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Some bikes like Trek and Specialized's top tube have a downward slope to the seat while some like Cannondale have a top tube that is pretty horizontal to the ground. is there an advantage to one or the other?
just curious
 

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dead flat, horizontal top tubes look better, imho (even though I ride an Allez).

other than that, i got nothing. compact frames might be lighter for the same stiffness, and the curved top tube plays into that strength…but…I'm not sure if that's marketing BS or real.
 

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Sucker for carbon
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I think a lot of it comes down to styling and marketing. But according to Litespeed, the top tube experiences 29% of the frame's stress from a vertical impact. I think that Specialized, Trek, etc. might try to emulate a leaf spring type of design for the top tube (roughly semi-elliptical) in order to create a smoother riding bike...

Notice this curvature is similarly applied to seatstays on many models in order to make a "more compliant ride." Also according to Litespeed, the seatstays take up 32% of a vertical impact's induced stress, so this bent design in theory has merit.

In the real world, I don't really think curving the tubes makes all that much difference in ride quality compared to tire width/pressure, saddle choice, and correct fit, but the engineering is interesting nonetheless.

Check it out http://www.litespeed.com/current/tech_mat.aspx
 

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One of the benefits for slope top tube for manufacturers is that they could fit more rider with less frame sizes. Instead of having frame sizes with a 2cm difference like traditional main triangle frames. (47, 49, 51, 53, 55, 57, 59, 61, 63). Bike companies could produce four/five sizes( xs, s, m, l, xl). Which translates to more profit.
 

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RoadBikeReview's Member
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RyanM said:
Some bikes like Trek and Specialized's top tube have a downward slope to the seat while some like Cannondale have a top tube that is pretty horizontal to the ground. is there an advantage to one or the other?
just curious
A compact frame (sloping top tube) allows for a smaller triangle in the main frame. Smaller = Stiffer. The smaller frame is compensated for with a longer seatpost. The large sizes of compacts can look really ungainly, as the head tube swells - look, for instance at a 58+cm Specialized Tarmac. They're quite ugly! Due to the nature of compacts, they fit great for normal people, but really shine for people with long torsos and short legs. If you have long legs and a short torso, compacts don't work nearly so well.

A traditional frame (horizontal) is a larger triangle, which is a bit flexier (in theory), but it has more traditional proportions.

The advantages are argued one way or another. A person earlier was spouting Litespeed propoganda, but if you talk to Colnago, or read Trek's earlier publications, etc, it all says different stuff. The frames all work about the same, pick the one that you like the most for looks and fit.
 

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skaruda_23 said:
I think a lot of it comes down to styling and marketing. But according to Litespeed, the top tube experiences 29% of the frame's stress from a vertical impact. I think that Specialized, Trek, etc. might try to emulate a leaf spring type of design for the top tube (roughly semi-elliptical) in order to create a smoother riding bike...

Notice this curvature is similarly applied to seatstays on many models in order to make a "more compliant ride." Also according to Litespeed, the seatstays take up 32% of a vertical impact's induced stress, so this bent design in theory has merit.

In the real world, I don't really think curving the tubes makes all that much difference in ride quality compared to tire width/pressure, saddle choice, and correct fit, but the engineering is interesting nonetheless.

Check it out http://www.litespeed.com/current/tech_mat.aspx
Pure propaganda. Litespeed has released some advertisements of extremely dubious technical merit in the past few years, they've lost a lot of credibility. I say this as a Litespeed owner.
 

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huvia ja hyötyä
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For a mere mortal road rider it is just styling.

On a mountain bike, a sloping top tube at least allows some standover clearance, with the tall suspension forks etc.
 

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pedalpedalpedal
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estone2 said:
Pure propaganda. Litespeed has released some advertisements of extremely dubious technical merit in the past few years, they've lost a lot of credibility.
Do you have articles to back this up? Not trying to be argumentative, I'd just like to see how they came up with those numbers and what others have to say about it.
 

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Another factor is how you climb out of the saddle. If you rock the bike side to side the compact frame can work better.

Jeff
 

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f3rg said:
Do you have articles to back this up? Not trying to be argumentative, I'd just like to see how they came up with those numbers and what others have to say about it.
With regards to those exact numbers? No, I don't have anything. But assuming exact proportions of stress on each tube are exactly the same on exactly every bike for exactly every weight of rider is dubious, at best. Different geometries will change the stress distribution, different rider positions (saddle vs handlebar)... even different rider styles can change that.

As to Litespeed's release of propoganda, I just searched YouTube for a few seconds, but couldn't apparently used the wrong catch phrases... Look for a comparison where they took Ti, steel, and carbon fiber bike tubes and ran them over with a truck. The way they performed the test gave an advantage to Ti, the Ti was unmachined while the other tubes were machined, and finally, crushing a bike tube with a car doesn't tell you that Ti is a better material, it just tells you that Ti is the best material if you're planning to be run over by a car at 1-2mph with any regularity. I'll keep searching around for that video throughout the day, but I know it's been posted here on RBR several times... if you really want to see it, go look for it (hoping you have better luck than I did!).
 

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I wasn't really trying to get litespeed involved with this... I just thought that it was handy that they gave some ballpark figures on their website and it looks like they'd done some FEA... I was merely trying to cite a source so that I could demonstrate roughly which members of the frame were highly stressed in certain situations. I wouldn't take it as gospel either; I was merely just throwing out the idea that the sloping top tube might be there for "compliance."

Every frame manufacturer has their own opinions and marketing strategies to establish their product as unique and superior. Whether these designs are founded on good engineering practices varies a lot. Lots of details like sloping tubing is probably just for show so that bike has a certain "fast looking" stance. Just my two cents.
 
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