canklecat

I'm looking to replace my Ultegra 6700 crankset (175 cranks, 53/39 rings). I'd prefer 170 cranks. Might even go shorter if I convert this Diamondback Podium to mostly TT/tri-bike configuration. Probably 50/34 rings, although I have no problem with the 53/39.

With age and injuries 175 cranks don't really suit me anymore. Used to feel fine but now it feels like I'm pedaling squares. And it's really cramped when I tried to use aero bars. (FWIW, I'm 5'11", 33" inseam, so 175 cranks were kinda marginal for me anyway but I managed for a few years.) After riding 170 cranks all of 2019 on my older Trek 5900, and 172.5 all of 2020 on my old Ironman, I'm sure I'll be more comfortable with shorter cranks. Unlike the old square taper sets on my '89 Ironman and '93 Trek 5900, it's all or none with 6700 and similar cranksets. Can't just replace the crank arms only.

I haven't had any problems with my Ultegra 6700 crankset... so far. I check it often. All the broken cranks or spindles/axles I've seen online were 6800 or newer. And, yeah, I know, statistically the reported broken Ultegra and Dura Ace cranksets were pretty small and appear to be related to atmospheric conditions that may have weakened the bonding. And maybe the 6700 spider was inherently stronger, I dunno.

But...

I wanted to get shorter cranks anyway. So, if I'm gonna try 170 or so cranks, I might as well consider a whole 'nuther brand or type of crankset. But checking the online catalogs I can't determine whether any of the currently available replacements are available with solid aluminum cranks, or whether it's all hollow tech or nothing. I suppose carbon fiber is a possibility but probably out of my budget.

Weight is no big deal. My fast days are long gone and we don't have any mountains here, so a few grams won't matter.

Thanks.

Racing Dan

105 and Ultegra are both Hollowtech, but not the same. Ultegra is bonded (glued), 105 is forged. 105 wont crack and break. Its available in short length as well. Or simply get a Tiagra solid crank. I have one. Its fine and cheap.

canklecat

Sounds good, thanks, Racing Dan .

Darth Lefty 

We are the victims of some confusing marketing.

“Hollowtech II” refers to the aluminum edit:steel tube spindle and 2- piece construction with external bearing bottom bracket cups. They have proliferated through the lineup… down to Claris and Alivio

“Hollowtech” is the hollow crank arms. I think it’s only on a few very top end groupsets. You can tell because they look like Hershey bars

canklecat

Yeah, it's confusing. Some older articles from several years ago say the 6700 cranks were solid forged aluminum. To me the 6700 cranks appear massively strong. I can't see any seams that might indicate hollow or bonded arms. But I wouldn't know what to look for. I pored over Shimano tech documents for days and couldn't find any specific info on the construction of the 6700 crankset, only what I could infer from the diagrams.

But my primary concern is finding comparable quality and strength in shorter crank arms, compatible with my existing components (a mish mash of 10 speed Dura Ace and Ultegra cobbled together from a TT/tri-bike with cracked frame, and the Diamondback Podium).

I'm not planning to update the group or spend much. It won't make me faster than my '93 Trek 5900, for which I already have older Dura Ace, 600/Ultegra and other square taper crank arms in various lengths. But the Diamondback is a nice bike and it'd be a shame to leave it gathering dust just because the crank length doesn't quite suit me anymore.

Iride01 

Why the obsession with strong cranks? Are you saying you put more power into a crank than Cavendish or Ewan? They ride hollowtech II don't they?

Darth Lefty 

Found this photo of a 6800 crank cutaway. This puts more material on the leading and trailing edges and less on the sides, but being a tube it resists torsion better than an i-beam or solid beam. Same reason as all the other tubes your bike is made of.



The outer chain ring is also hollow monocoque construction This is a cutaway view of a DA crankset, showing all three hollow things (spindle, crank arm, sprocket)




The hollow spindle is a good system. The arms, well... Based on what I've learned finding those cutaways, I've suddenly lost interest in a hollow-arm crank like this. There are many more than zero reports like this one.

failure shimano ultegra crank causes serious bicycle accident

canklecat

I'm obsessed with my testicles. They've been with me for a long time. I'd rather not plant 'em in the top tube.

Seriously, tho', I do get out of the saddle quite a bit, which could be awkward if something broke. If I only sit and spin it'd be less of a concern, but I'm not really good at churning butter at 100 rpm for long before blood starts squirting out of my eyes.

Anyway, according to most reports of breakage of the 6800 and newer hollowstuff, there are warning signs that some owners ignored. Such as creaking that they misattributed to the BB30 fit, but turned out to be an incipient bonding separation or crack. The pros have mechanics who can spot that stuff and replace 'em as needed. I don't have that kind of cash.

And if it's accurate that my 6700 cranks are solid, mebbe I'll just look for a good used set in 170 or maybe 172.5, and perhaps smaller chainrings, although I don't really have a problem with the 53/39 since we don't have any mountains here. The 39 chainring and 28 cog have been good enough for our short, steep hillettes when my legs are dead.

Iride01 

This is much like the old style seven stem being touted as dangerous. You are just succumbing to hysteria.

canklecat

Darth Lefty , yeah, there's an entire Instagram page devoted to pix of asploded Hollowtech cranksets. I think it's called "thanksShimano". I'm not sure how seriously to take it because they also gripe about stuff that can happen to any brand, like frayed cables.

And there's no real data available because of course Shimano isn't gonna provide that info. So while dozens of broken cranks seems like a lot, statistically it may be 1% or 2%? Who knows. And some anecdotes indicate it mostly seems to affect regions with hot, humid and/or salty air. But, still, just anecdotes without data.

Anyway, I'll probably go for another older 6700 crankset since it appears those are solid arms, or the 105 or Tiagra. I wouldn't get any real benefit from the 6800 or newer cranksets. Mostly I was just wondering what the options were for solid cranks, from Shimano or any other decent brand.

Racing Dan

Just to clarify my above post. Ultegra and DA are made from two clams shells that are glued/bonded together. Those are the ones that break from fatigue. 105 also has hollow arms and spindle, but is not bonded. Its made with hollow forged arms, that are a bit heavier but, to my knowledge, wont break. That would be my pick. Tiagra is made with solid arms and a hollow spindle. It wont break but is heavy, but fairly relatively inepensive.

EDIT: Its all in here.

himespau 

Are you wedded to shimano? I don't know how close the spacing is, but Campy 10 speed alloy cranks are beautiful and solid and may work with shimano FD/shifters. They use square taper bb though, so that introduces another variable.

terrymorse 

105 is less likely to crack and break. But since it's made of aluminum, it will break if used long enough.

Many examples of broken solid aluminum cranks exist.

Personal anecdote: I remove Shimano cranksets from my new bikes and replace them with FSA carbon cranks. My cranks currently have about 15,000 miles on them. No issues.

Darth Lefty 

In my day job we track risks. Our standard risk slide has four pieces of information: likelihood, consequence, mitigation plan, and budget. This one is 2nd on the risk scale - probably low but obviously not zero. If the consequence were low, it would be ok. The consequence is high. So you need a plan. Fortunately the plan is easy.

The Internet has changed how we buy and fix things like this. In the 20th century if you had a problem with your Toyota truck you were pretty much at the mercy of the shop or the Haynes manual. Today it's very likely if there were a million trucks made there are a thousand other people who've had your problem and a few dozen of them are telling about their fixes on the internet. That's not hysteria. It's good. It's how we know, for example, we are not alone when our 12 speed XT/XTR shifter stops working.

If you want to see hysteria, look at Consumer Reports tracking "exploding sunroofs" at the rate of maybe a dozen a year country-wide, nearly all in parked empty cars. They have to say "nearly 250 since 2010" to make it sound scary enough

Racing Dan

Blah! :-) Complete fearmongering! B52s, 60 years old still in service. I never heard of a 105 crank failing in a similar manner to ultegra and DA.

mstateglfr 

https://praxiscycles.com/product/alba/ Praxis Alba

popeye

Because Ultega hollowtech cranks were failing quickly for some period of time. My old WIFE killed one in just over a year. The bonding fails and then they crack. I think they fixed this and is no longer a consideration unless your crank is ~ 2 yrs old. I don't know that just guessing.

terrymorse 

B52s get regular airframe inspections, and cracked elements get replaced.

Iride01 

Definitely this is fearmongering. Solid cranks break too. Now if someone can come up with some overwhelming statistics that one fails more than the other.....


https://www.velonews.com/gear/techni...en-crank-arms/


Bikeville thoughts: May 2012


https://pardo.net/bike/pic/fail-001/FAIL-001.html


https://pardo.net/bike/pic/fail-001/FAIL-035.html



https://www.dracotorre.com/blog/bike-breaker-hill/


https://www.mtbr.com/threads/broken-....831123/page-2


https://felixwong.com/2004/06/bike-parts/

Jack Tone 

I've got 3 bikes with 6800 cranks. Now you've got me worried. Sometimes I put out over 300 watts in a sprint. What should I look for if it starts to separate? PS they live in a hot garage.

datlas 

Make sure your affairs are in order before your next ride.

ThermionicScott 

Well sure, with limitless taxpayer funding, you can keep anything in service.

Racing Dan

Well sure, with unlimited funding, you'd replace the ancient bird, if alloy fatigue was such a big problem. No need to keep it flying, just get a new one ;-)

- Imo, the issue with the Ultegra cranks is the bond failing, causing out of spec stresses and eventually fatigue and cracks.

datlas 

Anyone remember this classic? RIP PCAD.

Kimmo 

Jobst Brandt proposed a solution to this stupidity ages ago, that would allow for backwards compatibility, and to upgrade existing cranks to a proper pedal interface.

A 45° taper cut into the crank around the pedal thread, with split collets to adapt existing pedals, while future pedals could have the taper integrated. It'd prevent this sort of utterly preventable failure caused by the fretting inherent to this piss-poor interface.