am8117

Just wanted to give this a separate thread after the other recent crankset dicussions here so as not to steal those threads.

Is there any nice comparison NOT of the weights of the "new" 4-arm design, but potential chainring flex as opposed to the 5 bolts spreading out the load during pedal stroke?

It seems to have been completely left out of general discussion, sure one fewer bolt and material saved on the 5th arm "stub" shaved off weight and the plastics covered what would otherwise not be looking nice out of sheer practicality, but was there anything said anywhere about how the new design prevented more big chainring flexing with the loads spread through one fewer bolt without making them thicker? As in, are these different grade metals currently used than the 5-arm design used or is it just testing the limits of physics?

FastJake

This is a valid question but the answer is that the Rene Herse crank has shown that even three arms are enough, even with a tiny 70mm bolt circle diameter.

The downside to this design is that crank and chainring tolerances must be better, since the ring is not pulled into shape by 5 arms similar to the diameter of the ring itself.

https://www.renehersecycles.com/rene...strong-enough/

am8117

All my childhood road bicycles had 3 bolt cranksets and seems even long before I was a child but they were steel:

https://steel-vintage.com/course-gitane-1-red-200702-01

CliffordK

The other discussion about Hollowtech indicates that at least Shimano is making hollow outer chainrings which are stiffer than the older flat rings, and work fine with either 4 or 5 arms.

It used to be common to true the crank spiders and chainrings as part of the installation and maintenance. Done by physically bending the rings and spider.

It may be that new manufacturing methods, as well as integrating the right crank arm to the bottom bracket spindle improves tolerances so that everything runs truer right out of the box.

base2 

I concur with CliffordK
This week, I had an 86 year old man bring a Raleigh he bought new 65 years ago into the shop for "shifting issues." He claimed no one had touched it since the day he bought it. But the rounded off chainring bolts told a different story. I let him have his lie as he really was a sweet old man of kind demeanor.

The long & the short of it is he had been taking things apart & had the inboard & outboard rings swapped & had been trying to get it to shift to the other ring by bending the spider. Once I got things back straight & in a more conventional (little ring inboard) configuration with a new chain we still had to deal with clocking between the rings so that the new chain would pull up/down between the rings gracefully & then getting the rings to run concentric. Having sorted that out, I then grabbed a mallet to "cold set" the rings to run true as installed. To get that far though, I had to undo all the bending he had been doing to the derailleur so that I could see in which way the rings were bent. The whole project was a mess but rewarding when it was complete & worked as well as the day it was made.

It was 3 hours well spent. I charged him $10 for a chain & $15 for "adjustment" & didn't mention the necessary straightening of the rear derailleur hanger.

All that is to say that even though the crank had a 3 arm spider & the stamped steel rings were malleable, there were a total of 6 bolts in total (3&3, offset) keeping the rings together so they rely on eachother in use but can be trued independently. Which is ultimately what saved his bike.

Iride01 

Campy use to make three arm crank spiders back in the vintage days. I had one on my Raleigh Competition GS. I never once worried about bend or flex in a chain ring.

To answer your question about if there are any comparisons of flex, I've never seen them. Just us wanna-be engineers here with our own unscientific opinions or maybe scientific, but not the entire picture.

Whichever you get, the actual engineers and designers of it probably built it to handle the forces they intend it to handle. Four arm spiders have been being raced for many many years and I haven't witnessed one fail yet.

SoSmellyAir

I thought Hollowtech refers to the crank arms? The chain ring is also hollow? Or are you referring to the cutouts?

You are way too nice.

FastJake

Here is the link I wanted to post yesterday but couldn't find it. It describes how we got to where we are today regarding cranks:

https://www.renehersecycles.com/hist...uminum-cranks/

Racing Dan

Shimano 4 arm road chain rings are beefed up laterally to combat flex. - Some hollow, some with an insert depending on price point. Older 5 arm was just a (lighter) alloy ring. 4 arm designs might be a case of 1 step forward and 1 step back.

CliffordK

Yep, look at this clip from the other thread.


At about 2:50, he starts talking about chainrings.

The 6700 series, 5 arm Ultegra, as well as the 4 arm Ultegra (6800, R8000) got the hollow rings.

The 7800 Dura Ace looks somewhat similar, but got machined rings. The 9000 Dura Ace got the 4 arm cranks and the hollow rings.

It looks like the R7000 also got a deep cast chainring.

am8117

I tried but could not find any published on data on whether the alloy itself changed during the transition from 5 to 4 arms. Am I trying to find out something that is a "trade secret" or have I just overlooked it? It would be interesting to know what all has contributed to the new attributes other than e.g. different way of milling.

am8117

I am not the one you reacted to but I was under the impression the hollow originally only referred to the spindle alone, they have not renamed it to HT3,4,5,... since so probably not.

am8117

So looking at the lower end eg 4700 with the plasticky inside "ramp" ... that looks like stamped out and just adjusted to make it look like the new design without adding much actual benefit? I.e. getting 4-arm R7000 is very different to getting the new R3000. And I do not mean I want them to be equal, but the one is actually a structural upgrade the other is just for the looks.

CliffordK

I'm not quite sure what Hollowtech 1 was for.

I'm pretty sure the Hollowtech II was the Octalink cranks. While the Octalink spindles would have been hollow, I think the cranks were also hollow at that time.

Campagnolo had been using hollow spindles on their record square taper bottom brackets for a very long time. So, Octalink has a bigger spindle, but really hollow spindles is hardly a new technology.

I'm not sure why the bonded cranks aren't considered a new series (Hollowtech III).

I had intended to mean progress over decades. In the late 80's, I remember being in a bike shop in Parma Italy where the mechanic was building up a "new" Colnago. He put on the crankset, then got out the big Crescent Wrench to align it.

Presumably the older manufacturing of square taper had minor imperfections.

Once one attaches a bottom bracket spindle permanently to a right crank arm, then one can 100% predict where the crank spider will end up, and the teeth on the chainrings.

I'm not sure about alloys. 7000 series alloys are common for high strength aluminum applications like chainrings. However, casting, forging, extruding, welding, and bonding can all lead to different alloy choices. Even crank arms and chainrings might be different.

CliffordK

Hmmm, I have had a set of Octalink V2 Claris cranks. Not a bad crankset. But, I seem to have missed some of the newer Claris/Sora/Tiagra models. I could imagine a stand alone Channel or I-beam construction, covered with a cosmetic cover. Is that what they did? I could imagine it showing wear, but it could be made to be structurally sound.

CliffordK

I was browsing a bit. Because of the new hollowtech design of the Shimano outer chainrings, they only have a single vendor.

If Shimano would choose to stop supporting certain designs, then one would be out of luck.

And, the replacement rings are monstrously expensive.

Iride01 

I'm just unsure why the need to know so deeply? If you knew the material they are made of do you know enough to figure out it's suitability for the purpose used or that even if the same material as other rings and cranks that just simple differences in design don't make for any lost integrity created by the missing spider arm? Or that the cranks themselves are hollow.

History has plenty of solid cranks breaking. Some recently. All the quasi-intellectuals seem to be focused on Shimano's hollow crank arms and rings just because they... well are just quasi-intellectuals and can't see the whole picture. And think one failure is too many but for some reason the failures of solid cranks are just too boring to discuss.

If it was a big issue, there'd be more examples than the old examples still given. And like there'd be some government agencies up in arms about the statistics if they were anywhere near being unsafe.

am8117

I have no clue and in fact would be curious to know without destroying those I have at hand. But it's just weird when one can only see plastic covers from each side of the big ring and the teeth. As in, was there any evolution with the milling, forging etc at all (talking of the 105 and below) or is it just the same old design, maybe a bit more material milled off and the ramp is now plastic, considering the anchoring is with 4 bolts only now ... could it be they got more and not less flexing between the generations?

Haven't seen Shimano boast about what's it made of or anyone publishing any teardowns.

am8117

I just noticed some manufacturers would brag which alloy theirs are made off. Even being a google warrior one could get the idea in terms of practicality of use and more importantly price. Are they worth what they cost or is just nice design but ordinary material - talking of those heavily overpriced kinds. Lots of bike tech seems to be more about marketing than materials used / engineering involved.

base2 

Actual premium brags about engineering.

Compare the hype & filler of this common crankset

With the the write up of this actual premium crankset

Or this actual premium crankset

Or these actual premium chainrings

It's pretty stunning when you realize that given Shimanos size & reputation Shimano could be premium if they wanted to be. But the only thing hollow at Shimano is their engineering department.

Iride01 

If there is any bragging of alloys, it was mostly back in the vintage days of steel bikes from what I've seen. There were some rapidly changing tube technology back then and the tube construction (butted, double butted etc) and type of steel alloy seemed to be points the marketing folk liked to dazzle us with. And indeed the latest and greatest tube design and alloy did make the top end bikes of their day. Similarly today, you'll see high end bike frames made with the latest and greatest carbon fiber technology of today compared to less expensive bikes made with yesterdays not-so-high-tech-anymore CF that was pushed off the throne by today's CF tech.

I think you are getting led astray going by alloy types and which alloy is better. I'm not an engineer, but anyone that has an engineering degree can tell you that it's not so much the material as it is the design criteria to meet the characteristics of that particular alloy or material. Designs change to meet the characteristics of a particular alloy. So you can't really say that one alloy is better than the other as a blanket statement.

Your arguments/questions seem to be more about how bikes got so expensive. Do the marketers dazzle us? Of course they do. That's their job. That's how you sell bikes. The more expensive bikes have the newer technology and materials. Do we need that? Yes, even if you never buy a 12,000 to 14,000 bike, because ten to fifteen years in the future, that will be the low end bike produced then. Or at least most of it's technology will be used for low end bikes.

Those that buy the high dollar bikes either need them because they compete, or they simply can afford to buy the ultimate even if it really doesn't add to their everyday cycling performance.

You just need to figure out what's the stuff you want and can afford. If you aren't a designer with intimate knowledge of materials and structural design, then leave that to them. Just concentrate on what seems to work for the riding environment you'll be in.

ClydeClydeson

4 arm spiders have been the standard in mountain bikes since the late 90s. Modern Shimano 4 arm designs (with assymetrical spiders)are usually paired with some type of hollow chainrings, not just stamped out of 2mm thick aluminum plate and the whole assembly is probably stiffer than one with 5 arm s and flat rings. In my experience the new 4 arm crank/chainring setups are not excessively flexy.

am8117

I am not sure because while the whole discussion seems to go about where the development went (and most folks look at Ultegra for more "average" rider benefits), the way it trickles down is dubious at best.

This 4700 is the new design and looks like the chainrings were also designed somewhat in a new way:

Meanwhile this R3000 which I believe came out after the 4700 (it makes sense it trickled further down to Sora later on only) and stars the "new 4 arm" design looks like stamped out chainring which is more flimsy than the old 3500 were (around 1:45 mark):

So yeah design and design ... they made it look 4 arm, but are those chainrings really any better ... be it stiffness or shifting ... I wish I had that R3000 here to take off those Philips screws and see what that chainring actually looks like naked, because no engineering degree is needed to know that the 3500 ones are likely stiffer due to the cutouts.

https://bike.shimano.com/en-EU/produ...0/FC-3550.html

I understand there's some improvements actually done over the generations, but the whole trickle down seems to be more about looks than actual engineering in this case at least.

Oh, and we cannot compare if those two were made of the same alloy ...

am8117

They indeed look marvelous, but these are a whole different market segment, aren't they?

I don't even ride Ultegra let alone Dura-Ace myself and thus consider Shimano an average Joe's brand, but at the high end the price levels might have their customers think twice ...

Polaris OBark

They may look marvelous, but the galvanic potential difference at the carbon/aluminum interface might make Shimano's problem look inconsequential.