Crankset Selection: Part 2

Since determining that I would need to use a 46 tooth chainring as my big ring, I feel that using a 110 BCD crankarm would make the most sense.  I think that crankarms should be chosen based on the the larger chainring size, the reason being is that if crankarm's spider is lager then there will be less flex on the chainring and less stress on the crankarm itself.  I am also trying to achieve a wide range double crankset too, which wouldn't be possible with a 144 or 130 BCD as I have already determined my largest chainring will be 46 tooth.  If I was to use a 144 BCD the smallest ring I could use is a 41T and 38T with a 130 BCD crankset, but with a 110 BCD crankset I can have a chainring as small as 33T.  To find out about probably every other crankset's BCD, here's a link to Sheldon Brown's site on the subject here.

I have found some some examples of modern cranksets that I will be considering for this build.  All of the cranksets I have included in this post are cold forged aluminum with CNC machined chainrings.  Cold forging is the best method for manufacturing cranksets or any bicycle parts for that matter as this method makes aluminum its strongest.  Again, Sheldon Brown has a great article on his webpage describing the different methods of parts manufacturing.

Sugino Alpina, 665g, top.  Velo Orange, Grand Cru 110, 670g, bottom.

There are basically three cranksets I've been eying, one of them being the Sugino Alpina.  What I like best about the Alpina crankset is that it does away with the spider pattern the use on their other cranksets, which hides a chainring bolt behind the crankarm.  This crankset has a slightly more modern styling than the others I have been looking into, comes with 48-34T chainrings, weighs 665g and is also made in Japan.  IRD and Velo Orange both offer pretty much identical 1970's vintage looking cranksets.  The main difference between these two is chainring sizes.  The Velo Orange crankset comes with 48-34T, weighs 670g and the IRD comes with 50-36T, weighs 680g.  The IRD crankset is likely heavier due to the larger chainrings.  Velo Orange has already done a great contrast/comparison between the Sugino and Velo Orange crankset on their blog.

IRD Road Double, 110 BCD, 670g, 50-35T

Finally, I am also open to the idea of using the crankset seen below.  This is a copy of the old style TA and Stronglight cranksets starting from the 50's manufactuered by Velo Orange.  This crank claims to have extra strong chainrings to help alleviate flex and also offer by far the widest selection of chainring combinations.  Stock, this crankset comes with 46-30T chainrings, which are exactly what I was hoping to use, and is the lightest of all of these cranksets at 550g.

Velo Orange Grand Cru, 550g, 46-30

Crankset Selection: Part 1

When it comes to selecting a crankset my main consideration is gain ratio.  There are a couple of  web sites out there that allow you to calculate this, but I have found that this one by Mike Sherman the most useful.  It not only  gives you the calculation for gain ratio (the Sheldon Brown calculation), but also gear inch, speeds at a particular cadence and a roll out table.  Basically what all this can help you determine is the appropriate cassette/freewheel and chainrings sizes to use.

Sugino Mighty, 144BCD, 53/42

For my sportif bicycle I am going to be using a six speed cassette with a double compact double crankset.  The reason for selecting a double crankset instead of a triple is because where I live and ride, there just simply aren't that many inclines, and the ones that are around can easily be tackled with an appropriate sized inner ring.  Initially I was pretty set on using a 1970's, 144 BCD (bolt circle diameter) Sugino Mighty crankset I had acquired a while back, which was fitted with 53/42 chainrings.  52/42 chainrings are pretty common for road bikes, but I feel that gearing is not too useful.  After reading up on 144 BCD cranksets I found that the smallest chainring I would be able to get for this crankset is a 41 tooth, which when matched with say a 48 tooth chianring would make for a lot of very close gear combinations.  What I am hoping to achieve with this crankset/gears is a setup where I can ride in the large chainring for at least 90% of  the time and only have to shift into the smaller chainring for climbs.

6-speed cassette, 13-15-17-19-21-24

To achieve a suitable chainring size I first figured about what gear I ride with most often.  On one of my bikes I ride at a gear ratio of 4.6 and on the other 4.75.  That being said, I would be trying to achieve this gear ratio in the middle of my cassette, meaning that when in the larger chainring and in the middle of the cassette I should be able to ride with a gear ratio close to my most common gear ratio.  The cassette I will be using has the following cog sizes: 13-15- 17-19-21-24, therefore, the large chainring should be 46 to achieve this.  Here's what the gain ration chart would look like for this setup:

         13     15      17      19      21      24
46   7.12   6.17   5.44   4.87   4.41   3.86

Enough about technical data and chainring selection.  Next posting I'll outline my options for possible cranksets based on chainring compatability and quality.