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Crank test. What do you guys make of this?(10 posts)

Crank test. What do you guys make of this?Sintesi
May 20, 2003 5:47 PM
For what it's worth, the cheapest was the stiffest, the most expensive the least stiff. However, all measured deflections were minuscule. The difference between the heaviest and the lightest was 22 grams. Wow. That's nothin' kids. They (the testers) offer plenty of caveats and qualifications regarding their test so it's only worth the value you give it but nevertheless interesting and illustrative. So what do you get out of this? How would you change the test?

http://bikesportmichigan.com/reviews/crank.shtml

I'll tell you one thing, It made me feel good about my Ultegra cranks. :)
re: Crank test. What do you guys make of this?Spoiler
May 20, 2003 11:43 PM
It would be interesting to see what happens if they had been able to test with a traditional square taper cranks.
Then you could compare between Campy's aluminum and carbon cranks. If the aluminums were stiffer, you might create a carbon=flexy stigma.
I've alway heard that the hollow Coda cranks on Cannondales were the stiffest.
funnyfiltersweep
May 21, 2003 5:07 AM
I have an Ultegra crank myself... everything else is DA.

About the test: "(.082) under 124 lbs"- that really is nothing either- a wheel flexs much more than that. The other issue is simply that theoretically the wheel will move anyway- and the flex (if any) is against rider weight.
re: Crank test. What do you guys make of this?byker
May 21, 2003 5:13 AM
Thats a pretty good artical. They explained it very well.
Lateral stiffnes?Spiderman
May 21, 2003 6:17 AM
One thing they didn't mention (it looked their testing machine would have to be reconfigured) is the lateral stiffness of the cranks which would come into play standing on the pedals, or when you are throwing the bike from side to side (standing climbing and sprinting). Not a criticism, just a note of curiousity.

Also, i would think typically a crank is under a lot more pressure than 124lbs of pressure, but i am not an engineer, just a corporate monkey, so i could be wrong.
shockingDougSloan
May 21, 2003 6:41 AM
Hard to believe. With the price difference, you gotta believe the pricier stuff is better.

The weight difference likely is close to twice that, as they just weighed the drive side, apparently.

Another reason to get carbon over metal is vibration damping. That wasn't mentioned.

The crank really should be considered as a system with the bottom bracket. It's sort of meaningless to consider crank flex alone, then there could be magnitude of difference in flex at the bb interface (speculation).

I would change the test by installing the whole thing on a bike and measuring, but accounting for differnces in frame flex and bb/crank flex. You could build a mockup of a crank/bb with near infinite stiffness to eliminate the variable (build it out of pig iron).

Doug
Also...biknben
May 21, 2003 8:24 AM
As you pointed out. I immediately thought of what impact the bottom bracket has on the flex of the crank arm. At the other end of the arm they mount the apparatus to the pedal spindle, not the actual end of the crank. They are measuring the flex of not only the crank but the stub of the BB they used for mounting and the pedal spindle at the other end.

Because they use the same BB and asumming the same pedal spindle, it doesn't discredit the results between the cranks. In the future, if they were to expand the test to other cranks which require different BBs, I think the numbers would change dramatically. The BB would be a bigger culprit for flex IMO.

I new all those "free body diagrams" in physics would come in handy sometime.
frame, tooDougSloan
May 21, 2003 8:37 AM
Also, I've had the same Record 10 crank on a Bianchi EV2 and a Colnago C40, and noticed significantly different flex. With the C40, I could detect no crank/bb/frame flex at all; with the EV2, I could fairly easily make the chain rub both sides of the front derailleur cage, even sitting, and I'm not that powerful or heavy. So, me guess is that frame flex potentially have orders of magnitude greater contribution to flex that even the entire bb and crank/pedal system.

Doug
Also...biknben
May 21, 2003 9:21 AM
As you pointed out. I immediately thought of what impact the bottom bracket has on the flex of the crank arm. At the other end of the arm they mount the apparatus to the pedal spindle, not the actual end of the crank. They are measuring the flex of not only the crank but the stub of the BB they used for mounting and the pedal spindle at the other end.

Because they use the same BB and asumming the same pedal spindle, it doesn't discredit the results between the cranks. In the future, if they were to expand the test to other cranks which require different BBs, I think the numbers would change dramatically. The BB would be a bigger culprit for flex IMO.

I new all those "free body diagrams" in physics would come in handy sometime.
Bicycling Magzine did this testalansutton
May 21, 2003 3:58 PM
Bicycling Magzine did this test about 15 years ago during its consumer advocate days. Back then, it was a much less consumption oriented a magazine and worth reading. They built a massive steel device with a bottom fitting connected to hydraulic actuators and linear deflection gauges. They were able to measure both bottom bracket and crank arm stiffness. They measured about 20 cranks as I recall. Campy C-Record, new to the market at the time, rated the best. In hindsight, we had a lot of component choices back then. You could buy a complete groupo from Mavic, Galli, Ofmega, Suntour, Simplex, and Huret among others. I rode Galli parts back then because they were cheap. Now, when it comes to complete groups, we have 2 choices. Take it or leave it.