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PostPosted: Fri Nov 04, 2016 11:11 am 
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xena wrote:
Great info ,thanks . mattr
Had no idea that the walls were that thin.
I used have 7800 cranks , so glad I never drilled any holes " so tempted"

If you say you're fit enough just attach your saddle straight to your top tube to lose weight instead. Only need it to put weight over the rear when going through corners.


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PostPosted: Fri Nov 04, 2016 12:41 pm 
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Raccooningtanuki wrote:
mattr wrote:
And then there is a trade off with cost.

Looking at the cutaway of the da 9000 crank, the structure looks pretty dang simple. I'm 99% sure there's room for improvement there.
That'll be the trade off with cost ;)


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Posted: Fri Nov 04, 2016 12:41 pm 


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PostPosted: Fri Nov 04, 2016 1:01 pm 
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Raccooningtanuki wrote:
Looking at the cutaway of the da 9000 crank, the structure looks pretty dang simple. I'm 99% sure there's room for improvement there.
Just look at the 9100 cranks for improvements.
Shimano wrote:
  • Enhanced design saves 7g while maintaining rigidity
    • Iconic 4-arm construction
    • Optimized crank arm design strengthens key stress zones
  • New chainring tooth profile is adapted for race bike specific disc brake systems
    • Accommodates shorter chainstays (410mm) with 135mm OLD
  • HOLLOWGLIDE chainring construction
  • Crank arm lengths: 165, 167.5, 170, 172.5, 175, 177.5, 180mm
  • Rider Tuned gear combinations (2x11): 50-34T, 52-36T, 53-39T, 54-42T, 55-42T
  • Weight: 609g (50-34T), 621g (53-39T)

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PostPosted: Fri Nov 04, 2016 5:52 pm 
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^ mythical, this crank is still not really lighter is it? 7 grams is nothing, it's probably less than what is within margin of weights of products of this weight.
FSA told me it's 5-6%.

If anyone, you have the background and knowhow to design a crankset that set out to change.
Do you feel all in all, this crank is so much better than previous design?

Could be none driveside stiffness has been better compared to what was the result of FWB's test!?

Anyway, still no chainring combinations suitable for gravel.
Also wonder if the chainring pattern/ fitting has been changed from that of 6800/ 9000 series?

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PostPosted: Fri Nov 04, 2016 10:16 pm 
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Here's what I think. I consider Dura-Ace cranks the benchmark by which others are measured. Also, I don't think there's not much weight to drop considering that aluminum fatigues rather quickly and has less stiffness (see modulus) compared to materials like steel or titanium, let alone carbon, so safety factors need to be comparatively higher. This goes at the cost of weight, since a significant amount of aluminum is needed to perform the same function as could be done with less titanium or steel alloys. I'd say Dura-Ace cranks are as optimized as they can be.

Non-drive side stiffness is strongly correlated to axle diameter, and since Shimano stubbornly adheres to a Ø24mm x 90mm axle, they leave a bunch of free stiffness on the table. Still...given their stiffness number, these cranks ain't bad at all. Like I said, the benchmark against which all others are measured.

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PostPosted: Sat Nov 05, 2016 12:23 am 
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I like your points mythical. Has anyone ever tried making lightweight hollow cranks out of titanium? That could help to reduce the fatigue issues of aluminium. I assume engineering hollow titanium cranks would be a major undertaking though. Sorry for the rambling.


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PostPosted: Sat Nov 05, 2016 1:38 am 
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And TI is significantly heavier than AL.


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PostPosted: Sat Nov 05, 2016 5:01 am 
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Magnesium is the strongest and lightest structural metal. Too bad very few people are willing to experiment and market parts made of this metal.

Magnesium is the lightest structural metal currently available in the world. Its approximately 34% lighter by volume than aluminum and 50% lighter than titanium. Besides light-weight construction, a few of the other advantages that magnesium offers are: excellent fatigue resistance, denting and buckling resistance, and the highest known damping capacity of any structural metal. The result is a much smoother ride than any other material out there.

Image
Image


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PostPosted: Sat Nov 05, 2016 5:57 pm 
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euph wrote:
I like your points mythical. Has anyone ever tried making lightweight hollow cranks out of titanium? That could help to reduce the fatigue issues of aluminium. I assume engineering hollow titanium cranks would be a major undertaking though. Sorry for the rambling.
Yes, back in the 90's a number of companies made welded tubular cranks from titanium. Sweet Wings made a few titanium prototypes but founder Craig once told me that all were lost. Morati, a Czech aerospace company, had theirs in production but those cranks ultimately proved inadequate due to many customers experiencing failures.

Image

Then there are Breezer IRD titanium cranks, Cook Quality Products and a bunch of others that all have disappeared into history. The most notorious of them all are the extremely lightweight Fly Sports Propellor cranks. Sadly, these cranks weren't engineered to last.

Image
Image

The most recent iteration of titanium cranks I know of aren't light and made in China.
Image

Most of the problems with titanium cranks stemmed either from the engineering or were to do with welding and residual stresses within the crank arms, or both.

Back in 2007, I design my Myth crankset design with Reynolds 953 arms. We tried to make a titanium version with 6Al/4V tubes made by Litespeed (because Reynolds no longer made their seamless titanium tubing) but the tubes cracked at the seam, so that plan fell into the water. Currently, I'm developing a 3D-printed titanium crankset. This eliminates welding and makes for a lighter design with more freedom in terms of shape. We just finished the first prototype and proceed with testing.

darnellrm wrote:
And TI is significantly heavier than AL.
Yes, in terms of mass, but a titanium alloy makes for lighter crank arms with better stiffness and strength than an aluminum alloy because less of the material is needed to do the same job.

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PostPosted: Sat Nov 05, 2016 6:28 pm 
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euph wrote:
I like your points mythical. Has anyone ever tried making lightweight hollow cranks out of titanium? That could help to reduce the fatigue issues of aluminium. I assume engineering hollow titanium cranks would be a major undertaking though. Sorry for the rambling.


You might look up Werts forthcoming crankset. Your question is pretty much answered here.

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PostPosted: Sat Nov 05, 2016 6:42 pm 
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Impressive write up Mythical. I have seen tubular cranks before but never knew anyone tried to make them out of titanium. The Fly Sports Propellers are amazing. Your last point is something I forgot to say in my previous post; with titanium less material and thinner walls could be used to make lighter cranks if they had the development that modern hollow aluminium cranks do.

I will look up Wert's offering now. Thanks!


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PostPosted: Sun Nov 06, 2016 10:57 pm 
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wheelsONfire wrote:
You might look up Werts forthcoming crankset. Your question is pretty much answered here.


Interesting, but ABOVE Euro 1,250 . :shock:

Waaaay outta my budget, but will be interested to see them !!!


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PostPosted: Thu Nov 10, 2016 12:46 pm 
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Well, they are actually going to cost more. But they compete with THM Clavicula SE talking weight.
For those guys with deep pockets it's not a problem.

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PostPosted: Thu Nov 10, 2016 1:50 pm 
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Raccooningtanuki wrote:
Looking at the cutaway of the da 9000 crank, the structure looks pretty dang simple. I'm 99% sure there's room for improvement there.


You can take advantage of the parallel axis theorem and increase the distance from center of the walls of the crank arms to maybe save a little weight, but you can't make them much thicker because the rider's feet get in the way. Shimano increased the dimension in the other axis with the 9100 version. The same thing could be done with the spindle, but bottom brackets on bikes are only so big and there must be room for bearings....

Magnesium is 35% less stiff than aluminum and corrodes easily. I had some sunglasses made of it and sweat made it literally crumble.


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PostPosted: Thu Nov 10, 2016 3:48 pm 
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F45 wrote:
Magnesium is 35% less stiff than aluminum and corrodes easily.


Magnesium is also 35% lighter than aluminum. Hence you can use more of the material to create a larger cross-section and gain substantial stiffness.


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Posted: Thu Nov 10, 2016 3:48 pm 


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