Cycling UK Forum

do curved seat stays offer a noticeable amount of increased comfort / vertical compliance?
what's your experience or opinion?

Never tried them, but I have heard it said that they are more marketing than substance. Longer chain stays should increase vibration damping.

they are not all the same, obviously. So they won't work the same, either.

If they are doing anything much then a piece of taut thread between the rear DOs and the seat cluster would be expected to go slack and flap around when compared with a similar frame which has nasty stiff straight stays.

Anyone care to do the experiment?

cheers

I suspect that many differences in stay design are, as suggested, marketing driven more than performance related. On a recent club ride we compared rear triangle designs of our range of quality road bikes to find curved and straight, square and round (and star profile on my Colnago), and pencil to hefty. All bikes ostensibly filling the same market segment and probably similar handling and feel.

I think the most credible example of curved seatstays would be Dave Kirk's 'Terraplane' stays. Dave Kirk is an independent framebuilder from Bozeman, Montana, but before that he was R&D tech at Serotta for years. He exhaustively tested and developed fork and seatstay configurations using rigs and road testing - he's vastly experienced, his heroes are Colin Chapman and Alex Moulton, and what he doesn't know about road bike ride and handling probably isn't worth knowing - that's certainly how his peers see him.

In a post on the Paceline Forum, he explained: "I think the orientation of the stays matters much less than the curve's radius and duration, as well as the diameter and wall thickness of the tube itself. Very small changes make large differences in the way the stay reacts and the bike rides. I don't feel that the way a curved stay attaches to the dropout matters much; the diameter, wall, radius and duration of the bend are the things that matter in terms of ride and handling." So as Brucey said, they're not all the same.


This is the full story, from Dave Kirk's 'Smoked Out' entry on the Velocipede Salon, the framebuilders' forum:

"Shortly after I started Kirk Frameworks I started working on what would become the ‘Terraplane’ seatstay option. I’d worked on this kind of thing before when I designed the Serotta Hors Categorie and wanted to build on my previous work. While the Serotta-DKS worked well, I felt it had too much – too much stuff, too much weight, and too much travel. I wanted a more elegant and simple design that would keep the rear wheel firmly planted at all times.

I worked on many designs and settled on a simple ‘S’ curve to the seat stays. I took Kirk frame #1, my personal bike, cut the seat stays off it and set it up so I could try different stays on that same bike. It took a long time to get the radius and duration of the bends right to give the desired spring rate and a lot of steel went into the recycling bin. After testing many stays on the same frame it looked like hell. It had burnt yellow paint, a rear wheel travel indicator brazed onto it and it looked like a school science project gone wrong. But I’d arrived at the final design and it rode wonderfully – stiff and responsive when out of the saddle yet calm and stuck to the ground in corners and when going downhill. Ripping around corners it had that same hunkered down feeling the DKS had but without any feeling of softness. I loved it.

And then I started doubting myself. I’d cleaned the bike up and emailed photos of it to friends, family and a few customers along with an explanation of how it worked and waited for the positive feedback to come flowing in. It didn’t. Most feedback was negative and centered on how much they disliked the looks of the bike. I was pretty bummed. Even my mom said it looked ‘nice’ and you know what that means...

I kept riding the one and only prototype and despite the negative feedback from others I loved the way it rode. I then thought of a Henry Ford quote from the early days of the automobile. He said, “If I’d asked my customers what they wanted, they’d have said a faster horse.” With that in mind I decided to offer the Terraplane to see what would happen. The feedback online, before anyone had ridden one, was much the same as from my focus group – that thing is ugly and no one needs it. I even had ‘experts’ tell me that it doesn’t work. They’d never ridden one and didn’t know much about it, yet they knew it didn’t work. Alrighty then. But I kept it on the price list and over the next few months a few open-minded riders ordered them. Once I got them out there the owners started reporting back how they have never been able to corner so fast before – or they had never felt so confident descending. The customers were confirming what I already knew - that the Terraplane worked. In time other customers took a chance and they too liked the Terraplane. At this point, 6 years later [2010], about 50% of my customers chose the Terraplane seat stay option.

The Terraplane lesson was invaluable. It taught me that if I have a good idea and can back it up, I should get it out there and let the market decide if I was right. If I’d listened to the initially discouraging feedback I’d never have gotten the idea out there to let it prove its worth. It feels good to have done that. Ask any owner how they feel about their Terraplane and I’ll bet they’re glad I stuck with the idea."

http://www.velocipedesalon.com/forum/f2 ... 15424.html

^That whole thread is well worth reading if you have the time.

the Terraplane isn't a million miles away from a Curly Hetchins, is it....

BTW anyone who doubts that thin gauge steel (or CF) tubes can flex repeatedly without harm should take a look at golf club shafts; these are not a million miles away from the kind of tubes that are used on very lightweight seat stays. They can be flexed elastically so that the midpoint of the shaft is 2"-3" sideways from straight and seemingly not come to grief.

I have often wondered how much flex you could engineer into a 'rigid' frame; if you fit a shock in the stays, you can get about 1" of rear wheel movement, (even with no pivots in the chainstays); this is how the Moots YBBeat 'softail' system works.

cheers

Curly Hetchins, Bates Diadrant, Paris Galibier, Baines Flying Gate (and probably others).........all claiming mystical benefits from a "design" where the real benefit was that it was instantly recognisable ....at a time when racer's shirts didn't resemble advertising billboards.

And the press had to airbrush the frame makers name to satisfy the powers that were!

enigmatic wrote:And the press had to airbrush the frame makers name to satisfy the powers that were!

Airbrush?......"dodging" and "burning" under the enlarger!

Apart from wanting a saddle with more padding that looks just like the bike I'm looking for, so the big question is how much do these bikes go for nowadays? (warn me is I need to sit down and take a deep breath first)