...
Even so, with the average hub, torque arm etc etc weighing say, 10kg, this would mean that if a non suspended bike was capable of halving the acceleration, it would have to weigh no more than 20kg. (actually, it could weigh notably more than 20 since the forces arent acting towards the COM of the bike) but thats still a pretty big ask for the average ebike and rider...
i just dont see a suspended bike being harder on the hub components than a hardtail, all other things being equal. I appriciate your point that acceleration would be greater in a suspended hub, it just seems unrealistic that this would be a greater ratio than the unsuspended weight. Though certainly, this gap would narrow the more the rider is able to unweight the bike before impact.


Chalo said:
sn0wchyld said:
The way i see it, is that the internals of the hub (stator etc) wont see any difference in the forces it experiences, but the outer weight baring parts will.

Imagine running over a rock, say shaped like an average brick, at tge same pace, on a hardtail and a suspended bike. Both wheels must accelerate up and over the brick at the same rate. Hiwever, the hardtail must move the entire bike around the front axle, where the suspended bike only moves the rear wheel and linkages. Ignoring rider input, this means we effectively have two objects being accelerated at the same rate, but one with a lower mass than the other.

The suspended bike's wheel hub will accelerate more abruptly, because the suspension above it, and not the tire below it, is taking up most of the necessary movement. The peak forces at the axle, bearings, etc, are probably similar in both cases-- because of the forces carried into the frame and beyond on the unsuspended bike, and because of the more violent accelerations on the suspended one. The force variations on spokes are certainly higher in the case of the unsuspended bike, because the tire is deflecting more deeply and pushing harder against the rim surrounding the contact patch.

As for tires and maximizing their suspension qualities, try to look at it the same way as you would a mechanical suspension: The tire's inflated height off the rim is the "stroke length", and its inflation pressure is the "spring rate". In both cases the stroke length must be long enough, and the spring rate firm enough, to resist bottoming out. So for more active suspension in a tire, you simply want a wider tire at a lower inflation pressure.

It helps to use a tire that has flexible sidewalls and relatively thin, smooth tread, so that the tire's suspension qualities don't go hand in hand with major rolling resistance. Thus you should use only as much tread roughness as you need, and only as stiff and sturdy a tire as you need, so that its flexibility can work for you.

How low an inflation pressure you can get away with is a compromise involving many values. Pinch flat resistance, rolling resistance, vehicle weight, surface conditions, rim width, and riding style all enter into it. You have to try a range of pressures to see what works best. With fat tires (over 2" or 50mm), usually the tire will display signs of instability in turns before it is soft enough to present a serious risk of pinch flats on the street. But this is highly dependent on rim width, tire stiffness and, of course, how bad your streets are.

Chalo
 
maybe cause and result are turned around. The unsuspended rear-wheel-frame has lower acceleration BECAUSE it has a total higher mass as compared to the rear-wheel-swingarm that is connected to the frame with a shock. The lower mass of the independently moving wheel-swingarm means it can accelerate harder than the fixed rear wheel.

To me, this means that in terms of forces, the fixed rear wheel, due to having to move the larger mass, will be exposed to larger forces, as compared to the rear-wheel-swingarm, which only needs to move itself.

Given the same 5 cm bump, the rear-wheel-swingarm only needs to move itself upwards for those 5 cm. The forces needed for that are lower than compared to the forces to lift the whole bike upwards in a fixie.

Therefore, I agree that the suspended wheel is experiencing smaller forces.
 
The way I see it is that because of the higher inertia, the wheel and tyre of the unsuspended bike will distort more when going over a bump, so less movement and acceleration at the hub, but I don't believe it'll have any significant effect on the durability of the hub-motor. Depending on the geometry, suspension could have a beneficial effect by damping pedalling forces, which might save the free-wheel thread from breaking off.
 
d8veh said:
The way I see it is that because of the higher inertia, the wheel and tyre of the unsuspended bike will distort more when going over a bump, so less movement and acceleration at the hub, but I don't believe it'll have any significant effect on the durability of the hub-motor. Depending on the geometry, suspension could have a beneficial effect by damping pedaling forces, which might save the free-wheel thread from breaking off.


lower acceleration does not mean less force. the formula we are using here is F(force) = M(mass) x a(acceleration). another way of looking at it is this... how hard do you have to push a shopping chart to make it accelerate quickly to a running pace? not much. how about pushing a large truck to running pace? allot more. and if you were trying to push these objects to a given speed, then even though the truck would accelerate much slower than the shopping trolley, you would likely be putting far more effort (or force) into that push, to even get it going.

this is whats being discussed, is the difference in acceleration of the un-suspended wheel vs the suspended wheel greater (as a ratio) than the difference in weight being accelerated in each case? My intuition (ie thinking it through and doing the basic math) says no, not even close. I haven't done the complete maths, or any RL testing though so I cant be totally sure.
 
In any case, riding over the boulder strewn trails, I never broke an axle, broke a bearing, or had a part inside the motor come loose that didn't already have the solder melted on it. DD hubbies are pretty robust.

That's both with and without suspension. So back to the original question, I don't think a direct drive motor gives a shit. I'm not an expert on the gearmotors so I can't say with them.

Sure used to pinch flat tires with the hardtail though. It depends on the ride though. Obviously well figured out hucks can be landed on hardtails. My trails are often just like riding over a path made of softballs and bowling balls, with some stone steps thrown in. So for me suspension sure helped.
 
A motor in a swingarm can receive either harder or softer a beating than the one on a hardtail. This is about how you ride it and how the suspension is tuned, but the fact is that a well set suspension will act as a torque damper because a hard acceleration first unfold the swingarm travel sag before lifting the whole bike. For this reason alone, I'd say the suspension frame makes it easier for the motor, all other factors being equal.
 
sn0wchyld said:
Even so, with the average hub, torque arm etc etc weighing say, 10kg, this would mean that if a non suspended bike was capable of halving the acceleration, it would have to weigh no more than 20kg. (actually, it could weigh notably more than 20 since the forces arent acting towards the COM of the bike) but thats still a pretty big ask for the average ebike and rider...

The Surly Moonlander weighs a little under 16kg complete. It has 4.7" (120mm) tires that can be inflated as low as 0.3 bar.

IMG_0416-e1317829786942.jpg


Tell me how that isn't easier on your hub motor. The thing would be mounted inside an air bag.

This stuff can clearly be done the simple, reliable, proven bicycle-style way. Mechanical suspension is present on bicycles to serve a motor vehicle fetish as its primary function, with dynamic benefits as a secondary function. The former function is much better at selling bikes.

Chalo
 
Suspension is easier on bike components, including the wheels, spokes and motor, than no suspension. Look at it this way; you're riding along and hit a large obstruction, with no suspension the tire and wheel components take a major hit but with suspension the wheel can move out of the way with the shock absorbing a good part of the impact.

Yes if they fit on your bike big balloon tires will smooth out the ride on any bike, hardtail or suspension, as long as you keep the pressures low. I found however that even 50mm tires do not provide enough "cushion". The next mod on my (cheap-o) full suspension e-bike will likely be to fit 60mm+ tires to get a more supple ride over the little stuff.


-R
 
dont start straw manning my argument. I've stated right through my statements that this is a case of 'all other things being equal'. and yes, the bike weighs 16kg... without anything on it - ie batteries, motor and rider. how often do you ride your electric hub motor bike without batteries, motor, or you, on it? exactly. For all things to be equal, that means that the suspended bike will have these big fat cooshy tires inflated to .3bar too... and get the same airbag-like benefits from it.

and whilst I agree that some suspension (ie walmart bikes) is just wank, other suspension performs a useful purpose. look at dh and to a lesser extent xc. sure, it can be done on a hardtail, but there's probably a reason its often not, and I doubt its to serve the riders ego (mutch) :wink: .

Chalo said:
sn0wchyld said:
Even so, with the average hub, torque arm etc etc weighing say, 10kg, this would mean that if a non suspended bike was capable of halving the acceleration, it would have to weigh no more than 20kg. (actually, it could weigh notably more than 20 since the forces arent acting towards the COM of the bike) but thats still a pretty big ask for the average ebike and rider...

The Surly Moonlander weighs a little under 16kg complete. It has 4.7" (120mm) tires that can be inflated as low as 0.3 bar.

IMG_0416-e1317829786942.jpg


Tell me how that isn't easier on your hub motor. The thing would be mounted inside an air bag.

This stuff can clearly be done the simple, reliable, proven bicycle-style way. Mechanical suspension is present on bicycles to serve a motor vehicle fetish as its primary function, with dynamic benefits as a secondary function. The former function is much better at selling bikes.

Chalo
 
sn0wchyld said:
d8veh said:
The way I see it is that because of the higher inertia, the wheel and tyre of the unsuspended bike will distort more when going over a bump, so less movement and acceleration at the hub, but I don't believe it'll have any significant effect on the durability of the hub-motor. Depending on the geometry, suspension could have a beneficial effect by damping pedaling forces, which might save the free-wheel thread from breaking off.


lower acceleration does not mean less force. the formula we are using here is F(force) = M(mass) x a(acceleration). another way of looking at it is this... how hard do you have to push a shopping chart to make it accelerate quickly to a running pace? not much. how about pushing a large truck to running pace? allot more. and if you were trying to push these objects to a given speed, then even though the truck would accelerate much slower than the shopping trolley, you would likely be putting far more effort (or force) into that push, to even get it going.

this is whats being discussed, is the difference in acceleration of the un-suspended wheel vs the suspended wheel greater (as a ratio) than the difference in weight being accelerated in each case? My intuition (ie thinking it through and doing the basic math) says no, not even close. I haven't done the complete maths, or any RL testing though so I cant be totally sure.
I think you've missed my point. There's a certain amount of elasticity between the circumferance of the wheel and the axle. In both cases the point of contact with the road will experience the same acceleration, but the non suspension bike has a much higher mass attached to the axle. This means that there will be a bigger compressive force between the circumferance and the axle in the non suspension bike. This bigger force will distort the tyre and rim more so that the axle moves less distance and hence has less acceleration than the point of contact with the road. Less acceleration on the axle meand less stress on the motor, but a lot more stress on the tyre, rim and spokes.
 
I think hard tail takes a bit more punishment due to the 'impulse' of the forces. In a suspension bike, the peak forces are lower since the force is exerted over a larger period of time
 
d8veh said:
sn0wchyld said:
d8veh said:
The way I see it is that because of the higher inertia, the wheel and tyre of the unsuspended bike will distort more when going over a bump, so less movement and acceleration at the hub, but I don't believe it'll have any significant effect on the durability of the hub-motor. Depending on the geometry, suspension could have a beneficial effect by damping pedaling forces, which might save the free-wheel thread from breaking off.


lower acceleration does not mean less force. the formula we are using here is F(force) = M(mass) x a(acceleration). another way of looking at it is this... how hard do you have to push a shopping chart to make it accelerate quickly to a running pace? not much. how about pushing a large truck to running pace? allot more. and if you were trying to push these objects to a given speed, then even though the truck would accelerate much slower than the shopping trolley, you would likely be putting far more effort (or force) into that push, to even get it going.

this is whats being discussed, is the difference in acceleration of the un-suspended wheel vs the suspended wheel greater (as a ratio) than the difference in weight being accelerated in each case? My intuition (ie thinking it through and doing the basic math) says no, not even close. I haven't done the complete maths, or any RL testing though so I cant be totally sure.
I think you've missed my point. There's a certain amount of elasticity between the circumferance of the wheel and the axle. In both cases the point of contact with the road will experience the same acceleration, but the non suspension bike has a much higher mass attached to the axle. This means that there will be a bigger compressive force between the circumferance and the axle in the non suspension bike. This bigger force will distort the tyre and rim more so that the axle moves less distance and hence has less acceleration than the point of contact with the road. Less acceleration on the axle meand less stress on the motor, but a lot more stress on the tyre, rim and spokes.


gotcha, yea, the internals will experience slightly lower acceleration, but at the expense of higher forces on the weight bearing parts... sorry if I sounded patronising at all, it just sounded like you were saying less acceleration = less force.
 
sn0wchyld said:
dont start straw manning my argument. I've stated right through my statements that this is a case of 'all other things being equal'. and yes, the bike weighs 16kg... without anything on it - ie batteries, motor and rider. how often do you ride your electric hub motor bike without batteries, motor, or you, on it? exactly. For all things to be equal, that means that the suspended bike will have these big fat cooshy tires inflated to .3bar too... and get the same airbag-like benefits from it.

Sorry; I interpreted your earlier weight breakdown to indicate 10kg of electrics on a 20kg bike.

A 10kg (22 lbs) fully suspended bike is uncommon, very expensive, and fragile enough to be a poor choice for e-conversion. 22 lbs would be very light even for a rigid MTB with a rigid fork.

In practice, you either choose a super fat tired bike or a mechanically suspended bike, but not both. Choosing a fatbike like the Surly Moonlander means dedicating the weight and money you'd otherwise use for suspension parts on ultra-fat tires and rims instead (and on the special frame and fork to accommodate them). It would be mighty interesting for someone to build a fully suspended fatbike with power assist in mind, but to date nobody has done so. You could be the first!

Chalo
 
Chalo said:
sn0wchyld said:
dont start straw manning my argument. I've stated right through my statements that this is a case of 'all other things being equal'. and yes, the bike weighs 16kg... without anything on it - ie batteries, motor and rider. how often do you ride your electric hub motor bike without batteries, motor, or you, on it? exactly. For all things to be equal, that means that the suspended bike will have these big fat cooshy tires inflated to .3bar too... and get the same airbag-like benefits from it.

Sorry; I interpreted your earlier weight breakdown to indicate 10kg of electrics on a 20kg bike.

A 10kg (22 lbs) fully suspended bike is uncommon, very expensive, and fragile enough to be a poor choice for e-conversion. 22 lbs would be very light even for a rigid MTB with a rigid fork.

In practice, you either choose a super fat tired bike or a mechanically suspended bike, but not both. Choosing a fatbike like the Surly Moonlander means dedicating the weight and money you'd otherwise use for suspension parts on ultra-fat tires and rims instead (and on the special frame and fork to accommodate them). It would be mighty interesting for someone to build a fully suspended fatbike with power assist in mind, but to date nobody has done so. You could be the first!

Chalo

haha, i doubt it somehow given my student level income!! maybe in a few years? one things for sure... it'd look pretty mad. if I was going to go with super fat tires though, I'd probably look at motorcycle parts. a bit more of a weight hit, but for (what should be) a gain in durability, safety at speed and puncture proofness (is that the technical term?? :? ).

what I was refering too is the unsuspended weight on a suspended bike, ie hub, rim, spokes, tire etc etc would be ~10kg. less with a mac, more with a 5x crystalite, about spot on for a 9c/hx cristalite. thats the 'mass' being accelerated during an impact with a obstacle on a suspended bike, pluss a little bit of movement from the rest of the bike. so the 'total mass' of the unsuspended bike would need to be 'less than double' in the above example. hope that cleans up my reasoning!
 
To answer the original thread question; yes. Suspension does take lateral loads off the wheel hub (motorized or not)

Think about it like this, what would hurt more? Getting hit in the back with a solid iron rod, or getting hit with a long spring. :pancake:
 
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