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Old May 21st, 2016, 10:03 AM   #22
Armadillo
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Location: Chicago, Near the Lake
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Quote:
Originally Posted by Mort View Post
Here we go again. : /

If you were right about the roll line style wheels being so fast and good, why do long boarders who are after downhill speed use wheels with such thick urethane that "steals energy"?

Sometime tomorrow Ill be taking the roll lines vs atom poisons vs road hogs on several different surfaces. Finally got some time off work.

This "wave" is real. Its what happens when you roll over a surface. I never said that it propelled you. What happens is the urethane absorbs imperfect road and skating surfaces of outdoors, smoothing out the ride immensely. The roll lines cannot do this because the urethame is so flippin thin. The moment it starts to deflect/deform, its already at its limit for compression, everything else becomes vertical lift or it damages the urethanes crosslinking. Ontop of that the urethane doesnt seem to be very good, just from dropping a wheel you can see the energy potential of a wheel to maintain its roll. Good wheels bounce like crazy. Poor quality urethane wheels don't.

The wave of pressure and deflection travels around the wheel and inwards to the hub, since the wheels have ridges inside there if the urethane is thin , even on smooth ground mind you its like riding over a bunch of small ridges. This again falls back to the urethane being too thin. Simply put , the compressive wave has nowhere to go. If you watch iceroad truckers, you can see how compressive waves work as a semi drives across a road of ice. Granted its not the exact same, but the wave is there and the radial energy absorbed and ultimately consumed by such a thin layer is more in the roll lines than in any other wheel I have skated on outdoors.

To be fair ill test them thoroughly tomorrow.
It's NOT compressive, but I can confirm that the "squirm" wave is real, and since urethane does not compress, if the TENSION stress developed from the pinch against the hub goes too high, the urethane will squirm too far circumfrentially, and then the debonding of the urethane starts to happen, along with internal damage, just as mort indicates.

Once the debonding gets wide enough it quickly spreads across the wheel and eventually around it as well. The wheels start to make a horrible sound and they suck up rolling energy too. I have plenty of RD Twisters with this debonded condition.

Attempts to re-glue them onto hubs proved futile. Perhaps a non-solvent based urethane is needed. I haven't resumed that project yet.

On a totally debonded wheel, it feels like driving a car on a flat tire. The ring of urethane starts to be dragged all the way around the hub after so many revolutions (if hub has no protruding grip ribs).

Urethane gets damaged internally and swells up by ~5% starting at edges.
I have watched a lot of wheels with too-thin urethane layer cycle through this degradation process. All had 49mm size hubs and started new at 65mm or less urethane to give 7.5-8mm layer thickness. By the time they wore down to around 62-63mm size, death was knockin' on their doors.

IMO, 10mm should be the minimum thickness for urethane layer of outdoor wheels, and that will not give much life for them either. For 500+ miles of service and the typical urethane wear that will give, a better target would be 12mm of urethane layer, so that one or two mm can be lost without sinkung below 10mm.

-Armadillo
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