Trek USA agrees to investigate the QR/disc-brake wheel pop-out theory

Orbit in the UK has already said it will modify its disc-brake equipped bikes and now Trek's legal eagle in the USA has told BikeBiz.co.uk he will "definitely talk to the relevant vendors and take a look at this issue." What's needed are lab tests but even the proponent of the wheel pop-out theory doesn't believe the supposed problem can always be replicated away from the dirt. So, is it just a problem with Ti skewers and badly-angled drop-outs, a problem easily solved, or should bike trade execs be banging tech-heads together to find out if the problem is more widespread?
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Bob Burns, Trek's US-based General Counsel, has read the BikeBiz story from earlier this week and has agreed to investigate Annan's theory further. Trek is the first major company to agree to such an undertaking.

Burns reports that the Trek warranty department has had no reports of the kind of equipment failure described by Annan, the Scottish climate research scientist, based in Japan.

However, Annan says the problem he describes is usually mis-diagnosed as 'pilot error', in other words riders not fastening their QRs correctly. Because of the mis-diagnosis risk, Burns agreed to probe.

"Trek has not seen this, but [we] will be making inquiries of the relevant component manufacturers," Burns told BikeBiz.co.uk.

"Virtually all 'defective quick release' claims that I have seen relate to an improperly used quick release. Either the consumer has ridden with the QR open; ridden with the QR closed like a wing nut (rather than closing it over the cam); or ridden with insufficient tightness to the adjusting nut to engage the cam. You can generally determine this by examining the dropout surfaces, which will show the marks left behind as a consequence of the loose clamp force.

"We take great pains in our owner's manual to explain how to use a QR, as do most good cycling books."

Annan says this is all well and good for rim-brake set-ups but QR skewers may not be strong enough for disc-brake equipped bikes pushed hard and fast by enthusiast riders.

Bike boffin

BikeBiz.co.uk has shown Annan's calculations to Gil Bor, an Israeli professor of mathematics at the Centro de Investigación en Matemáticas (CIMAT) of Guanajuato, Mexico. As well as being an expert in differential geometry and mathematical physics (see Bochner formulae for orthogonal G-structures on compact manifolds, (with L. Hernandez). Diff. Geom. Appl. 15 (2001) 265-286), Bor is a cyclist.

He's going to be doing his own calculations over the next few days but believes Annan's calculation misses a few points:

"If you look at his calculation, there are actually two forces felt by the axle: the first is that 1825N acting down along the fork, pulling the axle out of the fork; but there is a second force, which he considers irrelevant and therefore ignores, of about 890N, acting on the axle in a backwards (and slightly downwards) direction, perpendicular to the fork.

"Now one can argue that this force is relevant, for example for increasing the friction between the axle and the drop out, thus increasing the holding power of the QR mechanism."

Annan disputes this and says that many bike techies and trained engineers have failed to find faults with his calculation.

Bor, however, doesn't feel splitting mathematical hairs is the way forward. He calls for testing.

"The way to decide if this is something to worry about is not by calculations but by making a simple experiment. It should be relatively easy to take a bike to some industrial lab, apply forces and see what happens."

Lab conditions

Annan agrees this is necessary but doesn't think the theory he proposes will be proved or disproved under "artificial" conditions:

"I suspect it would be possible for someone who does not have a good feel for the problem to incorrectly generate a negative result, by not accounting for one of the possibly important factors. Bumpy ground, vibration and intermittent braking may all be significant.

"For that matter, given the apparent rarity of the failure, it might take a lot of testing before it shows up. There is no doubt that the failure has been clearly seen in the field."

Oz perspective

John Stevenson, the former tech ed of MBUK and now on the editorial staff of Australia-based Cyclingnews.com, also wants to see lab testing but has similar reservations to Annan.

"Designing lab tests that usefully simulate what happens in the field is hard," Stevenson told BikeBiz.co.uk.

"Cracking this problem is going to take a combination of very careful examination of crashed parts, looking for scrape marks on drop-outs that indicate a hub being dragged from the drop-out while still under tension, ; arithmetical modelling and lab testing.

"I'm reminded of something Mike Burrows once said to me. 'Giant's downhill bikes last forever on the test rigs; they break under [Rob] Warner.'"

Not just QRs

Chris Juden, the technical officer at CTC, supports Annan's theory but doesn't believe it's a problem for QRs alone:

"It's important we avoid the simplistic association of this problem with quick-release fasteners," Juden told BikeBiz.co.uk.

"On the one hand there is no reason to suppose that any other kind of threaded, end-wise fastener (from old-fashioned axle nut to modern allen-screw skewer device) would be any better. And on the other hand it is probable that good designs of quick-release

and hub, incorporating hard steel radial serrations (e.g. Shimano) do emboss and grip the dropout in a manner that prevents unscrewing of the former and loss of the latter.

"I don't think anybody has yet demonstrated failure with a properly fastened, standard Shimano quick-release, despite their ubiquity.

"Traditional 'track-nuts' with similarly serrated captive washers should also be effective fasteners, as would any skewer substitute that also embodied such serrations.

"Just like the hoo-hah that originally gave us lawyers lips, a general problem with axial clamping of front wheels is in danger of becoming identified exclusively with quick-releases. Plenty of front wheels have fallen out over the past century due to people simply leaving the axle nuts too loose, but that was forgotten when the lawyers got their teeth into quick-releases."

What's to do?

Even though testing to prove or disprove Annan's theory will take some time, John Stevenson believes it's essential. And the bike trade shouldn't dismiss the theory out of hand.

"Ostrich attitudes from the bike industry won't help," warned Stevenson.

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