Sunday, August 22, 2010


Health Warning: this article is on the technical side - you may want to skip it entirely.  I wouldn't blame you.  In fact maybe I'll just give a couple of life updates first before boring you senseless.  First of all an Urban Foraging update.  There are tonnes of brambles around the place, most of the year just irritating tangled, spiky weeds.  However now they are fruiting and blackberries are can be had all over, even in London town if you venture out to some green areas.  Top tip is pick a load, freeze em, and then they make awesome smoothies with banana, yoghurt and a bit of milk.  As a good (Irish) friend of mine says "If it's free, take two".

Second, on the kit front I went out and bought the Garmin 310XT after a recommendation from my good (Irish) friend Marino.  So far it's awesome, it links up with my Powertap and existing heart rate strap no probs and gives me even more stats than I had before.  I'm amazed that such a small thing on my wrist talks to a satellite in geostationary orbit and then plots where I am, my elevation and all kinds of other stuff.  Crazy.

Third and not so good is I came off my bike last weekend and left a decent amount of skin that I was quite attached to on the tarmac.  The roads were slippery wet and I went into one of the tighter roundabouts on the route back from Box Hill at about 45kph and using a line that my coach later described as 'interesting'.  The wheels went out from under me and there I was skidding across the road, and also bringing down said coach, Jack who was close behind me.  Jack qualified for Kona at Utah earlier this year and since has had a string of very frustrating injuries.  My little caper has set him back another few weeks, and I feel pretty awful about that - sorry Jack!

One thing I did learn from this experience (I already know I'm rubbish at cornering), is how to treat a cycle graze (graze? gash maybe).  I went to the St George Walk-In Clinic and the guy there tells me first, clean out the wound - saline solution works great for this, but you can use the normal antiseptic products too.  Then the wound should be covered so that it can heal while still moist.  This is apparently 4 times faster than letting the wound dry out as some people recommend.  1 week later my elbow already has a decent skin covering and the hip is well on its way.  He gave me some fantastic antiseptic dressings that enable all this and also stick well and come off easy.  They are called Mepilex Border Lite in case you need to know for future reference.

OK that's all the life updates.  Now on to gearing - look away now if you are bored by bike geek speak.

First a little primer if you're not big on what this is all about.  Gearing is the configuration of your front chain ring (big cogs which your pedals are attached to) and rear cassette (little cogs on the rear wheel).  Your front chain ring will either be a double with 2 rings or a triple with, yes you got it, 3.  Triples tend to be at the novice end of the market, so I'll leave those out of this discussion.

A double will typically come as standard (53-39) or compact (50-34).  The numbers represent the number of teeth on each of the rings, and a bigger ring on the front is harder to turn.  There are other sizes but the ones above are what are normally out there and since this is a discussion about what I want to use come race day, that's what I'm going to talk about.  A compact would usually be recommended for more serious climbing like going to the Alps, and the standard chain ring for everything else, however as will become clear later, the compact may be an interesting choice for Ironman.

On the rear cassette there are all kinds of sizes, but standard are 11-23, 12-23, 12-25 and 12-27.  The numbers represent the number of teeth on the smallest ring up to the biggest ring.  The biggest ring on the rear cassette is easier to turn, the opposite of the front ring.  A 12-27 is often regarded as laughable by 'real' cyclists who will swear blind you need nothing other than an 11-23 or 12-23.  12-25s are sneered at as well.  I typically ride a 12-27 as it means I can spin on climbs to keep the legs fresh - this is what I had in Utah.  However I did just check my training wheels and actually I have a 12-28!  I bought a new cassette recently and ordered a 12-27, but seems like something went a little wayward - need to have a small chat with my mechanic.  A 12-28 is cheerleader status, and I better keep that one quiet.  Thank God hardly anyone reads this blog.

OK so finally we come on to gear ratio.  Gear ratio, in layman's terms, tells you basically how hard it is to turn a certain gear combination.  So if you're in the 53 ring on the front and the 19 on the back, and you're riding a standard 700-23 wheel (you probably are), then your gear ratio is 73.4.  This is pretty much the same as being in the smaller 39 ring on the front and the 14 on the back, where the ratio is 73.3.

The question I want to answer: what is the best gear ratio for me in IM Utah next year?  The options on the front are standard or compact, and the back are 11-23, 12-25 or 12-27.  Utah is a moderately hilly course, with potential for strong winds, and a monster marathon to back it up.  Requires careful pacing on the ride and avoidance of power spikes caused by mashing gears too much.  However there are also fast sections, especially with tailwind, where it would be useful to have harder gears.

The options are compact (50-34) with 11-23 or 12-25, or standard (53-39) with 12-25 or 12-27. I would not use compact with 12-27 (too easy), or standard with 11-23 (too hard), so have left those options out.

Here are the gear tables with full options. A smaller number means easier, a bigger number means harder.

Small Chain Ring Comparison

34 34 39 39
11 81.3
12 74.5 74.5 85.5 85.5
13 68.8 68.8 78.9 78.9
14 63.9 63.9 73.3 73.3
15 59.6 59.6 68.4 68.4
16 55.9 55.9 64.1 64.1
17 52.6 52.6 60.3 60.3
19 47.1 47.1 54.0 54.0
21 42.6 42.6 48.8 48.8
23 38.9 38.9 44.6
24 42.7
25 35.8 41.0
27 38.0

There are 10 rings on the rear cassette and I have left blank where there is no combination. You can see that the 12-27 necessarily jumps from 21 to 24 and from 24 to 27. This is one of the disadvantages of the 12-27 in that in the lower gears there are 2 large jumps and you could be in a situation where one gear feels too hard and the next too easy - it's not as smooth as the 11-23.

I've stricken out the 2 hardest gears. That's because you shouldn't be crossing the chain from the small ring on the front to the small cogs on the back, and vice versa. Effectively you shouldn't be using those gears (instead you would change the ring you're using at the front and adjust the back accordingly).

Same again now but this time on the big ring:

Big Chain Ring Comparison

50 50 53 53
11 119.5
12 109.6 109.6 116.2 116.2
13 101.2 101.2 107.2 107.2
14 93.9 93.9 99.6 99.6
15 87.7 87.7 92.9 92.9
16 82.2 82.2 87.1 87.1
17 77.4 77.4 82.0 82.0
19 69.2 69.2 73.4 73.4
21 62.6 62.6 66.4 66.4
23 57.2 57.2 60.6
24 58.1
25 52.6 55.8
27 51.6

Now we can summarise this by looking at the usable ranges for each combination:

Compact Standard
11-23 38.9 - 68.8, 69.2 - 119.5
12-25 35.8 - 63.9, 62.6 - 109.6 41.0 - 73.3, 66.4 - 116.2
12-27 38.0 - 73.3, 66.4 - 116.2

What is surprising here is that the compact with 11-23 has a wider range than the standard with 12-25 and almost for the standard with 12-27 as well. There is a very minor difference on the easy end, the 34-23 selection is just a shade harder (38.9) to push than the 39-27 combination (38.0).

However one of the major advantages of the 11-23 cassette is that there are no big jumps - the shifting is a lot smoother and you have a better range of gears. You can see that there is a fair amount of overlap between the big and small chain rings using a standard, but not so with a compact. And for those macho cyclists out there who say using a compact is for girls, well the 50-11 combination is harder to push (119.5) than the 53-12 (116.2). This will be handy in Utah, as there is a fast downhill section back to town, and if there's a tailwind as there was last year, I'll be able to get up more speed before spinning out.

All credit for this idea goes to Jack, who told me that compact and 11-23 is a really strong option. I would never have thought of the idea myself, but doing the analysis backs up the statement. Of course I could have just saved the hours it took me to write this post and just listened to his expertise, but I've learned a fair amount by doing this research. Congrats if you managed to read the lot - I hope it was useful!


  1. Glad you're liking the 310XT. The thing that amazes me the most on trail runs is it's unerring ability to maintain satellite lock even through really, really thick tree cover. It's certainly a cool bit of kit, and Garmin makes excellent hardware. All their PC software however is rubbish - I wouldn't recommend their logging software at all. Instead I synch to Sporttracks on my PC, which is very flexible

  2. You never told me you rode a 12-28?! This may change our relationship......

  3. Robby - I'm just as mortified as you! Making some purchases today to rectify the situation as soon as..

    Marino - I hear you on the Garmin software, it is pretty dodgy and I struggled to get the first sync to work. I'm also looking at Training Peaks WKO+ which is meant to be the bomb for cycle power analysis