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Hello Ian,
I’m Lino and I’m current on a speedmax cf Slx 2019 small. My bike fit was done with retül and 51speedshop ultimate and I’m using the specialized sitero saddle. I’m looking for recommendation of a short crank for being more aero and I would appreciate if you can help me. I’m a competitive triathlete and I’m working everyday with my flexibility. Actually I’m using a 58T chainring and riding with a cadence of 67. My average speed is 39-41km/h in 120km in a flat course with 800-1000m during training.
Height 165cm
Weight 60kg
Pad Y 59cm
Pad X 56cm
Crank 170mm
Saddle height 68.7cm
Pad width (center to center) 16cm
Saddle nose to clip (center) 50cm
Thank you for you help.
Lino Nardin
Lino,
At your height I would just assume that a crank shorter than 170 would be better. My thinking is not complex, it's based around this simple idea: if you rode with your aero bars lower you might (MIGHT) slip through the wind a bit more/have less drag. The common problem with lowering your bars while leaving your cranks long is that at the top of the pedal circle the long crank raises your leg to a point where the flesh in the hip starts to bind up and you a) are made uncomfortable by that and/or b) the leg circle is slowed by that impinged area. If you shorten the crank then the leg flows through the top of the pedal circle smoothly, quickly, easily.
Keep in mind: lower is NOT always faster. If there's something that keeps you from being comfortable lower then don't go there. Also, 165 is the shortest that the big brands go. I would think you'd do well on a 155 or 160 and for that you'd need to go to Cobb or Rotor or some other brand - all very good cranks by the way. It's not possible for me to be more specific without really seeing you on the bike and knowing some key measurements.
I am a coach as well as a bike fitter so I'd like to make comment on your cadence... Creating power on the bike is our goal. The formula can be expressed pretty simply and pretty accurately as: Cadence x Torque = Power. Let's pretend for a minute that your best ironman distance race would come from 200 watts of power (just a number to use an an example).
One way to make 200w is...
67rpm X HEAVY torque on a 58 tooth chain ring = 200w
My worry here is that your legs might be too tired from this style of riding to run well off the bike
Another way to make 200w is...
110rpm X very light torque on a 50 tooth chain ring = 200w
You're still making your 200w but you're doing this with a wildly fast cadence that might also leave your legs in bad shape for the run
Perhaps the best way to make 200w might be....
78-82rpm X moderate torque with a 52 or 53 tooth chain ring = 200w
You've still got your 200w and the hope is that your legs are fresher for the run
Even if you were just a time trialist - a cyclist who doesn't run - I would still want to explore the idea of increasing your cadence to increase power.
Thanks for letting me share my thoughts on that.
Ian
Ian Murray
http://www.TriathlonTrainingSeries.com I like the pursuit of mastery
Twitter - @TriCoachIan