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.


James Annan said...


the lawyer tabs themselves are apparently c.4mm deep

Do you recall if this was suggested as the value for each one of the tabs separately, or both together? The way you have written it suggests the former but surely they are not usually so deep. I don't have any to look at myself. A 2mm lip and 1.65mm lever throw would imply that not much unscrewing is required.

Mark said...

good question, Im not clear myself. However, I'd point out that the QR springs (if properly installed) will only aloow 0.825mm of clearance at each dropout face if the cam is open.

James Annan said...


I don't think the claim that the springs should keep a loose QR centred is remotely credible. The spring forces are very small - they are zero by definition at the balance point, and it only takes a modest finger touch to push a loose skewer to the side such that the full gap is at one end. Try it - I just did! Now imagine 3000N of force trying to pull the (bevelled?) edge of the QR nut over the (rounded?) edge of the lip on one side. 5N pulling on the QR nut is hardly going to affect things.

(I realise you are only reporting what was being said.)