Saturday, 28 April 2012

Cranky delays to my home-build project

Most of the components I bought for my new bike have come preassembled ready to be fitted.  However, there was one component I had difficulty sourcing: the crankset.  How can buying a crankset be so hard?  After years of cycling on 170mm cranks I've decided to go shorter and ride on 165mm cranks.  This is partly because I tend to spin a bit but also because I find that my saddle adjustment height has very little room for error.  Last time I changed my frame I suffered a little knee pain on longer climbs (especially if I was sitting back).  Moving the saddle up solved the problem.  This is a fairly well known effect, I found this blog post on an Audaxing blog in which the author covers some fine adjustment issues for injury prevention (though take note of the comments at the bottom of the page as the knee conditions have been transposed in the main article).

There is plenty on the net written about crank length, much of it contradictory.  Performance cyclists are always looking to gain an advantage so it is not surprising that the subject has been studied but the surprising conclusion seems to be that the optimum range of lengths for a given rider is quite large.  Sheldon Brown comes to a similar conclusion with a more general purpose outlook after experimenting with a wide range of sizes.

Despite all this orthodoxy telling riders that one of three sizes fits all I've still decided to go with the 165 and ride for enough miles to see if I like it.  Clearly shortening the crank length by 5mm will mean moving the saddle up by the same amount to maintain the same leg extension at the bottom of the pedal stroke.  At the top of the stroke the foot will then be 10mm lower than before - a significant reduction in the height of the knee.  There are so many articles on crank length on the internet it is hard to pick out particular ones - and anyway, I'll surely just pick the ones that agree with my own analysis!  Still, this blog post makes the point above very clearly: Crank Length - which one?.  The shorter crank will also reduce toe-overlap as my foot will be retreating by 5mm from the front wheel.

Starting from this year, Campagnolo are making a Centaur crank in a 165mm size.  According to the brochure "it allows for an agile pedal stroke and a correct movement in relation to the length of the lower limbs".  By the way, at the time of writing nobody has told the webmaster at Campagnolo so the product page still lists 170mm as the smallest size and the link to the 165mm crank goes to the Athena 11speed crank but I can confirm that I do have a 2012 10-speed 165mm Centaur crankset.

Campagnolo Centaur Crank
Campagnolo Centaur 50/30 Compact Crankset: including warning stickers!
The crankset is only available on the more expensive carbon version unfortunately and I struggled to find anyone in the UK who had anything other than the compact 50/34 and even that was hard work (and like buses, you wait ages for one and then two turn up at once - isn't internet shopping fun).  Judging by the number of people that offered me the 'black/red' version (which is the same crank with red bolts) this looks like a bit of an unnecessary addition to the product range and inventory might have been better served by reducing the colour options and concentrating on the different lengths and chain ring configurations.

The thought of a 34T chain ring scares me a bit, even with the shorter crank that would be a lot of gears that I only ever used when taking holidays to places with long steep climbs.  To put this in perspective, the average force required on each peddle stroke with the 165mm crank is roughly equivalent to adding a single tooth to the chainring, so my 34T would feel a bit more like a 35T.  That would still be a big change from the 50/39 I currently use.

On the plus side, a larger difference between the two chainrings reduces the overlap in gear ratios.  For example, on a standard 12-25 set of 10-speed sprockets only 5 of the sprockets used with the 50T ring result in longer gears than the longest available on the 39T ring (ignoring the small-small combination).  With a 34T inner ring this increases to 7 sprockets.  On the minus side the bigger spread of gears inevitably means more frequent changes between chain rings or more temptation to cross-chain.

Campagnolo don't make different chain ring sizes for the lower-end Centaur but there are third party rings available that fit the Campy 10s cranks so a little experimentation seems possible.  As a result, I did go with the 50/34 compact but I also bought myself a 36T ring made by TA, as the graph below shows, this basically represents a single downshift on all the sprockets with a new hill-climbing gear that may come in handy next time I visit Holme Moss.

Typical bike speeds for different chainring and sprocket sizes.
Before anyone gets the idea that this blog is recommending you attempt to change your own chainrings, let me remind you that Campagnolo suggest that this can only be done by them (doubtless with approved parts) and that you risk ending up with rings that are out of true, followed shortly afterwards by accident, injury and even death.  The cost of the carbon-wrapped cranks is a bit eye-watering so I don't think one should undertake this job lightly.

TA Nerius 36T ring for Camagnolo compact crnnkset

The 5th Chainring Bolt Mystery

Firstly, the chainrings are fixed with 5 bolts, 4 on the rings/spider and a 5th bolt that goes directly into a thread in the crank arm itself.  The bolts all have a T30 torx screw head but on the reverse the 4 main bolts have solid nuts (which are actually the bolts as it turns out) with wide slots.

Also, to make life interesting the 5th bolt has what looks like a tamper-proof plug in it.  A pair of tweezers reveals that is actually just a removable plastic plug - my assumption is that it is to keep the dirt and water from going down the Torx head and into the crank arm where it might cause trouble (such as corroding the thread in the crank itself).

Seeing red

The bolts are alloy rather than steel and the crankset stipulates a torque of 8Nm, however, the ones supplied with my crankset were stuck fast with what looks like a white, dry thread locking compound.  Most of them came away without too much trouble but two of them were stuck so fast that I damaged the slot-heads trying to remove them.  Beware, the teeth on those outer rings bite!

Initially I tried to undo them by holding the crank arm using the gentle grip of my workmate (which has soft wooden jaws) just to hold it still.  This frees up both hands to work on the bolts.  However, with stuck bolts I needed this lifesaving tip from the 'boston bicycle mechanic' to help me free them up.  With the torx head held fast by the jaws of a vice I could use the slot-headed driver in one hand and my other hand was free to turn the whole crank in sympathy with the nut.  If I had read that article first I might have saved myself some time and money!

So, having compromised a bit on getting a compact, mainly because I couldn't find anyone who could supply a 165 without red bolts, I now faced the prospect of sourcing replacements anyway.

Spare Parts

Full marks to Campagnolo's website for the pretty PDFs with clear pictures labelling the various spare parts.  It was clear they came as a set though it was a bit disconcerting that the picture didn't match the bolts I'd just taken out.  Also, my bolts are clearly marked with the codes from the Record bolts of 2010 and earlier (the images above can be expanded to read the FC-RE303 printed on the 5th bolt).  There are various (cheaper) third-party bolts which look like they've been designed as replacements for the Record bolts but nobody has updated their catalogs to say, one way or the other, if their bolts will fit the 2011 Athena/Centaur/Veloce cranks.  For the avoidance of doubt, BBB's BCR-53C product "specially designed to be compatible with Campagnolo compact cranksets" do not fit, though BCR-54C looks tantalisingly like the right thing, despite being described only as "compatible with Campagnolo 11 speed chainrings".

Having already had to wait to do the build due to work commitments, travel plans and then illness I was in a hurry to get this problem sorted so ordered a new set of Campy original bolts from Belgium (from All4Bikes) and watched my profit margin from doing a home build go up in smoke.

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