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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&utm_medium=Default&utm_source=AskAndAnswer&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 & 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 & 11x28): http://www.trekbikes.com/us/en_US/bikes/road-bikes/performance-road/madone/madone-9-5/p/1472000-2017/

Trek Emonda (50/34 & 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 & 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 & 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 & 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 & 11x28): https://www.giant-bicycles.com/us/tcr-advanced-sl-1

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

Is there some reason 52/36 & 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?

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    D. Hicks, I did not decide on chain length yet, I did not say I decided on chain length anywhere in my post, I'm not sure what you are referring to. I plan on setting chain length the usual way (chain around the largest chainring at the front and the largest cog on the cassette at the rear, line up and gently pull hand tight, then add two links).
    – cdahms
    Commented Feb 5, 2017 at 13:45
  • OK, I misread "crank length". It's too early in the morning!
    – Daniel R Hicks
    Commented Feb 5, 2017 at 14:02
  • Where do you feel that you are weak? Personally if the grade gets over 10% I slow down dramatically, so I have a low-low of 28/32 on my road bike. Do you spin out on downhills and fast flats? ie, keep trying to change for that one-more-gear ?
    – Criggie ♦
    Commented Feb 6, 2017 at 9:48
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    As a possibly unrelated aside, crit races are flat and you typically don't want huge jumps in the rear cogs. That's solvable, however, with an extra cassette that you swap on for racing.
    – R. Chung
    Commented Feb 6, 2017 at 16:33

2 Answers 2

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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.

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  • Thanks for the quick response. I did notice on the Chain Reaction site if I choose the 11x32 cassette option, it makes me choose "Medium Cage Rear Derailleur" rather than "Short Cage Rear Derailleur" if I choose 11x25 or 11x28. I hadn't considered the weight/aero penalty going from the short to medium cage derailleur so I guess that's something to consider. In the end I'll still probably go with the 11x32 so I can go up steep hills when needed.
    – cdahms
    Commented Feb 5, 2017 at 13:49
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    Weight and Aero characteristics between long cage and short cage is insignificant. (long cage means wider gear spread, means more and/or bigger cogs, means more weight, more aero drag, so the deraileur becomes insignificant in the equation, getting a hair cut and shaving legs and arms before you ride will make more weight and aero difference anyway) The issue is long cage does not provide as crisp shifting, but the bigger issue is running long cage (and lower gears the mean you need it) on a roadie is likely to subject you ridicule from peers.
    – mattnz
    Commented Feb 5, 2017 at 21:28
  • True, the weight and aero penalties are insignificant, but it is also an extremely low hanging fruit. The shifting is done with upper pulley, which is not affected by cage length. Could you explain the mechanism how cage length affects shifting?
    – ojs
    Commented Feb 6, 2017 at 2:28
  • This is a good answer. I would clarify that when you say "your combination would require 37 teeth" that you meant the difference between the two chainrings (52-36 or 50-34) is 16, the difference between the smallest and largest rear cog is 32-11 = 21, so the total range that the rear derailleur must "absorb" is 16+21 = 37 chain links. In addition, I'd drop the second bullet point -- the first bullet point explains the reason sufficiently well.
    – R. Chung
    Commented Feb 6, 2017 at 15:43
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On your CoMax, with a typical climbing cadence on a steep climb of about 87 would be going at 11.7 km/h

These calculations are with 700x25c tire and wheel.

Lets look at the differences:

Current CoMax: 50/34 crank and 11x32 cassette, cadence 87 = 11.7 km/h

You Custom Combo: 52/36 crank and 11x32 cassette, cadence 87 = 12.4 km/h

Difference betwen the top two .7 km/h

'A' Typical: 50/34 crank and 11x28 cassette, cadence 87 = 13.4 km/h

Jump between CoMax and the above setup 1.7 km/h

'B' Typical 52/36 crank and 11x28 cassette, cadence 87 = 14.2 km/h

jump between CoMax and this setup 2.5 km/h

The difference between your CoMax and the jump you suggested to be a prime increase for higher speeds on the road as compared to your speed up steep climbs on trails are only a difference of .6 km/h This is not a very considerable difference as traveling up a steep climb off road which is what a cross bike is deigned to be able to do, is a lot steeper of a climb than any typical climb that you will see on a road that motor vehicles are able to navigate.

Reasons why your assumption may not be correct

  1. Most avid cyclist even at below optimal conditioning can maintain 13 km/h up most road climbs. Any slower than 11 km/h and you out of the saddle quite often if not most of the time.

  2. You are not ever going to typically need a 36/32 gearing combination unless you weigh 280 lbs or more and /or extremely out of conditioning.

The Trek Domane SL 6 (50/34 & 11x32) however, suggest this combination of gearing is available on bicycles other than cross bikes but is aimed at a market of bicycle enthusiast that want a good quality bike and a large range of gearing as they may ride only once per weekend and could be 'out of condition' and not competitive and also offers less rigidity and more comfort for an all around versatile bicycle riding styles and roads. It come with a long cage derailleur which is no untypical these day as there are a number of these gearing combination offerings on production bicycles, just not as typical or common and the smaller number as the whole of retail bicycle sold.

This gearing is also prevalent on Cross Bikes since they are designed for off and on road competition where they will typically be off road over trails, grass and weds going up steep trail climbs and across gravel and mud. In these competitions they throw in everything including the kitchen sink to bunny hop over and then you may be back on a road segment. This type of bike need to be very versatile with a gearing combination to match.

The 'A' Typical gearing is more suited for road competitions like long road rides and criteriums where there are some fast sprints and maybe some rolling hills and climbs but no steep mountains with long fast descents as even a pro rider which can spin a faster cadence than the typical rider will spin the top gear out at around 69 km/h on a long fast decent. Their gear combinations are not always 'off the shelf' typical as some run a 52/36 crank and 11x32 cassette.

The 'B' Typical is the average typical gearing for all around training and competition for the average competitive weekend warrior and racer for long stages. Most avid and competitive rider have no problem keeping 9-10 mph average up the steepest road climbs and the the 52 ring gives a good extra 4 km/h for long downhills.

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  • +2 for a nice answer. -1 for not following Rule #24
    – andy256
    Commented Feb 6, 2017 at 2:19
  • Ok, guess I will have to recalculate.
    – Rich Manson
    Commented Feb 6, 2017 at 7:49

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