Deep-V imminent rim failure

I've gotten damage like this when riding with a flat; the sidewalls of the
rim seem less heavily built than others I've used. I would suspect impact
damage rather than failure. I think Velocity picked a poor place to save
weight in that design,.

"Nick Payne" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less
braking than the front rim. While servicing the bike I noticed two places
like this, about 45 degrees apart on the rim, and both on the left side,
where the top of the braking surface has bulged out (according to my
calipers the rim width at that point is about 0.5mm more than elsewhere).
Even when the tyre is deflated the rim still bulges at those two points.

I measured the width of the braking surface at several other points and
compared this with the unused rim that I bought at the same time and kept
as a spare (40-hole rims weren't easy to get), and there is less than
0.1mm of wear per side from braking, so this doesn't seem to be a failure
due to excessive wear of the brake track. I suspect that the final
machining of the brake track has left a couple of places in the rim wall
where there was so little material that the rim has started to bulge due
to tyre pressure, which leads to more wear at that point from the brake
blocks, and more bulging, and more wear, and so on. However, the tyres we
use are 700x28, and as we only weigh a bit less than 120kg for the pair of
us, I only inflate them to 105psi by the gauge on my track pump, so I'm
rather surprised that this has happened. The front rim (also a Deep-V rim,
same tyre, same tyre pressure) shows no such problem.

Not for nothing can rims with machined sidewalls be described as
"pre-worn".

Nick Payne

I suspect impact damage as well although the rim wall was probably weak
to start. The bend looks very similar to what I had on a rear rim once
after crossing some tracks even though I didn't get a pinch flat.

Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg

Bummer of a failure on a tandem! Although the wider tire makes sense
for a tandem, it adds bending force to the rim, even though 105psi
doesn't seem like "overinflation".

In my experience with these rims on single bikes, the sidewalls are a
little weaker than other rims. I've seen slight bulges similar to
yours, even though the rider hadn't pinch flatted either.

When I've sawed sections out, the Velocity Deep V and Aerohead rims
I've looked at have two characteristics that may partially explain
this:
1. Thinner side walls than other rims, and
2. Taller side walls (or deeper drop to the bead seat, however you want
to look at it).
Both of these design features add bending stress to the side wall.

As for machining, Velocity's process seems more consistent in thickness
than other brands. I'd have to section a few more rims to be more
certain. Maybe Velocity grinds instead of machines the side walls?
Anyway, even an unmachined rim, if it were forced to fail like this,
would initiate failure *somewhere* (i.e., not evenly everywhere). So in
my opinion the fact your rim is bulging in a few spots isn't necessaily
a condemnation of machining per se, but evidence of a combination of
factors.

If you're changing rims anyway, consider fewer than 40 spokes. With
thread locker and 30mm rims, tandems can use as few as 24 spokes, maybe
fewer. I've heard of some tandem teams using Vector Comps or Vector
Pros (20 or 16 spokes!).

Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less braking
than the front rim. While servicing the bike I noticed two places like this,
about 45 degrees apart on the rim, and both on the left side, where the top
of the braking surface has bulged out (according to my calipers the rim
width at that point is about 0.5mm more than elsewhere). Even when the tyre
is deflated the rim still bulges at those two points.

Sure looks like an impact bulge to me. I have never seen a DEEP V rim
bulge from tire pressure

Quoted message said:

Nick Payne

Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less braking
than the front rim. While servicing the bike I noticed two places like this,
about 45 degrees apart on the rim, and both on the left side, where the top
of the braking surface has bulged out (according to my calipers the rim
width at that point is about 0.5mm more than elsewhere). Even when the tyre
is deflated the rim still bulges at those two points.

Nick,

It's possible to do impact damage to a rim without pinch flatting; I've
done it - on the rear wheel of our tandem when I hit a particularly
nasty pothole at dusk (didn't see it coming). The tire never flatted,
though I was sure it would; however, we put a flat spot in that wheel
that bump-bumped at us for the rest of the ride.

Mark

Nick,

I use 36 hole Velocity Aero (Not Aerohead) rims on my tandem and
usually put 125 psi in the tires which are Continental Gatorskin
700x25. I have never had a problem with this setup. My wife and I weigh
about 250 lbs together. Can't comment on why your rim is failing but I
would not take any chances and quit using it as going down on tandem is
not recommended.

Joel

Nick,

I use 36 hole Velocity Aero (Not Aerohead) rims on my tandem and
usually put 125 psi in the tires which are Continental Gatorskin
700x25. I have never had a problem with this setup. My wife and I weigh
about 250 lbs together. Can't comment on why your rim is failing but I
would not take any chances and quit using it as going down on tandem is
not recommended.

Joel

Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less braking
than the front rim. While servicing the bike I noticed two places like this,
about 45 degrees apart on the rim, and both on the left side, where the top
of the braking surface has bulged out (according to my calipers the rim
width at that point is about 0.5mm more than elsewhere). Even when the tyre
is deflated the rim still bulges at those two points.

I measured the width of the braking surface at several other points and
compared this with the unused rim that I bought at the same time and kept as
a spare (40-hole rims weren't easy to get), and there is less than 0.1mm of
wear per side from braking, so this doesn't seem to be a failure due to
excessive wear of the brake track. I suspect that the final machining of the
brake track has left a couple of places in the rim wall where there was so
little material that the rim has started to bulge due to tyre pressure,
which leads to more wear at that point from the brake blocks, and more
bulging, and more wear, and so on. However, the tyres we use are 700x28, and
as we only weigh a bit less than 120kg for the pair of us, I only inflate
them to 105psi by the gauge on my track pump, so I'm rather surprised that
this has happened. The front rim (also a Deep-V rim, same tyre, same tyre
pressure) shows no such problem.

Not for nothing can rims with machined sidewalls be described as "pre-worn".

Nick Payne

My experience with Deep V rims is that they have very consistant sidewall thickness, but a rather tall sidewall.
The non-machined silver anodized version has thicker sidewalls, but doesn't seem to be available in drillings other than 32H.
I know it wouldn't be a cosmetic match, but the best rim I have found for tandems and touring is Velocity Dyad. Dyad is suitable for 28 mm and wider tires.
I agree with the other responders about impacts being the cause for your sidewall bulges. Now that the bulges are there your brakes will work at bringing them in, and thus thinning the walls at that point and making further bulging (and blowing off of the tire) eventual.

Nick Payne wrote:
<snip>

Quoted message said:

Not for nothing can rims with machined sidewalls be described as "pre-worn".

"pre-worn"??? that pre-supposes unbelievable incompetency in not making
the original extrusion thicker to compensate for the material lost in
machining. it's the kind of comment may suit those with some kind of
perverted "ma2" ax to grind, but it doesn't withstand the slightest
technical scrutiny.

Really? Unless the extrusion as made into a rim is extremely true to begin
with, the machining leaves a sidewall of uneven thickness. And if it's that
true to begin with, then the machining serves no purpose except to reduce
the life of the rim.

"jim beam" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Nick Payne wrote:
<snip>

Quoted message said:

Not for nothing can rims with machined sidewalls be described as
"pre-worn".

"pre-worn"??? that pre-supposes unbelievable incompetency in not making
the original extrusion thicker to compensate for the material lost in
machining. it's the kind of comment may suit those with some kind of
perverted "ma2" ax to grind, but it doesn't withstand the slightest
technical scrutiny.

Nick Payne said:

Quoted message said:

Quoted message said:

Not for nothing can rims with machined sidewalls be described as
"pre-worn".

Quoted message said:

Quoted message said:

"pre-worn"??? that pre-supposes unbelievable incompetency in not
making the original extrusion thicker to compensate for the
material lost in machining. it's the kind of comment may suit
those with some kind of perverted "ma2" ax to grind, but it doesn't
withstand the slightest technical scrutiny.

Quoted message said:

Really? Unless the extrusion as made into a rim is extremely true
to begin with, the machining leaves a sidewall of uneven thickness.
And if it's that true to begin with, then the machining serves no
purpose except to reduce the life of the rim.

Oh but there is another sinister reason for machining sidewalls, which
is to make an LP record of the braking surface using essentially a
fine thread cutting tool. Microgrooves help suppress squeal when a
customer applies the brakes on a new bicycle on a test ride in the
parking lot. In olden times Martano tubular rims were extruded with a
1mm square wave pattern for that purpose. Then as now the reason was
kept obscure, explained by a raft of non sequiturs.

In either case, the feature went away from braking on wet roads that
flush road abrasive into the brake interface and wear the rim to its
natural braking surface finish.

Jobst Brandt

Quoted message said:

Nick Payne said:

Quoted message said:

>Not for nothing can rims with machined sidewalls be described as
>"pre-worn".

Quoted message said:

Quoted message said:

"pre-worn"??? that pre-supposes unbelievable incompetency in not
making the original extrusion thicker to compensate for the
material lost in machining. it's the kind of comment may suit
those with some kind of perverted "ma2" ax to grind, but it doesn't
withstand the slightest technical scrutiny.

Quoted message said:

Really? Unless the extrusion as made into a rim is extremely true
to begin with, the machining leaves a sidewall of uneven thickness.
And if it's that true to begin with, then the machining serves no
purpose except to reduce the life of the rim.

Oh but there is another sinister reason for machining sidewalls, which
is to make an LP record of the braking surface using essentially a
fine thread cutting tool. Microgrooves help suppress squeal when a
customer applies the brakes on a new bicycle on a test ride in the
parking lot.

eh? jobst, you are the most ridiculous paranoid. before, you used to
say this "groove effect" was for the visual results. now it's squeal
suppression??? it's neither - if you knew much about machining, you'd
know about cutting tip profiles with materials that were prone to
pile-up and gouging, like those used in rims.

reality is simply that it requires a fine tip and production expediency
means we can't take all day doing it.

Quoted message said:

In olden times Martano tubular rims were extruded with a
1mm square wave pattern for that purpose. Then as now the reason was
kept obscure, explained by a raft of non sequiturs.

red herring.

Quoted message said:

In either case, the feature went away from braking on wet roads that
flush road abrasive into the brake interface and wear the rim to its
natural braking surface finish.

red herring. rims are machined to give 100% braking efficacy from day
one, /not/ relying on the rim/brake block wearing to a conformal fit.

Quoted message said:

Jobst Brandt

Nick Payne said:

Really? Unless the extrusion as made into a rim is extremely true to begin
with, the machining leaves a sidewall of uneven thickness. And if it's that
true to begin with, then the machining serves no purpose except to reduce
the life of the rim.

nick, section a rim and study the wall thickness of the machined area.
it's as thick, or even thicker in some cases, as some of the much
vaunted unmachined rims. as stated before, the purpose of machining is
to provide a flat surface onto which a brake pad can be 100% effective
from day one. if premature failure was the objective, a thinner
extrusion is a /much/ cheaper way of executing the conspiracy.

Quoted message said:

"jim beam" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Nick Payne wrote:
<snip>

Quoted message said:

Not for nothing can rims with machined sidewalls be described as
"pre-worn".

"pre-worn"??? that pre-supposes unbelievable incompetency in not making
the original extrusion thicker to compensate for the material lost in
machining. it's the kind of comment may suit those with some kind of
perverted "ma2" ax to grind, but it doesn't withstand the slightest
technical scrutiny.

Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less braking
than the front rim. While servicing the bike I noticed two places like this,
about 45 degrees apart on the rim, and both on the left side, where the top
of the braking surface has bulged out (according to my calipers the rim
width at that point is about 0.5mm more than elsewhere). Even when the tyre
is deflated the rim still bulges at those two points.

for whatever reason the rim isn't strong enough to hold back the tire
bead. this is usually how rims react when the sidewalls are worn out.
it isn't from an impact, those dings are much more localized.

-Amit

quote=''Nick Payne said:

See the photo at http://www.users.on.net/~njpayne/bikestuff/rimfailure.jpg
(198Kb). It's the Deep-V rear rim on our racing tandem, which hasn't gone
very far (about 3000km), has never been pinch flatted, and sees less braking
than the front rim. While servicing the bike I noticed two places like this,
about 45 degrees apart on the rim, and both on the left side, where the top
of the braking surface has bulged out (according to my calipers the rim
width at that point is about 0.5mm more than elsewhere). Even when the tyre
is deflated the rim still bulges at those two points.

for whatever reason the rim isn't strong enough to hold back the tire
bead. this is usually how rims react when the sidewalls are worn out.
it isn't from an impact, those dings are much more localized.

-Amit[/QUOTE]
I have seen impact damage that looks the same to me from a rear wheel that took a couple of 12" drops off curbs. The rider stayed seated and the tube didn't pinch flat. The wheel belongs to a neighbor who was "following" his son who was riding a new BMX bicycle. I saw the wheel before and after watching the spectacle. The wheel was fine before, but certainly not after.

Quoted message said:

Quoted message said:

-Amit

I have seen impact damage that looks the same to me from a rear wheel
that took a couple of 12" drops off curbs. The rider stayed seated and
the tube didn't pinch flat. The wheel belongs to a neighbor who was
"following" his son who was riding a new BMX bicycle. I saw the wheel
before and after watching the spectacle. The wheel was fine before,
but certainly not after.

i've never seen a rim get bent only at the bead from damage like that.
when the sidewall fails the damage follows the curve of the rim, from
an impact the dent would be some other shape at least, no ?

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

Quoted message said:

Quoted message said:

-Amit

I have seen impact damage that looks the same to me from a rear wheel
that took a couple of 12" drops off curbs. The rider stayed seated and
the tube didn't pinch flat. The wheel belongs to a neighbor who was
"following" his son who was riding a new BMX bicycle. I saw the wheel
before and after watching the spectacle. The wheel was fine before,
but certainly not after.

i've never seen a rim get bent only at the bead from damage like that.
when the sidewall fails the damage follows the curve of the rim, from
an impact the dent would be some other shape at least, no ?

Maybe both arguments are true? I think an impact deflection of the tyre
(but not enough to squash the tyre completely) would still cause the rim
spreading forces to increase because the angle the tyre sidewalls make to
the rim changes to a more outward spreading angle.

Mark Janeba said:

It's possible to do impact damage to a rim without pinch flatting; I've
done it - on the rear wheel of our tandem when I hit a particularly
nasty pothole at dusk (didn't see it coming). The tire never flatted,
though I was sure it would; however, we put a flat spot in that wheel
that bump-bumped at us for the rest of the ride.

I've done it too. As a matter of fact, the rim *cracked* and I didn't
pinch-flat. That rim must have been a real loser.

--
Dave
dvt at psu dot edu