Why are the powercranks so big and bulky? And weigh so much. can’t achieve the same result with less weight and would mean a cheaper retail price? Is their a theory? Is there a short answer or is it beyond my knowledge as a nonsciencetist?
They are big and bulky around the hub because they have to support the clutch and they are heavy because they have to incorporate a bunch of hardened steel so the clutch will hold up.
The arms don’t have to be so big but my intial attempts to “lighten” them made almost no difference in the weight and then I figured out, that since they were meant to be training devices that that weight out there was actually a plus AND it made them less susceptible to fatigue failure.
Now that people are going to be racing on them I am currently exploring making the crank arms out of carbon. It won’t lower the total weight to normal crank range but will get rid of about half of it and it is the weight where it matters most.
Frank
Frank,
I think it was you who said that the average person is only pushing with about 50 lbs of pressure on the down stroke. With the cranks the way they are, I am getting an extra 5 lbs on the down stroke. When you lighten the crank arms, I will lose 10% of the force on that part of my pedal stroke. Can’t you figure some way to make the weight be at the pedal end of the crank arm for the down stroke and at the other end during the up stroke?
You have figured out that all that weight I am making you lift on the back stroke you get back as power on the downstroke. Power output will probably be more with the cranks I have (when the rider starts to tire) as the weight forces you to do a minimal amount of work on that upstroke. That being said, the fascination with weight amongst cyclists and triathletes seems all encompassing. One thing I expect these “carbon racing” cranks will offer though, from a race perspective, is an airfoil shape giving better aerodynamics.
I will leave it up to some of the other engineers out there to figure out a mercury-hydrogen pump that will pump mercury into a hollow crankarm for the downstroke and replace it with hydrogen gas for the upstroke.
I will leave it up to some of the other engineers out there to figure out a mercury-hydrogen pump that will pump mercury into a hollow crankarm for the downstroke and replace it with hydrogen gas for the upstroke.
Sounds to me like the beginings of a perpetual motion machine.
When do you expect the carbon cranks to be ready? I’m seriously considering the PCs now and would wait for carbon cranks to save weight. How much do expect the cost difference to be from the non-adjustable?
Thanks.
I expect to have my first prototypes sometime this summer. Depending upon how much tweaking will have to be done I may have them for sale later in the year or next year. The real problem will be the support for the clutch, inadequate radial support and the clutch will fail.
Cost, not sure.
Regarding waiting, I would recommend you go ahead now. The weight is insignificant on your performance compared to the delay in getting started on them as improvement may continue for 5 or more years. I will probably offer an “upgrade” to current users who want are racing on them and want to save a little weight.
Frank
Great. I’d be interested in the carbon crank arms when they are available. Thanks.
Just got some news that might make you reconsider waiting for lighter cranks. This last weekend Todd Herriott won the GC of the Vuelta Ciclística a Cuba. He told me he was intending to race on his PC’s this year (the heavy model) except, perhaps, for criteriums where the cranks might distract other riders. I haven’t confirmed that he did actually race on them but if he did it clearly shows that the weight of the cranks is not a big deal.
Frank