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Why are modern bikes still built with traditional geometry?

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Why are modern bikes still built with traditional geometry?

Old 01-27-18, 03:24 PM
  #26  
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Originally Posted by tyrion View Post
For better strength/weight and some people prefer the aesthetics.

Slanted top tubes allow fewer sizes to fit more people so it's a cost saving design, also more crotch clearance for off-road bikes.

edit: and a slanted top tube with a longer seatpost with some flex can provide a little more cushioning.
Given that seat post is generally much thicker walled than frame tubing, and compacts make that supple frame tubing shorter and stiffer, is there actually more cushioning?



All of which may be academic. Is any actually making true compact frames anymore? All the sloping bikes I've seen of late have tall head tubes and use as much or more material than in traditional frames.

Last edited by Kontact; 01-27-18 at 03:34 PM.
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Old 01-27-18, 03:29 PM
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Seems as if OP happened upon some old Giant advertising material.
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Old 01-27-18, 03:37 PM
  #28  
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Originally Posted by CampioneDItalia View Post
So around 2000, Giant discovered the advantages of compact geometry. They could produce a bike with the "same" fit as a trad bike, using less tubing (saving weight) and increasing stiffness (smaller triangle reduces lateral torsion). The only difference is that the rider would have to use a longer seatpost.
The number 1 advantage of a "compact" frame is that a vendor needs to stock fewer sizes. It's debatable that a sloper produces a stiffer frame: not only are you losing some strength through deviating farther from a triangle than a level top tube frame, but you're adding a long flexible seatpost (which probably weighs more than the equivalent length of seat tube). The number 2 advantage is that it looks "normal" to an eye raised on mountain bikes. BTW - I wouldn't call it "geometry" - the geometry doesn't need to change if you shorten the seat tube and slope the top tube down.
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Old 01-27-18, 03:45 PM
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I'm just curious why a compact makes it so you no longer need the same number of increments in top tube length. I suppose if your only sizing criteria is standover height it might make some sense, but otherwise...
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Old 01-27-18, 03:57 PM
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Originally Posted by Kontact View Post
Given that seat post is generally much thicker walled than frame tubing, and compacts make that supple frame tubing shorter and stiffer, is there actually more cushioning?
That's the marketing hype (mostly for the newer gravel/endurance bikes). I don't have first hand experience with this but it makes sense to me, especially if the seatpost is designed to flex.

And maybe "cushioning" isn't the right word, maybe "vibration dampening" is more accurate.
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Old 01-27-18, 04:05 PM
  #31  
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Originally Posted by tyrion View Post
That's the marketing hype (mostly for the newer gravel/endurance bikes). I don't have first hand experience with this but it makes sense to me, especially if the seatpost is designed to flex.

And maybe "cushioning" isn't the right word, maybe "vibration dampening" is more accurate.
I've heard that a lot, too. I just don't know if it makes sense that seat posts flex at all giving their wall thickness.

The same gets said about carbon bars, but most of what I've read in tests are that carbon bars don't actually damp more than aluminum.

Unless the compact frame maker also makes a special seatpost for the frame, it seems like a leap.
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Old 01-27-18, 04:14 PM
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Originally Posted by Kontact View Post
I've heard that a lot, too. I just don't know if it makes sense that seat posts flex at all giving their wall thickness.

The same gets said about carbon bars, but most of what I've read in tests are that carbon bars don't actually damp more than aluminum.

Unless the compact frame maker also makes a special seatpost for the frame, it seems like a leap.
Yeah you'd need a seatpost designed to flex.
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Old 01-27-18, 04:23 PM
  #33  
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Originally Posted by Kontact View Post
I've heard that a lot, too. I just don't know if it makes sense that seat posts flex at all giving their wall thickness.
Oh, seatposts flex!
Even though they are thicker-walled than tubing, they are hanging out from the frame, not joined and triangulated as frame tubes are. So they will flex in proportion to their thickness and length. Same with forks.
Also true of frame tubes. If they are thin-walled and long enough, you can see it. I have a very lightweight steel mountain bike where, if you hold the front brake and push hard into the handlebars, the top tube visibly bows upward.

Originally Posted by Kontact View Post
The same gets said about carbon bars, but most of what I've read in tests are that carbon bars don't actually damp more than aluminum.

Unless the compact frame maker also makes a special seatpost for the frame, it seems like a leap.
I guess it would help to define better what "damp" means. If you mean "absorb energy," then that's basically correct. In fact, no frame or component material itself absorbs a meaningful amount of energy unless it bends or breaks or gets warmer.
If you mean "slow down the transmission of shock to the body by bending elastically" then what flexes most without bending will damp most. A long seatpost will do a fair amount of that sort of damping. But so will the saddle frame and shell. They are almost always more flexible than the post itself.
The second definition I'm offering is, practically speaking, what "damp" means unless you have an actual shock-absorbing mechanism. The amount of energy that is actually dissipated into the materials is infinitesimal.
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Old 01-27-18, 04:46 PM
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Originally Posted by Kontact View Post
Maybe you don't get something for nothing, and the weight required to make a long post as stiff as a normal post is not actually less than the weight saved by angling the frame tubes?
Yeah this has always been my belief, though I like both traditional and compact frames.
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Old 01-27-18, 05:26 PM
  #35  
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Originally Posted by Ghrumpy View Post
Oh, seatposts flex!
Even though they are thicker-walled than tubing, they are hanging out from the frame, not joined and triangulated as frame tubes are. So they will flex in proportion to their thickness and length. Same with forks.
Also true of frame tubes. If they are thin-walled and long enough, you can see it. I have a very lightweight steel mountain bike where, if you hold the front brake and push hard into the handlebars, the top tube visibly bows upward.
Everything on a bike flexes, but whether a seat post flexes more relative to the frame is the point of my post.



I guess it would help to define better what "damp" means. If you mean "absorb energy," then that's basically correct. In fact, no frame or component material itself absorbs a meaningful amount of energy unless it bends or breaks or gets warmer.
If you mean "slow down the transmission of shock to the body by bending elastically" then what flexes most without bending will damp most. A long seatpost will do a fair amount of that sort of damping. But so will the saddle frame and shell. They are almost always more flexible than the post itself.
The second definition I'm offering is, practically speaking, what "damp" means unless you have an actual shock-absorbing mechanism. The amount of energy that is actually dissipated into the materials is infinitesimal.
I think what you meant was "flexes most without permanently deforming" as "flex" and "bend" means the same thing. "Damping" can mean absorb energy, but it can also mean that the material tends to shift frequencies so vibrations we don't like get turned into frequencies we don't notice, or get cancelled out completely. Steel, carbon and titanium all make very efficient springs, but they don't transmit sound and other vibrations equally.
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Old 01-27-18, 05:28 PM
  #36  
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Originally Posted by exmechanic89 View Post
Yeah this has always been my belief, though I like both traditional and compact frames.
I like the look of level TTs, and since I ride smaller frames I appreciate being able to use two full size water bottles. But anyone who like compacts is welcome to them. We should just understand that nothing is free - there is a trade off whenever you add and remove materials.
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Old 01-27-18, 06:03 PM
  #37  
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I LOL at the advantages listed for compact frames.
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Old 01-27-18, 07:10 PM
  #38  
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Originally Posted by Kontact View Post
I think what you meant was "flexes most without permanently deforming" as "flex" and "bend" means the same thing.
Yes, that's right. I intended the unqualified "bending" to mean "deforming plastically" as contrasted to the "bending elastically" I wrote later. Shouldn't have used the same word.

Originally Posted by Kontact View Post
"Damping" can mean absorb energy, but it can also mean that the material tends to shift frequencies so vibrations we don't like get turned into frequencies we don't notice, or get cancelled out completely. Steel, carbon and titanium all make very efficient springs, but they don't transmit sound and other vibrations equally.
Yes exactly, that's probably a better way of saying the same thing I did, as frequency is by definition a time-dependent attribute.
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Old 01-27-18, 08:00 PM
  #39  
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Long seatposts flex a lot

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Old 01-27-18, 08:14 PM
  #40  
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Originally Posted by Lazyass View Post
I don't think you'll find many, if any, compact frames that come in 2cm increments.
Maybe it's not the norm, but some have been. My '06 Bianchi San Mateo has a sloping top tube and was sized in 2 cm increments.
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Old 01-27-18, 09:43 PM
  #41  
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Dunno, but maybe they shouldn't be, especially with squiggly and "flowing" tube forms (that aren't designed by me).

62cm Pinarello Dogma:



They look much better and look to be designed better in a much shorter height:

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Old 01-27-18, 09:49 PM
  #42  
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Originally Posted by vettracer View Post
That looked like a frame flexing a lot.
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Old 01-28-18, 07:57 AM
  #43  
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Originally Posted by Bandera View Post
That would actually be:



BTW: In what way is >2000 production C&V?

-Bandera
This is the problem with this C&V group not having established a clear criterion.

Also this is more of a product engineering/product design question, and we really don't have a product design forum.
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Old 01-28-18, 08:18 AM
  #44  
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Originally Posted by Chuckk View Post
Real men don't ride a bike that looks like a lady's step-through.
That may be some of it. There is so much talk about clearance and "jewels", but it really doesn't make much difference.

Colnago does put a sloping TT on some of their frames, but I think the C40, C50, and C60 lugged CF are still popular frames, although the line is being slowly replaced.



Actually, I can't read the numbers on the frame that the OP posted, but I think it may be the C50. It shows a 5-bolt crankset and 10-speed shifters.

So, it makes an excellent example of a "modern" frame using a photo of a 10 year old bike.
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Old 01-28-18, 08:31 AM
  #45  
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Originally Posted by Road Fan View Post
This is the problem with this C&V group not having established a clear criterion.

Also this is more of a product engineering/product design question, and we really don't have a product design forum.
It couldn't possibly be that because the 41, where a thread like this belongs, is such a pit of endless bickering, pissing contests and faux-expertise that it ends up in C&V looking for a straight-up response by default?

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Old 01-28-18, 08:40 AM
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@Bandera, FTW! +1 most definitely. With the civil discussion here so far, its no wonder that things started here with this thread, rather than the 41, or worse, General.

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Old 01-28-18, 09:49 AM
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Originally Posted by Bandera View Post
It couldn't possibly be that because the 41, where a thread like this belongs, is such a pit of endless bickering, pissing contests and faux-expertise that it ends up in C&V looking for a straight-up response by default?

-Bandera
SSHHHHsshhhh! Don't say that too loud, or the Mod Squad will move it, or make a new subthread for it.

My main point, and perhaps I wasn't too clear, is that we really don't have a place to discuss design of bicycles or product engineering without being domain-specific, i.e. Road, MtB, Race, C&V, Long Distance, et cetera.

And you're right, there is by far less noise here than there.
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Old 01-28-18, 09:49 AM
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A better question would be:
Why should my biking choices be driven by the profitability needs of a few large companies?


I would submit that there are certainly more builders producing frames with level top tubes (or nearly level). Just in lower volumes.


The few high volume builders crank out thousands of sloped TT bikes, but more builders are producing traditional diamond frames. Cost savings & profitability drive the big companies. Marketing & "innovation" serve the sales needs at big companies. Satisfied customers and word-of-mouth referrals drive sales at the smaller shops.


So who is right? So which is 'best'? Neither, if the bike fits without compromises.
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Old 01-28-18, 09:50 AM
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Originally Posted by qcpmsame View Post
@Bandera, With the civil discussion here so far, its no wonder that things started here with this thread, rather than the 41, or worse, General.
Just say NO to the "Modern" and ask a Mod to move non-C&V threads to the appropriate BF bickering-troll-land where nano-tech-hydro-electric doo-dads can get the 15 minutes of attention they deserve before becoming a forgotten footnote in cycling tech.

Keep C&V obsolescent at least, quaint and completely obsolete by choice.

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Last edited by Bandera; 01-28-18 at 01:50 PM.
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Old 01-28-18, 09:53 AM
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Originally Posted by Wildwood View Post
A better question would be:
Why should my biking choices be driven by the profitability needs of a few large companies?

Irrelevant in a C&V context, the point here is:
"They" don't make "them" anymore.

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