- Jul 23, 2005
ColnagoC60 said:So Alfie, educate me a bit further.
What is a "Q Factor" and what does the "Q" stand for?
I was taught it was measuring band width of a resonant system?
Some people use it as a bad slang English word to describe the width, between where a bicycle's pedals attach to the cranks, but how would you relate that to anything to do with the dimensions inside the bottom bracket between the bearing outer race cups, or between screwed in frame cups, or between pressed in cups? I am confused, how would that have anything to do with an air gap in the hirth joint, or causing the click sound? I just read each and every of your posts again and don't understand why you did not rather just copy and paste, as they all say exactly the same thing. I still don't get it, it makes no sense to me?
Could you try and describe it a little different, please?
"Q" == "Quack"
As I recall, the term was coined (in the 60s(?), but perhaps it was earlier-or-later) because someone thought cleated cycling shoes made a person walk-like-a-duck ...
And, somehow the term was transferred to the width of the cranks where the pedals are connected ...
Undoubtedly, someone else will be able to elaborate and/or correct the history of the term.
FWIW. I measure the distance from the tip-of-the-Hirth-Coupling-teeth to the inner face of a 6805-6 bearing as being ~41.0mm (?) on the non-driveside & ~40.8mm (?) on the driveside...
Despite an overlap of the teeth of what appears to be about 3mm, I measure the distance between the bearings as 80.0mm when the teeth are fully engaged ... because the tips of the teeth are squared off, there is a visual, variable gap of slightly less than 1mm between the tip of the teeth and the rounded bottom of the troughs (this is NOT the ~1.0mm which affects the spindle's stability which I have been referring to) ... feel free to do-and-use your own measurements ...
You will observe that ALL of the sides/(contact edges) of the teeth of one spindle half are in contact with ALL of the sides of the teeth of the opposite spindle half ...
AND, if you measure the Q-FACTOR of the joined halves, you will see it is 144.5mm.
AGAIN, I could-or-should have simply said "the measured outside width of the steel spindled UT cranks at the pedal holes is 144.5mm."
When the UT crankset is mounted with the Wavy Washer, Clip, and/or shims, the Q-FACTOR is (prescribed to be) 145.5mm ... that is, "the measured outside width of the steel spindled UT cranks at the pedal holes is 145.5mm."
AND/BUT, that necessarily means that the distance between the bearings can no longer be 80.0mm ...
If the arms are 1.0mm further apart, then the bearings are 1.0mm further apart (~81.0mm apart), and that means that the tip of the teeth are 1.0mm further from the bottom of the trough they are meant to engage.
So, before you put the UT crank back in your frame, backing/(loosening) the connecting bolt out by 360º +/- will allow you to be able to simulate the separation of the crankarms to have a 145.5mm Q-FACTOR ...
NOW, observer that distance between the tip of the teeth & bottom of the trough has indeed increased ...
And the the sides of the teeth are no longer fully engaged ...
The teeth CAN-or-WILL become engaged when you begin to pedal and the leading edge of the teeth of one spindle's Hirth Joint will engage the trailing edge of the teeth of the other spindle UNTIL you turn the crank over by ~180º when the leading edge of the teeth which were being contacted as the trailing edge now become in contact with the trailing edge of the formerly leading teeth. I refered to THAT, earlier, as gnashing ...
If you can't picture it, then consider ONLY the driveside's teeth. The teeth would be akin to the tabs on the inner circumference of a Cassette's Cogs engaging the splines on the Freehub & disengaging as the force is subsequently applied by the non-driveside, and then re-engaging, et cetera.
The connecting bolt is what is holding the two halves together
BUT, worse ... if you were to simply grab either arm, you will see that you can wiggle the spindle & the OTHER crankarm which you are not holding will flop as you wiggle the the crank arm which you are holding!
THAT's probably not a problem with a steel spindled Ultra Torque crankset, but Titanium is comparatively fragile ...
And, the oft pictured broken UT spindle can certainly be considered to be evidence of at least one instance of a fatigue break.
So, despite the inclusion of the Wavy Washer & Wire-Clip AND a suggestion that there is an allowable compatibility width for the BB shell, it appears (to me, at least!?!) that the nesting surface of the THREADED Ultra Torque BB cups was actually spec'd to allow an Ultra Torque crankset to mounted without the inclusions IF-and-WHEN the width of the bottom shell is (in the words of the Rogue Mechanic suggested) "exactly 68mm."
AND SO, the unshimmed distance between the BB cup nesting surfaces is apparently (must be!) the fore mentioned 80.0mm when mounted in an English threaded BB shell whose width is 68.00mm.