Cycling UK Forum

I was cleaning my aluminium road bike and spotted two cracks in the downtube on the underside of my bicycle frame which I assume were caused from potholes, would be great to understand if this is repairable? I've attached some photographs. It appears to have taken place nearby the lugs which support the gear cables. I've also attached a picture of the bike from one year ago when I purchased some NOS CXP30 wheels.

Pretty gutted about it because I love the retro look of my bike, I've spent money on various new parts and would love to keep her on the road if possible. I mostly use it for commuting around 300 miles a month.

Thanks in advance.

Ps. Having a problem loading photos, will try to sort out.

Await photos, but it sound from you description that the frame is scrap.

If they are cracks, the cause is fatigue from repeated flexing....welding cable stops to the tube may have caused stress-raisers, or altered the characteristics of the alloy.
You might find somebody who would weld up the cracks, but I doubt you could get a guarantee........

Await Brucey's response..............!

If they really are cracks then, if the frame was mine, I'd never ride it again - cracks get worse under strain and I wouldn't want to risk a complete failure on a fast descent on a busy commuter road. Proper repairs to alu aren't easy, and as Colin says, it's probable that no repairer would offer a guarantee. Speaking of guarantees, how old is the frame, and where did you buy it?................even if it's way out of guarantee a decent LBS should at least be able to advise.

Although you 'love the retro look' an alu frame won't be all that retro, and it could be that you couldn't simply move all the parts onto a decent steel frame. With so much contemporary tackle, good though a lot of it is, not everything is compatible with anything else.

Spa steel frames would be a good place to start at reasonable prices.

There have been other threads on this Forum about cracked alu frames.

However, before you loose all hope, check that they really are cracks.

Strip the paint chemically, mechanical removal can cover the cracks, inspect with magnification.
Dye penetrant kits are cheap and easy to use, but I would never be comfortable even suspecting a crack.
Bin it !

Check the warranty on the frame. I had a Giant brand bike and the seat tube cracked about the BB. I discovered that the frame had a lifetime warranty. The Giant people gave me a new replacement bike!

I recently discovered that my wife's Specialized Dolce Elite has a cracked frame. It's been making an awful creaking noise, coming from the BB area. I took the chain set and BB out and refitted and the noise was just as bad as before. Then a noticed a small crack running around the outside of the BB shell, about 7mm in from the edge, on the drive side.

Frame has a lifetime warranty, if you can prove purchase. We no longer have the receipt as the bike is 6 years old but I'm going to try to claim anyway. The bike was bought from Evans.

It's interesting that so many similar defects seem to arise near the bottom bracket or around the down-tube/head-tube joint. It's not surprising though, considering the stress diagram that some knowledgeable member put on a thread on the forum some time ago. I wish I could find it now.

From observation I believe that the most common frame material over the last 10-ish years has been alu, probably because it's the cheapest way of achieving lightness. I've never had an alu frame, but from the evidence of the experience of others I don't think I ever would.

However, a few of my cycling colleagues have bikes built around 'Tiffosi alu' frames - either built by themselves or by their LBS, and I've personally not heard of any them having these problems.

One of the things about aluminiun is that it has a fatigue limit. That is, there is a limit to the number of cycles it can withstand. So, it will eventually fail. If it is well designed, that failure can be set outside a typical lifetime. If it is overdesigned, the failure can be set outside possible usage, but then you are likely to end up with a heavy, inflexible thing that no one wants to ride.

Steel has an indefinite fatigue life, which means it can withstand repeated load cycles without breaking.

One of the reasons that many high-mileage cyclists avoid aluminium is that they are more likely than average to experience frame failure.

p.s. a cracked aluminium frame is, IMO, scrap. Although a crack could conceiveably be repaired, soemthing else is likely to break in the relatively near future, as the fatigue life has been exceeded.

p.p.s. second the recommendation above for thorough inspection, preferably with dye penetrant.

JohnW wrote:...Although you 'love the retro look' an alu frame won't be all that retro...

Aluminium has been in use as a frame material for well over a century. How old are you if you don't think that could be retro?

JohnW wrote:...considering the stress diagram that some knowledgeable member put on a thread on the forum some time ago. I wish I could find it now...

There are lots of finite element analyses of bicycle frames out there, including some quite artistic ones.

Mr Evil wrote:

JohnW wrote:...Although you 'love the retro look' an alu frame won't be all that retro...

Aluminium has been in use as a frame material for well over a century. How old are you if you don't think that could be retro?

JohnW wrote:...considering the stress diagram that some knowledgeable member put on a thread on the forum some time ago. I wish I could find it now...

There are lots of finite element analyses of bicycle frames out there, including some quite artistic ones.

Mr Evil - I hope that's a misnomer

Thanks for the links - not the one that I recall but some do confirm the stress concentrations around the bottom bracket.

The photo of the original poster's bike hasn't appeared yet, but welded-on 'lugs that support gear cables' don't suggest something as retro as you have a memory of When the photo arrives, then we'll all know.

it'd be nice to see some pictures.

Most welded aluminium frames are doomed to fail by cracking at a weld toe, in a weld HAZ, or at some other geometric stress concentration/weak spot.

I've broken several, and (in the broadest terms) the nicer they rode, the quicker they broke.

cheers

JohnW wrote:It's interesting that so many similar defects seem to arise near the bottom bracket or around the down-tube/head-tube joint. It's not surprising though, considering the stress diagram that some knowledgeable member put on a thread on the forum some time ago. I wish I could find it now.

From observation I believe that the most common frame material over the last 10-ish years has been alu, probably because it's the cheapest way of achieving lightness. I've never had an alu frame, but from the evidence of the experience of others I don't think I ever would.

However, a few of my cycling colleagues have bikes built around 'Tiffosi alu' frames - either built by themselves or by their LBS, and I've personally not heard of any them having these problems.

Well, I've recently broken my 7 year old steel audax frame - it's the 6th steel frame that I've broken - 3 of those had a design fault (badly positioned braze-on causing a stress point), but the others have just broken after a similar amount of time. I did have one steel frame that lasted over 20 years, but for me, that is the exception rather than the rule.

I've also broken one Alu frame, but that was a design fault too.

The moral for me is that things don't last forever, not when you are 6ft 2 and weigh over 100kg, anyway.

TrevA wrote:

JohnW wrote:It's interesting that so many similar defects seem to arise near the bottom bracket or around the down-tube/head-tube joint. It's not surprising though, considering the stress diagram that some knowledgeable member put on a thread on the forum some time ago. I wish I could find it now.

From observation I believe that the most common frame material over the last 10-ish years has been alu, probably because it's the cheapest way of achieving lightness. I've never had an alu frame, but from the evidence of the experience of others I don't think I ever would.

However, a few of my cycling colleagues have bikes built around 'Tiffosi alu' frames - either built by themselves or by their LBS, and I've personally not heard of any them having these problems.

Well, I've recently broken my 7 year old steel audax frame - it's the 6th steel frame that I've broken - 3 of those had a design fault (badly positioned braze-on causing a stress point), but the others have just broken after a similar amount of time. I did have one steel frame that lasted over 20 years, but for me, that is the exception rather than the rule.

I've also broken one Alu frame, but that was a design fault too.

The moral for me is that things don't last forever, not when you are 6ft 2 and weigh over 100kg, anyway.

You've has a bad time Trev..........very unlucky. Notwithstanding your bad luck, considering the millions of steel frames manufactured down the decades (centuries?) I support my submission the evidence of many experiences - witnessed and reported - that alu frames aren't as reliable as steel. You've either had rotten luck or perhaps you're a man mountain of incredible strength (in which case, what's your secret?) or your frame builder needs some lessons. Down the years (starting about 1955 and not counting playing-out-childrens'-bikes) I've had 11 steel frames - I still have 5 of them and 4 of them still being ridden, the oldest 1981 build. The still 'resting' frame is from 1972, which was used for time trialling and not been used for 30 years! 5 have been written off in prangs and of the others, one (1979 build) is having a second life with someone else. I submit that your experience is far from typical and that the original poster's experience is more typical.

I will not be entering into a steel versus the rest debate, but the original question was for advice about decision making on a possibly cracked alu frame - and the consensus is to not take a risk, and to take it out of use. "Bin it" was one advice, which I'd endorse. Advice requested also seemed to include the step to take once the alu frame was taken out of commission, and I mentioned Spa steel frames - that's where steel came into it.

I also submit that age is not a yardstick - miles, type of riding and strength or rider are the issue.

Vorpal wrote:...Steel has an indefinite fatigue life, which means it can withstand repeated load cycles without breaking.

Strictly speaking, steel does have a fatigue life. It differs from aluminium in that at low stress values the life is infinite. Above a critical stress value, the life becomes finite and then reduces with higher stresses. The critical stress value varies with grade of steel but is typically around half the failure stress. I don't know for sure, but I imagine that many steel bike frames will experience stresses above the critical value.

In respect of the OP: A cracked aluminium frame has not cracked due to the main riding stresses. If it had the frame would have failed in a more obvious and spectacular way. It is most likely that secondary stresses were present around stress concentrations. These are "cycled" by pedaling and road vibrations so reach the fatigue limit and a crack forms. Continued use can either cause the crack to grow or could have relieved the stress concentration. In either case, the surrounding metal will have also seen the same number of load cycles but at possibly marginally lower stress. This means that even if a repair is feasible, the surrounding metal may very well be close to a more catastrophic failure.

I would recommend replacing the frame as soon as possible. I would also recommend cutting the cracked frame so as to prevent it "inadvertently" being re-used.