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Basic geometry question

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Basic geometry question

Old 06-14-06, 08:30 AM
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Granny
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Basic geometry question

In looking at frames I'm seeing that they fall into two obvious categories - those with the top tube roughly parallel to the ground (what I would call "traditional") and those that have a top tube angled down at the seat tube with much longer seat posts.

For example, the Litespeed Vortex: http://litespeed.com/bikes/2006/road/vortex_.aspx and the Ultimate http://litespeed.com/bikes/2006/road/ultimate_.aspx have the "traditional" geometry, while the Ghisallo http://litespeed.com/bikes/2006/road/ghisallo_.aspx and the Siena http://litespeed.com/bikes/2006/road/siena_.aspx have the angled top tube.

I find the traditional geometry to be more aesthetically pleasing. Are there pros/cons to this basic difference? Looks as if you have less frame material with the angled geometry (less weight) - but you have more seat post.
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Old 06-14-06, 08:34 AM
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The ones with the sloping TT are called compact frames. Those tend to have shorter TTs than traditional frames. I agree that traditional frames are more aesthetically pleasing, but I've heard that compact frames are often more comfortable.
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Old 06-14-06, 08:49 AM
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I have what Felt calls a Semi-Compact frame. It still slopes pown but not as much as some. As far as the top tube length (or "effective TT length" for compacts), mine has a longer effective top-tube. I usually ride a ~54cm size on a 'traditional' frame but on my 'semi-comact' Felt, a 52cm fit best due to the longish effective top-tube.

Oh, I prefer the look of compact frames and IMHO, 'traditional' framed bikes look slower than 'compacts'

But in all honesty, I like the looks of both.
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Old 06-14-06, 08:52 AM
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The downward sloping top tube doesn't have anything to do with providing more comfort, per se. It provides more standover height for any given frame size. However, that difference may allow a prospective buyer to select a larger frame than he or she would otherwise fit. Generally, a larger frame will also have a longer head tube length, so, a larger frame may help a rider acheive a more desirable riding position (e.g., a less aggressive riding posture because of a more ergonomic handlebar position), and that would be more comfortable.

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Old 06-14-06, 09:04 AM
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Originally Posted by (Y(L|S+
I have what Felt calls a Semi-Compact frame. It still slopes pown but not as much as some. As far as the top tube length (or "effective TT length" for compacts), mine has a longer effective top-tube. I usually ride a ~54cm size on a 'traditional' frame but on my 'semi-comact' Felt, a 52cm fit best due to the longish effective top-tube.

Oh, I prefer the look of compact frames and IMHO, 'traditional' framed bikes look slower than 'compacts'

But in all honesty, I like the looks of both.

I have a Felt as well. It is a 54 but due to the very slight slope of the TT the effective length is actually 55. BEar that in mind when measuring frames with a sloping TT.
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Old 06-14-06, 09:33 AM
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Originally Posted by Miller2
I have a Felt as well. It is a 54 but due to the very slight slope of the TT the effective length is actually 55. BEar that in mind when measuring frames with a sloping TT.
Uhh... I thought that's what I said. If not, that's what I meant .
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