cyclezen

Hi All !
I'm in the evaluation of buying or building a 'new/modern' bike (meaning adding/moving to a Disc Brake, possibly E-shift roadie, carbon). My Most Modern roadie is a 2015 Spec Tarmac w/rim brakes and mech/cable braking.
SO I'm doing my usual, over-analyzing everything. In particular the frame designs available. Seems 'Aero' is still a major thing (understandably). But extreme aero for mass start road racing is being modified. Spec 'Venge' is already passé' but 'less weight' is still the Golden Fleece.
so the two things which seems to vary significantly in frame design are toptube shape & SLOPE; and Seat Stay config.
I can see that most designs have gone away from sharp TT slope (prolly an aero consideration).
But I do see quite some variety in Seatstay design and attachment. Old standard Long Seat Stays attached at the toptube/seatpost cluster, variation of that with a 'wishbone' stay which varies from at the TT attachment point or varying points lower on the Seattube, and then what was dominant a season or 2 back - dropped stays attached directly to the seattube some significant distance below the TT. Here's a pic from Cycling Weekly (their copyright), showing a variety of these designs.

World Tour Bikes - Image copyright Cycling Weekly

So, anyone have knowledge or opinion on the advantages/disadvantages of any of these possible variations - Why?
CF construction appears very flexible, so likely any of these have no real construction issues...
Your own preferences ? Why?
again the consideration is 'road' group riding, not TT, not gravel, not bikepackingg/touring...
love to hear what you all think.
Ride On
Yuri

chaadster

I tend to think that because so much can be done with fiber type, fiber orientation, and construction method, its effectively impossible to deduce anything about ride comfort by looking at the seatstay design. Given that, it’s probably more effective to listen to what the manufacturers have to say about their frame design.

Sierra_rider

I think the most commonly cited reason for dropped seatstays, at least by the manufacturers, is that it allows more flex/compliant ride qualities. I don't necessarily buy that reason, as any flex in a triangle(either the rear or front) seems to be more related to tube shapes and carbon layups, rather than the length of the sides...but I'm not an engineer, so I could be wrong. Also with the prevalence of disc brakes, they don't have to have the chain stays in traditional spot.

Me personally, my main road bikes(Canyon Endurace and Ultimate) have more of a sub-compact geometry(slightly sloped top tube) and don't have much in the way of aero concessions. The seat stays meet the top tube just in front of the seat tube, so not really dropped stay IMO. I don't really like the look of dropped stays anyway, so either bike looks "modern," but also has enough of a traditional "bike look" for me. The Endurace is a somewhat racy endurance frame and the Ultimate is a race bike/climbing bike. The frames look very similar to each other, but the Endurace has a smoother ride, which I attribute to a different carbon lay up and a springy seat post. The Ultimate isn't as smooth, but does an amazing job of transferring power to the wheel...it just feels fast/efficient when pedaling. It's just an example of how a very similar frame design can be altered with different carbon lay ups to have much different ride qualities.

Kontact

Everyone went to those low, boxy type of stays like the Merida or S-Works because of aerodynamics. The shape is good for air flow around the seat tube, and they are the lowest height that is UCI legal (otherwise CF aero bikes would have no seat stays).

The other shapes are largely designed to look comfortable or cool. But it is true that if you want the chainstays to flex but not be paper thin, small diameters work best.

PeteHski

Most aero focused bikes will have dropped seatstays. As for ride comfort I don’t think it is important. I have 2 endurance road bikes and 1 has dropped stays (Giant Defy) and the other has full length stays (Canyon Endurace). Both have very similar feel. Seatpost flex and tyres appear to be the dominant factors for ride quality. I don’t think the seatstays do very much on modem carbon frames and are certainly not a consideration unless you have a strong aesthetic preference. Most people prefer the look of full length stays, but I don’t care either way.

eduskator

Is Trek going to try to make their awful writing even bigger? That's the question I have.

chaadster

Yeah, I understood dropped seatstays to be an aero thing.

In your second paragraph, I don’t know if you meant to change to chainstays, but you’re absolutely on point that it’s the chainstays which provide bump compliance. Seatstays are largely a vestige of a bygone era, and not necessary elements with modern materials. Back in the ‘80s, Trimble was making seatstay-less frames, and Trek’s Y-Foil in the ‘90s was very successful seatstsy-less design. Cervelo’s P5X from around ‘16 is a more recent example.

Those are carbon fiber, but looking at English Cycles steel designs with their literally pencil-thin seatstays, on frames meant for crit racing, not comfort— and you have to wonder if the seatstays don’t inhibit bump compliance rather than provide it.

Troul 

Dropped imo from riding a few allows the frame to flex, whereas the uniformed frame increases the rigidity... a dropped design might be better for non composite frames, & the other likely wouldn't induce a noticeable harsher ride when used with a composite material.

Kontact

Yes, I meant seat stays. And if seat stays are UCI necessity, making them long and narrow is going to allow them to flex better than any other configuration except for something pre-bowed.

But seat stays also prevent the wheel from twisting around the axis of the chainstays.

chaadster

Right, and that all really depends on what the chainstays are going to do. Adding stays (of any kind) to a Giant MCR (from’97, btw), for example, won’t do anything other than add weight.

We talk about seatstays and compliance, but we really should be talking about chainstays and compliance if not frame design and compliance.

In terms of feel at the saddle— distinct from compliance, which I think of physical displacement of the frame, or flex— seatstays do seem like a main conduit for shock waves from bumps to reach the rider, so maybe we could talk about shock attenuation from seatstay design rather than [bump, or vertical] compliance.

Kontact

The point I was making was that a bike designed to use both seat and chain stays is using those chainstays to prevent the wheel from twisting, not just increasing vertical stiffness.

A seat stay-less design does both with that massive chainstay, but may not flex vertically much at all due to the rigidity needed to stop twisting.

Iride01 

You can't just focus on that one thing without taking all the rest into consideration.

What that accomplishes for one bike model might be handled differently to achieve almost the same thing by another bike model design. And it might be in things you can't tell from the external appearance. Different internal dimensions, different materials or different fabric and layup or any other possibilities.

mschwett 

these days, i’m pretty sure you can use the properties of the carbon layup to create almost whatever amount of compliance, flex, stiffness you want with dropped or traditional seat stays. so while optimizing aero properties undoubtedly affects stiffness (the elongated / boxy shapes that are aero are also stiffer in one axis than another, etc) a good design process can optimize both - or choose not to.

i have two carbon road bikes at the moment, and the one with traditional/undropped seat stays (s works aethos) is a much smoother, lighter ride than the one with dropped stays. sloping top tube also helps, i’m sure, but again, could almost certainly be cancelled out by the carbon design.

my preference, based entirely on aesthetics and my personal experience, is for a slightly sloping top tube, undropped stays, and slightly tapered slightly elliptical tubes. not the most aero thing, but light and beautiful. like the cervelo at bottom right of your roundup.

tFUnK

Whether dropped seat stays provide more compliance has been debated. One source I do not recall argued that dropped stays = smaller rear triangle, which in turn gives a stiffer ride, and that compliance instead generally comes from a frame having a lot of exposed seat post. The latter point I tend to agree with in my experience - frames with an integrated seatpost/seat mast (popular in the early 2010s) were really stiff feeling.

Jughed

Limited data set here - but my CF cyclocross frame, Giant TXC, has dropped stays and a "flexy" seat post and it's the harshest bike I've ever ridden. Even when it has my cross/gravel tires installed and running lower pressures.

jonathanf2

I have both dropped and high seat stay road bikes. On fast downhill road descents, my drop seat stay bike with more exposed seat post definitely dampens road chatter. My high seat stay bike with less exposed seat post tends to be more bumpier. In terms of visuals, I prefer high seat stays. It just looks better to my eye. Plus I feel that stiffness allows me to put down slightly more power on the pedals. My gravel bike has a wishbone style, high seat stay setup with 38c tires and comfort on that is just fine. Wider tires can even out the comfort level level between the two designs.

If I were to buy another road frame, I would probably get something that looks like a Cervelo R5.

13ollocks

BITD, Litespeed marketed their characteristic radial seat stays as being compliant for all-day comfort etc etc. Pure marketing BS, IMO - the stays on my ~24-year-old frame are beasts - I can't imagine them flexing worth a damn under any circumstances, although they do look pretty. In addition, when I see some of the comparatively wispy yet adequate seat stays on any number of modern CF frames, it's clear that the thicker stays on older frames were, in many cases, overkill, adding unnecessary weight and likely stiffness. Frame design has certainly evolved since then.



Many years ago, I had the opportunity to spend a few summers riding one of these - talk about curly stays! I honestly don't recall if it was any more comfortable as any other bike I rode.

chaadster

the only problem is that seat stay attachment points (i.e. high or low) don’t have any relationship to amount of exposed seat post, though.

PeteHski

Yeah, it’s the top tube slope that matters for seat tube exposure.

tFUnK

It could be coincidental that the dropped stay frame just happens to also have more exposed seat post.

PeteHski

It’s actually more likely that the dropped stay frame will have a longer seat tube. Look at the photos in the first post. Most of the modern bikes with full length stays have a steep sloping TT and short ST.

Kontact

This is kind of weird engineering problem. On the one hand, if you want something to flex more easily, building a curve into it should encourage it to flex with that curve. On the other hand, titanium gets stiffer as you cold work it, and Serotta discovered in the '80s that their S curve chainstays were stiffer than straight ones.

OTOH, Dave Kirk's curved stay frames are assembled under bending tension - like a preloaded suspension spring.

Kimmo

Weight is overrated according to the science, but this overlooks the placebo angle and the fact light bikes are more fun; on the other hand frame weight is probably not such a big deal because you can have a heavier bike that feels light if the weight is concentrated lower down and behind the head tube.

Aero totally matters, and due to the exponential nature of drag, it's worth chasing marginal gains if you like to go fast.

Compliance also matters, not just because a softer bike is more pleasant, but because you're slower if you have to put more energy into dealing with bumps, and because bigger hits translate some of your horizontal motion into vertical. Mitigation of the latter is a lower-order effect unless you're riding something seriously compliant like a beam bike, though. The importance of compliance scales with the typical distance you ride, bearing in mind that you're probably prepared to ride a plusher bike further. Also remember that you can stuff a lot of tyre in modern bikes, and that makes more difference than almost anything you change with the frame, short of doubling the amount of exposed seatpost or putting a suspension beam under the seat.

All else being equal, you pay for aero with weight and more stiffness. The simplest and lightest way to get compliance is to have a long round seatpost, which can make as much difference as a few extra mm of tyre. The most aero setup has become a boring cookie-cutter consensus - level top tube, dropped stays, aero seatpost, fork crown faired in to downtube; all this jazz started off with a pretty hefty weight penalty, but I gather they've figured out how to make it a bit lighter by now.

It tends to be fairly stiff due to the level top tube and shorter aero seatpost, although there's potential to compensate for that with careful layup - the frame can be engineered to allow the seatpost to flex backwards as the seat tube bows a little with the seatstays pushing on it... but to allow a meaningful amount of flex without compromising durability that's a significant amount of engineering, so I would expect most bikes which look like this to be pretty stiff, with the situation gradually improving over the coming years.

Oh yeah, forgot to mention that they've come up with a truncated airfoil section with a flat back which is nearly as aero, and allows for lighter and more compliant construction, so look for that.

Kimmo

The TCX has a round post, doesn't it? If so, replace it with the lightest one you can find. Some carbon posts are way overbuilt.

Jughed

No, it has a shaped post that is designed for flex.