|   WH-M535 | bullet
Jun 9, 2002 5:12 PM | | Does anyone have the weight for the M535 Shimano wheelsets without the QR`s?
`How are they holding up for Road use on a MTB? I heard they spin good but are on the heavy side but they should be solid- |
| Very poor design... | Bianchi4Me
Jun 9, 2002 10:53 PM | | They really designed these around "gee-whiz" looks. Performance was a secondary consideration.
Very heavy at 898g front, 1146g rear, and that's the optimistic factory claimed weight.
Laterally flexy due to the reduced spoke count.
Uses oddball 13/14 gauge spokes that aren't commonly available. So if you break one you'll probably be out of commission until your shop special orders one in.
Uses extremely high spoke tension, which requires a heavy reinforced rim. That concentrates weight out on the periphery of the wheel. The further out from the center of the wheel a weight is placed, the harder it is to accelerate. So these perform poorly under acceleration, even compared to other XC wheels of similar weights.
Unless you are getting them extremely cheap, I'd steer clear. |
| Very poor design... | Dougal
Jun 9, 2002 11:38 PM | | The old rotating weight inertia argument doesn't work for wheels. Anything rolling breaks down into force=mass*acceleration.
This is true regardless of the size of the wheel, from road wheels to 24inch Dh wheels, weight is the only real concern.
Whether you have heavy rims/tyres or heavy hubs doesn't matter.
Of course big wheels roll over obstacles easier so offroad a few other factors are introduced (like strength as well).
If you want the physics proof let me know.
Dougal.8m.com |
| Then why are flywheels... | Seb
Jun 10, 2002 5:24 AM | | built with extra heavy peripheries, and not extra heavy axles? Its obvious in flywheel design that mass at the periphery requires more energy to spin up, and keeps spinning longer under declerative friction. That applies to wheels as well- substitute "pedaling" for "spinning up", and "braking" for "declerative friction".
It is certainly questionable how much difference it makes to final rider performance, but wheel designs of the same mass can have different rotating inertias, no doubt about it. |
| Because they don't roll. | Dougal
Jun 15, 2002 8:55 PM | | If you're spinning stationary then the angular inerita counts big time (where weight further from the hub counts).
If you're rolling it doesn't matter, it boils down to force= mass*acceleration.
Dougal.8m.com |
| Wheels still rotate | Seb
Jun 16, 2002 6:24 AM | | It doesn't "boil down" at all. With a wheel, you have to overcome roational inertia (as with a flywheel) AND you have to accelerate the mass in the direction you want the rest of the bike to go.
There's a really basic demonstration of this that most good physics classes have. You roll wheels of equal mass and diameter down an inclined plane. The only difference is, one is a solid disc (mass equally distributd), one is a donut (mass near the periphery) and one has a heavy "axle" and light rim (centralized mass). The donut looses every time, and the one with the axle wins.
Why? Becuase they aren't just sliding down the ramp, which would follow norma F=MA rules. Nope, they are being SPUN- slowly at first, then faster as they roll faster. Since eacy weighs the same, so each feels the same torque, the one with the least rotaional inertia will reach the bottom first. |
| Wrong analogy, try this. | Dougal
Jun 16, 2002 4:01 PM | | First read my response to B4Me below.
Rolling and spinning are completely different behaviours.
Then try this.
Get a long pipe and a short pipe with the same section. Now these have the same mass distribution, but the longer one is both heavier and has a bigger I value.
Roll them down a hill together and the resulting speed is exactly the same at the bottom.
Here is the maths and physics.
____________________________________________
Analysis of a rolling hoop (wheel or pipe)
Here is the working:
Torque = inertia * angular acceleration(alpha)
Torque = I*alpha
but alpha = a/r
Torque = I*a/r
but I= m*r^2
Torque = m*r^2*a*r
cancel out r's.
Torque = m*a*r
But torque = force*radius
Force/r = m*a*r
cancel out r's.
Force = m*a
The acceleration of a rolling hoop boils down to
force = mass * acceleration. No different to any other mass.
________________________________
Analysis of a rolling cylinder
Torque = inertia * angular acceleration(alpha)
Torque = I*alpha
but alpha = a/r
Torque = I*a/r
but I= 1/2m*r^2
Torque = 1/2m*r^2*a*r
cancel out r's.
Torque = 1/2m*a*r
But torque = force*radius
Force/r = 1/2m*a*r
cancel out r's.
Force = 1/2m*a
The acceleration of a rolling cylinder
boils down to force = 1/2 mass * acceleration.
This is due to the different mass distribution of the cylinder.
Dougal.8m.com |
| Might be a variable you are overlooking... | Bianchi4Me
Jun 10, 2002 11:27 AM | | Here's a pretty good explanation, courtesy of Mad Sci. Got all the formulas and everything. Original question the answer pertains too was:
"I have these two wheels with the same mass. One has weights attached all around the edge of the wheel. The other has all the weights concentrated in the center where the axle should be. When I race the wheels down an incline plan, the one with the weights in the center always wins. It accelerates faster every time. They both have the same initial potential energy but it appears that they both do not have the same kinetic energy at the bottom of the plan since one is going faster. I am confused and it would be really helpful if you could explain this too me. If I let the wheels keep going after the plan on a flat surface, would they both stop in the same spot the same distance away? do you know any formulas that go with the theory?" |
| Nope, can explain that too. | Dougal
Jun 15, 2002 9:07 PM | | I've seen the same experiment done at school, but they aren't comparing similar but heavier objects, they're comparing objects with different distributions of mass.
A wheel is like a rotating pipe. Roll a short section of pipe and a long section of the same pipe down the same hill and they'll be at equal speeds (despite different weights due to length).
This is because the weight distribution is the same.
Likewise roll two solid cylinders down a hill (a long one and a short one), they'll get the same speed. But roll the pipe and the cylinder, the cylinder will always win for the same weight.
Dougal.8m.com |
| Very poor design... | bullet
Jun 10, 2002 2:12 PM | | hm, claimed weight at shimano.com is equal 819g for both rear and front,
they are LX after all so i wasnt expecting much...
What are better wheels for Road use on a MTB in this price range then?
I got a XTR/517/DT wheelset now wich is pretty good and light but i want something a little more aerodynamic, my rims are starting to wear off--
some more wider, low profile more smooth aerodynamic rims?... anyone knows? i use rim brakes.
thanks.
oh, and i got a DuraAce drivetrain on my MTB so its all about speed.
weight too of course- |
| Wider and lower is the opposite of aero. | Bianchi4Me
Jun 10, 2002 4:32 PM | | If these are going to dedicated road usage rims, then you want to get the narrowest, tallest, cross-section for the weight that you can find. Unless you are going to running narrow 1" slicks, it probably doesn't really matter what rim you use, because the airflow over a 2" knobby tire will be totally disrupted by the time it gets to the rim. Also, you'll very little practical benefit from aerodynamically optimized wheels if your speeds are under about 20 mph. Once you get in the 20-25mph, it really starts paying off to worry about cutting drag.
Then you have the practical issue of trying to fit narrow slick tires on wide rims. Not the best combo. Your X517 is actually a pretty good choice for a "road" set-up. Velocity's AeroHeat AT is heavier at around 440g, but has a relatively tall, smooth profile for a MTB rim. Sun's new UFO rim might be perfect since it is tall and skinny and pretty light at 425g. Not sure about availability on those. The true aero-weenie would run a Velocity Deep Vee, which is 30mm deep and super-slick aerodynamically, but those are hefty! |
| Wider and lower is the opposite of aero. | bullet
Jun 10, 2002 5:49 PM | | Bianchi4Me, that came out a little wrong,,,
i should have mentioned that i run 1.25-1.6 semi-slick and im trying to loose that ballon look you get from most rims with semi wide tires... i could mount 1" slicks but whats the point in riding a mtb then?(i feel more secure for the riding style and streets i ride being on a mtb but i want it to be fast, fast as possible, if i could ride 80 i would, and usually end up at places you dont take your road bike to.)
i want that road wheel look that the tire is equal wide as the rim only in a sligtly wider version... having a more rounded wheelset design pays off even in wider dimensions i believe so i dont think useing a wider rims hurts to much when its under the tire width-
second, what i meant with a low profile rim is for the rim brake surface and not the rim in general, i mean the usual brake surface on most rims looks to be designed for those old chunk brake pads that were used for cantilever brakes, the pads have almost lost x2 the height and so should the rims in having a more neat aero design...
I dont mind a high rim in general but it usually gets expensive, so im mainly just looking for a wider low profile rim :)
Well, ive been thinking about building a Hugi240-Valiant setup since i got a deal on $300 for it... so if theres anything thats good out there under this price im interested. ill check out the VelocityDeeVee. |
| Wider and lower is the opposite of aero. | bullet
Jun 10, 2002 6:12 PM | | something like this in a wide 26" version would be the thing..
Mavic CXP33 700c |
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