Barchettaman

My commuter was hit by a bus yesterday and took a hefty bang on the back wheel.
It's too far out of true for my basic trueing skills, I'm wary of even attempting it.
As the wheel is nearly new, the hub/spokes/rim seem OK, I'd be seriously hacked off if I had to write it off.
Vertical true seems OK.

Is there a 'rule of thumb' for when a rim is too far gone?
Thanks all

PS the bike was parked when the bus hit it, so I'm OK!!

IthaDan 

does it hit the stays or just the brake pads? My experience says if it's within the width of the stays, you can get it back. Might take some whacking on the ground, but you can get it back to a rideable state.

Homebrew01

I prefer to carefully step on the rim while it's on the ground. Loosen all the area spokes first, rim bulge towards the ground, then step on each side, forcing the bulge back in.

If it's too far gone, buy a new rim with the same ERD, and swap it over. Tape the new rim too the old, and move each spoke over.

reptilezs

when the out of true spot is very abrupt and sharp, the rim is usually toast. a gentle curve can usually be pulled or banged back. i did have a college student with access to a shop press(went to an engineering school) and he pressed a mavic rim straight. the unlaced a mavic ksyrium pressed it flat and rebuilt it. not bad for 15 bucks he spent on the wheel

Zef

Typically a wheel is "too far gone" when the actual rim is bent beyond its elastic yield limit. Sometimes the rim can be bent back into shape with good results but this can cause work hardening and a weakened rim. Unless you face a budget constraint it may be most prudent to replace the rim.

With respect to ecomonmy of time the fastest approach would be to find an identical rim or one with the same ERD, tape the new rim to the old wheel and transfer the spokes over one at a time...then tension, true, and dish the new wheel.

-j

cny-bikeman

There is simply no rule of thumb that would apply except to extreme cases where the rim has been crushed or similar. It is dependent on the skill of the mechanic and the tolerance of the rider. As noted above when a rim has been physically bent, so that the spokes on the side toward the bend are loose and on the opposite side tight, it is not possible to true the wheel until the rim is bent back. Not everybody is skilled at rebending, not every attempt is successful, and in pretty much every case it is nowhere near "as good as new." The idea of transferring over to an identical rim is indeed the most straighforward, but even then you need to study wheel building a bit if you only have basic truing skills, as lacing a wheel is the most elementary part of building.

prathmann

I have gotten rims back to true even after they've been severely bent (i.e. not anywhere close to fitting through the frame) by unlacing them, bending them back into approximate flatness by clamping them and pulling on the bent section and then rebuilding the wheel. But I agree with 'Homebrew' that the best course is to buy a new rim of about the same ERD, tape it alongside the current wheel and then move the spokes over to rebuild. Even if you can reuse the old rim it'll never be as strong as it was, won't be as easy to true and won't stay true as well.

wroomwroomoops

As some have said already, even rims that have plastic deformations (i. e. not just elastic ones), can be salvaged. What I can say for almost sure, is that a missing spoke will make it impossible to true a wheel to satisfaction.

However, there are a few elite wheelbuilders around here, who will give you much more detailed answers.

bradtx

Barchettaman, My experience is similar to IthaDan's. If the wheel can still rotate within the stays and the rim's joint isn't involved, there is at least hope.

Brad

Barchettaman

Huge thanks to all for your responses, interesting stuff.
I will be back in Frankfurt next week & so will take the wheel to my LBS mech, along with a sixpack of fine Belgian beer, and see what he can do.
The rim is 'wavy' rather than suddenly out of true, IYKWIM.

Barchettaman

The rim does not foul the stays, but it ain't far off.

cny-bikeman

Again, not possible to tell to what degree it can be saved - even a mechanic with the wheel in hand cannot tell you ahead of time, nor can we tell you if you can do it yourself. All the "I did it, no problem" stories in the world will not tell you if you have the feel, instincts and knowledge to succeed. There are multiple techniques, none more valid than another. I've stood on wheels, whacked them (tire still on) on the ground, pushed out the bend with my hands on either side and the rim on the edge of a bench, levered them in a slot between benches (sometimes twisting if an asymmetrical bend) and hit them with a dead blow hammer. Creative Googling can show you a variety of approaches described.

Whether the rim save should even be attempted depends on what your needs are. If you are a commuter who depends on his bike to get to school or work, and especially if you are heavier or a harder rider, a saved wheel is less acceptable than if you occasionally ride short distances with no load.

You also have not described the circumstances. There are a variety of situations where you may be able to be compensated for the cost of repairing the bike. Don't do anything, especially on your own, until you determine what options are available. Should not be hard to find out - check with your insurance company and with the bus company - though deductibles can come into play if it is your own insurance. If you can prove the bus driver was at fault you have more than the bike that should be addressed. Of course this portion is better addressed in the Commuting or Safety and Advocacy forums.

HillRider

Will the bus company pay for a new wheel?

dsbrantjr

If the bike was legally parked when it was hit the bus company should fully compensate your loss. i.e new wheel or at least new rim properly assembled. I would not accept a repaired rim as a replacement for an almost-new one.

Perhaps if you remind the bus company how lucky they are that you were not on the bike when it was struck they will see the reasonableness of your request.

ka0use

if it looks like an infinity symbol you might start looking for a new one.

wroomwroomoops

All rims look like an infinity symbol - only some are very, very, very flat infinity symbols

mrrabbit 

1a. When the rim has general fatigue such that it cannot hold tension without buckling upon tube inflation and immediate use.
1b. When the rim can only remain true with the spokes considerably under-tensioned - which results in a non-functional wheel.
2. When the joint pins/sleeves have broken AND alignment of the rims ends cannot be maintained under tension.
3. When the holes have cracked such that the spokes for all effective purposes provide no support.

Rims can be unbent, untacoed, unflatspotted, unsqueezed, untwisted, unsplayed, etc...which is great and all. Miracles can happen...the miracle though depends upon 1-3 not being the case.

=8-)

mrrabbit 

Here's a question for everyone:

After all my years of building and re-building wheels, when it comes to "catastrophic" rim rescues, my experience has been that the success rate is much higher for single-wall rims.

That's just my off-the-head memory and observation...

So what's your guys observation/experience?

=8-)

FBinNY 

+1 Sharp local bends involve the rim having a set, and it takes far too much spoke tension difference to overcome that, especially on a strong rim. Some skilled mechanics can straighten the rim with brute force, then align the wheel close to perfect with much smaller spoke tension differences.

Large curves, like the classic potato shape, don't involve local bends in the rim itself, and can usually be trued perfect, with very tiny diferences in spoke tensions.

As far as to what't the worst that can be straightened, it depends on what you'll accept as a passable result. I've saved wheels that were out of true by well over 6" and some approaching one foot of total runout. As rule, a badly bent rim will never be perfect, but can usually be made very passable for use on a commuter or utility bike.

Dan Burkhart 

My observation/experience is that for the wholesale price of a new rim, it ain't worth the time to try when measured against the best expected result.

FBinNY 

I've done better with double wall rims which seem to have much less tendency to twist -- one flange higher than the other, even when the rim is true -- When single wall rims are bent badly, twist becomes one more thing to manage. However, I find that lighter rims are much easier to work with because of their lower resistance to the spokes' forces.

As to what's worth saving, it depends on circumstances. I once had to save a rim folded nearly in half after a crash. It was when leading a tour, and there wasn't much choice. Straightened it by levering it in a grating until it was decent, then aligning. The rim cracked part way through, but survived 200 miles until we could get a replacement. At home, I would have simply written it off.

3alarmer 

To all of the preceding, I would only add that mostly it is a call made by
simplifying the complex equation of:

Your own skills vs the value of your time to you vs the cost of the skills you're hiring.

Materials costs are minimal for a fix of this nature, so I see a lot of time devoted to
truing wheels at the bike coop that I,personally, would not mess with.

But when I was a lot poorer and younger, I mostly rode on wheels that people gave
up on, so there really is no rule of the sort you are looking for.

If you're gonna ride this for a while (and it is your commuter), you're almost always
better off devoting the time to relacing with a new rim, especially if your spokes
can be reused and are not in question as to reliability.

My own opinion, YMMV.

cale

Barchettaman, If you had written that your bike had been hit by a car, a horse, or even an elephant, I'd be inclined to have hope for your wheel. But a bus? Couldn't you have found something lighter to run into your bike?

mrrabbit 

Was looking for a quacking duck smiley...couldn't find one.

mrrabbit 

Quote: "However, I find that lighter rims are much easier to work with because of their lower resistance to the spokes' forces."

I can imagine old Martano's and Fiamme's falling in that category...

=8-)