pstake 

Looking for opinions about the use of 853 fork blades over less expensive 631. What is the trade off?

guy153

853 is the same metal as 631 only heat-treated. My understanding is that this trades ductility for ultimate strength. So if they're the same gauge I would actually prefer 631 because I'd rather the fork bent in a crash if it had to.

In theory you could make the 853 blades a bit thinner and lighter but I don't know if this is the option you have.

pstake 

First, thanks, Guy, for responding. My question is admittedly pedantic.

Reynolds itself used to recommend in literature that builders pair 853 frames with fork blades made of 631 or 725. I think they started offering 853 fork blades more recently but i could be wrong about that.

I'm wondering what applications would make sense for 853 fork blades over 631. Especially wondering because Reynolds itself didn't recommend 853 fork blades with 853 frames.

Andrew R Stewart 

Perhaps marketing is the real function, because the 853 blades will sell better to those who just read the headlines and skip the body of the "articles". Andy

guy153

I suspect they didn't recommend them just because they didn't make them (presumably because of lack of demand) so recommended 631 or 725 as close alternatives.

I had a look at their catalogue and they do make some 853 blades that are thinner than any of the 631 ones so that would be a possible reason to use them.
​​​​​

Reynolds 531 

So an alternate theory would be that "thinner heat treated blades" are the same strength, but weigh less than "thicker non heat treated blades".

guy153

Yes that is the idea and they do offer some 853 blades that are a bit thinner. You can also get them in exactly the same dimensions as 631 or 'R' (which is presumably regular cromoly) and given that most of those are designed for brazing anyway you might as well get the 'R' ones as the benefits of 631 over cromoly are only realized if you weld it.

But I think there is often some marketing value just in being able to say the whole frame including the fork is 631 or 853 and using 'R' (or 631 on an 853 frame) might be perceived as a downgrade.

In fact I wonder if the reason for branding the "basic" blades 'R' rather than 525 was to try to stop people thinking of them as a downgrade since they generally pitch 525 as a bit low end even going so far as to disdain it with a number less than 531.

​​​​In reality they are all very fine tubes and there isn't really a huge difference across the range between 525 (which is DOM 4130 cromoly) and 853.

​​

Kuromori

The UTS of 853 is higher than 631. What causes 631 to get bent is that it has a lower yield strength.

631 is the same alloy as 853, except bendable because it lacks the final heat treatment. While I remember seeing recommendations of pairing 725 stays with 853, I don't recall 725 fork blades, but I'd be happy to see literature showing them if you could direct me to it. They would have the same issues as 853 and 753 fork blades. You can't bend them because of the heat treatment. The yield strength is too high to reasonably get them to take a set. In fact, Reynolds used to recommend 531 fork blades with 631 and 725 frames.

Are we talking about the MAX style fork blades? Those are thinner gauge because it starts off with an oversize ~28mm OD blank instead of a ~24mm OD blank.

Reynolds doesn't like thin fork blades with the exception of 953. The rest of their fork blades are either beefy disc blades, the aforementioned MAX style aero blades, or the same butting profiles they've been making them in since the 70's, or even earlier for the Imperial blades. Lots of other companies will do a fork blade using a 0.9/0.6 blank in plain old cr-mo or make a even-thickness fork blade in 0.9 out of plain old cr-mo. Fork blades are thick enough to not really need extra dent resistance, and thinning the tubes results in a flexier fork blade.

Most companies have found it prudent not to mess with 0.8mm or thinner fork blades, even if they have new super strong alloys up to the task, or ridiculously thin frame tubes. They stick with 0.9 or 1.0 constant thickness blades because that's what makes a compliant fork that handles well for a continental oval. If you want to compensate for loss in stiffness, it requires a redesign for a component many customers will happily swap out for a carbon substitute anyways. Making oversize fittings cancels out any weight loss, as fork crowns are quite a bit thicker than tubing. A MAX crown will weigh ~30g more than a conventional continental crown, canceling out any weight savings. It's simply hard to leverage the advantages of 853 in a fork blade, all while costing more and being harder to fabricate.

However, 631 does in fact air harden if you brass braze it, even if the current staff at Reynolds seems to have forgotten that fact. If anything, cr-mo is the alloy that suffers more during brazing. If Reynolds really cared about brazed forks, they'd make 531 blades, as they've said for much of their history 531 is the superior alloy for brazed applications.

Of course, being able to offer the best on a flagship product is important to perceived value and prestige. For customers willing to pay for top shelf product, the kind of person that will buy Super Record or Dura Ace over Chorus or Ultegra, I can't think of any way that an 853 fork is any worse other than price and not being able to custom rake it.

guy153

Yes, that's the only one that's actually thinner. I'm assuming they think you actually need 853 for that one (and so it's following the pattern of thinner wall and oversize to get the stiffness back).

This is a very good point. They do have unicrown blades in 853 but they're actually thicker than any of the 631 ones for some reason.

Yes this is a good point-- it should get stronger at all temperatures up to its own melting point whereas CrMo will still be weakened a bit by the heat of brazing.

Interesting. Did they give any convincing reasons why 531 was better than CrMo for brazing, and are we sure it wasn't just marketing? And why should 531 be better than 631?

pstake 

This is the marketing language from Bob Jackson, which offers 853 blades as an upgrade. I don't understand why they would be any stiffer if they are the same size and gauge as 631 or 725 blades. I'm also not sure why they disallow this upgrade on certain models.

"This Upgrade applies to the fork blades only to make the fork much stiffer.

PLEASE NOTE these blades are very stiff and as such we cannot change the rake that we receive from Reynolds."
Reynolds 853 Fork Blades | Bob Jackson Cycles

unterhausen

there is a significant number of framebuilders that have no idea about the properties of metals but are not afraid to talk about it like they do. This is pretty fundamental though, people should know the modulus of elasticity if pretty constant among steels. On edit: they are right, the 853 blades are larger than normal, thus stiffer.

Higher UTS should mean they are marginally less likely to bend, everything else being equal. But I believe a majority of the people that want steel would want them to be lighter and more flexible as long as they are strong enough.

Kuromori

No strict need for 853 for MAX blades, Columbus makes them, so does NOVA's supplier. You can make fork blades from 0.9/0.6 blanks, Reynolds just doesn't like to make blades that thin. However, if you make MAX blades the way Columbus makes them, there is a section of the fork blade that is only 0.6mm thick, then wall thickness increases towards the tip. Higher strength steels would offer increased dent resistance here.

The 853 unicrown variant is also larger in diameter. It looks to be for people who want a very strong and very rigid fork blade.

853/631 will only harden if brazed at high temperatures or welded. Silver will damage the heat treatment of 853 because it doesn't bring the steel up to quench temperature, it just tempers it. It's probably not any worse than silver on 753 or 725, but it won't air harden and it will weaken in the HAZ.

531 was developed specifically for brazed construction. The higher manganese content is supposed to help it retain more strength after heating. The difference in strength is mostly marketing as cr-mo is perfectly adequate in practice. There are higher strength non-heat-treated steels than either 4130 or 531 now, so the difference is moot, but Reynold's position has always been that 531 is superior to cr-mo for brazing. I suppose 531 isn't really superior to 631, just to cr-mo. It just means I can't in good conscience put triangle stickers on framesets made with current production 531.

Kuromori

Most of the 853 blades are the same size. Most framebuilders don't distinguish between vibration damping and shock isolation even though they are different things. It's something few that bothered to investigate, and mostly likely, something completely dwarfed by tire selection. The microstructure of metals has an impact on damping, and there are alloys designed with the purpose of damping, an effect independent of the relatively constant stiffness of steel. How much it varies in steel cycling applications is a mystery because no one cares to put money in running experiments. It's probably not very high, but may be noticeable to some.

Too much flex in a frame is a bad thing even if it's strong enough. There's a youtube video of someone that replaced the main tubes of a bicycle with springs the results are what would be expected. Flex can cause serious handling issues and a noodly feel. If the flex overwhelms the damping of the system (mostly supplied by the rider and tires for higher amplitudes), it can lead to oscillation, sometimes dangerous like a speed wobble. Thinner tubes increase the amplitude of deflection and lowers the natural frequency, possibly towards a frequency that is more likely to be encountered on the road. Frame building practices are largely based on trial and error, the wisdom of experience, and small incremental changes, verified by practical experience, much the way bicycle geometry was developed even though no one understood the mechanisms by which bicycles actually worked, and I think the cycling industry has hit the too flexible mark many times in the past.

unterhausen

If you have any pointers to literature about damping in high strength steels, I would be interested in seeing it

Kuromori

Nearly none, because as I said before, people don't put money into doing this kind of research. Most scholarly articles are about damping alloys specifically made for damping, but it's pretty well accepted heat treatment has an effect on microstructure and damping, likely tied at least in part to grain size and shape. I believe it's also pretty accepted that heat treatment has a discernible affect on sound for musical instruments.

I think I was clear in stating that how much this actually applies to bicycles is unknown, and speculate that the effect is small, and possibly unnoticeable. What I'm saying is there's a non-zero chance that something about different fork blades makes them feel noticeably different, and while not a difference in stiffness, there may be something to it. The assertion that the blades are stiffer is basically wrong. The perception that there is something noticeably different which is interpreted as inaccurately "stiffer" may not be. It's also true that people tend to spread myths not based on any hard evidence. I don't have enough money to go making dozens of nearly identical forks to test this, and merely pointing out the possibility due to the fact that there may be more to the story than Young's modulus. Damping in 4130 and similar materials is merely incidental, no one picks 4130 for damping or lack of damping.

"Damping Capacity of Materials" (Maringer, 1966) does include a little bit on some steels. For "silver steel" a high-strength tool steel, the spheroid annealed state has nearly twice the damping capacity as the quenched state, and it also shows large differences between various alloys, with mild steel having a particularly high damping capacity. It also notes that it will vary based on amplitude. Once you add in an actual damper like rubber tires, I don't know how insignificant it becomes. You might be able to find some further studies on spring steels. "Damping Properties of Selected Steels and Cast Irons" has some info on 4140 and 1020 showing how little the specific damping at one stress level can be extrapolated to another stress level. Being steel, it should be a small effect, but the question is if it's big enough to subtlety but noticeably affect perception of vague things like buzziness, liveliness or deadness, or if it really is insignificant after all things are considered.

guy153

I don't understand, what triangle stickers?

Back when 531 came out brazing was the usual way to join thin material anyway as TIG welding hadn't been invented yet. With a lot of skill you probably could have oxy-acetylene welded a bike frame (if you'd used a suitable alloy) but brazing was the preferred option.

Then 4130 came along, and, a bit later, TIG welding (according to this history: https://www.aedmotorsport.com/news/t...ess-round-tube). I don't know if 4130 was specifically designed to be weldable as if you were working with thin-walled tubes you probably would still have been brazing it anyway between the 1930s and 1960s.

This ad from 1931:

https://www.bikeforums.net/classic-v...l#&gid=1&pid=1

linked from here:

https://www.bikeforums.net/classic-v...ed-frames.html

is claiming that cromoly gets stronger after brazing... No doubt Reynolds made similar claims about 531.

Kuromori

Reynolds traditionally used inverted triangle decals for their fork blades. They've since switched to modern decals.

Yes, brazing was typical when 531 was developed, which is why it was developed for brazing. More than that, it wasn't just developed to be merely suitable for brazing, it was an improvement over Reynolds H.M., an alloy steel which was already being brazed, to perform even better post-brazing. Fatigue testing was done in a post-brazed state. Micrographs taken in a post-brazed state. It's like taking 525 which is suitable for welding and comparing it to 631 which was designed for improved joint integrity after welding. Reynolds as a company tended to focus on joint integrity rather than just overall strength. That's why they invented butting, and that's why despite offering heat-treated 531 in the 40's, they didn't really make a big deal out of it until heat-treated 531 was revived in the 70's to compete with new frame materials. It was was developed with preserving strength in a post-brazed state in mind. It turned out to not be particularly suitable for welding (at the very least, not superior for welding), something that didn't hold it back in cycling applications until the 90's or so.

Keep in mind, just because brazing was typical back then doesn't mean all alloys were formulated to be brazed. To take a modern example, 7075 aluminum is one of the higher strength alloys, stronger than most aluminum used in aluminum frames, but widely accepted to be unsuitable for welding, even if it is technically possible with difficulty. It's used for things made out manipulated tubes, plate, or billet rather than welded assemblies. 4130 traditionally being brazed only means the alloy was designed to be suitable for brazing, not modified for increased post-brazing performance. Note that those articles you link only mention 4130's improved strength over 1025 (hi-ten in bike parlance), with the post-braze performance of 1025 setting the benchmark, not another alloy steel. 4130 is also used in non brazed/welded applications. I can't deny the possibility 4130 was designed to minimize strength loss during brazing, but I haven't seen anything to indicate it either. It is simply that 4130 turned out to be more suitable for welding than 531 after the technology was widely adopted. It's also for all intents and purposes perfectly satisfactory for brazing on bicycle frames. Then again, so is hi-ten.

There is an utter lack of technical data on A&P's steel. There is no indication that Kromo was the same as 4130, or even that similar. If you flip through A&P advertisements since surviving catalogs seem to not exist, they sometimes mention softening, but not hardening. Some people have asserted it is an early air hardening steel. It's also quite possible to achieve the same results with 4130 if you deliver it in an annealed (weak) state and brazing will end up normalizing the steel, marginally hardening it. I'd love to get a chance to review any A&P technical documents, but they basically seem not to exist.

Reynolds merely made the claim that 531 wasn't weakened by brazing at most, often with admissions that the physical properties were merely similar after brazing, or slightly weaker, but not as much as crmo.

pstake 

Thanks for all the information -- related and unrelated. Very interesting. I feel like i just took a class! Sort of confirms my suspicion, though, that using 853 blades vs 631 is just marketing. No real advantage all else the same.