Cracked head tube
A fatigue crack, beginning underneath and close to the head-tube/down-tube junction, then growing upwards, is a common frame failure mode. It arises simply from riding the bicycle: ‘over the rocky roadsteads of this parish’, as Flann O’Brien put it. One generally has to ride a bike a whole lot further than you and your wife are likely to have ridden in only five years before it begins to ‘crack up’.
But aluminium is less resistant to fatigue than steel, so a crack is likely to manifest sooner in that material, which is why alloy frames tend to come with much shorter guarantees, sometimes as short as five years. It’s nevertheless worth checking the paperwork that came with those bikes, in case you are entitled to a no-quibble replacement.
Even if they’re out of warranty, the Sale of Goods Act gives the purchaser six years to claim that goods are not fit for purpose due to a manufacturing defect. And I think these frames are most probably defective. The location of the crack speaks to me of excessive tensile strain from fitting the headset, additional to the normal strains of riding the bike. For a crack to appear here, one or both of the following must apply: the tube walls are too thin and/or the headset fit was too tight.
I cannot imagine any plausible abuse that you and your wife might have perpetrated upon your bicycles, so as to cause such cracks in both. And in so far as the shorter crack in your wife’s frame is consistent with her weighing less than you and/or using the bike a little less often, this would support a contention that the cracks arise from normal use and hence the goods are unfit for purpose. However, you are now rather close to the six year cut off, after which any failure becomes fair wear and tear – even if the goods have been used so little that doesn’t seem very fair! So the best you might expect is a discount on the cost of a new frame, and in that case it’s probably not worth the trouble of going to court.
It would not be economical to repair these frames. They could perhaps be reinforced against complete collapse. A tightly-fitting steel ring, pressed over the bottom of the head tube, would relieve stress on this tube and may prevent growth of the crack, which must be marked and closely monitored. A small round hole, drilled at or slightly beyond the visible crack tip, might also help, but will not by itself arrest further growth.
Do not ride the bikes until the frames have been replaced or reinforced. The crack in yours is already quite long and would not have to grow much further (if at all) before the next bump could split open the head tube, releasing the fork and dumping you onto the road!
This was first published in the December 2013 / January 2014 edition of Cycle magazine.