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 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.

If the Bike fits, buy it!

When you do a Google search for information about choosing a frame size and fitting a bike you'll find a huge number of articles.  How do you choose whose advice to follow?  Also, at the end of the day the choice of frame size for all but the top end frames is going to be a simple multi-choice with most frames coming in 4 or 5 set sizes.

The starting point for selecting frame size is usually matching your height and inside leg measurement to the stated size of the frame.  For most bikes this is the measurement between the centre of the bottom bracket to the top of the seat tube.  The online bike shop Wiggle have quite a good page on bike fitting that covers the basics but also introduces perhaps the most important concept which is that the type of bike and what you intend to use it for makes a big difference.  Following the general advice on that site I'd expect to be looking at a 48-50cm road frame or XS-S compact frame.  I particularly liked their 'Ape Index' which introduces the idea that reach is also important and can be used as a sort of tie-breaker when you seem to be on the boundary between sizes.  Unfortunately it doesn't help me as my arm reach is basically identical to my height putting me on the boundary there too.

If you want to dig a bit deeper then you'll find that Wikipedia is a great resource for cycling information.  The page on Bicycle Frame Size goes into all the details.

Another highly respected source in the world of cycling is the late Sheldon Brown.  Sheldon Brown's website is a fantastic treasure trove of articles and advice on all aspects of choosing and maintaining bicycles.  His articles tend to go into a little more depth than other sites but I like his writing style and the way he is prepared to challenge existing ideas.  Unsurprisingly, in his "Revisionist Theory of Bicycle Sizing" he comes to the conclusion that the seat tube measurement should be secondary to the top tube measurement (the tube between the saddle and the head tube).

To help me visualise this problem I drew some pictures.  Using the published frame measurements it is possible to draw the range of saddle and bar positions for different frames, relative to the bottom bracket.  (The position of the bottom bracket relative to the ground and the wheels will change slightly with frame design and size.)  I used the adjustment ranges on my Cinelli Vai Bianca seat post and Selle Italia C2 saddle.

The first picture shows the range of saddle positions for a number of the frames mentioned in my first blog post.  The bold black circle has diameter 10mm and represents my current seat position.  Notice that the Ribble small frame appears too large here but in practice it is probably safe to insert the seat post further into the frame than the post markings indicate but on the more compact frames this would not be possible without the risk of fouling the bottle cage lugs (which protrude into the seat tube on a carbon frame).  This picture tells me that on seat tube length alone, the small Sportive and the medium Saetta are both likely to result in very small amounts of seat post being exposed.

My gut feel is that too much seat post inserted in the frame is as bad as too little, more contact area to get stuck perhaps?  In fact, the Saetta came with a 130mm alloy insert for the seat tube which you can see in the following picture.  Note that the fixings for the bottle cage lugs and 'braze-on' adaptor can be clearly seen in the tube (and will prevent the seat tube from being inserted too far anyway).

Moving to the front of the bike, a similar picture can be drawn for the bar position.  In this case the shaded areas result from changes in the number of spacers on the steering tube and the length of the stem.  Again, I chose to compare using a single product for comparison (the Cinelli Vai Bianca stem). You can get shorter or longer stems but the extremes seem best avoided if possible (as they leave less wiggle room later).  However, there is also considerable variation in stem angle which can be used to raise and lower the bars.  As far as I can see carbon frames tend to have taller head tubes (or it may just be the fashion of the day) but combined with the shallower angle of the Cinelli stem it makes for a higher bar position on the selected frames (key as above).

Despite my 'Ape Index' coming out neutral all of these frames represent a significant reach leaving me looking at the shorter stems, equivalent to selecting the right hand edge of each range.  The position of the Battaglin frame may be a bit inaccurate as they don't publish the head angle and I had to estimate this based on the likely fork dimensions and the top-tube length.

If you are having difficulty picturing the way these diagrams fit with the bike, here is both diagrams with the (fixed) bottom bracket position shown and the wheels added for context.

As I drew these diagrams (with a little help from my computer!) I did get to thinking about the triangle made by the three contact points: the cranks, centred on the bottom bracket, the saddle and the bar.  It is possible to rotate the triangle while keeping the same shape.  Rotating backwards will take a little of the weight off your arms while likely increasing your wind profile and rotating forward will do the opposite.  This point is made in another article on Sheldon Brown's website: The Myth of KOPS.  As a result, I marked rotations of 1 and 2 degrees either side of my current position on the diagrams which explains the smaller grey circles.

As you can see, within reason, adjustments to the stem and the saddle/seat-post can be used to adapt different frames to the same rider.  There was certainly a time when people were advised to ride the smallest bike they were able to get away with.  The argument then was that smaller frames weighed less.  These days, with materials like carbon fibre being affordable this may no longer be true.  Heavier riders can probably usefully use the extra strength provided by the larger frame sizes.  But as for the variation between manufacturers, perhaps the initial conclusion in "Bike Frame Sizes, Geometry, Angles and All That!" is valid in this price range: you might as well choose on the basis of colour.

So how did I choose?  Choosing a frame that I could source through my favourite bike shop was high on my list of priorities along with a little brand loyalty and romance (read 'colour') for Columbus/Cinelli.  The handling of my current bike could be improved by moving my centre of gravity back a little and increasing the distance between knee and handlebar - yes these have been known to collide when I'm out of the saddle at the end of a long day!  Strangely, the Saetta M is clearly too large for me but the S and XS are very similar in size.  I went for the S, rather than the XS - figuring that the slightly longer wheelbase might be more useful for reducing toe-overlap.