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.
3) Alloy screw nuts on steel skewers can wear such that THE NUT IS SUSCEPTIBLE TO UNWINDING THROUGH VIBRATION ONCE TENSION IS LOST IN THE SKEWER
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
6) Loose screwing nuts CAN UNWIND VERY QUICKLY THROUGH VIBRATION
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 firstname.lastname@example.org