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Top Tube: Level or Slanted?

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Top Tube: Level or Slanted?

Old 04-20-15, 11:02 AM
  #26  
carpediemracing 
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Originally Posted by Tiglath View Post
I am looking at the Parlee Z2 and Z3 and initially I wanted an old style bike with a level TT, that would be the Z2; the Z3 is the same bike but with a slanted TT geometry. I am no expert but I understand that, as far as geometry affecting ride, it is not an important measure. It does screw up the sizing though, when the size is taken from the seat tube. On a level TT my size is 51, on a slanted one 48. To me, it boils down to looks.

I like the look of my Cinelli Supercorsa with a level TT, and I thought that was my preference, but after getting a Cannondale CAADX with a slanted TT, it's beginning to grow on me.

Terrible problem, isn'it?

What's your taste?
I like the sloped top tube. The main reason is when I'm out of the saddle - the bike feels more toss able with more of its mass located closer to the BB. I even try to get lighter saddles and reasonably light posts to help reduce outlying weight. I also rest my leg on top of the top tube when coasting up to a stop/light, which I realized just the other day. With a level top tube I can't do that.

I ride a (cheap) custom frame so I got to spec out everything geometry/etc. I asked for the shortest possible seat tube, modeled after my size S Giant TCR. It's a 40 cm c-c seat tube, I think 44 cm c-top. It's small enough that I don't have much room for a tall bottle or a frame pump. I was on a size 52 Cannondale, to give you a level top tube size.

I got a second frame and asked for some changes with the tubing, aero style. This required a more level top tube, about 4 cm more seat tube, so about 44 cm c-c. Geometry (length, seat tube angle, etc) are the same, and when I had them both built up they used the same saddle, bars, stem, etc. I preferred the sloping top tube bike.

Currently I have just one set of functioning parts. I put them all on the sloping top tube bike. The more level top tube bike is currently unrideable.
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Old 04-20-15, 11:13 AM
  #27  
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Originally Posted by Lazyass View Post
Yes but bikes with compact geometry tend to come in fewer sizes. For instance, the Giant Defy comes in six sizes, 3cm apart. The CAAD10 comes in 8 sizes, 2cm apart, as it should be.
Colnago frames are 1cm apart .
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Old 04-20-15, 11:33 AM
  #28  
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Originally Posted by Lazyass View Post
But different stem lengths and seatpost setbacks change your position on the bike.
Yes and no. Relative to the three touchpoints on the bike, the saddle, bar, and pedals different stems , spacers and sestpost setbacks are used to position the rider exactly where he wants to be. Relative to the center of mass of the bike or some other reference point thst affects steering, braking, stability and other ride characteristics, the stem, sestpost, spacers modifications do possibly put the rider in a place he would rather not be. Generally the former is considered more significant.
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Old 04-20-15, 11:40 AM
  #29  
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My new frame has a slightly slanted TT, but it's not a compact frame design.
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Old 04-20-15, 11:48 AM
  #30  
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I like the looks of level top tubes, but I don't look at it while riding it, so let's be honest, I prefer the one that leaves my wallet a little fatter at the end of the day. If that's the level one, great, if not, well maybe I'll ride it more and look at it less.
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Old 04-20-15, 11:52 AM
  #31  
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Modern bike fitting theory is fairly consistent and provides that stack and reach are the principal variables thst have to be right for a bike to fit. A slightly less precise way to look at this is that the important variables are the top tube and head tube lengths as modified by the seat tube angle and front center. So how much difference is there between the top tube lengths of two bikes 3 cm apart in nominal size? 1.0-1.5 cm? And the head tube? 2 cm? Of course it varies by size and design, but those are a common ranges. So the size can't be "wrong" by more than 7 or 8 mm in the top tube and 1 cm in the head tube relative to a fit based on 1 cm nominal size spacing. That's less than 1 stem size difference and a couple of spacers. What's the big deal?
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Old 04-20-15, 12:14 PM
  #32  
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Sloping top tubes allow more clearance for the crotch, which is important for mountain bikes. Not so for road bikes, unless you're falling off of your bike and crushing your 'nads regularly. But ex-mountain bikers coverting to roadies are the biggest sales demographic right now, so if the customer wants a sloping top tube because it makes for an easier sale, they should get it.

Overall the sloping top tube frame design makes for a heavier frame/seatpost combo, due to the extra seatpost length and the extra frame material required in the seatpost insertion region. And as far as stiffer, if you've ever drafted someone with a whole bunch of carbon seatpost showing, it is truly an impressive sight. Every oscillation is one stress cycle closer to an emergency trip to the proctologist. I've seen seatposts wagging back and forth by as much as an inch. Where does this pedaling energy go?

Sloping top tube designs are usually coupled with a high head tube. Superficially, this is to allow a for a higher bar position for the 'comfort' demographic. It would actually be lighter overall to use a shorter headtube and more spacers and a riser stem. But that wouldn't look cool, because our heros (the pros) ride negative rise stems and them slam them. Your average Gran Fondo Fred doesn't want to look like a dork, hence the high head tubes on the latest bikes.

It's all about stylin'.
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Old 04-20-15, 12:23 PM
  #33  
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Different frame styles fit people with different proportions. Men's/unisex frame fit people with a wide range of leg to body height proportions. Women's frames are made to accommodate people with longer leg/shorter torso proportions, and bikes with slant top tube/compact geometry fit people with shorter leg/longer torso proportions.

Find the bike size that fits you, that you are willing to accept the cosmetics on and ride. That's all there is to it.
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Old 04-20-15, 12:48 PM
  #34  
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Originally Posted by Dave Mayer View Post
Overall the sloping top tube frame design makes for a heavier frame/seatpost combo, due to the extra seatpost length and the extra frame material required in the seatpost insertion region. And as far as stiffer, if you've ever drafted someone with a whole bunch of carbon seatpost showing, it is truly an impressive sight. Every oscillation is one stress cycle closer to an emergency trip to the proctologist. I've seen seatposts wagging back and forth by as much as an inch. Where does this pedaling energy go?
If you think the seatpost is deflecting by 1 inch, I've got a bridge in Brooklyn I'd like to sell you. It's the entire bike wagging back and forth, and it's regardless of top tube slope.

Sloping top tube designs are usually coupled with a high head tube. Superficially, this is to allow a for a higher bar position for the 'comfort' demographic. It would actually be lighter overall to use a shorter headtube and more spacers and a riser stem. But that wouldn't look cool, because our heros (the pros) ride negative rise stems and them slam them. Your average Gran Fondo Fred doesn't want to look like a dork, hence the high head tubes on the latest bikes.
A longer head tube with the slammed stem puts the bearings of the headset much closer to the end of the steerer tube. On a carbon steerer, this reduces or eliminates a stress riser below the base of the expansion plug (depending on the length of the expansion plug and the size of the spacer stack). It's a stiffer, safer and therefore better design.

It's all about stylin'.
Except when it's not.
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Old 04-20-15, 12:53 PM
  #35  
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Originally Posted by Dave Mayer View Post
Sloping top tubes allow more clearance for the crotch, which is important for mountain bikes. Not so for road bikes, unless you're falling off of your bike and crushing your 'nads regularly. But ex-mountain bikers coverting to roadies are the biggest sales demographic right now, so if the customer wants a sloping top tube because it makes for an easier sale, they should get it.

Overall the sloping top tube frame design makes for a heavier frame/seatpost combo, due to the extra seatpost length and the extra frame material required in the seatpost insertion region. And as far as stiffer, if you've ever drafted someone with a whole bunch of carbon seatpost showing, it is truly an impressive sight. Every oscillation is one stress cycle closer to an emergency trip to the proctologist. I've seen seatposts wagging back and forth by as much as an inch. Where does this pedaling energy go?

Sloping top tube designs are usually coupled with a high head tube. Superficially, this is to allow a for a higher bar position for the 'comfort' demographic. It would actually be lighter overall to use a shorter headtube and more spacers and a riser stem. But that wouldn't look cool, because our heros (the pros) ride negative rise stems and them slam them. Your average Gran Fondo Fred doesn't want to look like a dork, hence the high head tubes on the latest bikes.

It's all about stylin'.
Do you really know how less frame with more post compares in weight to more frame with less post. I don't think so. And your oscillating sestpost image is ridiculous. Unless poorly chosen and insufficiently inserted, a carbon seatpost just doesn't behave that way. Stiffness is their signature virtue. Your story is cute, but only that.
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Old 04-20-15, 01:03 PM
  #36  
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Originally Posted by Dave Mayer View Post
And as far as stiffer, if you've ever drafted someone with a whole bunch of carbon seatpost showing, it is truly an impressive sight. Every oscillation is one stress cycle closer to an emergency trip to the proctologist. I've seen seatposts wagging back and forth by as much as an inch. Where does this pedaling energy go?
O, rly? An inch. Don't buy it. You're eyes must be seeing the "watch I can turn this pencil to rubber" wiggle it between your fingers trick.
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