What makes aluminum frames crack
 

I recently purchased a Masi Coltello frame and am curious to know what can cause aluminum frames to crack, as this is my first alum frame. Does going off curbs hurt the frame? Pardon my ignorance...

Usually metal fatigue. Not hard core stress, at least in my usage. Normally just behind the seat tube at the top adjacent to the top tube. YMMV, and there are sure to be many answers after mine. I've had two Diamondbacks fatigue in the same spot.

Interesting.
My 1994 Cannondale owners manual came with a warning to regularly inspect the area under the point where the downtube meets the head tube.
It's now 16 years old, and I am still riding it.
(Of course the only original parts are the frame, fork, and handlebar.)

wmgreene85,

Good question. I don't know the answer. Years back, I punched a hole through the BB of a Cannondale M2000 mountain bike frame. It hurt like hell and bruised my leg something fierce. But, in defense of Cannondale I sent them the frame and they sent a better, complete bike back. No charge. During the wait time I destroyed my beloved Breezer Storm by wrapping it around a tree. That left a mark.

"Adjacent" is probably the wrong word. Mine cracked in the back of the tube. Just below the integrated clamp. The second bike was a Giant, now that I think harder about it. Maybe it's my style of riding. A Lakeside and I don't know what the Giant model was. It had been in a fire, but part of the Giant decal was still on the down tube. They were definitely fatigue cracks.

Fatigue caused by millions and millions of load cycles makes aluminum frames crack. The more severe the load cycles, the fewer number of load cycles the frame will withstand. The number of times you ride off a curb is insignificant compared to how many pedaling cycles you exert on the frame. Stop worrying and ride your bike.

i just simply wouldn't jump curbs on a coltello, the tubes are so thin it just wouldn't be worth it to me.

Fixed.

Want to know what will really kill a frame? Riding it on a trainer. All that flexing and nowhere to go. Rollers are different.

Relax grumpy old man, I ride my bike plenty. Its not like we're on a bike forum or anything

I assume that you are doing tricks? If so, I would say that using a frame for which it was not designed would cause it to crack.

Want to do tricks and not have your frame crack on you? Get a BMX.

But about curbs, yeah dropping off curbs is not a good thing. But, road bikes are designed to withstand basic road bumps.

No. I am not doing tricks on a Masi Coltello.

denting it is no good.
riding it off a curb you could do, but I would avoid doing hard landings.

In terms of metal fatigue, aluminum does not do well compared to steel.

Road vibration and pedal cycles cause metal to fatigue.

That said, I doubt if anyone reading these words will put enough miles on their aluminum frame bike to make fatigue a factor, and so enjoy riding your aluminum bike.

......... No man, just no.

I'll attempt a straight answer: Aluminum has a "memory", similar to glass. Every little jolt, slowly weakens the frame. Steel and Titanium do not have this "memory". After enough little stresses on anything aluminum, it becomes brittle and easier to crack. I used to hear that the lifespan of an aluminum frame is about 5 years. That makes sense to me. Steel is forever, as long as you can keep rust away. Aluminum tends to also be a harsher / stiffer ride, but I'm sure you already know that.

Steel is not forever. Don't believe that tripe. No metals have a memory, they have a crystalline structure that increasingly hardens until the stress pulls the weaker crystal cleavage apart.

I've busted lots of steel bicycle frames. Many from stress cracks, some from simply killing them. I haven't busted an aluminum frame yet.

Go ride your bike.

I've busted 7 aluminum frames.

Okay, sorry - NOTHING is forever. There. Ain't that the truth? Is the concept of "time" forever? I'm getting too deep.

I have heard of people getting excited about vintage steel frames... but do people buy older aluminum frames? Why not?