Mountain Bike Reviews Forum banner

1 - 20 of 29 Posts

·
Banned
Joined
·
5,770 Posts
Discussion Starter #1 (Edited)
test: integrated cranks...

german magazine "Mountain Bike" did a comparison test of 11 different integrated cranksets.
they measured weights and stiffness as well.
Gewicht: weight
Steifigkeit: stiffness
SGI: stiffness to weight factor (stw)

as you can see the XT is the big winner here. its stiffness is well above XTR and the weight still pretty light. the FSA V-drive gets the "buy-it" tip as it is the best value for the money.

and finally they show the ancient XT combos and the according numbers. see the small scan below where they show the numbers for 1998 square XT crankset,2003 octalink and finally the 2005 integrated version.

what the added stiffness all means:
they say you can feel it as the shifting precision is better and chainrings don't rub on the front derailleur in hard sprinting situations as was sometimes the case with older setups.

i also added that older crank stiffness test done by another magazine about 2 years ago. don't compare numbers 1:1 as they tested differently but still you get the point. we see Deore square cranks get 83 N/mm reading which is about what the XT has in the little scan of this actual test (84,76 N/mm). we have many octalink cranks in the 100 N/mm region and ISIS cranksets way above (118 N/mm for a FSA ISIS crankset) so the difference in stiffness compared to these new, integrated cranks isn't that different...oh - i almost forgot to mention the famous XTR octalink crankset: at 88 N/mm definitely much weaker than most actual cranks but i can't remember people saying the stiffness was low on those cranks...

my question however if that added stiffness actually has any power benefit isn't answered...too bad. i would really like to see some numbers. does a "flexy" crankset have an influenece on power output or not? my chainrings don't rub and shifting is good so i don't have a problem there. if i would have serious powerloss i think i would have to change....but so far i don't see or feel any disadvantage. on the road peloton almost half the field is using Campagnolo which has square BBs only so it can't be that bad powerwise;)
 

Attachments

·
Banned
Joined
·
5,770 Posts
Discussion Starter #3
correct...

bike_freak said:
Pretty cool stuff.

So if I am reading this right... then the Deus cranks are the 2nd flexiest?
yes - these numbers don't lie!
 

·
chips & bier
Joined
·
1,597 Posts
Keep in mind...

that the integrated desgins are still twice as still as many square-taper models, and few were complaining then. Also, crank (lack of) stiffness becomes most noticeable if you have a rather stiff frame. Us all being weight weenies (well, many of us): how many here have a heavy, über-stiff frame?
 

·
Lactic Acid is my friend.
Joined
·
365 Posts
Comparing my Trek that has RF Next LP with American Classic square Ti BB and my Serotta with the new XTR, I can definelty say I notice a difference. The chainrings on the Trek rub the front derailleur pedalling hard even in the saddle, and I've adjusted the derailleur countless times to try to get it out.
 

·
Registered
Joined
·
1,167 Posts
Describe the test method.

Please describe the test method. I assume the stiffness measurement is the force required to flex the cranks a given number of degrees in the direction of rotation with the chainrings held in a fixed position? If it measures lateral (inward) flex, it seems like a useless test.

I have noticed that the Deus cranks I have feel less stiff laterally than my previous Next LP ISIS, but I have never noticed a difference in stiffness in rotation between any crankset.

Personally, I would be more interested in fatigue and bearing test results along with actual weights as always of course.
 

·
Registered
Joined
·
489 Posts
Interesting. I like the looks of Saint but i reckon the XTs offer me all the performance i need for my biking. I would be interested in seeing some figures for road cranks as well.
 

·
Registered
Joined
·
790 Posts
Road Cranks

erol/frost said:
Interesting. I like the looks of Saint but i reckon the XTs offer me all the performance i need for my biking. I would be interested in seeing some figures for road cranks as well.
Note that Velo News published a test of crank stiffness about a year ago or so, and Dura Ace with the external BB was way stiffer than naything else. Included in the test were Campy Recod Carbon, FSA carbon, and anything else that might be considered high-end.

Nino: I do believe that Campy is going to be producing external BB cranksets very soon, in order to compete with the stiffness of Dura Ace.
 

·
Registered
Joined
·
1,167 Posts
But how is it being measured?

What sort of stiffness are we talking about? We don't really care if it is inward flex. We care about rotational stiffness. In other words, does the bottom bracket spindle twist or do the crank arms deflect in the direction of rotation when placed under load?

At one point, someone here said the German tests measured inward flex. This is useless information since the power loss due to such flex would probably be unmeasurable.
 

·
Registered
Joined
·
2,152 Posts
The're also a torsional load on the crak arm, not just a bending load in the direction of pedalling. How far from the crank arm centerline is the center of your cleat? You could easily make a crank that is really strong to resist bending, but twist like a noodle. That's why I'm curious as to how the test was done. A while ago someone posted a rodie crank arm stiffness article and they applied the load directly to the crankarm. This test totally neglected any torsional force on the crankarm.
 

·
Registered
Joined
·
1,167 Posts
Good point.

That's another important measurement of "stiffness" that matters. In fact, I bet this one would result in the most wasted power input since I suspect the other measurements I mentioned would show results that are high enough.

I doubt there is much to be gained with stiffer cranks anyway (except sales). I went to the external bearing type design mostly with hopes of finding greater bearing life. Since I have had a Next LP ISIS arm crack due to fatigue, I would also be interested in any fatigue test results.
 

·
Registered
Joined
·
2,152 Posts
B R H said:
That's another important measurement of "stiffness" that matters. In fact, I bet this one would result in the most wasted power input since I suspect the other measurements I mentioned would show results that are high enough.

I doubt there is much to be gained with stiffer cranks anyway (except sales). I went to the external bearing type design mostly with hopes of finding greater bearing life. Since I have had a Next LP ISIS arm crack due to fatigue, I would also be interested in any fatigue test results.

That was the jist of that road bike crank comparison. They stated through thier testing (which neglected torsional forces) that all high end crankarms were so close in stiffness that it didn't matter.

Here're some plots to illustrate my point. It's hard to read the text, all shrunk down, but the one w/o torsinal load has a deformation scale of about 30:1, and the other one about 4.4:1. This shows (of my extremely simple) I-Beam crankarm is damn stiff in bending but quite noddley in torsion.
 

·
Registered
Joined
·
2,152 Posts
One more.. I thought I'd do a tubular arm to compare (take my word for it, this arm is hollow). This arm is the same mass as the I beam version, (+1g), but is more than twice as strong in torsion, while having identical strength in bending. This proves that in a test that neglects torsion, you could state that crankarm x and y are just about the same in stifness, or worse, say x is stiffer than y, but the truth would be completely opposite.
 

·
Registered
Joined
·
1,167 Posts
Neat images. I think the Deus (I-beam type) actually feels less powerful than my old Next LP (sort of tubular?). Your work tends to make me believe that twisting is the likely culprit. It's hard to stand on my bike and watch for twist, but I sure can see the Deus arms flex inwards when I press down hard on the pedal. This was one of the first things I noticed when I installed them. I still don't think it matters much when actually riding but I did prefer the feel of the Next LPs. However I MUCH prefer the bearings in the Deus. Can't wait for X-type Next w/carbon.
 

·
Registered
Joined
·
49 Posts
I think we have to train harder not to take care about crank stiffness... :rolleyes:
The engine is the rider and it is not because your cranks is a bit flexier than an other that you are not going to loose. If you do long races, you are never at 100% of your power so the difference of the stiffness become so little. But i think the weight is more important. On marathon races we spend a long time climbing with a high legs rotation speed not to burn all the glycogene.
In fact, when we do our custom made mtb it depends of which races we will do.
 

·
Registered
Joined
·
184 Posts
Interesting. Baidsed on the stength analyiss, hollow cranks are far supirior to I-beam design. I smell a senior project for my Manufacturing Enginineering degree coming on!! I love this stuff. Great thread!
 

·
Registered
Joined
·
2,127 Posts
That was fun reading. My SweetWings steel, tubular cranks were the first external BB cranks I used, and they remain stiff and very reliable. I waited and got the new, hollow, aluminum XT external BB cranks as soon as they became available, and they've been great, too. At 210-230 lbs (winter happens), I notice when cranks, BB spindles and frames flex, and I like the XT set a lot.

On bearing issues: the XT use the same size, but not quality, of bearings as on the non-drive side of my years-old SweetWings. When I got them, I opened up the XT bearings and found them nearly without lube grease. With that remedied, I expect they'll last a good long time.
 

·
Registered
Joined
·
161 Posts
one thing to note whenever looking at finite element analysis pictures, is that they are pretty. however, they're often misinterprited. pretty pictures or not, you still have to use your brain.

when comparing from one analysis to the next, you can't just go by which has more or less yellow, blue, or red. make sure to look at the scale legend. most analysis packages set 'red' to be whatever the highest load in the entire analysis is. that typically throws colors off in the area that really matters. be careful about this. plus, analysis is ONLY valid when constrained properly. this is a VERY important part of the process, and is extremely difficult in most scenarios, requiring experimental validation to set up in the first place.

finite element simulations are useful for finding the areas of peak von-meisis stresses, but the plots given here don't indicate overall strength or stiffness. that too can be found, but it's something entirely different. i've said it before, but overambitious techno-engineering heads need to spend more time remembering not to confuse stiffness with strength.

looking at crank structures for senior project? comeon, apply yourself dude. here's the result for you. i-beams are stiffer/stronger from a strength to weight perspective from vertical bending moments. round, circular, or square designs suffer (again, when same linear mass/volume is used) vertically, but are more even vertical/horizontal, and are stronger torsionally. two designs specialized for two different things. Moments of inertia, MY/I formulations, etc...
 
1 - 20 of 29 Posts
Top