Friday, September 28, 2012

Equipment - Aerodynamics and Frame Fit

The other day I saw this article on aerodynamics, a kind of "ramble in font" by Chris Boardman. He explains, in very layman terms, his very layman way of reaching his optimal position on his bikes.

I knew, from his GAN days, that he rode about a 53 cm frame, meaning a frame with a 53 cm seat tube length. Nowadays that doesn't mean much what with compact versus regular frame set ups, seat tubes measured in all sorts of different ways, and of course the fact that the seat tube has nothing to do with length/reach, very little to do with saddle to bar drop, or even very little to do with the saddle height. The basic 53 cm frame size immediately says a few things though - you can expect a top tube length of about 54 cm and a head tube length of maybe 14 cm.

What's surprising on Boardman's regular looking 53 cm track bike (with drop bars) are the other dimensions.

63 cm top tube?!
17 cm stem?!

To look at him on the bike he doesn't look wrong at all - in fact he broke the non-aero hour record astride the machine.

He came to the position using a couple basic principles plus an open mind. He wanted to keep frontal area to a minimum (although this is technically flawed it's better than nothing) and he had to be able to put down reasonable power (i.e. threshold, since, by definition, he'd be making a 60 minute effort).

(Which makes me realize that his threshold lets him ride at over 31 mph. His threshold! I'm so far into the red at 31 mph it's crazy. Jeepers creepers and holy canolies. Wow. Okay, fine, he was a great short distance time trialer, he broke the hour record, but he was, with all due respect, basically nowhere in the big races. Wowsers. Anyway, back to the post...)

He pointed out that he avoided measuring things until after he set up a position that worked for him. He used a powermeter and pedaled at 50% of his threshold, give or take. By not measuring he let himself let go of any preconceived notions of what would or wouldn't work.

(Incidentally if I rode at 50% of my threshold I'd be doing about 100w, which, honestly, I could do in almost any position. I guess he just kept his pedals turning so anything they tried would be somewhat reasonable.)

One thing you'll notice is that if you look at Boardman on the hour record bike versus a road bike (even a TT bike) you'll see that the head tube on the road bike is much shorter. This is because the bottom bracket on a track bike is higher, by about 1.3 cm. Since frame "size", i.e. seat tube length, is measured from the bottom bracket, if you move the bottom bracket up 2 cm then the frame suddenly looks about 2 cm higher.

As an example look at my 50 cm track bike, which, I have to point out, can't do 31 mph for even 3 km:

Note head tube length.
I wonder if a 63 cm top tube would help.

This head tube looks shorter.
Saddle height is the same. 56.5 top tube.

The Riggio has a 16 cm total head tube height, with headset. The Tsunami is 11.5 cm with the headset too. With spare bars on the track bike, the same make/model as the bars on the Tsunami (Mavic 315 bars, crit bend, circa 1997), I need a slight rise to fit the Riggio properly.

I'm veering hard off my original thoughts though, that of Boardman's approach to fit. The most important thing was that he threw out any preconceived notions on what should or shouldn't work. He admits in the article that if he took measurements while changing stuff around he probably would have ended up with a more conservative set up.

That BikeRadar article made me go "hm." Boardman's had a good approach to his fit, unconcerned about staying within his comfort zone, open minded as far as possibilities.

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