Reusing a slightly tacoed rim?

[[email protected]]

I recently had a low speed crash that tacoed my rear wheel slightly.
Since I had trouble truing the wheel afterwards, I changed the rim.
The tacoed rim is a fairly new Mavic CXP 33, which is a nice but
expensive rim, so I would like to know whether it is possible to
salvage the rim and how to do it.
When i place the rim on a flat surface one half of the rim lies flat,
while the other half buckle upwards perhaps 5-7 mm at its worst.

I have tried to press the rim by holding it at 6 and 3 o'clock and
while applying force at the 12 o'clock position. It only seems to make
matters worse. So here I am asking you what to do.

Should I:
1. Sandwhich the tacoed rim between to straight rims /spare wheels,
and squeeze them together using clamps and zip-ties?

2. Put the rim on a flat surface and hammer it straight with a rubber
mallet?

3. Put the rim on a flat surface, place a piece of wood on top of the
bend, and hammer it straight with a rubber mallet?

4. Give it up, since it never will be a good rim again, and therefore
very hard to build a new wheel with.

--
Regards

Peter S.

 

[Phil, Non-Squid]

[email protected] wrote:
> I recently had a low speed crash that tacoed my rear wheel slightly.
> Since I had trouble truing the wheel afterwards, I changed the rim.
> The tacoed rim is a fairly new Mavic CXP 33, which is a nice but
> expensive rim, so I would like to know whether it is possible to
> salvage the rim and how to do it.
> When i place the rim on a flat surface one half of the rim lies flat,
> while the other half buckle upwards perhaps 5-7 mm at its worst.
>
> I have tried to press the rim by holding it at 6 and 3 o'clock and
> while applying force at the 12 o'clock position. It only seems to make
> matters worse. So here I am asking you what to do.
>
> Should I:
> 1. Sandwhich the tacoed rim between to straight rims /spare wheels,
> and squeeze them together using clamps and zip-ties?
>
> 2. Put the rim on a flat surface and hammer it straight with a rubber
> mallet?
>
> 3. Put the rim on a flat surface, place a piece of wood on top of the
> bend, and hammer it straight with a rubber mallet?
>
> 4. Give it up, since it never will be a good rim again, and therefore
> very hard to build a new wheel with.

Use two blocks of wood lying down, both 90 degrees away from the bend.
Place the rim on those blocks with the bent part upwards (so that the rim
bends towards the sky). Use force to bend the upwards bend back down. Use
light force and make small corrections and retest with a flat floor or
existing good wheel. You should be able to get things down to a < 3mm
wobble which will then build up in to a true wheel without too much
differing spoke tension.
--
Phil

 

[[email protected]]

Peter S? writes:

> I recently had a low speed crash that tacoed my rear wheel slightly.
> Since I had trouble truing the wheel afterward, I changed the rim.
> The tacoed rim is a fairly new Mavic CXP 33, which is a nice but
> expensive rim, so I would like to know whether it is possible to
> salvage the rim and how to do it.

> When I place the rim on a flat surface one half of the rim lies
> flat, while the other half buckle upward perhaps 5-7 mm at its
> worst.

> I have tried to press the rim by holding it at 6 and 3 o'clock and
> while applying force at the 12 o'clock position. It only seems to
> make matters worse. So here I am asking you what to do.

> Should I:

> 1. Sandwich the tacoed rim between to straight rims /spare wheels,
> and squeeze them together using clamps and zip-ties?

> 2. Put the rim on a flat surface and hammer it straight with a
> rubber mallet?

> 3. Put the rim on a flat surface, place a piece of wood on top of
> the bend, and hammer it straight with a rubber mallet?

> 4. Give it up, since it never will be a good rim again, and
> therefore very hard to build a new wheel with.

Don't try straightening the rim when it is un-spoked. Straighten it
when it is a wheel and the spokes are not slack but not tight. When
you have the wheel in that condition follow the procedure described
and shown in picture in "the Bicycle Wheel" The warp you describe
sounds minimal and easy to fix. Do it!

Jobst Brandt

 

[[email protected]]

Phil Lee writes:

>> I recently had a low speed crash that tacoed my rear wheel
>> slightly. Since I had trouble truing the wheel afterward, I
>> changed the rim. The tacoed rim is a fairly new Mavic CXP 33,
>> which is a nice but expensive rim, so I would like to know whether
>> it is possible to salvage the rim and how to do it.

>> When i place the rim on a flat surface one half of the rim lies
>> flat, while the other half buckle upward perhaps 5-7 mm at its
>> worst.

>> I have tried to press the rim by holding it at 6 and 3 o'clock and
>> while applying force at the 12 o'clock position. It only seems to
>> make matters worse. So here I am asking you what to do.

>> Should I:

>> 1. Sandwich the tacoed rim between to straight rims /spare wheels,
>> and squeeze them together using clamps and zip-ties?

>> 2. Put the rim on a flat surface and hammer it straight with a
>> rubber mallet?

>> 3. Put the rim on a flat surface, place a piece of wood on top of
>> the bend, and hammer it straight with a rubber mallet?

>> 4. Give it up, since it never will be a good rim again, and
>> therefore very hard to build a new wheel with.

> Use two blocks of wood lying down, both 90 degrees away from the
> bend. Place the rim on those blocks with the bent part upward (so
> that the rim bends toward the sky). Use force to bend the upward
> bend back down. Use light force and make small corrections and
> retest with a flat floor or existing good wheel. You should be able
> to get things down to a < 3mm wobble which will then build up in to
> a true wheel without too much differing spoke tension.

Don't do that if you want to reuse that rim. Spoke it up and do it
right.

Jobst Brandt

 

[[email protected]]

On 22 Feb., 20:39, [email protected] wrote:

> Don't try straightening the rim when it is un-spoked.

Too late. Just tried the above method. Didn't work for me though;
Sometimes the applied pressure made bend even worse than before. The
process was very counterintuitive regarding results, so I gave up,
hopefully before I did too much damage.

> Straighten it
> when it is a wheel and the spokes are not slack but not tight. When
> you have the wheel in that condition follow the procedure described
> and shown in picture in "the Bicycle Wheel"

I actually ordered you book two weeks ago (it is hard to get in
Europe). Never occurred to me that it could contain a section on this
before I posted. Now I just have to wait 2-4 weeks before I get the
book though.

> The warp you describe
> sounds minimal and easy to fix. Do it!
>
> Jobst Brandt

Thanks for the encouragement.

--
Peter S.

 

[[email protected]]

Peter S? writes:

>> Don't try straightening the rim when it is un-spoked.

> Too late. Just tried the above method. Didn't work for me though;
> Sometimes the applied pressure made bend even worse than before. The
> process was very counterintuitive regarding results, so I gave up,
> hopefully before I did too much damage.

>> Straighten it when it is a wheel and the spokes are not slack but
>> not tight. When you have the wheel in that condition follow the
>> procedure described and shown in picture in "the Bicycle Wheel"

> I actually ordered you book two weeks ago (it is hard to get in
> Europe). Never occurred to me that it could contain a section on
> this before I posted. Now I just have to wait 2-4 weeks before I get
> the book though.

>> The warp you describe sounds minimal and easy to fix. Do it!

> Thanks for the encouragement.

Just in case you can visualize this, let me describe the method, one
with which I have rescued riders with bent wheels on my rides in the
Alps. Riders who believed they couldn't continue without a new wheel.

http://www.trentobike.org/Countries/Europe/Tour_Reports/Tour_of_the_Alps/

With the spokes moderately tightened, lay the wheel with the largest
wobble downward against the floor. Press down with hands on either
side of this wobble over a span of a bit less than 1/4 circumference
from which you should get an over center type response as the wheel
warps. Do this lightly checking for how much you advanced each time
until it is close to straight. If the wheel is tightly spoked, this
may require more force, so put your knees on the rim between your
hands an lunge on it... carefully. When it looks fairly straight,
finish it by spoke adjustment (truing the wheel) as you make it tight.

The reason this is done with a whole wheel is that the rim will not
respond to straightening in a clamp and will most likely become
unround as well. With the spokes holding the rim, it responds
entirely different from a bare rim. I don't know what your preferred
language is, but the book is also available in German from:

Craig Maynard <[email protected]>

Jobst Brandt

 

[John Everett]

On 22 Feb 2007 10:24:14 -0800, [email protected] wrote:

>I recently had a low speed crash that tacoed my rear wheel slightly.
>Since I had trouble truing the wheel afterwards, I changed the rim.
>The tacoed rim is a fairly new Mavic CXP 33, which is a nice but
>expensive rim, so I would like to know whether it is possible to
>salvage the rim and how to do it.
>When i place the rim on a flat surface one half of the rim lies flat,
>while the other half buckle upwards perhaps 5-7 mm at its worst.
>
>I have tried to press the rim by holding it at 6 and 3 o'clock and
>while applying force at the 12 o'clock position. It only seems to make
>matters worse. So here I am asking you what to do.
>
>Should I:
>1. Sandwhich the tacoed rim between to straight rims /spare wheels,
>and squeeze them together using clamps and zip-ties?
>
>2. Put the rim on a flat surface and hammer it straight with a rubber
>mallet?
>
>3. Put the rim on a flat surface, place a piece of wood on top of the
>bend, and hammer it straight with a rubber mallet?
>
>4. Give it up, since it never will be a good rim again, and therefore
>very hard to build a new wheel with.

Here's what I did with a rim that was worse than yours:

In spite of Jobst's advice I unlaced the rim. I layed it down on the
floor (carpeted) convex side up. I shimmed under the rim at the point
of most bend, about an inch, also padded with carpet. I stood on the
two high points and bounced up and down. I then checked the results on
a flat surface, my coffee table. It took a couple of iterations but I
got the rim flat to within a millimeter or so.

It's been back on my touring bike for two full seasons now without
problems.


--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)

 

[[email protected]]

John Everett writes:

>> I recently had a low speed crash that tacoed my rear wheel
>> slightly. Since I had trouble truing the wheel afterward, I
>> changed the rim. The tacoed rim is a fairly new Mavic CXP 33,
>> which is a nice but expensive rim, so I would like to know whether
>> it is possible to salvage the rim and how to do it. When i place
>> the rim on a flat surface one half of the rim lies flat, while the
>> other half buckle upward perhaps 5-7 mm at its worst.

>> I have tried to press the rim by holding it at 6 and 3 o'clock and
>> while applying force at the 12 o'clock position. It only seems to
>> make matters worse. So here I am asking you what to do.

>> Should I:

>> 1. Sandwich the tacoed rim between to straight rims /spare wheels,
>> and squeeze them together using clamps and zip-ties?

>> 2. Put the rim on a flat surface and hammer it straight with a
>> rubber mallet?

>> 3. Put the rim on a flat surface, place a piece of wood on top of
>> the bend, and hammer it straight with a rubber mallet?

>> 4. Give it up, since it never will be a good rim again, and
>> therefore very hard to build a new wheel with.

> Here's what I did with a rim that was worse than yours:

> In spite of Jobst's advice I unlaced the rim. I laid it down on the
> floor (carpeted) convex side up. I shimmed under the rim at the
> point of most bend, about an inch, also padded with carpet. I stood
> on the two high points and bounced up and down. I then checked the
> results on a flat surface, my coffee table. It took a couple of
> iterations but I got the rim flat to within a millimeter or so.

That's a lot more spoking than I want to do if it is not necessary.
What I don't understand is pressing the rim against a flat surface
won't get it straight with no overshoot to counter spring-back. To
select appropriate shims to achieve necessary overshoot seems another
problem. Straightening with a whole wheel is simple and doesn't
require any shims.

> It's been back on my touring bike for two full seasons now without
> problems.

I'm glad you were able to make it work. Next time, it there is one,
try the wheel bending method.

Jobst Brandt

 

[John Everett]

On 23 Feb 2007 18:58:27 GMT, [email protected] wrote:

>John Everett writes:
>
>> Here's what I did with a rim that was worse than yours:
>
>> In spite of Jobst's advice I unlaced the rim. I laid it down on the
>> floor (carpeted) convex side up. I shimmed under the rim at the
>> point of most bend, about an inch, also padded with carpet. I stood
>> on the two high points and bounced up and down. I then checked the
>> results on a flat surface, my coffee table. It took a couple of
>> iterations but I got the rim flat to within a millimeter or so.
>
>That's a lot more spoking than I want to do if it is not necessary.
>What I don't understand is pressing the rim against a flat surface
>won't get it straight with no overshoot to counter spring-back. To
>select appropriate shims to achieve necessary overshoot seems another
>problem. Straightening with a whole wheel is simple and doesn't
>require any shims.

As with any story it's actually a bit more complicated. I unlaced it
and took it to my local Fuji dealer to order a replacement. Turns out
Alex DA16s just aren't available in the US. So before deciding on a
replacement I though "what the heck, it's worth trying to straighten
it." Thus the brute force and ingorance method. I never changed the
height of the shim. I just kept bouncing harder until I acheived
success.


--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)