# Curved Top tubes



## Banjo (17 Jun 2011)

I read a cycling plus review about an alloy bike with a curved top tube which stated "the curved top tube acts like a leaf spring smoothing out bumpier rides" (wording m,ay not be exact).

This sounds like BS to me. Firstly a large section tube isnt going to flex in that length , if it did I would expect it to crack before long. To my eye any improvement in the bikes looks are lost by the cables being more obvious.

There are a few bikes with curved top tubes that I like and would buy .But probably in spite of rather than because of the top tube.


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## TheDoctor (17 Jun 2011)

The last thing you want an aluminium tube to do is bend.


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## Smokin Joe (17 Jun 2011)

Probably gives greater structural integrity than a straight tube allowing for a thinner wall.

But then again, maybe not. I often don't know what I'm talking about.


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## Davidc (17 Jun 2011)

TheDoctor said:


> The last thing you want an aluminium tube to do is bend.



If that one bends so will the down and seat tubes.

On a steel, carbon or titanium frame you'd expect some flexing of the tubes, with aluminium no thanks!


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## raindog (17 Jun 2011)

"Curved Top tubes Are they just for looks?"

I hope not, because I think they look crap. 





They're supposed to be more comfortable, filter road noise out or something.


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## mickle (17 Jun 2011)

Curved top tubes are a way of connecting the top of the seat tube with the top of the head tube whilst optimising stand-over clearance. or to make a style statement which is more often the case. A non straight tube must be made stronger than an equivalent straight tube to achieve the same structural integrity.

If someone tells you it's to provide 'flex', 'comfort', 'damping' or other such nonsense don't buy a bike from them for they are a idiot.


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## Angelfishsolo (17 Jun 2011)

It certainly sounds like BS to me.


Banjo said:


> I read a cycling plus review about an alloy bike with a curved top tube which stated "the curved top tube acts like a leaf spring smoothing out bumpier rides" (wording m,ay not be exact).
> 
> This sounds like BS to me. Firstly a large section tube isnt going to flex in that length , if it did I would expect it to crack before long. To my eye any improvement in the bikes looks are lost by the cables being more obvious.
> 
> There are a few bikes with curved top tubes that I like and would buy .But probably in spite of rather than because of the top tube.


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## corshamjim (17 Jun 2011)

I'm rather fond of my curvy tubes (ooh err missus).






I'll admit probably the only thing they contribute to the design is aesthetic, and if anything they add to the weight.


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## phil_hg_uk (17 Jun 2011)

For some reason I like this one:


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## david1701 (17 Jun 2011)

phil_hg_uk said:


> For some reason I like this one:



isn't that one a mis-mold


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## phil_hg_uk (17 Jun 2011)

david1701 said:


> isn't that one a mis-mold



This is mine it was a challenge mounting the pump on the crossbar:






it also has a curvy backend


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## slowmotion (17 Jun 2011)

phil_hg_uk said:


> For some reason I like this one:



I don't know why, but I would call that "bent" rather than "curved". Kinda cool though.


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## Banjo (17 Jun 2011)

I am not knocking a curved top tube at all it would neither attract me to or put me off a bike .

Just challenging Cycling pluses assertion that it can in some way soften the ride.


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## Nebulous (17 Jun 2011)

Well I'm remarkably fond of my Allez - in red - but don't let my prejudices put you off!


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## Fnaar (17 Jun 2011)

phil_hg_uk said:


> For some reason I like this one:


Are we sure this one hasn't been in an accident?


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## samid (17 Jun 2011)

Fnaar said:


> Are we sure this one hasn't been in an accident?


LOL


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## phil_hg_uk (17 Jun 2011)

Fnaar said:


> Are we sure this one hasn't been in an accident?



I guess it could be a problem if you did have and accident on it, how would they know if it had been damaged or not


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## Cubist (17 Jun 2011)

phil_hg_uk said:


> This is mine it was a challenge mounting the pump on the crossbar:
> 
> 
> 
> ...


Forgive me, but does anyone else think the underslung cables look kinda "orphaned" hanging there under the top tube? Any bike builder worth their salt would have simply clipped in a full length outer to the tube to follow the curve!

Flex in an alluminium top tube? Are they taking the piss?


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## mickle (18 Jun 2011)

Cycling Pus is and always has been full of shoot, and don't get me started on that Paul Vincent character.


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## Night Train (18 Jun 2011)

Banjo said:


> I read a cycling plus review about an alloy bike with a curved top tube which stated "the curved top tube acts like a leaf spring smoothing out bumpier rides" (wording m,ay not be exact).
> 
> This sounds like BS to me.



It would be BS.

It is marketing speak to explain why the curved tube provides less structural stuffness then a straight tube would.


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## slowmotion (18 Jun 2011)

Night Train said:


> It would be BS.
> 
> It is marketing speak to explain why the curved tube provides less structural stuffness then a straight tube would.



Yeah, right. My Secteur has a bent and tapered aluminium top tube. The motor's crap too....


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## TheDoctor (18 Jun 2011)

'Stuffness' is an excellent word !! 

More stuffness and less stiffness.


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## mickle (19 Jun 2011)

TheDoctor said:


> More stuffness and less stiffness.



You can get pills for that.... It's just your age.


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## gaz (19 Jun 2011)

curved tubes are sexy (if they curve the right way)


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## Night Train (19 Jun 2011)

I suppose you can have a curved tube that doesn't affect the stiffness of the frame but it would need to be a larger tube with more weight to it.

Curves do look good but to an engineering eye they look odd on a triangulated structure if there is no need for it to be there.

My first full sized bike had curved tubes.


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## Smokin Joe (19 Jun 2011)

Banjo said:


> I am not knocking a curved top tube at all it would neither attract me to or put me off a bike .
> 
> Just challenging Cycling pluses assertion that it can in some way soften the ride.


To quote what I posted in another thread in Bikes And Accessories -

"As 90% of modern cycling journalists are clueless self-gratification artists who swallow any old shoot fed to them by marketing men they write exactly what the manufacturers intend them to write, ie crap that is designed to make the readers think they must have a different bike for evey day of the week".


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## Banjo (19 Jun 2011)

Smokin Joe said:


> To quote what I posted in another thread in Bikes And Accessories -
> 
> "As 90% of modern cycling journalists are clueless self-gratification artists who swallow any old shoot fed to them by marketing men they write exactly what the manufacturers intend them to write, ie crap that is designed to make the readers think they must have a different bike for evey day of the week".



I am tempted to write to C+ probably best if I dont quote your comments though Joe  

Be interesting to see if it gets printed or if I get any form of reply.


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## Willo (19 Jun 2011)

I wasn't keen on the curved tube on my Allez at first, but have grown to like the shape of it now, with no knowledge of whether it's a good or bad design functionality wise. However, have to agree with the earlier points about the cable hanging below the tube, as can be seen below, which is a little daft design wise (and means I have to take a little extra care when putting it on the rack on the car.


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## notthebuzzard (20 Jun 2011)

Thought I'd chip in to this as I have a vested interest. What with me being the editor of Cycling Plus and all. I've just looked back over the last issue and found the offending caption and hands up, I missed it. That said, I'm no engineer so I'm going to consult one to check if this is, indeed, BS. (Yes, it's a bit late now but...)

But a couple of points: Mickle "Cycling Pus is and always has been full of shoot, and don't get me started on that Paul Vincent character." You're perfectly entitled to your opinion about the magazine, and I'm perfectly entitled to disagree but for future accuracy Paul left Cycling Plus some time ago.

And Smokin Joe. Likewise we're all entitled to an opinion but I definitely don't agree with: "As 90% of modern cycling journalists are clueless self-gratification artists who swallow any old shoot fed to them by marketing men they write exactly what the manufacturers intend them to write, ie crap that is designed to make the readers think they must have a different bike for evey day of the week" They're not and they don't.

Rob


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## mickle (20 Jun 2011)

Fair do's.


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## Norm (20 Jun 2011)

Greetings, Rob, welcome to Cycle Chat. 

I like the look of sloping top tubes, my Secteur rides nicely with one, but then the Tricross and the old steelie ride nicely without.


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## Smokin Joe (20 Jun 2011)

notthebuzzard said:


> Thought I'd chip in to this as I have a vested interest. What with me being the editor of Cycling Plus and all. I've just looked back over the last issue and found the offending caption and hands up, I missed it. That said, I'm no engineer so I'm going to consult one to check if this is, indeed, BS. (Yes, it's a bit late now but...)
> 
> But a couple of points: Mickle "Cycling Pus is and always has been full of shoot, and don't get me started on that Paul Vincent character." You're perfectly entitled to your opinion about the magazine, and I'm perfectly entitled to disagree but for future accuracy Paul left Cycling Plus some time ago.
> 
> ...


We all have our opinions, like you say.

Be good if you stick around and put your side of the story when we criticize C+ (which I buy) and the cycling press in general.


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## Banjo (20 Jun 2011)

notthebuzzard said:


> Thought I'd chip in to this as I have a vested interest. What with me being the editor of Cycling Plus and all. I've just looked back over the last issue and found the offending caption and hands up, I missed it. That said, I'm no engineer so I'm going to consult one to check if this is, indeed, BS. (Yes, it's a bit late now but...)
> 
> But a couple of points: Mickle "Cycling Pus is and always has been full of shoot, and don't get me started on that Paul Vincent character." You're perfectly entitled to your opinion about the magazine, and I'm perfectly entitled to disagree but for future accuracy Paul left Cycling Plus some time ago.
> 
> ...



Welcome to the forums and well done for responding Rob. 

In fairness it was only a small caption containing the offending words. When I tried to find it again I struggled to see it and thought for one horrible moment I had seen it in a different bike mag  

I would be interested to hear an engineers opinion but do we really need an engineer to tell us if a top tube bends like a leaf spring or not?


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## Norm (20 Jun 2011)

Banjo said:


> ... but do we really need an engineer to tell us if a top tube bends like a leaf spring or not?


Well, I'm an accountant but, IIRC, all other things being equal and simplifying hugely, a solid bar will bend, a hollow tube will crumple. 

This is why things that we want to bend, like springs, are made out of solid bars whereas things that we want to be stiff (like frames) are made out of tubes.

Although anyone who has looked along the wing of an aeroplane in turbulence will know that there is further simplification behind the line that aluminium doesn't flex and it'll break if it does so.

I guess we do need an engineer after all.


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## Tim Bennet. (20 Jun 2011)

Well here goes! 

We all know that a triangle is very rigid in the plane of its component parts. What ever loads are applied to the corners in the direction of that plane are resisted by each of the three constituent parts being either under tension or compression along their axis. The only way a triangle can 'fail' is if one of the sides that is under compression comes out of column (in other words bends or buckles) or a side under tension fails (breaks).

The main frame of a bicycle is admittedly slightly more complicated as it is not a perfect triangle_. _ The top tube is subject to a combination of compression and a bending moment imposed by the leverage imposed by the fork. These forces are resisted by the 'stiffness' of the top tube and, especially with compressive loads, by it remaining as a straight column. Any deformation below its elastic limit will see the tube's 'springiness' return it to its original shape when the load is removed.

Now a 'bent' tube can be equally capable of resisting the bending moments but will be far less capable of resisting the compression loads. As it's already 'out of column' a much smaller compressive load will get it to continue to bend compared to a straight tube. This might be seen as a bad thing, but as long as the 'springiness' of the tube is sufficient to return it to its original shape, then you have a mechanism that can absorb, rather than simply resist the loads. 

A common spring of this shape is indeed the leaf spring but the analogy is poor because the way a leaf spring is loaded is rarely by compression and a bending moment imposed along it's length.

The theoretical rationale is ok, whether it works in practice - I have no idea.


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## Night Train (20 Jun 2011)

I would hazard a guess that it probably works in practice but whether or not it is necessary or effective as a design is another point.

It may add a weight penalty but that depends on how close to design tolerence the simple straight tubes are.


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## Smokin Joe (20 Jun 2011)

Tim Bennet. said:


> The main frame of a bicycle is admittedly slightly more complicated as it is not a perfect triangle_._


It isn't actually a triangle at all, it has four tubes.


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## oldroadman (20 Jun 2011)

Tubes should be straight, and thin, and light, and made of steel, aluminium, titanium (the best!!) or carbon. There was a silly designwith an unsupported "beam" top tube to give a "softer ride". Which simply flexed the distance betwen saddle and chainset - not the best idea. Some of the bikes pictured would be bought by triathletes or the dafter (more gullible) members of the fraternity. Like a lot of things, it's probably a marketing thing looking for a market, and offers nothing new to what is a virtually perfect design, the basic bike frame.


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## keefus (20 Jun 2011)

you leave my top tube alone!


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## slowmotion (20 Jun 2011)

Tim Bennet. said:


> Now a 'bent' tube can be equally capable of resisting the bending moments but will be far less capable of resisting the compression loads. As it's already 'out of column' a much smaller compressive load will get it to continue to bend compared to a straight tube. This might be seen as a bad thing, but as long as the 'springiness' of the tube is sufficient to return it to its original shape, then you have a mechanism that can absorb, rather than simply resist the loads.




Well put. That makes a lot of sense.


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## sunnyjim (21 Jun 2011)

Norm said:


> Well, I'm an accountant but, IIRC, all other things being equal and simplifying hugely, a solid bar will bend, a hollow tube will crumple.
> 
> This is why things that we want to bend, like springs, are made out of solid bars whereas things that we want to be stiff (like frames) are made out of tubes.
> 
> ...




I'm an engineer and IMO bike companies can make more money selling gimmicky shaped frames than boring conventional ones. They've probaby got more accountants than engineers.


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## BrumJim (21 Jun 2011)

Engineer here:

Concur with the above. Would expect a curved tube to be less stiff, and therefore absorb forces better, but since most loads will be coming up from the road, it is the shape of the front forks and the rear stays that is probably the most important. Would need to fire up an FEA package to look at the real effects, as not too sure what the effects of the various bike loads are on the structural members without spending a bit of timing thinking about it. Can't imagine that the top tube makes much difference, though, to transmitting road loads to the rider. Heard another reason, is that the aesthetics of the top tube are better when bent, as a compact frame looks a bit wrong on a road bike without this.

So, over to the designers on here for comment...


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## mickle (21 Jun 2011)

Designer here:

http://www.facebook.com/photo.php?pid=418159&l=00520c7a25&id=100000936421951

Sloping top-tubes are nothing new...


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## dellzeqq (21 Jun 2011)

Tim Bennet. said:


> Well here goes!
> 
> We all know that a triangle is very rigid in the plane of its component parts. What ever loads are applied to the corners in the direction of that plane are resisted by each of the three constituent parts being either under tension or compression along their axis. The only way a triangle can 'fail' is if one of the sides that is under compression comes out of column (in other words bends or buckles) or a side under tension fails (breaks).
> 
> ...


I had always thought that the intention behind bending the top tube was to make the connections at either end of the tube closer to 90 degrees, which would reduce the propensity of the tubes to tear apart at the top when the bike is compressed front to back - the crudest example I can think of would be a rear end impact. The Spesh top tube to head tube connection is broad, and, I would imagine, very stiff and strong. I don't particularly care to think about this, but it might be better able to resist the tension force that gave me a small crack in the lug of my conventionally framed bike.


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## John the Monkey (21 Jun 2011)

Well, I'm not an engineer, but I much prefer the look of a traditional, horizontal top tube frame. At a pinch, a compact frame would be acceptable. All this sweepy swoopy stuff, no thanks!


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## BrumJim (21 Jun 2011)

dellzeqq said:


> I had always thought that the intention behind bending the top tube was to make the connections at either end of the tube closer to 90 degrees, which would reduce the propensity of the tubes to tear apart at the top when the bike is compressed front to back - the crudest example I can think of would be a rear end impact. The Spesh top tube to head tube connection is broad, and, I would imagine, very stiff and strong. I don't particularly care to think about this, but it might be better able to resist the tension force that gave me a small crack in the lug of my conventionally framed bike.



My guess would be that on a welded aluminium bike the major design consideration at the joins is fatigue adjacent to the weld, rather than maximum load seen in an accident. Therefore design in this area would reduce the stress at the joint by making it larger in the plane of most stress, improving fatigue.


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## gaz (22 Jun 2011)

1430931 said:


> Why are dam walls curved?



So the pressure of the water that is building up behind it actually makes it stronger.

Obviously that is your classical dam shape, some dams are not curved


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## nmcgann (22 Jun 2011)

phil_hg_uk said:


> For some reason I like this one:


 head-on crash into a lamp post.....


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## slowmotion (22 Jun 2011)

1430931 said:


> Why are dam walls curved?


They bulge towards the contained water because it means that the curved dam wall is in *compression* 
rather than tension. Tension means that you have to stuff in a whole heap of reinforcing steel. Expensive. Look at an arch in virtually any church built before 1850 and they just rely on the "stuff" taking compression forces.

Sorry, that wasn't very well explained.


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## slowmotion (23 Jun 2011)

A dam.

[media]
]View: http://www.youtube.com/watch?v=Qdk3b7sHdPA[/media]


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## rowan 46 (23 Jun 2011)

As far as I can see they are an abomination and should be banned. Look what they lead to. By all accounts the ride on this is very hard and as you can see the top tube is very curved.


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