From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: When to Change the Rim?
Date: 28 Apr 2000 21:25:51 GMT

Tom Nakashima writes:

> I just purchased a new set of Mavic MA-2 rims, knowing one of these
> days I'll have to replace them, plus they were at a great price.  I
> took a 1" mic and measured the thickness of the new rim and
> compared it to my 3 year old Mavic MA-2 set that's on the bike.  The
> rim on my bike measures .790" in thickness, while the new rim
> measures .800".  Seems as though I have worn off .005" of each side
> of the rim due to braking.  I've been taking good care of my wheels,
> making sure they're well tuned.  Just not sure now thin you can wear
> a rim before it becomes dangerous to ride on.  Anyone have the
> answer to this?  Has anyone wore a rim down to beyond the safe zone?

The MA-2 is 1.5mm thick in that area when new (0.060").  I have ridden
them to less than 0.5mm (0.020") and do not recommend it.  I think
0.5mm is the limit but in my case, I was riding in the Alps in the
rain and each descent from a high pass ate another 0.1mm or so from
the rim.  I descended the Stelvio in the rain on the rear brake alone
because I was certain that I would split the rim if I used the front
brake on the hollow cheeked rim.  After returning home and sectioning
the rim, I discovered how correct I was in estimating the condition by
the feel of running my thumb and index finger across the cusp in the
rim sidewalls in the manner of a caliper.

I think you have a long way to go.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Rim Wear Question
Date: 23 Aug 2000 21:26:26 GMT

Erik Brooks writes:

>> All of that extra rain can wear through rims quickly.

> Amen to that - Last winter seemed unusually dry in town.  Two years
> ago I also had an 'incident' where the rim blew out due to neglect
> of sidewall thickness.  I wasn't hurt, but I'll watch it more
> carefully from now on.

As I said, the observant rider can probably feel the state of the
rims by making a caliper of thumb and forefinger to rub up and down
over the brake surface.  To me the hollowness is so easily felt that I
don't worry about measuring my MA-2's.

>> Rinsing off the rims doesn't do a whole lot of good, because the
>> next ride in the rain will pick up a lot of grit again.

> I think that seems like a good idea, actually.  If it rained every
> day, like it seemed to 2 winters ago, I'd agree it's useless.  But
> if it doesn't rain for several rides, I'd think it would help with
> rim wear.

> Question - am I correct to think that a greater problem is the grit
> that gets embedded in the brake pads?  Harder to clean, of course.

Riding with embedded grit in the pads is OUT in the first place and
has little to do with wet weather induced rim wear.  That eats rims
even in the dry.  Embedded abrasives is why you should use Kool-Stop
pads.  Road water contains a slurry of fine sand that is even more
prevalent in mountains where the gradient makes roadside water run
down and across the road.  It is this continually supplied road slurry
that eats rims and there is little you can do about it.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims don't *all* suck
Newsgroups: rec.bicycles.tech
Message-ID: <15t0c.4641$_3.72637@typhoon.sonic.net>
Date: Sun, 29 Feb 2004 21:46:37 GMT

Carl Fogel writes:

> Jobst, do you (or anyone else) have any close-up pictures of
> brake-wear failures on unanodized rims that could be put up for
> comparison with Dave's rim pictures? The ones of the Mavic 221,
> although dramatic, aren't nearly detailed enough to show the edges
> where things tore.

I don't have any among all the worn and dented rims in my collection,
none of which are anodized.  The claim that rims bend outwards when
they wear thin, in my experience, is an incorrect assessment.  These
rims have been worn hollow and to casual observance appear to be
flared out.  My worn out rims looked that way too but were in fact
unchanged when measured internally.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: mavic rims don't *all* suck
Newsgroups: rec.bicycles.tech
Message-ID: <VlR0c.5012$_3.76806@typhoon.sonic.net>
Date: Tue, 02 Mar 2004 01:23:01 GMT

A points to consider about rim failures:

If a rim flares from too thinly worn sidewalls, then it must be
operating at yield stress, a condition that WILL cause failure in a
few thousand loaded wheel rotations.  That is about three to six
kilometers.  The tendency to spread rim sidewalls is also largely
affected by tire size and pressure, larger cross section tire casings
pulling on the rim at a lower (more lateral) angle.

Having ridden minimal thickness rims for more than 500 km without
failure, I am convinced that inflation pressure and rolling forces are
not the culprit and that they are insignificant for a 25mm cross
section tire.  Changing wire bead, closely fitting tires also has not
caused rim deformation.

Jobst Brandt
jobst.brandt@stanfordalumni.org