Tom,

It was not clear to me if you were measuring twisting deflection or bending deflection or both. Can you clarify? You also said you couldn't do the non-drive cranks but I am not sure why other than you would have to push "backwards" on them, not a big thing for a symmetrical device.

Also, can you throw a PC on there? Just curious as to how much "deflection" there is in the clutch because clearly there won't be much in the crank.

Frank

---

--------------
Frank,
An original Ironman and the Inventor of PowerCranks

John went into a long disertation about why he decided to apply force to the crank arm the way we did. My take-away from that is the forces applied by the test apparatus are applied in a manner to mimic pedaling as closely as we could given our many limitations. I don't know if that answers your question. In this test we didn't begin with the intention of "proving" anything in particular. We just wanted to see what would happen.

---

Tom Demerly
The Tri Shop.com

I wasn't sure if deflection was measured at the end of the crank arm (which I think was the case) which would measure primarily bending or at the point of force application (pedal) which would measure a combination of twisting and bending.

It would also be interesting to mount a rigid block to the spindle and measure deflection to see how much is coming from the spidle deflection. I suspect a fair amount of the deflection seen is from the spindle twisting, making each of the cranks even more rigid than they seem already and making this aspect of choosing a crank even less important.

Frank

---

--------------
Frank,
An original Ironman and the Inventor of PowerCranks

Thanks Tom. Now I can't use the stiffness/weight/performance argument on my wife when convincing her how much I need the FSAs

To be seriuos, though....You'd better be careful with this road you're on. Pretty soon your customers will realize they will be as fast on a Felt S22 as they will on a Blade with carbon and titanium goodies everywhere (provided, of course, that the bikes fit properly). I, for one, don't really want them to realize its all about the motor. I'd rather they support your living buying expensive "speed" than actually training!

Good point. Forget all the stuff i said in that article....:)

---

Tom Demerly
The Tri Shop.com

So, allow me to cast the first stone at the test methodology....

I think it is important to note that this test provides data only in regard to the stiffness of the crankarm itself, and only in relation to the fixed BB point. There are marked differences in the stiffness of the spider assemblies of these various cranksets, and I have seen test data to indicate that the deflection variability introduced in this part of the drivetrain is, in fact, responsible for more difference in overall stiffness/performance vis the drivetrain than the arm stiffness (which, as your tests show, does not differ all that much between high-end cranksets.) For example: FSA in-house testing indicated an (approx.) 15% difference in overall stiffness between the Team Issue and the Carbon Pro cranks, attributable entirely to the carbon vs. the aluminum spider. The arms themselves would test out essentially identical in testing of the sort done by Tom, but from a system/performance standpoint, there was a clear difference in performance, the carbon spider outperforming the aluminum one.

This is, of course, the problem with testing. This test appears to be a good test of crankARM stiffness. I just don't think it necessarily provides much useful information about crankSET stiffness, or at best, it provides a very incomplete analysis.
The important thing, ultimately, is how efficiently a crankset transfers energy from your legs to your drivetrain, and the stiffness of the armset is only a part of this equation.

MH

---

Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

This is 100% true: The spider did not play any role in this test because of the test apparatus and how the crank was mounted to the test apparatus. It only tests arm stiffness.

Your ponit is relevant enough so that I will include mention of this in an ammendment to the article this Friday morning. Excellent observation and the reason why I post on this forum. I thank you for this. I will also pass this information on the John (guy who built the machine). If John is so inclined (he loves doing this stuff) maybe he will build a device or apparatus that includes the spider, which I think would be a more accurate or complete analysis of crank properties.

---

Tom Demerly
The Tri Shop.com

No Campy? Square taper BBs are still the most difficult to produce well and Campy does it better than anyone...

Let's not forget that they actually know a thing or two about cycling in Italy as well;-)

BTW, Tom, you refer to the Soloist as a "Ferrari?" What does that make a C-40?

---

http://wattieink.com/elite-team/
Raising funds to help wounded veterans and racing RAAM 2013 with http://team4mil.org/
"If you are gonna charge... CHARGE HARD!"

expensive.

---

Tom Demerly
The Tri Shop.com

Casting another stone.

I think that including the spider is a great idea. But to evaluate the stiffness of a crankset you must include both of the arms which transmit the force through the BB, spider and chainring to a fixed chain. I was also wondering if the deflection was measured from a preloaded condition. If the deflection was measured between 75 lbs and 125 lbs the slop, if any in the test rig might be eliminated by the time you reached 75 lbs. Also. when comparing wt. the other arm should also be included. Your on the right track, keep up the good work.