Avanti Circa - is this the forks about to give way?

[wafter]

Further it's interesting to consider the mode of failure. There's bubbling around the ally crown around the brake / mudguard mount at its centre; presumably because the fixing has abraded the paint, allowing moisture ingress in this area (so tatty but probably non-critical).

Further down however we have cracks on both front faces, apparently at the junction between the ally steerer / crown and placcy legs. This is probably the result of cyclic loading from braking, as the front edges of the fork (especially nearer the steerer tube) will be the area most stressed in tension. It looks like this crack has then allowed moisture in, causing the corrosion.

As @fossyant alludes to there's very likely the potential for that water to have made its way down into the interface between the two dissimilar materials; possibly compromising strength without this being obviously so.

IMO you're absolutely right to junk the fork and I think this serves as yet another example of why to avoid CFRP. While an alloy steerer tube is arguably "safer" (or at least more tolerant of abuse / predictable) than CFRP, the need for interfaces such as this bring with them a whole host of other problems.

As usual, full steel for the win tbh!

 

[DCLane]

Thanks @wafter for a level of technical analysis I just don't have.

 

[wafter]

Thanks @wafter for a level of technical analysis I just don't have.

No worries; thanks for sharing

Do you think that once-replaced it might get chopped up to see what's really going on inside?

 

[fossyant]

No worries; thanks for sharing

Do you think that once-replaced it might get chopped up to see what's really going on inside?

It would be interesting - corrosion around the brake hole is OK, but where it was forming at the 'joint' that would worry me. I've had similar construction forks, which, as far as I knew last year (sold the bike and got an update from the happy owner) these were still fine - the bike is over 15 years old !

 

[DCLane]

@wafter - I'm going to sell the frame but probably only offer the fork to the buyer. I'll doubt they'll want it and, if not, get the electric saw out.

If they do want it I'll direct them to here and suggest they engage.

I've done 3500 miles on the Avanti, although it'd been used for about 4-500 miles before then, so it's not high mileage. And whilst it's a cyclocross frameset I've gone no further off-road than the local towpath. As a result I'm surprised, and concerned, it has this level of degradation.

 

[Jody]

......... if not, get the electric saw out.

You know you want to

 

[C R]

You know you want to

Well, WE want to, with loadsa photos, and that's what matters 😉

 

[wafter]

@wafter - I'm going to sell the frame but probably only offer the fork to the buyer. I'll doubt they'll want it and, if not, get the electric saw out.

If they do want it I'll direct them to here and suggest they engage.

I've done 3500 miles on the Avanti, although it'd been used for about 4-500 miles before then, so it's not high mileage. And whilst it's a cyclocross frameset I've gone no further off-road than the local towpath. As a result I'm surprised, and concerned, it has this level of degradation.

Ta - sounds like a fair way to proceed and I'd certainly be interesting to see it dissected if the opportunity arises!


Sadly that doesn't sound like a lot of mileage; but I guess it has to be considered from the persepectives of use / cost / target market.

Unfortunately I think some (myself included) have an expectation of longevity based on old steel, that's simply not realistic with modern stuff.

Not that I'm defending the position, but it could be argued that it's done a lot of miles for a CX bike (if used for its intended purpose of competing), while if it's a more entry-level bike I suspect many consumers at this price point wouldn't cover such distance in their entire lives.

As you may or may not remember my ally Giant OCR frame cracked / failed at maybe 5-6k miles.. I wonder if the higher-end offerings were any better in this regard..? Either way I'm not a fan of ally or CFRP for bike frames, for this reason and others.

The corrosion will be more of a function of environment, although could of course be a function of mileage to an extent if it's been used in the wet but otherwise lives in the dry. While I know steel corrodes, typically it seems less rampantly than this (it is less reactive than ally).

I'd agree that it's disappointing, but (perhaps even more miserably) not unusual for modern products in our consumptive, disposible age

 

[wafter]

Just happened across this while venturing down the current Shimano-sponsored "things that break" rabbithole..

Might be of casual interest and if nowt else drives home the potential consequences of a fork failure

 

[ColinJ]

Unfortunately I think some (myself included) have an expectation of longevity based on old steel, that's simply not realistic with modern stuff.

The owner of this steel bike had just descended a steep hill and only then noticed that his front wheel was 'wobbling' from side to side... I had stopped to ask if he needed help. He thanked me very much, but said unless I happened to have a spare fork in my bag then it was a walk to a call box for him (pre mobile phone days). I think that his front teeth and his neck had a very narrow escape that day!

I did wonder if he ever actually looked at his bike because that corrosion was not exactly subtle and must have been developing for months or even years!

 

[Jameshow]

View attachment 709969


The owner of this steel bike had just descended a steep hill and only then noticed that his front wheel was 'wobbling' from side to side... I had stopped to ask if he needed help. He thanked me very much, but said unless I happened to have a spare fork in my bag then it was a walk to a call box for him (pre mobile phone days). I think that his front teeth and his neck had a very narrow escape that day!

I did wonder if he ever actually looked at his bike because that corrosion was not exactly subtle and must have been developing for months or even years!

Better off with carbon forks tbh...!🍿🍿🍿

Think it was the Dolan perfissimo that had a similar problem. Alloy steerer bonding into a full carbon crown / legs is probably a better design.

 

[fossyant]

The forks on my CX are all carbon, including the steerer, but my previous commuter was the alloy steerer and crown, carbon blades, and alloy dropouts.

 

[wafter]

View attachment 709969


The owner of this steel bike had just descended a steep hill and only then noticed that his front wheel was 'wobbling' from side to side... I had stopped to ask if he needed help. He thanked me very much, but said unless I happened to have a spare fork in my bag then it was a walk to a call box for him (pre mobile phone days). I think that his front teeth and his neck had a very narrow escape that day!

I did wonder if he ever actually looked at his bike because that corrosion was not exactly subtle and must have been developing for months or even years!

I'm not suggesting that steel's indestructable, but it's a lot more robust and predictable than CFRP, while more resistant to fatigue and corrosion than ally.

At least your mate had some warning and the failure wasn't utterly catastrophic - unlike with CFRP or other bonded structures which would more likely have been a case of "fine-fine-fine-A&E"..

In addition I'd wager that bike was a fair bit older, and possibly with more miles on it when it failed than the subject of this thread.

 

[Illaveago]

It seems that 7000 ally is much more prone to corrosion than 6000. My Boardman Sport had the same corrosion around the brake mounting whereas my Carrera with 6000 ally is fine . I also had to scrap a 7000 ally Carrera Vulcan due to age stress cracks in the head tube . They just started appearing as it was in my garage .
It would be interesting to see just how the carbon forks attach to the aluminium crown? I would expect them to have a tongue and socket otherwise I would go right off them !

 

[Illaveago]