road bike - how to choose chainring (crankset) and cassette size? I'm going through a 1st bike build (road bike) and looking for some advice on choosing chainring (crankset) and cassette size.

I'm pretty much decided on the Shimano Ultegra Groupset (6800), which I plan on purchasing from Chain Reaction:

http://www.chainreactioncycles.com/us/en/shimano-ultegra-6800-11-speed-groupset/rp-prod110818?utm_campaign=bazaarvoice&amp;utm_medium=Default&amp;utm_source=AskAndAnswer&amp;utm_content=Default

I've already decided on crank length, so now it's down to chainring and cassette size.

My current cross bike is a Giant AnyRoad CoMax which has a 50/34 crank and 11x32 cassette.  This is pretty much perfect for this bike, on occasion downhill I'll be in 2-11, and on occasion on a super steep climb into the wind I'll be in 1-1.  This bike weighs about 22.75 lbs, and the road bike I'm building will weigh in at about 16 lbs, so I should be going at least a little bit faster.  The spread between the rear gears seems about right, I don't think I would like more fine spacing between gears.

Based on this, my inclination for my road bike build would be 52/36 &amp; 11x32.  The odd thing is that I can't seem to find a single major manufacturer that uses this combination on a high-end road bike.  For example:

Trek Madone (50/34 &amp; 11x28):
http://www.trekbikes.com/us/en_US/bikes/road-bikes/performance-road/madone/madone-9-5/p/1472000-2017/

Trek Emonda (50/34 &amp; 11x28):
http://www.trekbikes.com/us/en_US/bikes/road-bikes/performance-road/%C3%A9monda/%C3%A9monda-slr-6/p/1470000-2017/

Trek Domane SL 8 (50/34 &amp; 11x28):
http://www.trekbikes.com/us/en_US/bikes/road-bikes/performance-road/domane/domane-slr-8/p/1477400-2017/

Trek Domane SL 6 (50/34 &amp; 11x32):
http://www.trekbikes.com/us/en_US/bikes/road-bikes/performance-road/domane/domane-sl-6/p/1460000-2017/

Specialized S-Works (52/36 &amp; 11x28):
https://www.specialized.com/us/en/men/bikes/road/performance/sworks-tarmac-duraace/128538
https://www.specialized.com/us/en/men/bikes/road/performance/tarmac-pro-ultegra-di2/118441

Giant TCR (52/36 &amp; 11x28):
https://www.giant-bicycles.com/us/tcr-advanced-sl-1

Felt FR1 (52/36 &amp; 11x28):
http://www.feltbicycles.com/Global/2016/Bikes/road/race/FR/FR1.aspx

Is there some reason 52/36 &amp; 11x32 seems to be a taboo choice by manufacturers?  The 11x32 I'm running on my cross bike currently seems to provide a fine choice between rear gears, if anything I wish the difference between gears was not quite so fine, so sticking with 11x32 at the rear and upping the front from 50/34 to 52/36 to adjust for anticipated slightly faster speed all round seems to be the natural choice.  Anybody have some thoughts or advice on this?
The main reasons your combination is avoided are as follows:


It would require a long cage derailleur. The maximum a Shimano short cage derailleur can handle is 33 teeth, and your combination would require 37 teeth. Long cage means extra weight, wind resistance and cost, none of which the manufacturer wants.
34/28 is already extremely low. Not many people who ride racing bikes need gears lower than that. Compare that until few years ago, the standard used to be 52/39 and 12-23.


Of course, since you are building a custom bike, you can just order a long cage derailleur and build what you want.