Frame question
 

If you wreck a CARBON or ALUMINUM frame are they trashed? Can they be repaied?
What is the strongest and lighest frame?
Thanks for the input,
John

Post this in bicycle mechanics forum.

Yes-trashed-most steel also trash-VERY FEW WORTH REPAIRING.
 

Yes, once you bend/break aluminum or CF "tubes" they are junk.In fact most steel frames are junk also unless you know someone who is handy with a welder(for cheap heavy steel frames), or the frame is so valuable that it is worth sending off to be repaired.It would probably cost $400 to repair/repaint an old 531 frame that had one crunched tube. Most aren't worth $300, so that is it for that frame-same story for Columbus tubing and even more so for Champion tubing since older Japanese frames are worth 1/2(at best) what 531 and Columbus vintage frames are.
Cheap old steel frames are actually the most repairable since they usually break at the old weld, and the tubing is so thick it can be rewelded. Of course, they are worth the least, so you need a buddy withy a welder.
Don't buy a frame based on how repairable it is alleged to be. It is a bit of a myth that steel frames are "easy" to repair, and are safer to ride with heavily dented tubes.$$ for $$$ almost no frames are worth repairing, if you actually pay the repairman what he should charge.
Luck
Charlie.
Part of the reason CF and Aluminum aren't considered repairable is that it is assumed-correctly-that the other welds/joints have been damaged when one tube/joint fails and the frame bends. Steel is a lot more elastic/flexible, so the other parts of the frame are less likely to be damaged(they might be of course).

Any frame that has suffered enough damage is likely to need replaced. Steel is more forgiving and can be bent back in a number of cases while Al or CF will further weaken due to metal fatigue.

This is IMHO, but if a frame failed once for me, it gets replaced. I much rather spend $500-$2000 for a new frame than $tons for a new nose, lower jaw, and skin grafts.

Here are some repair prices for steel and Ti so you can see the cost-effectiveness.
Calfee repair carbon frames.

The common location for frame failure is drive-side chainstay, not a safety critical location for normal riding. People have done home repairs on all kinds of frame material using glass or carbon fibre tape wrap and epoxy. Its not something to attempt on the front end where a failure can dump you, or for off-road use.

$187 for one steel tube-
 

MichaelW-whooo- $187 just to replace on steel top tube.Factor in the paint-another $300 to paint the entire bike-shipping both ways-at least $100+ I think there was some sort of realignment charge-and it is $800-$500 if you skip the paint. Since most steel frames aren't worth $500- a decent 531 frame will go for $150 or less on Ebay-you can really only repair for sentiment-(which is a pretty good reason).
Thanks,
Charlie
PS-Interesting-it is cheaper to repair CF than steel. Guess I shouldn't be surprised since they are fabric and "glue/polymer".
PPS-MLTS22 has a good point-why trust a frame that has proven to be untrustworthy, or was so damaged to need repair.

Carbon and aluminum forks and frames can NOT be repaired if a tube is cracked or broken. They are like stale pretzels. They don't bend. They don't flex. They simply fail when heavily stressed. The factory might be able to replace a cracked carbon tube, but the cost would be very high.

High quality steel frames and forks don't crack or break under the stress of a typical crash. Steel will simply bend a bit.

Any good bike shop can realign a steel fork that is a bit off kilter after a crash. I paid $40 to get a fork realigned last year. If a steel tube got loose at a joined area after a crash, there are many frame builders who could rejoin the tube for moderate cost (under $100 if the tubes are not damaged). I've never seen a top quality steel frame come apart though.

Steel bikes can and do crack under the "right" conditions, usually involving some concentration of stresses in a weakened zone. The classic one is the driveside chainstay but the front mech brazeon and downtube lever brazons are also favoured spots. I know of one steel steerer tube that cracked. A crash will usually result in bending but crashes are not the only problem.

I've got a carbon fiber handlebar on my mountain bike, it's quite flexy. It actually has some damping characteristics, too. Hardly a "stale pretzel." And aluminum is actually quite a flexy material, relatively speaking. If you don't believe me, check out the difference between steel drop bars and aluminum ones. The reason aluminum frames are generally quite stiff is the dimensions of the tubing, not the material itself. Because of aluminum's lack of a fatigue limit, an "overbuilt" frame with large diameter tubing (to keep the frame from flexing much) is necessary for durability. That being said, I'd never have a broken or cracked aluminum frame repaired because most aluminum that's used in bike frames is heat treated in a very controlled environment at the factory (at least in the case of 6061 aluminum), and this would be difficult, or prohibitively expensive, to replicate in a repair situation.

Yes, they are repairable...but it's cheaper to just replace the broken components.