Today I compared a Mavic Cosmic Carbone rear road wheel and a Mavic CrossMax ST D MTB wheel against a 60 and 90 mm HED rear Stingers.
When you turn with your fingers (like when turning a knob) the hub axle of these wheels, it takes considerably more force to turn the HED axles than the Mavic axles. The difference is so much that it surprised me and left me wondering if you can save some watts using the Mavic hub.
I can imagine that the first thing to consider is how these two hubs compare under load and that maybe this is not a good way to compare wheel hubs, But again I was surprised… and I have to confess a little bit worried. My kid loves his HED Stinger 60/60/90mm set and I think that they are great wheels but the difference is so much that he also raised his eyebrows and put a worried face when he felt the differences.
I will appreciate your comments regarding this anecdote.
This is something that came up when one of the ST posters (i think jens) was commenting on Zipp ceramic bearing performance compared to Zipp steel bearing performance and possibly aftermarket (cheaper) ceramic bearing performance in hubs. The free spin to stop times were measured and the differences were significant. But on the bike performance differences were so small as to appear to be insignificant.
It was then speculated the measuring bearing performance when there was no bearing load and believing that these measurements were equivalent to bearing performance when bearings were loaded was making a serious scientific error. An engineer type (PhD?) then posted that this was in fact true that bearing performance had to be evaluated under real world conditions (bearings loaded) and that spin tests with no loads were in fact meaningless.
Now let and advertising or marketing type get ahold of this free spin test data and that although the differences are significant and real, those differences could be used to influence wheel purchasing decisions in spite of the fact that after the bearings were loaded the differences in bearing performance at real world speeds were closer to insignificant!
Would the increased mass of the stingers not have a greater effect on the amount of power required to initiate the movement be greater than that at the bearings? I would imagine that being true for the Crossmax against the Stingers and think it seems reasonable to assume that since the disc carries a more constant mass from the hub to the rim that this would be true in that case also.
Julian, the comparison I did yesterday was at the hub axle, not spinning the wheel. If you turn the end of the axle of the Mavic and the HED hub in the same way that you turn the volumen knob of a radio, you will see that the HED axle is considerably harder to turn. I agree that once you get rolling, this difference might be negligibly.
Yes, rotational mass of the rim, aero ability and structure of the spokes, and construction would all affect the ‘free spin’ of the bearings hence the reason why the test is meaningless if ‘smoothness’ is being evaluated.
It depends on the type. Arguably since the mass of a disc is greater than a wheel (generally), its rotational inertia dictates things anyway and would take more energy to get going although, again, aerodynamics would play a part in this and therefore distort the results.
I think the summary here is basically wheels should be tested under load but in the real world environment this isn’t realisitic to get consistant methodology.
I do know of some TT’er that strip their bearings and replace grease with a light motor oil and play with bearing cup adjustment. I have no data or information on what difference bearing design actually means in current availalble products though. Josh from Zipp would be a good man to ask on this one…
It was a constancy of the mass through the area of the disc that lead me to that conclusion, thanks for clearing that up. Did you see Xterra UK yesterday?
No. That channel wasn’t free to NTL - only sky sports news. I wasn’t happy.
On the bearings thing, my smoothest running wheel I own is my old clincher Hed 3. the fact it’s aero and relatively heavy at the rim is probably no coincidence. Yes, in a moment of boredom I checked this last year…
I would also be curious how old the respective hubs you spun were? I’ve heard anecdotally that certain hubs are “packed” tighter than others and that it takes a period of time to “break them in” … I don’t know if this has any effect on what you found, but I imagine that wear on the bearings plays a role in how freely they spin. Might also the tightness of the bearings have some effect on how quickly the hub engages? I.e., a tighter set of bearings is more responsive to each pedal stroke??? I don’t really know the answer to these questions, as I am not a mechanical expert by any means, but I’d be curious to know what others might think.
Yes, thanks to Gerard (again) I now see another bike is on the market to clear out my bank account with. It will be interesting to see what starts coming out when the Flemish classics get underway though. I intend to go with a similar build due to my riding ‘style’
