Re: [CR]Bearing quality still an issue.

(Example: Framebuilders:Doug Fattic)

Date: Sat, 14 Jul 2001 22:34:20 -0400
To: "garth libre" <rabbitman@mindspring.com>, <classicrendezvous@bikelist.org>
From: "Harvey M Sachs" <sachs@erols.com>
Subject: Re: [CR]Bearing quality still an issue.
In-Reply-To: <000801c10cbd$0b78c160$68b256d1@Marta>


At 19:29 7/14/2001 -0400, garth libre wrote:
>Like so many other bike enthusiasts, I do all or most all of regular bike
>maintenance myself. I have found, as no doubt have many others, that
>modern manufacturing processes have not really perfected the bearing
>quality of mid-range bike gruppos.

<snip>
> Of the half dozen Japanese-equipped bikes I have worked on in the last
> twenty years, the bearing quality has been uniformly so so and not up to
> Campy Record or Dura Ace or Suntour Superbe standards. On most of these
> Japanese parts, the sweet spot is a very narrow area, and it may take me
> several tries to get it right on, where it feels somewhat smooth and
> still has miniscule or no play. (I prefer no play).

I think that there are two separate issues Garth is raising:

1) Adjustment capability. The older Campys and outstanding Japanese hubs I've owned have had very concave cone faces, and contacts fairly low on the face of the cone. In that range, there is more turn of cone on hub per unit of advance along the axle than with a straight-cut cone. That accounts, I expect, for the sense that one can adjust more finely.

2) Hitting the "sweet spot." Garth remarks that he likes "miniscule or no play." Jim Papadopoulos, a fine engineer, showed me an old experiment once that is an eye-opener. Take a hub, and adjust it to that point. Now, put on the QR, with a stack of washers instead of the dropouts. Or put the hub into a frame. Clamp it down. You actually shorten the distance between the cones by tensioning the skewer. The point is that hubs not adjusted a leeeetle beeeet loose will be "preloaded". Harder to turn. What I don't know is whether that really is bad for the bearings, or "good" in preventing chatter and brinneling. Just seems that the answers aren't obvious at my level - a decent wrench but not an engineer.

BTW, you have to do the experiment with a naked hub. A built wheel has so much more inertia that you just can't feel differences until the bearing is really out of whack.

just my 2c...

harvey "clumsy" sachs
mclean va