Chalo said:
You're still conflating structural forces and accelerations.
Force = Mass*Acceleration
Chalo said:
Structural forces only matter to the structural elements of the bike, for instance the bearings as you point out. But the structural parts of the bike are designed to tolerate those forces. Transient peak forces on the structural parts of the bike could be higher for either bike, depending on many factors of the surface and the suspension's characteristics.
"Transient peak forces on the structural parts of the bike could be higher for either bike" ---> Now you are talking. Particularly the hard-tail.
Chalo said:
In many cases, the structural peak forces on a rigid bike will be higher than that of a sus bike.
Yup that is what everyone here is telling you.
Chalo said:
And the structural force peaks will almost always be longer in duration (rider "landing" on bike vs. wheel extending and briefly smacking on the ground).
For which bike? I would say the full suspension. But keep in mind what you said before.
Chalo said:
There is more work (F * D) in the high stress level regime of those unsuspended hits, even if the transient peaks are just as high for the sus bike.
I am not convince. Work = energy. And law of conservation of energy say in both cases, the energy dissipated from the transaction is equal. I am not convince the transient peaks are just as high for sus bike. You said yourself before "the structural peak forces on a rigid bike will be higher than that of a sus bike."
Chalo said:
So if you want to bend a bike, use a rigid one. But that's not what I'm talking about.
Not sure what you mean here. I would much rather bend a sus bike. It's much easier. LOL.
Chalo said:
The magnets in the motor are not structural. They're not in the force path. Same with wires, halls, plugs, pass-throughs, printed circuits and other critical bits that are not part of the bike's structure. The forces that will cause a magnet to unstick, a wire to fatigue and break, or an electrolytic capacitor to bust one of its leads, are strictly due to acceleration (not in the vehicular sense, but in the physics sense).
I think you mean vibration which are impulses with opposite signs in rapid succession.
Chalo said:
The hub of a sus bike sees higher and more frequent acceleration forces because it moves around more. There's more shock and vibration in the unsuspended parts of a suspended vehicle than in any part of an unsuspended vehicle on the same course.
Right... But compare for me the forces of between those. I mean which would you prefer? I whack you with a inflatable toy hammer a hundred times. Or I use a real hammer and whack you only ONCE. I would go with the former easily!
Chalo said:
And the hub is not suspended.
So you are saying if the hub was suspended it would be better? hummm this seems so much similar to having a sus bike. Instead of have the hub suspended, we just have the thing holding the hub suspend.
Chalo said:
As an illustration of the forces I'm talking about, consider this. When I build or repair a spoked wheel, I get the spokes good and tight-- always at least 100kgf of tension on the spokes of the tighter side, but sometimes more. Friction in the spoke nipples and rim holes leads to a residual twist in each spoke that I can only partly remove by backing up a little when I tighten them. Each time of the spokes unwinds, there is a little "tick" or "ping" sound as it releases.
Sounds to me you are using inertial to your advantage. Once you can't tight anymore and try to apply torque on the spoke, it will not give. However if you loosen a bit and then twist again, the momentum, in some cases, is enough to push you pass the initial stop position.
Chalo said:
And you can only get it to release by applying a big enough load to the rim that the spoke's tension drops low enough for it to unwind. If I go out and test ride the bike, a few of the spokes will relax, but not all of them. I weigh about 325 pounds! If I sling it around turns or really mash the pedals from a standing position, I can get a few more to unwind. But if I continue down that path, I'll hurt the wheels I just repaired.
Not sure how this relates.
Chalo said:
You know what does allow the spokes to unwind? Me bouncing the wheel and tire on the ground like a basketball. The acceleration of the relatively low mass wheel and tire hitting the ground produces a force spike, very short but intense enough to unload the spokes and let them unwind.
Yup you just prove our point. The impulse are deforming the threads to a point to allow you to loosen them. Think of the toy hammer vs the real hammer example. Do you think soft bounces will get the spokes to unwind?
Chalo said:
The amount of physical work involved when I roll up against a curb is huge compared to just bouncing the wheel, but the transient force of bouncing the wheel is actually higher, and the spokes let me know that with a distinctive sound.
Yup work and power are totally different beast. There is definitely more work done when you roll up against the curb than bouncing the wheel. And yes the transient force is much higher on the bouncing the wheel. Hurray! you just proved our point.
Chalo said:
That is why the hub of a sus bike sees harder accelerations than the one on a rigid bike.
Nope. Everything you said before supports the opposite.
Chalo said:
It moves farther, faster, and it starts & stops more abruptly.
which part? Now tell me about the hard-tail and how it moves.
Chalo said:
The structural forces transmitted through the hub are less, but the inertial loads on the hub are more.
I think this was the point of the thread. The guy was asking if it's better for the hub to be on sus vs hard-tail. You said here the force through the hub is less! Ummm. If you think about it a bit, the inertial load on the hard-tail is actually more. You have more mass to move.
Chalo said:
Structural parts of the hub (flanges, shell, sidecovers, bearings, axle) have to withstand both transmitted and inertial loads, but nonstructural parts only see the inertial loads.
Yup again this is the point of the thread. The bearings has to withstand the transmitted forces and it is less as you said for the sus bike. I don't think it needs to withstand inertial loads. Because inertial loads has nothing to do with how long the bearings will last. Its a property of the object. It it does not have to withstand itself. More mass more inertial loads.
Chalo, sounds like you are agreeing with us without explicitly saying it. In my books, this is good enough for me.