why are ultra thin seat stays all the rage right now?
05-21-15, 04:17 PM
#27
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seatstays thin at the top
05-21-15, 04:30 PM
#28
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Eh. A common answer. But in my experience, engineers have enough work to do to make something actually better - which they can then use to sell bikes - that they don't need to make arbitrary changes just to sell bikes. It's not Red Cross CPR.
I would sooner expect that given the material and structural development, seat stays are becoming less and less necessary, so they're approaching legacy. ... which would be really weird.
I would sooner expect that given the material and structural development, seat stays are becoming less and less necessary, so they're approaching legacy. ... which would be really weird.
05-21-15, 04:45 PM
#29
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05-21-15, 06:03 PM
#31
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Finally after all the responses, a cogent answer. Engineers have transferred the section modulus required to stabilize the rear triangle to the chain stays because they figured out its win/win for compliance by decreasing the strength/increasing flex of seat stays and increasing chain stay thickness in part due to increase BB strength and down tube diameter. This has largely come into being because of the development of carbon fiber but then it was determined it had companion application to Aluminum bikes which could closely replicate tube asymmetry of molded carbon. This largely obsoleted steel because of forming limitations to get the same balance of torsional stiffness to vertical compliance.
And if your goal is only to increase comfort and you care nothing for efficiency, you can even beef up the seatstay and get ride of the chainstay. Design students (not to be confused with engineering students) more interested in winning design contests than building practical stuff seem to gravitate towards these kinds of designs.
There are no hard and fast rules in framemaking. It's really designer's choice where to distribute the stresses in a frame.
Incidently, if you are an engineering student wondering why you have to take statics, this is the difference between a frame and a truss. A truss will always have the same loads regardless of how the members are made. Every joint is a pivot and every member is either in tension or compression. A frame is a statically indeterminate structure meaning the stresses on the members of the frame are dependent on how these frame members deform relative to one another.
Getting back to the OP, contemporary frame designers choose to load up the chainstays and make these super stiff while skinny-ing up the seat stays to get that vaunted "vertical compliance". It's designer's choice. You'll still find beefy, stiff, seat stays on bikes built for sprinters.
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Last edited by Brian Ratliff; 05-21-15 at 06:06 PM.
05-21-15, 06:34 PM
#32
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05-22-15, 06:43 AM
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Obligatory counter statement that steel is not obsolete.
05-22-15, 09:15 AM
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It is in numbers by a long shot. People need to smell the coffee. The industry has moved on but many on the 41 who are my age and grew up riding steel like I did haven't. Europe is even more evolved than the US. Almost impossible to buy a steel bike in Europe. How many steel bikes do the top guys make? A handful compared to a zillion Al and carbon bikes. This is for good reason. Aluminum bikes can be made lighter, more laterally stiff and more vertically compliant than steel. Al has largely obsoleted Ti and certainly carbon has as well at the same price point. I have owned all of them.
So those stuck in the 60's who still have fondness for their old steelie will want to relive the past and order a custom steel bike and pay a ridiculous premium when more performance can be had with a number of different Al bikes like a CAAD10, Spesh Allez or the bike I just bought...a Secteur. There are no steel bikes that will rival the performance of these bikes overall. You can say its so, but it isn't for the simple fact that steel is heavy and can't be formed like Al can and the shape of the tubing is largely what gives a bike its performance.
So those stuck in the 60's who still have fondness for their old steelie will want to relive the past and order a custom steel bike and pay a ridiculous premium when more performance can be had with a number of different Al bikes like a CAAD10, Spesh Allez or the bike I just bought...a Secteur. There are no steel bikes that will rival the performance of these bikes overall. You can say its so, but it isn't for the simple fact that steel is heavy and can't be formed like Al can and the shape of the tubing is largely what gives a bike its performance.
05-22-15, 09:19 AM
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Yes. This is exactly right. The larger point is there is no fixed rules for how loads are distributed in a frame. It depends on how you make the frame. You can put the loads from the rear wheel onto the chainstays or the seatstays, designers choice. Or they can distribute them evenly. If you only care about stiffness, you make both the chainstay and seatstay equally stiff and make both of these components as stiff as possible. If you want comfort and efficiency, you beef up the chainstay and leave the seatstay compliant. You might disconnect the seatstay from the seat tube all-together. You can even eliminate it entirely.
And if your goal is only to increase comfort and you care nothing for efficiency, you can even beef up the seatstay and get ride of the chainstay. Design students (not to be confused with engineering students) more interested in winning design contests than building practical stuff seem to gravitate towards these kinds of designs.
There are no hard and fast rules in framemaking. It's really designer's choice where to distribute the stresses in a frame.
Incidently, if you are an engineering student wondering why you have to take statics, this is the difference between a frame and a truss. A truss will always have the same loads regardless of how the members are made. Every joint is a pivot and every member is either in tension or compression. A frame is a statically indeterminate structure meaning the stresses on the members of the frame are dependent on how these frame members deform relative to one another.
Getting back to the OP, contemporary frame designers choose to load up the chainstays and make these super stiff while skinny-ing up the seat stays to get that vaunted "vertical compliance". It's designer's choice. You'll still find beefy, stiff, seat stays on bikes built for sprinters.
And if your goal is only to increase comfort and you care nothing for efficiency, you can even beef up the seatstay and get ride of the chainstay. Design students (not to be confused with engineering students) more interested in winning design contests than building practical stuff seem to gravitate towards these kinds of designs.
There are no hard and fast rules in framemaking. It's really designer's choice where to distribute the stresses in a frame.
Incidently, if you are an engineering student wondering why you have to take statics, this is the difference between a frame and a truss. A truss will always have the same loads regardless of how the members are made. Every joint is a pivot and every member is either in tension or compression. A frame is a statically indeterminate structure meaning the stresses on the members of the frame are dependent on how these frame members deform relative to one another.
Getting back to the OP, contemporary frame designers choose to load up the chainstays and make these super stiff while skinny-ing up the seat stays to get that vaunted "vertical compliance". It's designer's choice. You'll still find beefy, stiff, seat stays on bikes built for sprinters.
