Fork lifetime....

[StreetCowboy]

Five and a half years ago I bought an aluminium road / cyclocross bike with carbon forks.

 

Back in the day, back in the old country, on my steel "racing bike" the front fork failed at the axle cut-out, and I had to get it brazed up at the local garage.  It was probably not a suitable bike for delivering newspapers, and suffered from so many kerbs.

 

How long can I expect a carbon fork to last?  What would be the indicators that it was reaching its end of life?  They've run 27,000 km so far, mostly on road, some gravel, sand, rocks and river bed, and plenty of pot holes and spilled concrete.  I was having a bit of bother with the front brakes, one of the pistons was not retracting properly and it was rubbing.  The guy in the shop assured me it was just that the pads were shot (which they were) but I reckoned he would find any other problems while he was about replacing the pads.  I reckon he did a fair job, since he replaced the headstock bearings, which had been nearing end of life 5,000 km previous.  Anyway, his view was that the brakes were fine, but the mountings were fractionally not quite square - either a manufacturing defect (I was sceptical, since no-one had mentioned it before) or deformation of the forks over time.

 

1) Do carbon forks have a limited life? What life can I expect from road bike forks that are not gently treated?  What would be the indicators that they were nearing end of life?

2) How difficult is it to replace the forks?  Can I go into any bike shop and ask for a replacement and expect to be satisfied without drama?  I would not want shorter forks, as that would reduce the stability of the bike, and to be fair, it's stable enough that I probably don't want longer easy-rider forks.

 

The rest if the frame is all aluminium, and in my view does not see such a hard life, so I am not worried about the frame, or seat-post.

 

SC  

[MikeN]

This info is from what I learnt from a GCN Youtube video, when they said that carbon forks do have a limited life, especially older technology like your 5 year old ones .....trouble is there are no signs to warn you ! Just look for warped and misaligned forks, and any sign of paint cracking. At 27,000 Kms of fairly rough treatment I would guess yours are on the downhill stretch but you could get many more kms out of them.

 The good news is that unless you have some obscure Chinese brand of clunker, the steerer tubes are nearly always one of two sizes so replacement forks should be easy.

[StreetCowboy]

9 hours ago, MikeN said:

This info is from what I learnt from a GCN Youtube video, when they said that carbon forks do have a limited life, especially older technology like your 5 year old ones .....trouble is there are no signs to warn you ! Just look for warped and misaligned forks, and any sign of paint cracking. At 27,000 Kms of fairly rough treatment I would guess yours are on the downhill stretch but you could get many more kms out of them.

 The good news is that unless you have some obscure Chinese brand of clunker, the steerer tubes are nearly always one of two sizes so replacement forks should be easy.

Thanks, Mike!

I’ll mark new forks down as this year’s Christmas present.  I suppose the length of the forks is more or less fixed by the size of the wheel.

[MikeN]

15 hours ago, StreetCowboy said:

Thanks, Mike!

I’ll mark new forks down as this year’s Christmas present.  I suppose the length of the forks is more or less fixed by the size of the wheel.

Don’t forget tyre clearance too, not just the length of the forks. The trend is for slightly wider tyres nowadays so I think most road bike forks would be wide enough at the top for at least 700*28C.

[StreetCowboy]

6 hours ago, MikeN said:

Don’t forget tyre clearance too, not just the length of the forks. The trend is for slightly wider tyres nowadays so I think most road bike forks would be wide enough at the top for at least 700*28C.

And disc brakes.  I should mention disc brakes while I’m about it

[bobfish]

Carbon fibre doesn't have any fatigue life in the usual sense. So age alone is not a factor.  Failure would be caused by a breakdown of the matrix, either by poor manufacturing design/QC or by an outside source such as a force greater than design load, percussive damage or UV etc.

The tricky part is identifying faults before catastrophic failure: the warning signs you mentioned are the obvious ones to look out for. Short of having access to some form of imaging equipment to scan your fork [Ultrasound/CT...], you could try tap testing to identify any dull sounding areas which may have poor compaction or bonding. 

To really cheer yourself up, you could take a look at a few of Raoul Luescher's videos on the subject. Here's a starter:

 

 

 

If you're intent on buying a new fork, ensure you buy on with the same spec: ie steerer tube, length and offset should be identical to your old one [and compatible with your braking and axle type].  I wouldn't get too hung up with width, so long as there is room for your current/preferred tyre.