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155mm cranks for Jules

Since I started work at Cyclefit, Jules has been moaning about how he can't climb or time trial because his legs are too short (please read my previous, related post about Joaquim Rodriguez - http://tinyurl.com/2vmjoda ). This is, of course, VITALLY important for the annual GPM10 trips to Majorca, so we set about trying to improve this problem.

Traditionally riders only consider 3 crank lengths- 170mm, 172.5mm, and 175mm, but is that enough to truly accommodate the huge range in leg lengths? The table below is a rough estimation of the ratio between saddle height and crank lengths of a few riders (pulled from cyclingnews pro bike articles). Phil is 'Mr. Average' when it comes to saddle height- please no jokes. If we treat Phil as a baseline, for Jules to achieve the same ratio as Phil or Mr. Armstrong he has to ride 155 cranks.

Name	Crank Size	Saddle Height	Ratio
Jules	155	67	2.31
Jules	165	67	2.46
Jules	170	67	2.54
Phil	170	74	2.3
Sandy	172.5	78.5	2.2
Boonen	177.5	80	2.22
Gesink	175	83.5	2.1
Sastre	170	72.5	2.34
Cavendish	170	70	2.43
Armstrong	175	75	2.33

The reason this is a useful ratio is that it gives some indication of the range of angles that a rider has to handle throughout a pedal cycle. Gesink will not have to maintain nearly as acute an angle at the top of his pedal stroke as smaller riders such as Jules.

Jules finally ignored the stigma attached to short cranks, which I can imagine comes from some kind of subconscious male instinct that I won't discuss, and put on a TA Agilis 155mm crankset. We also raised the saddle 15mm to maintain the same leg extension at the bottom. Using some before and after analysis on Dartfish, Jules' hip angle at the top of the pedal stroke was consistently 10 degrees less acute than with 170mm. We also compared the hip angle when climbing, and found that it was also 10 degrees on average. The leg extension at the top of the pedal stroke was on average 10 degrees more obtuse than with 170mm. Here was Jules' initial reactions-

'Cranks are good, pedal stroke is smoother much less ‘up and down’ of legs and more open hip angle.

Less leverage from the lights when starting for the first two or three revs but once in the saddle acceleration is quicker to cruising speed.

Maybe for cross 160mm cranks would be better, or 155mm cranks with Rotor Q rings….

Do not feel the need to keep getting out of the saddle as much as before.

Climbing seems OK so far – maintaining cadence is the key.

Handlebar position good, saddle much more comfortable'

I need to put some solid numbers behind my theory, but I feel many riders should consider smaller cranks. Feel free to comment with your opinions.

Gent Six Day Leg Extension

Its the first day after my knee op, and I am already bored, so I decided to download a 30 day trial of dartfish (www.dartfish.com). This is the software we use at cyclefit analyse a rider's biomechanics.

I used it to analyse the leg extension of some of the riders at the 2008 Gent Six Day's penultimate madison. It was interesting as racing a track bike on a 166 metre velodrome has so many differences to standard road riding that we usually see. Here is a list of some of the differences.

1. possibility of shorter cranks

2.more aggressive (shorter/ lower) position as using smaller frames and always on drops

3. narrower q-factor

4. g forces pushing when through the banking

5. Non- symmetrical riding

6. very little out the saddle effort

7. higher cadence

8. fixed gear

My estimates are only rough. I can't go down there and put tracking dots on their knees! But the theme of the results for leg extension were interesting.

-Bruno Risi 32.5°

-Leif Lampater 40°

-Schep 35°

-Andreas Beikrich° 45-50

-Keisse- 43°

-Zabel 37°

With the exception of Bruno Riso, Schep, and possibly Zabel, all the riders seem to have very low saddle heights. When I am fitting at Cyclefit I get an average of about 32/33°. The demands of the track are obviously a lot different. I feel there are several reasons.

1. It enables the riders to maintain a more stable pelvis for the much higher cadence's used

2. The lower handlebar position puts more strain on the hamstrings so reaching a larger extension is very difficult- especially repeated night after night

3. the fixed gear at high cadences puts less torque on the joints (just speculating)

4. It is more stable when doing a madison change

On the other hand, the wide range (32.5° to almost 45) shows that I might be completely over analysing their reasons for having a lower leg extension, but the mean of the extension's is 39 degrees. Personally, I think that around 35-37° (on average) is perfect for the Gent track if we look at the two extremes, Keisse and Risi. I am not convinced that Keisse is achieving his full power output, as we can see when he drops his heel during a sprint to achieve a larger angle. I think that Bruno Risi is slightly too high as his hips are rocking and he grips the handlebars quite tightly in comparison to the other riders to stabilize himself. Just some thoughts...