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Old 09-12-12, 03:01 AM   #1
Lasse
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Cranks: 2014 or 6061 alloy?

Could anyone help me decide on which alloy to choose for a pair of new cranks?

Apparently the Sugino XD2 cranks are being sold in at least 2 versions: the Sugino branded one in cold forged, anodised 6061 aluminium and the Spa Cycles unbranded one in forged, polished 2014 aluminium (also Sugino made, according to pictures of the stamp on the rear of the crank). The latter alloy is claimed to be of higher strength by the shop, but I have no clue if that makes them more suitable for use as year round cranks on a touring bike (mostly in cold, rainy Western Europe with salt on the roads in winter).

Some quotes from around the web about both alloys:

Wikipedia confirms the higher strength of 2000 series:
Quote:
-2000 series are alloyed with copper, can be precipitation hardened to strengths comparable to steel. Formerly referred to as duralumin, they were once the most common aerospace alloys, but were susceptible to stress corrosion cracking and are increasingly replaced by 7000 series in new designs.
-6000 series are alloyed with magnesium and silicon, are easy to machine, and can be precipitation hardened, but not to the high strengths that 2000 and 7000 can reach.
Ibex Bicycles says 2014 is impossible to weld, while 6061 is. Has anyone ever welded cranks or is this factor of no importance at all?
Quote:
There are many other aluminum alloys like 7075 and 2014 that are stronger than both 6061 and 7005, but are not appropriate to making bike frames because they are nearly impossible to weld.
Tech-faq.com mentions some advantages of anodizing, which sound important for cranks:
Quote:
Anodized aluminum has several advantages that regular aluminum does not. Anodized aluminum has a much more porous surface that allows adhesives, lubricants, and dyes to be absorbed into the alloy. Anodized aluminum also has better natural protection against corrosion and wear, due to its rougher surface and the thick oxide layer that surrounds it. Likewise, anodizing prevents aluminum from cracking or peeling from regular use.
So, could anyone push me in the direction of the better choice, please?
The price difference is not big enough to make it the deciding factor, unless both are equally good.
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Old 09-12-12, 05:35 AM   #2
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Which cranks are you looking at? If you are looking at the ones from Spa Cycles, they currently only have a limited number of sizes, so this would limit choice.

For material, how it's made has an impact as well, it is forged / machined, others with more knowledge can extrapolate, but if it's made by Sugino, would trust that they have made a quality product (have used their cranks before with no issues).

Welding? when was the last time you saw a crank with welds? unless they are steel, cranks normally aren't welded, so not an issue.

For a better choice, what is your budget, ring requirement (number and teeth count), BB type etc. You haven't given any real info on your first proposed choice, so this is pretty hard to do with the limited info provided.
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Old 09-12-12, 06:23 AM   #3
Lasse
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Jimc101, thanks for the reply.

I want to buy triple Sugino XD2 cranks (because of square taper, many good reviews and price/quality) in 175mm length and will add TA 24/34/46 chain rings. Currently I'm running Shimano Alivio cranks on my custom LHT but their Q-factor (ca 195mm with 50mm chain line) forces my feet into an annoying position.

Spa Cycles claims that their version of the XD2 is stronger than the Sugino branded one, hence my question. The Spa Cycles cranks are cheaper, but the Sugino branded ones aren't too expensive to consider. The only differences appear to be technical and I'm not specialised in alloy qualities for cranks construction, so help is appreciated.

Usage is year round in Europe and a 3 month trip throughout Eurasia (Belgium to Nepal) is being planned together with a couple of friends, so it should be good enough for that journey in the middle of nowhere as well.

Last edited by Lasse; 09-12-12 at 06:26 AM.
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Old 09-12-12, 06:57 AM   #4
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Unless you are incredibly strong I doubt that you would be able to break a crank, hence concerning yourself with the ultimate strength of the various alloys is of little value. Since the actual strength the finished product achieves is highly dependent upon the manufacturing and heat treatment processes used the potential strength of the alloys is rather meaningless anyway.
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Old 09-12-12, 07:04 AM   #5
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You'll not break either one, so really your choice, all other things equal, is cosmetic. Anodizing is good, at least up front. It will probably resist the elements better. It will never polish up as much as a non-anodized version, though. On the flip side, once anodizing gets scratched or pitted, there's no fixing it. You'll just have to live with the marks. On a polished crank, a little fine steel wool/scotchbrite and/or wax/polish and you're as shiny as new.
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Old 09-12-12, 07:16 AM   #6
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people is super anal with some stuff... probably a pair of shimano 600 arabesque 70's cranks will do just fine for what you want too Just get the ones you like the most, will take probably like 300 years of daily use for any of them to be explode suddenly because of over use, and i doubt you will be alive to see that day. Japanese cranks are good, you wont go wrong with any.
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Old 09-12-12, 07:33 AM   #7
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I'd say if you're splitting hairs like this then you'd enjoy having the best square-taper cranks available.

And since there's a pretty strong argument to be made that nobody has done a better job than Shimano's FC-7600 (there was prolly an XTR equivalent), where each crank arm is cold-forged as a single, hollow piece, and the next level down is likely to be a fair bit cheaper because it's not just the next level down, but because it's been a while since Shimano did square-taper, and it's not as collectable as first-tier stuff. So you can prolly pick up second-hand Ultegra or XT cranks in good nick for about the same as new cheapies.

IIRC the hollowness filtered down to 105 after a bit; I think the first hollow DA cranks had sections welded on the back, then they figured it out for the next year and either did Ultegra as well, or waited another year to trickle it down, I'm not sure. But I think you're looking at three or four years of these cranks, although I'm not sure the tech was used for MTB. There'd be Ultegra and 105 triples I think, 50/40/30 if memory serves.

Last edited by Kimmo; 09-12-12 at 07:38 AM.
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Old 09-12-12, 02:34 PM   #8
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Ok, so it doesn't really matter that much. Good to know.

Thanks for all replies!
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Old 09-12-12, 07:32 PM   #9
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Yeah, doesn't matter. Because the crankarm don't actually take ALL of your pedaling loads simultaneously. The crank ends up spining the BB as a result of force at the pedals, so the peak loads on the crankarm itself is lower. And the manufacturers design in a huge amount of safety overhead for fatigue-resistance and crashes.

Back when I was racing BMX as a teenager (over 30-years ago), I used to break crankarms by doing +10ft drop-offs. The landing would have me standing on both pedals simultaneously to use my knees to cushion the landing. With one crankarm being pushed forward and one backwards, there's no rotation and that loaded them with over 2G of force. Twisting the crank wasn't uncommon. The only ones that really lasted were Bullseye triangular-profile hollow chromoly cranks. Extremely beefy and only slightly heavier than solid aluminium ones.
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Old 09-13-12, 08:29 AM   #10
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Quote:
Originally Posted by Kimmo View Post
And since there's a pretty strong argument to be made that nobody has done a better job than Shimano's FC-7600 (there was prolly an XTR equivalent), where each crank arm is cold-forged as a single, hollow piece, and the next level down is likely to be a fair bit cheaper because it's not just the next level down, but because it's been a while since Shimano did square-taper, and it's not as collectable as first-tier stuff.
Hmmm:



http://www.yellowjersey.org/jayscranks.html
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Old 09-13-12, 09:47 AM   #11
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Originally Posted by JohnDThompson View Post
OK, anything can fail on occasion but that looks like a break induced by a serious scratch or other stress raiser across the crank arm.
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Old 09-13-12, 11:18 AM   #12
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Originally Posted by HillRider View Post


OK, anything can fail on occasion but that looks like a break induced by a serious scratch or other stress raiser across the crank arm.
I'm not really familiar with those cranks, but it appears there is an insert in the arm (perhaps for the "Octalink" splines?), and the failure propagated from the end of that insert.
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