Dented Aluminium Frame - Serious?

[Mr Will]

To cut a long story short, I was knocked off my bike at the start of last month by a van driver who turned across a bus lane without looking or indicating. I am fine but the bike has taken a bit of a knock, both shifters are scuffed and battered but there is also a small dent in the top tube.

Originally I was just going to ignore it as I doubt it can be fixed without replacing the frame, but I'm now starting to worry it might have long term effects. Is a dent in an Aluminium frame a problem, or will it likely be okay?

Pictures:


IMAG1147 by Mr_Will, on Flickr


IMAG1148 by Mr_Will, on Flickr

[Mars]

The beauty of metal of carbon fibre is that it can take a knock without instantly losing its integrity. However, aluninium doesn't reject damage as readily as, say, steel. It will have weakened but I doubt the frame will be designed to be as light as possible at the expense of its strength. The weight/strength compromise is always that - a compromise - but I just don't believe it's designed so far towards the "weight saving" end of the scale that it will fall apart the first time you encounter a bump.

You should be fine.

[anonymous-user]

I've dented Allu frame mountain bikes and they've never failed. I've not dented a road bike though

BTW. How did you hit the underside of the top tube, did it land on a curb or something raised? .

[Mr Will]

el stovey said:

How did you hit the underside of the top tube, did it land on a curb or something raised? .

Not 100% certain as there was a lot of tumbling and sliding involved, but I landed on top of the bike after the van hit me which would explain it.

[Fatman2]

Mars said:

The beauty of metal of carbon fibre is that it can take a knock without instantly losing its integrity.

Carbon fibre does not instantly 'lose' it's intergrity unless an impact is sufficient to cause delamination/cracking etc. Whether the impact that caused the aluminium frame to deform would have caused any damage to a carbon frame is impossible to ascertain given the limited info.

OP, it looks to be a fair dent in your top tube and this will undoubtedly affect it's ability to resist bending/buckling. However, depending on the type of riding you do it may never become a problem. By the type of riding I mean fast decents on poorly surfaced roads, cobbled streets in town, riding down kerbs or any other scenarios that may cause the frame to be loaded heavily.

In truth it doesn't look like a massive dent so you could be ok but without knowing how thick/thin the tubing is you can't be sure. Thus I would measure it and keep an eye on it to see if it gets any bigger.

[shalmaneser]

I wouldn't worry about it at all. It's a bit unsightly, but it's not in a high stress area. Check the welds around the headtube more regularly than you normally would, but it looks fine.

I'd bet a carbon fibre frame would have splintered with that impact, good choice on the metal frame!

[Mars]

Fatman2 said:

Carbon fibre does not instantly 'lose' it's intergrity unless an impact is sufficient to cause delamination/cracking etc. Whether the impact that caused the aluminium frame to deform would have caused any damage to a carbon frame is impossible to ascertain given the limited info.

OP, it looks to be a fair dent in your top tube and this will undoubtedly affect it's ability to resist bending/buckling. However, depending on the type of riding you do it may never become a problem. By the type of riding I mean fast decents on poorly surfaced roads, cobbled streets in town, riding down kerbs or any other scenarios that may cause the frame to be loaded heavily.

In truth it doesn't look like a massive dent so you could be ok but without knowing how thick/thin the tubing is you can't be sure. Thus I would measure it and keep an eye on it to see if it gets any bigger.

I know a bit about CF. An impact hard enough to dent an ali frame like that in the middle of the tube-length where CF tubes tend to be at their thinnest in bikes, would likely have caused enough damage that you'd fear for its integrity. The problem being that, like motorcycle helmets, you never know. Ali is a much safer bet/lower risk.

[louiebaby]

I have no special knowledge in the area, but I would play it like this:

It will be fine to use.

The missus knows it was damaged.

Use it as an excuse to get something shiny and new.

Keep this bike for commuting.

[itsnotarace]

That will be ok, as said above it's in a low stress area. Looks like it was made by the handlebars turning round.

[NitroNick]

I bought a Aluminum framed bike from an ex-pro, it had been damaged (almost identically to the damage your frame has) in transit back from the Australian olympics.
The guy used it as a training bike that winter, then sold it to me the following year. There was never any issues with it for the 2 subsequent years I had it.

[craig_s]

louiebaby said:

I have lots of special knowledge in the area, so I would play it like this:

It will be fine to use.

The missus knows it was damaged.

Use it as an excuse to get something shiny and new.

Keep this bike for commuting.

Sounds like this man knows his onions. I'd definitely take this advice.

More seriously, like the others have said, it will most probably be fine as long as you keep an eye on it and watch out for it changing size or shape.

[Mr Will]

craig_s said:

louiebaby said:

I have lots of special knowledge in the area, so I would play it like this:

It will be fine to use.

The missus knows it was damaged.

Use it as an excuse to get something shiny and new.

Keep this bike for commuting.

Sounds like this man knows his onions. I'd definitely take this advice.

More seriously, like the others have said, it will most probably be fine as long as you keep an eye on it and watch out for it changing size or shape.

Unfortunately I have no missus to try and get things past, so the excuse is not needed, and any shiny things would only be coming out of my wallet.

The problem with the "Keep an eye on it" plan is that if it does get worse in 6 months time, I'll end up having to pay for it, whereas at the moment there is still a chance that the van driver will pay if it does need replacing. But on the other hand, I don't want to sting him for a new frame if it isn't needed.

It's been packed off to the bike-shop today anyway, so let's hope they can help.

[Fatman2]

Mars said:

I know a bit about CF.

Then we're a pair

I know a bit about CF too, hence why I made the comment. As before though. We don't know enough to make sweeping statements like that

[Mars]

Fatman2 said:

Then we're a pair

I know a bit about CF too, hence why I made the comment. As before though. We don't know enough to make sweeping statements like that

You missed the point - which was that you just don't know with CF.

[louiebaby]

Mr Will said:

But on the other hand, I don't want to sting him for a new frame if it isn't needed.

Very level headed and honourable of you sir.

The bike shop, provided it's a reputable one, should be handy, make sure you let us know the outcome.

[shalmaneser]

To be fair, it's damaged, and the man in question needs to return it to the condition it was before the accident. So you need a new frame. I'd be very surprised if your LBS said anything different.

It will be, however, fine to ride.

[pokethepope]

Agree with the above, it was his fault, so if theres even a small possibility of it being damaged (which in this case it clearly is) he should pay for a replacement, regardless of whether the damage is critical or not.

[Fatman2]

Mars said:

You missed the point - which was that you just don't know with CF.

Sorry, must have something as I thought you originally said that CF instantaneously loses it's integrity upon impact compared to metal

Now you're saying that you just don't know, which is a bit of a U-turn


But yes, I agree, it's impossible to tell without carrying out some NDT

[robpearson]

I believe aluminium has a habit of being ok to bend once, but if someone were to pull the dent out as you might on a piece of steel the aluminium will likely fail and crack. I have a more dramatic dent on my yeti mountain bike, and have carried on riding it for the past two years without any issues.

[anonymous-user]

given where the dent is, i would say that there is no problem if you continue riding on that especially as its a road frame. there wont be too much power going through the top tube and it wont stress that much.