August 26, 2011 at 3:05 pm #93196Keymaster
Len, the chain does not resist windup from the spider in 360 degrees. Only about 90 degrees of chainwrap actually does loading (both in the testing rig and in the real world.) The rest of the chain is basically just laying without load on the ring to keep it out of the way. The measurement taken from the ring is just a secondary measurement that we take just for fun, but really doesn’t have bearing so we don’t publish it. The actual deflection measurement is taken directly. It’s measured at the upper end of the jig at the end fo the rod that pulls the arm and the strain gauge. This measurement because it’s taken centered in the pedal spindle includes both vertical and twist.
Some comments on the 7900 crank. This test has been going on for several years and we just keep adding new cranks to the test. That’s the reason for the inclusion of some older cranks. In the end we should have a nice list of cranks that cover quite a few years. 7900 will be included on the next test. The numbers for 7900 really didn’t change in any significant way from 7800 so we didn’t feel a rush to get it included in the test.
We also hope to soon add bb30 to the test which means being able to test the SIsl.August 30, 2011 at 8:47 pm #93197Participant
bb30! SiSl! Great and thanks!February 24, 2012 at 11:23 pm #93198Paul
What about the Shimano RX100?! A glaring omission. They must still have ‘it’ as they’re what I’m turning over on my Singlespeed when I pass guys riding with the latest (and “greatest”) up our local climbs.
Great test work otherwise. Keep it upMarch 1, 2012 at 3:14 pm #93199James
Great post. Two suggestions:
1) Can you add some low level cranks, like FSA Gossamer etc
2) Can you add MSRP or some other cost factor as it would be nice to see S/W per dollar or something along those lines. Many of these cranks are not that much stiffer (albeit perceived) but may be lighter and cost much more. It would help to see what exactly you are getting for the additional cost.
Cranks seem to be the mattresses of the bike industry. The different companies but different labels on them but they are the same thing underneath.July 22, 2012 at 3:23 am #93200Matt
so going on these figures… in terms of stiffness differences i may as well keep my FSA SLK cranks rather than spend money on rotor or hollowgrams?? there doesn’t seem to be much difference in numbers so effectively in real life you would notice nothing at all?November 19, 2012 at 7:05 pm #93201Francisco de Almeida
Great test, thanks!
You state that “The measurement taken from the ring is just a secondary measurement that we take just for fun, but really doesn’t have bearing”. It may however be an indicator of potential rubbing of the chainring on the deraileur cage. If so, it would be interesting to include it in you next report. Kind regardsDecember 15, 2012 at 5:55 am #93202Francisco de Almeida
It may be interesting for the overseas folks to be able to convert Jason’s results into N/mm. It’s easy, just divide 35 by the deflection in inches, e.g. for a deflection of 0.279 the stiffness in SI units is 35/0.279 = 126 N/mm.
The German Tour magazine often publishes crank stiffness values. Their test protocol differs from Jason’s, but since 2006 they follow a roughly comparable setup. They hang a 100 lb weight on an 4.19″ spindle but measure the deflection nearer to the crank arm, at 1.71″ from the crank face. Supposing that Jason applies the load about 2.25″ along the spindle, and that the bottom bracket bearings behave as the fixed nodes in the load case, my w.a.g. is that Jason’s numbers will be about 20% higher than those from Tour.
The best of all is that Jason measures the deflection on both cranks while Tour only looks at the non-drive-side. Take that, you Bayern!January 9, 2013 at 9:12 am #93203Joe
Thank you for the excellent test!
Wonder how the Look ZED2 crank would perform in this test.March 21, 2013 at 5:34 am #93204Gordon Leverich
Hi. Very nicely done. I am considering going from Octalink Ultegra 9 speed to the new 6750 model. I would expect the 6750 Q to be the same as the Dura Ace you tested? Any idea what the old octalink would be?