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Advantages of Different Seatstay Designs on CF Road Race Bikes?

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Advantages of Different Seatstay Designs on CF Road Race Bikes?

Old 04-25-24, 07:03 PM
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Originally Posted by Jughed
No, it has a shaped post that is designed for flex.
Giants - yet another thing that hasn't been great since the noughties. (Like car styling and popular music)
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Old 04-26-24, 03:24 AM
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Originally Posted by Kimmo
Giants - yet another thing that hasn't been great since the noughties. (Like car styling and popular music)
Those are not facts.
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Old 04-26-24, 07:37 AM
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Originally Posted by chaadster

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.
.
The Trimble has a much beefier “main tube”.

The Y-foil has a rear triangle (from the photo course if found).

The PX5 has much beefier chain stays.

I’m not sure if the last two were intended to be particularly “comfortable”. I’m not sure if the frames were particularly light. That bikes like this aren’t really made any more suggests they weren’t better than the standard frame that has stays.

So, it seems you don’t need seat stays but it appears there might be compromises needed to remove them.

Given the variety of stay arrangements, it doesn’t seem to matter much where they are placed or their shape. (But manufacturers will certainly still say what they do is the best. Until they change it.) That disc brakes allowed more freedom to move them about makes sense. Lower might be more aerodynamic but, maybe, not by much.
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Old 04-26-24, 08:03 AM
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Originally Posted by njkayaker
The Trimble has a much beefier “main tube”.

The Y-foil has a rear triangle (from the photo course if found).

The PX5 has much beefier chain stays.

I’m not sure if the last two were intended to be particularly “comfortable”. I’m not sure if the frames were particularly light. That bikes like this aren’t really made any more suggests they weren’t better than the standard frame that has stays.

So, it seems you don’t need seat stays but it appears there might be compromises needed to remove them.

Given the variety of stay arrangements, it doesn’t seem to matter much where they are placed or their shape. (But manufacturers will certainly still say what they do is the best. Until they change it.) That disc brakes allowed more freedom to move them about makes sense. Lower might be more aerodynamic but, maybe, not by much.
Of course there are always compromises, but that wasn't my point in mentioning those designs or the Giant. My point was that seatstays are probably not the crucial element to comfort, and just looking at them almost certainly won't tell you anything about comfort.

Anyway though, the reason those roads designs did not persist is because they were not UCI compliant, not because they weren't better, which they almost certainly were from a variety of perspectives.
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Old 04-30-24, 06:33 PM
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Originally Posted by njkayaker
The Trimble has a much beefier “main tube”.

The Y-foil has a rear triangle (from the photo course if found).

The PX5 has much beefier chain stays.

I’m not sure if the last two were intended to be particularly “comfortable”. I’m not sure if the frames were particularly light. That bikes like this aren’t really made any more suggests they weren’t better than the standard frame that has stays.

So, it seems you don’t need seat stays but it appears there might be compromises needed to remove them.

Given the variety of stay arrangements, it doesn’t seem to matter much where they are placed or their shape. (But manufacturers will certainly still say what they do is the best. Until they change it.) That disc brakes allowed more freedom to move them about makes sense. Lower might be more aerodynamic but, maybe, not by much.
Just any FYI, in '98 the UCI put a restriction in place, requiring a traditional 'Triangle' for all bikes certified for UCI sanctioned races/racing. Which put 'paid' to these designs and others departing from the traditional 'triangle' of down,top and seattubes. Some others.... ZIPP, Softride (which was one of 1st to 'lose' the traditional Triangle) and Graeme Obree and his 'Old Faithful'.
Whose to say whether those design directions might have developed into more or less aero forms in comparison to today's offerings...
However, Triathlon not falling under UCI, meant that they continued to use bikes with these designs, and some can be seen in competition today. Certainly Bike sponsorship will be a big restriction of what you see under the top level Triathletes...

It'll be interesting to see how UCI reacts when REAL electronic shifting comes about - electronic internal hub systems with settable gear ratios, and prolly running belt drives, rather than the 800 lb gorilla of unnecessary weight - the bike chain. There's no reason why an internal gear change system can't be located in the crank/BB location and the rear be a single 'cog'... 'Direct' drive? Possible, depending on material engineering! Motos have had direct drive for many decades,, because weight is much less of a consideration.
At the moment 'Electronic shifting' is pretty much like the electric knife...
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Old 05-01-24, 04:29 AM
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Originally Posted by cyclezen

It'll be interesting to see how UCI reacts when REAL electronic shifting comes about - electronic internal hub systems with settable gear ratios, and prolly running belt drives, rather than the 800 lb gorilla of unnecessary weight - the bike chain. There's no reason why an internal gear change system can't be located in the crank/BB location and the rear be a single 'cog'... 'Direct' drive? Possible, depending on material engineering! Motos have had direct drive for many decades,, because weight is much less of a consideration.
At the moment 'Electronic shifting' is pretty much like the electric knife...
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Yuri - not sure I'll still be breathing when the really new and juicy stuff hits the road...
I have to say I’m surprised how long the derailleur drivetrain has been dominant. It is at least now very well refined! I think the FD will be first to fall with 1x and internal hub/BB gears. But I think the RD still has plenty of life left.
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Old 05-01-24, 08:29 AM
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Originally Posted by PeteHski
But I think the RD still has plenty of life left.
As does the chain, a pretty darn efficient mechanism.
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Old 05-01-24, 08:50 AM
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Originally Posted by terrymorse
As does the chain, a pretty darn efficient mechanism.
I agree, but I do find them a bit of an inconvenience. Belt drives are efficient too, just need the gearing range etc. I'm surprised there are not more options. We had a couple of belt drive kids bikes and they were great for maintenance.
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Old 05-01-24, 09:02 AM
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Don't discount one of the primary, if not, the primary drivers in attracting customers in this category – aesthetics. I'll admit the dropped seat stays simply look better. Part of it may be that they make the saddle look higher – and that makes it look like a pro's bike and that make it makes it look like… yeah - aesthetics.
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Old 05-01-24, 09:28 AM
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Originally Posted by PeteHski
I agree, but I do find them a bit of an inconvenience. Belt drives are efficient too, just need the gearing range etc. I'm surprised there are not more options. We had a couple of belt drive kids bikes and they were great for maintenance.
There's a rider in our Sunday group, aussie, who had a custom TI frame made, built up the rest himself, using an IGH and belt drive, otherwise upper level road components...
Just from the 'heft' test, bike weight seems about the same as a Mid-level CF bike. He's solid middle of pack rider and has no issues on the climbs...
The bike is wonderfully silent and he always seems to have the 'right' gear for the occasion ... I'll have to take a pic and post, when we're both on the next ride...
Between Ski season (WInter lasts until Mid April in the SIerra and Mammoth stays open usually to well past May- last year End of July) and now the Best times to hike in our Back Country, I've been missing the Sunday Rides... The Back Country will soon turn into an Oven, and Sunday Coastal Rides will seem like heaven (which they are...).
Ride On
Yuri
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Old 05-01-24, 09:28 AM
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Originally Posted by Zaskar
Don't discount one of the primary, if not, the primary drivers in attracting customers in this category – aesthetics. I'll admit the dropped seat stays simply look better. Part of it may be that they make the saddle look higher – and that makes it look like a pro's bike and that make it makes it look like… yeah - aesthetics.
I got the impression that most people still preferred the look of full length seatstays, but maybe that is starting to change. I think both can look good in the overall design.
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Old 05-01-24, 09:31 AM
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Originally Posted by cyclezen
There's a rider in our Sunday group, aussie, who had a custom TI frame made, built up the rest himself, using an IGH and belt drive, otherwise upper level road components...
Just from the 'heft' test, bike weight seems about the same as a Mid-level CF bike. He's solid middle of pack rider and has no issues on the climbs...
The bike is wonderfully silent and he always seems to have the 'right' gear for the occasion ... I'll have to take a pic and post, when we're both on the next ride...
Between Ski season (WInter lasts until Mid April in the SIerra and Mammoth stays open usually to well past May- last year End of July) and now the Best times to hike in our Back Country, I've been missing the Sunday Rides... The Back Country will soon turn into an Oven, and Sunday Coastal Rides will seem like heaven (which they are...).
Ride On
Yuri
Interesting. That would be a good subject for a new thread. Future drivetrains.
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Old 05-02-24, 07:51 AM
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Having read a fair amount of reviews (and presuming those authors have read the marketing bumpfs), it sounds like the modern frame double diamond design is driven more by aerodynamics than comfort:


- Flat top tubes present the smallest forward aspect relative to any sloping top tube design
- Dropped seatstays put the seatstay/seat tube joint right in front of the top of the tire, where the air is already being spoiled anyway, rather than higher up, which adds to its own drag
- Standard for these days D-shaped seat and down tubes

Comfort is thrown in by way of wide tires, flexy seatposts, and odd suspension designs (ahem, Roubaix and Domane). The ‘default’ race design these days (as outlined above) doesn’t really provide for inherent comfort due to the lower amount of exposed post (flat top tube) and tight rear triangle (dropped stays). An argument could be made that the seat tube itself could be made to flex at the seat stay joint, but any flex there would also impact the top tube and head tube joint as the seat tube bends and effectively shortens that side of the triangle.

So short version… first conclusion: dropped seat stays and flat top tubes are for aero, not comfort.

Of course, regardless of whether your stays are high up or low down, this all happens behind a rider’s thighs and feet, which cause plenty of airflow disruption of their own anyway. Manufacturers are trying to tell us that an extra three inches of half-inch wide seat stay will provide meaningfully more drag, even though it’s primarily in the wash of my 7” diameter thighs and size 10 shoes as they go round and round? Sure, when the absolute most marginal race gains are to be considered, the tiniest fraction of a watt and handful of grams that a shorter stay provides could prove beneficial - or at least, matching what the big boys do is good for optics, both at the start line and on the showroom floor. After all, when Specialized shows up with its new Tarmac, Bianchi and BMC can’t be seen putting "last year’s” technology out there.

Short version, conclusion 2: Marketing wants to make sure our new bike doesn’t look old next to the other guy’s new bike
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Old 05-10-24, 10:02 PM
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Originally Posted by PeteHski
Those are not facts.
How perspicacious of you to recognise a value judgement.
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Old 05-11-24, 08:41 AM
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Originally Posted by Kimmo
How perspicacious of you to recognise a value judgement.
It was more a recognition of a pointless value judgement. Just highly subjective personal opinion, which didn't even have any thread relevance. Giant bikes, car styling and pop music FFS! lol
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Old 05-15-24, 06:41 AM
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Just a comment on dropped seat stays, or no seat stays at all. Yes there are the questions of aero, compliance etc, but there's also the question of torsional frame rigidity. If you removed the seat stays all together or had radically dropped seat stays, all other thihgs being equal the frame is going to lose torsional rigidity. Fine if you're riding in a straight line but not so good if you want to go around corners.
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Old 05-15-24, 07:02 AM
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Originally Posted by Sapper69
Just a comment on dropped seat stays, or no seat stays at all. Yes there are the questions of aero, compliance etc, but there's also the question of torsional frame rigidity. If you removed the seat stays all together or had radically dropped seat stays, all other thihgs being equal the frame is going to lose torsional rigidity. Fine if you're riding in a straight line but not so good if you want to go around corners.
All other things being equal?? We’re not talking about 12 year olds taking a cutting tool to granddad’s old Schwinn Varsity, here.
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Old 05-15-24, 07:37 AM
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My guess: different seat stay configurations differ only minimally, and maybe not at all, with respect to power transmission, vertical compliance, etc. That seat stays are still used for carbon frames is probably down to UCI mandates.

For your reading pleasure:

UCI regulations for racing bike frame designs
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Old 05-15-24, 07:40 AM
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Originally Posted by Sapper69
Just a comment on dropped seat stays, or no seat stays at all. Yes there are the questions of aero, compliance etc, but there's also the question of torsional frame rigidity. If you removed the seat stays all together or had radically dropped seat stays, all other thihgs being equal the frame is going to lose torsional rigidity. Fine if you're riding in a straight line but not so good if you want to go around corners.
The forces that pro bikes encounter are laughably minimal compared to the strength of a well-designed carbon fiber structure.


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Old 05-15-24, 11:25 AM
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Originally Posted by chaadster
All other things being equal?? We’re not talking about 12 year olds taking a cutting tool to granddad’s old Schwinn Varsity, here.
This is true. The point is, even with the most advanced materials, designs etc, if you removed that part of a structure you'd have to compensate elsewhere. In a frameset without seat stays or radically dropped seatstays, you'd need to come up with some other way to introduce torsional rigidity so the rear wheel doesn't twist' independently from the front wheel. This is a consideration people often forget when they look at the two-triangle design of a bike frame.
https://www.cyclist.co.uk/in-depth/bike-frame-stiffness
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Old 05-15-24, 11:38 AM
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Originally Posted by Trakhak
The forces that pro bikes encounter are laughably minimal compared to the strength of a well-designed carbon fiber structure.

You may have noticed this is a TT bike.
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Old 05-15-24, 11:56 AM
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Originally Posted by Sapper69
You may have noticed this is a TT bike.
Yes. TT riders do high-speed cornering, sometimes on very hilly courses (see. e.g., Olympic and World Championship time trial courses over the years), accelerate out of corners, etc. The differences between TT bikes and road and track bikes with respect to the forces the frames are subjected to are inconsequential for well-designed carbon frames.

The UCI didn't ban bikes without seat stays because they were concerned that handling would be affected. They banned them because they were obviously designed to circumvent the restrictions on changes made purely to improve aerodynamics. And under their blanket policy that bikes should look like bikes, dammit.
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Old 05-15-24, 12:31 PM
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Originally Posted by Trakhak
Yes. TT riders do high-speed cornering, sometimes on very hilly courses (see. e.g., Olympic and World Championship time trial courses over the years), accelerate out of corners, etc. The differences between TT bikes and road and track bikes with respect to the forces the frames are subjected to are inconsequential for well-designed carbon frames.

The UCI didn't ban bikes without seat stays because they were concerned that handling would be affected. They banned them because they were obviously designed to circumvent the restrictions on changes made purely to improve aerodynamics. And under their blanket policy that bikes should look like bikes, dammit.
I'm not here to defend the UCI. The OP asked a genuine question about design considerations for seat stays. A lot of people responded with observations about vertical stiffness vs compliance, which is one of the main considerations of bike frame design. Another is torsional stiffness, which is one key reason for having seat stays, unless you have an unlimited budget for exotic materials etc . Yes, you can go around corners on a TT bike, but you can also do a TT on a 'regular' road bike. A TT bike is optimised for aerodynamic efficiency and compromises for handling, weight etc. Other bikes are optimised for say climbing, sprinting or endurance/comfort, while compromising for aero and other factors. This is before considering the budget of the everyday cyclist. There's no one single bike design (or any other mechanical device for that matter) that's optimised for every different purpose and every budget. This is an objective observation of reality.
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Old 05-15-24, 12:48 PM
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Originally Posted by Sapper69
I'm not here to defend the UCI. The OP asked a genuine question about design considerations for seat stays. A lot of people responded with observations about vertical stiffness vs compliance, which is one of the main considerations of bike frame design. Another is torsional stiffness, which is one key reason for having seat stays, unless you have an unlimited budget for exotic materials etc . Yes, you can go around corners on a TT bike, but you can also do a TT on a 'regular' road bike. A TT bike is optimised for aerodynamic efficiency and compromises for handling, weight etc. Other bikes are optimised for say climbing, sprinting or endurance/comfort, while compromising for aero and other factors. This is before considering the budget of the everyday cyclist. There's no one single bike design (or any other mechanical device for that matter) that's optimised for every different purpose and every budget. This is an objective observation of reality.
All true. I was addressing the suggestion that bikes missing seat stays would be inferior in some way to those with seat stays - full length, mid-seat-tube length, or vestigial. I know of no evidence showing that seat stays are needed for any modern (carbon fiber) bike, regardless of application. ("It's obvious!" doesn't count.)

And note that that Lotus is missing not just seat stays but also a down tube. Heat diagrams have shown that the down tube is one of the most stressed elements in a bike frame (and that seat stays are the least stressed).

And then there are Slingshot bikes, beloved of our own SpeedOfLite. I wouldn't have believed those bikes could be ridden 100 yards without collapsing, but there they are. Maybe that's what started me on the path of skepticism regarding received wisdom about bike frame designs. (I know, for instance, that my aluminum bikes are no different from my steel bikes with respect to riding comfort.)
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Old 05-15-24, 12:59 PM
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Originally Posted by Trakhak
All true. I was addressing the suggestion that bikes missing seat stays would be inferior in some way to those with seat stays - full length, mid-seat-tube length, or vestigial. I know of no evidence showing that seat stays are needed for any modern (carbon fiber) bike, regardless of application. ("It's obvious!" doesn't count.)

And note that that Lotus is missing not just seat stays but also a down tube. Heat diagrams have shown that the down tube is one of the most stressed elements in a bike frame (and that seat stays are the least stressed).

And then there are Slingshot bikes, beloved of our own SpeedOfLite. I wouldn't have believed those bikes could be ridden 100 yards without collapsing, but there they are. Maybe that's what started me on the path of skepticism regarding received wisdom about bike frame designs. (I know, for instance, that my aluminum bikes are no different from my steel bikes with respect to riding comfort.)
The question of what's superior/inferior isn't just about optimal design and materials. We could argue all day about what 'significant' torsional loads are, but even if we agreed on an 'optimal' design, then there would be questions about affordability, durability and so on. UCI or no UCI, 99% of cyclists will be riding bicycles with seat stays for the foreseeable future.
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