Friday, 13 February 2009

Blogging exclusive!

Well, I understand that an out of court settlement was reached late last year before a judgment was handed down and confidentiality clauses prevent the parties to the case discussing the settlement further. So it seems we will never know how a court might have decided on the evidence that was presented.

As my parting comment on this I'll just say that while the case itself was to resolve historic events and their causes, at least the design changes that have developed over the years since (whether or not as a consequence of Russ' accident) such as forward facing drop outs and 20mm/15mm bolt through systems provide excellent alternatives for those that seek some comfort (although wouldnt it have been nice to see a common licenced 20mm standard eh? :)

As Mike Davis of Bike Magic once said, "If any engineer sat down with a clean sheet of paper, they wouldn't come up with a design like the one we have for holding wheels into disc-equipped bikes."

The inertia of legacy systems and designs is strong, but despite the slow machinations of the world of fork/hub/brake development the days are numbered for the QR in sport MTBing regardless of their culpability or not. The arguments, however, may be longer lived!

some links for further reading
unfortunately some STW links are now dead since their site was borked.

Wednesday, 5 November 2008

In Court 21, Wednesday morning.

Witness evidence concluded this morning with the cross examination of the defence technial witness by the claimant's counsel.

Although I have so far only commented on the technical evidence of the witnesses, I feel I ought to say here just how competent this witness came over. Not only was he very clear in his technical evidence but his style of delivery and the way he had approached his report and his time in the witness box marked him out as someone who obviously has a lot of experience in givening expert testimony as well as standing up to thorough cross examination. Claimant's counsel had a difficult time finding any significant weaknesses in this witnesses testimony.

Going back to his key assertion, that there are additional forces working on the axle under braking than have previously been described in all other theoretical technical testimony, he advanced that there are at least three or four further forces that he was aware of that ought to be taken into account when trying to distil the phenomnen into something as over-simplified as a force diagram.

Firstly, as mentioned before, there is the frictional force acting against the force component in the direction of the drop out opening.

Secondly the normal force resulting from the effect of gravity on the rider's mass.

Thirdly the backward directed force as a result of the action of deceleration/braking

and finally the effect of force sharing through the fork arch to the other leg.

This is where my very naive grasp of physics really gives up. Ill leave it to others to have a stab at guessing what the final resultant force on the axle may be!

However, notwithstanding a very clear explanation of the possible/probably existence of these additional force components (which obviously all have components AWAY from the drop out opening) the witness was unable to provide any measurement of these forces (or indeed a force diagram) and could only posit that since he could not recreate a forced wheel ejection except under unrealistic conditions in testing (very low downward force on bars and very high braking force) then he could only conlcude that the combination of these forces was significant enough to cancel out the resultant force generated at the axle by the braking forces at the pad/rotor interface.

He made a comment that of the QRs tested at the facility in California (CID, "Collision Incorporated Dyanamics", great company name. Only the Americans could come up with a name like that :), which he had bought from a nearby LBS, all of them had plastic thread locking inserts. Whereas the claimant witness was testing QRs bought from LBSs in Bristol (3 guesses?) which seemingly none had plastic thread locking insert. It wasnt made clear in court just how prevalent or not it is to find locking plastic inserts in QRs. I cant say Ive ever checked myself...

That brings to an end the court testimonies. The closing arguments are pencilled in the diary for wednesday week the 19th. I may be able to be there to hear the summing ups. I have no idea how much time the Judge will need to consider his findings though.

Tuesday, 4 November 2008

Tuesday report from the afternoon session in Court 21.

Follow up to Friday's report:
Managed to get confirmation that the diagram that I referred to in my last post about 4,340N forces was indeed published in 1999 by Hayes, the brake manufacturer.

I spent much of Saturday trying to find the patent application in the online databases but with no joy. I have had it confirmed that the patent was never granted though.

However, the document below is the 07 catalogue which does refer to the new design drop outs and given it would be published in 06 based on designs from 05 sort of ties in with the patent application.

Tuesday report from the afternoon session in Court 21.

I was unable to be in court on Monday or this morning. This morning's testimony was given by the claimant's technical witness. Defence continued their examination of the claimant's technical witness in the afternoon before claimant's council cross examined. After that, defence were able to question their own technical witness.

What has become clear from the technical witnesses is that there is a broad agreement on a number of the key physical charactersitcs and mechanical forces in question. I shall try and summarise them and then I can concentrate on the differences between the two sides technical arguments.

Firstly, both sides broadly agree that there is a component of force in the direction of the drop out if the drop out is aligned parallel to the forkleg.

Secondly, lateral forces can initiate an unwinding of the QR screw nut.

Thirdly, that vibrations could continue to unscrew the locking nut in certain circumstances

Fourthly, significant forces (in the order of c4,000n) could be generated at the brake pad centre

Fifthly, that the wheel could theoretically be forcibly ejected if the QR was undone sufficiently to pass the lawyer tabs.

All of those points have variously been in the public domain/discussion and given the basic theoretical principals are hard to argue against. However, cause and influence of the above phenomena have been subject to arguments.

The claimant's witness undertook tests to demonstrate there existed forces at the brake pad centre. He did not though investigate whether they could actually forcibly eject a front wheel under braking in practice. He also undertook clamping force tests on the QR. When questioned as to whether Russ "dropping" the bike at the top of the run could have dislodged/opened the QR lever, the witness said that since testimony suggested he "dropped" it on the left hand side then he didnt believe it to be the cause of the QR lossening.

As to why Russ could have ridden many miles (and indeed the very trail of the accident at least 10 times) without the wheel coming out, the witness said that whilst the theoretical sequence could be defined it was only in a combination of many complex factors (many of which he believed were either not able to be identified yet, or if they are not adequately explained) acting in exactly the right manner that the very unfortunate sequence could occur in real life.

The defence witness gave very clear and well described testimony. He initally, briefly criticised James Annan's theory for it's assumptions of no load sharing between fork legs and no modelling of inertial momentum. However his key argument surrounds the component of force that acts perpendicular to the drop out slot. Whilst most if the discussion has been in describing the production of the force component in line with the drop out, he explained quite clearly how no tests or theories had taken into account the frictional effect of the brake force component that acted to push the axle into the drop out side. In testing he was only able to recreate a forced wheel ejection when the downward force on the fork (effective body weight - very low) was 20lbs and the braking force at the disk was 1,000N - although e too did not have any measurements as to the frictional force generated by the 90 degree component. So he concludes that it is the NET resultant force in the direction of the dropout that matters and that he has been unable to demonstrate a sufficiently high dropout directioned force to eject the wheel because of the frictional effect of the 90 degree force. He has calculated that the component of force in direction of the drop out (with the caliper head tube set up on Russ' bike - a 20 degree angle from pad centre to axle compared to the drop out direction) was 37% of the total force generated at the axle.

One other assertion of note from the defence witness was that the manufacturing tolerances of the drop out width were sufficient that should there be any force in the hub even at 90 degs to the slot direction that was sufficient to break any frictional forces of the QR it would result in sufficient movement to initiate an unwinding of the screw nut - i.e. the 40 degree dropout may not neccessarily have solved the QR lossening phenomenon. The dropout slot is manufactured to 8.4mm +/- 0.333mm which would allow upto 0.7mm of movement - sufficient to initiate an unwinding - even in a 40degree drop out.

Finally looking at the QR screwing nut and the lack of a plastic locking system. The Syncros one that Russ used, and shown to the court, showed that the aluminium nut without a plastic locking insert on a steel skewer could become very worn indeed - you could feel it move on the thread and it was very loose to wind. However claimant counsel got the witness to agree that a plastic insert could also wear eventually so that it was ineffective too.

Quick Release Mechanism.

Below I have summarised all the agreed technical evidence with respect to Quick Release behaviour. This is intended to show to those of you using quick releases on disk braked forks what the technical witnesses from at least one side if not both believe can (not will!) happen with a QR, so that you can make your own mind up.

1) Disk braking forces can create lateral forces at the screw nut/drop out interface SUFFICIENT TO UNWIND THE SCREW NUT.
2) Worn cams can reduce the resultant tension force in the skewer by up to 50% from that which an unworn cam would generate given THE SAME AMOUNT OF FORCE APPLIED TO CLOSE THE QR LEVER.
4) Plastic locking inserts in screwing nuts can significantly REDUCE THE EFFECT OF VIBRATION ON THE SCREWING NUT
5) Plastic locking inserts can ALSO WEAR OUT OVER TIME

If I were of a nervous disposition, and still used QRs, I would probably investigate how loose my screwing nut was to move by hand first, and then the QR cam second to see if it was worn. After that, then as long as you do the QR up well enough it's a case of keeping a close eye on it.

You'll by now have noticed that I havent named any of the witnesses. I just dont see the point in naming them at this stage. Maybe after the trial.

The defence witness is due back in the dock for cross examination tomorrow morning. After that there are no more witnessed to be called. I have been told that summing up may not be for a few weeks unfortunately. I shall endeavour to be there, but if not, this will probably be my last report on the case unless I can get to court tomorrow morning.

feel free to post comments here, or in a related Singletrackworld thread. Or email me on

Friday, 31 October 2008

Friday in Court 38

As promised in the thread on Thursday, I returned to the court room today for what I thought would be the summing up. Also at the court today was David Arthur a journalist from Bikemagic who will be following the remainder of the action and reporting on it on the Bikemagic website. My intention was to be able to report the key technical arguments from both sides. However there were some "dramatic" developments in court this morning from the start. Due to start at 10:30, the defence asked for a "pre-emptive" recess for both teams to consider a new document that was being submitted at the start of the day. I say pre-emptive recess as the defence were only too aware that the complainant team would certainly have requested one themselves.

As part of the pre trial process each party is statutorily obliged to disclose all existing relevant material that they might have and submit copies to the court to be distributed to the other side. In this case that would have been sometime at the back end of last year.

4 days into the trial the defence team submitted a previously undisclosed document to the court: a patent application for a "new drop out design". The delay in submitting the document is an acute embarrasment to the defence team and they are adamant that this is only through oversight that it was missed in the original disclosure pack and over the weekend the defendant's team back in California will be checking that there are no more relevant documents missing form the disclosure pack. The patent application itself is in the public domain anyway.

The defence team had previously contended that in making a design change in c.2005 from a vertical to a forward facing dropout (* BTW, vertical in this sense means parallel with the fork leg and in line with the head tube angle) was not driven by any safety concerns over the vertical drop out design and that there were no concerns prior to 2005 as to the level of force that is experienced at the disk side drop out.

In October 2005 Fox submitted a patent application in the names of two of their designers (one of whom was in the witness box as the paper was disclosed). The patent application was for a "new design of dropout"; specifically one that had a forward facing angle relative to the fork lower of 40 degrees. As part of the application commentary was the phrase "massive forces through the centre of the disk brake pad". These forces, the maximum recorded in a document published by Hayes the brake manufacturers in 1999, were around 4,430 newtons, represented simultaneously a force in the order of 3-4,000 newtons on the axle at the disk brake side drop out. Reading from the patent application the plaintiff's counsel asserted that the patent application design change was "specifically to prevent ejection of the wheel under braking forces".

It was not until 2005 that Fox claim to have begun to look at the impact of these very large forces that occur when braking in a moving model. The defence witness then described how the force would be directed at approximately 61 degrees below horizontal - obviously in a vertical drop out this means that there is a force component in the direction of the drop out opening. If you assume, say a 72 degree head tube angle you can see that by rotating the drop out angle by 40 degrees forward then a 61 degree force on the axle would then be transferred almost perfectly perpendicularly to the side of the dropout with no component in the direction of the dropout opening. It wasnt clear exactly what set up created a force at -61 degrees but mention was made of 170mm and 180mm disc rotors. As some of the more observant in the forums have noted the larger the rotor the smaller the angle below horizontal of the force acting on the axle.

Although as I have mentioned in the past , there is no presumption of defective design just because of a later improved design coming into existence, this does open up some questions wih regard to whether sufficient exploration of the effects of such "massive" forces was undertaken at the earlier design stages, principally the 2000 design window for the 2002 release fork which is the subject of the case especially.

Notwithstanding the issue of forced ejection of the wheel because of dropout design, there continue to be complex questions to answer surrounding the performance of the QR. There are obviously a number of different scenarios with regard to the effectiveness or otherwise of the quick release and its contribution to the accident cause. I am not able to go into them all here as I was not in the court on Thursday. However there is an independant expert technical witness due to give evidence on Monday or Tuesday next week. The defence "Mountain bike crash investigation expert" with a significant amount of experience (c.2-2,500 bicycle crash cases) from California came to give verbal evidence following his written report.

His opinion was that a good deal of the potential for an accident rested on the fact that the screw nut on the Syncros quick release skewer did not have a Nylon insert (effectively a permanent threadlock) to prevent the continued unscrewing of the screw nut due to vibration. He agreed with other mechanical engineer's evidence that the sliding action of two surfaces (screw nut face and drop out outer face) can cause a threaded fixing device to unwind. However a nylon locking device would prevent the screw nut unwinding sufficiently for the inside dimensions of the QR to exceed the outside dimension of even one of the lawyer tabs on the dropouts. The cam action of the QR lever has a draw of 1.65mm, whilst the lawyer tabs themselves are apparently c.4mm deep. So if only the QR lever flipped up, and so 0.825mm of room became available on each side of the drop out outer faces then the wheel could never be ejected from the drop out without severe scoring of the lawyer tab faces - which is not in evidence in this case. This also relies upon both QR springs being in place correctly and acting correctly to evenly locate the QR in the centre of the axle. The expert suggested, but could provide little eveidence for the fact, that Russ' QR springs might not have been installed correctly.

Ultimately his sugestion was that while friction forces could unwind the screw nut such that the QR becomes loose, further vibrations and the lack of a nylon locking device could lead to the QR unwinding sufficiently to allow it to pass the lawyer tabs on one or both sides without catching or leaving a mark, and, on braking this would forcible eject the unhindered wheel from the drop out. His evidence was that this happened on the QR side of the wheel, the right hand side of the axle dropping out and then rising back up again such that the wheel rubbed on the inner face of the left hand lower and ultimatley breaking the fork at the arch and stanchion hole in the crown.

The plaintiff's counsel countered that the rubbing on the inside of the left hand lower could also be accounted for by the wheel dropping out on the disk side only first. The expert witness said that the physical indications on the drop outs suggested otherwise - particularly the "erosion" of the bumps (embossing) made in the inside dropout face by the clamping of the serrated QR nut face. However plaintiff counsel looks likely to question that latter with regard to materials hardness given the lowers are believed to be harder Magnesium alloy than the Aluminium alloy of the QR faces.

I wont be able to get to court on Monday (Court room 38 I believe), but maybe one of the Bike Magic team can.
I hope to be able to see the final comments on Tuesday afternoon although the late disclosure of a key document could stretch proceedings further.

email me at if you have any questions.