SW Tarmac SL crank: Q-factor and centering

Last week I went for a bike fit with Dr. Pruitt, and one of the things discovered is that I need to have custom axle-length Speedplay Zero pedals in order to fix an alignment problem. To make a long story short, I went home and measured from the center of the seat tube to the outer surface of the crank, where the pedal contacts it. My P3 with FSA SLK Light was centered. The PT300 trainer was centered.

The '07 Tarmac SL with the S-Works carbon crank (the bike I was fitted on), however, was not. The left pedal is 4mm inward compared to the right, and it is this left side (read: issues with my hip) that is driving the pedal selection to an axle 1/8" longer. So, essentially, the cranks are not centered, that is, my left foot is about 4mm closer to the longitudinal axis of the bike than my right.

Has anybody ever heard of such a discrepancy in a stock bike? Any idea what could cause such an occurrence? I'm going to bring the bike in to the dealer tomorrow and see what they say, as I'm not fond of spending $400 for new pedals and shoes if it is to fix a problem that should not exist.

Thanks in advance for any input,

J\V

__________________

'07 S-Works Tarmac SL, Polar CS600+Power
2008 Cervelo P3C, Zipp 900c+808

'07 Specialized Epic Marathon w/Crossmax SLRs
CycleOps Pro 300PT Indoor Cycle Trainer (my winter ride)

Not sure about the frame/crank issue but you can buy one axle, $50 per axle for the longer ones if steel.

IME, cranks/pedal attach points should be symmetrical tho.

I don't know why SPECIALIZED clearly has had some quality control problems with some of their frames, but 'yes' I have encountered a similar situation on a mid-70s FUJI frame where the non-driveside was about 4mm wider than the driveside.

Did someone FACE the BB shell ... is it (still) 68mm wide?

Undoubtedly, I would never have noticed the asymmetry of the FUJI frame except for the fact that I was trying to dump -- I mean "use" -- one of my Hollowtech II cranks onto the frame. I just couldn't get the crank (almost-)centered until I shimmed the driveside cup with a spacer from an old 8-speed cassette (i.e, 3mm) + an additional ~1mm shim ...

In YOUR case, you would use an appropriately wide spacer(s) on the non-driveside to move the external bearing 4mm further outboard & thereby make the non-driveside cup's outer surface equidistant from the centerilne as the driveside cup's outer surface.

Shops which have been in business for more than 10 years may carry BB spacers OR you can use/(i.e., cannibalize) spacers from an extra cassette OR [recommended] the spacers from a turn-your-freehub-into-a-single-speed-kit OR "cut one" from some ABS/PVC plumbing pipe.

Now, in the case of the FUJI frame, it was undoubtedly some engineer's clever idea of makiing the BB stiffer-by-making-it-wider because ANY modern cartridge BB (e.g., Campagnolo 102mm Chorus, Shimano 6500, etc.) properly centers the appropriate crank relative to the stays.

BUT, since your frame is more contemporary by several decades AND fabricated after the widespread use of external BB cups, there is NO EXCUSE for your frame's odd specification and/or poor fabrication, IMO.

FWIW. Since 'I' have the broader option of using any BB/crank combination on the particular FUJI frame, I opted to use the Campagnolo BB + crank pairing rather than the Shimano Hollowtech-II BB & crank combination BECAUSE the particular FUJI's BB shell makes the Hollowtech-II crank's spindle 8mm "shorter" than the norm which Shimano expected if I want the crank arms to be centered ... the offset on the FUJI could probably have been fudged by using a 6603 crank, or equivalent, whose spindle is ~5mm longer.

Thanks, didn't know that.

As far as the frame goes, Specialized tech rep reports that the Tarmac is designed with an asymmetrical seat tube, thus taking measurements in the way that I did will make it appear to be 'off' by about the amount that I noted.

__________________

'07 S-Works Tarmac SL, Polar CS600+Power
2008 Cervelo P3C, Zipp 900c+808

'07 Specialized Epic Marathon w/Crossmax SLRs
CycleOps Pro 300PT Indoor Cycle Trainer (my winter ride)