Weird bearing drag at high speeds ??

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LouisN
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Joined: Mon Feb 19, 2007 3:44 am
Location: Canada

by LouisN

Yesterday I experienced something weird when riding.

When riding on a fast descent, at roughly 75-80 km/h, I felt the bike slowing down, just like if the brakes were on.

Checked for the latter, nothing, brake pads weren't touching anything.

At the bottom of the descent, when the speed came down to 35-40 km/h, everything back to normal :noidea: ...

I checked for bearing "feel" by rolling them in my hands, they are smooth as butter. DtSwiss 240S rear and Alchemy ELF front.

The hubs have approximately 10 000 km, never touched them yet.

Could it be the vibration ( from speed) that caused friction in the bearings ?
Should I overhaul the bearings ( hubs and freehub) even if they still "feel" like butter smooth ?

scratching my head...thanks for the heads up !!

Louis :)

alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Maybe balance the wheels, ensure that they are true and have good spacing between pads and rims.

At those kinds of speeds I think it's hard to be perceptive enough to notice even simple inbalances. Also take in mind that the speed often can amplify whatever small and negligable inbalance thay may otherwise exist.

Wind resistance is probably 90% of your total resistance at that speed so the odds are against you that it's your bike that's significantly slowing you down. Maybe you just lost weight and your flapping clothes together with less weight to accelerate you is the explanation. :D

/a

by Weenie


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wheelsONfire
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by wheelsONfire

Perhaps deflection of the rim/ rims, making them touching brake pads?
Wind pressure at such high speeds can probably induce great force on rims, causing deflection.
How about trying to use a bit larger gap between brake pads and rims?
Bearings should not be affected in an on/ off manner if they aren't damaged. But then again, the wheels wouldn't roll so well as you describe if bearings actually were damaged.
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perwjensen
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by perwjensen

It's entirely possible that a piece (dirt, broken seal or other) could have been stuck in the ball race and then cleared out. I would change the bearings if it was me, as a precaution. You could risk a full blockage next time.

RyanH
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by RyanH

This is speculation but if there was something going on that was capable of noticeably slowing you down at that speed, I'd think it'd get pretty hot at the end of the descent so you may want to check there.

MiddMan
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Joined: Sun Jun 07, 2015 4:54 pm

by MiddMan

Was the pavement the same all the way down? If it was a forceful braking feeling then never mind, it's a moot point, but otherwise a change in pavement types might also have an effect on perceived (and actual) speed.

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bm0p700f
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by bm0p700f

It wpnt be the bearings. They cant produce higher drag for a short time. If they are smooth they are fine. a piece of grit wont change rolling resistance enough anyway.

More likey a change in wind conditions or road surface is the cause.

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