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Please help me understand sloping top tube frame sizing.

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Please help me understand sloping top tube frame sizing.

Old 01-23-12, 03:52 PM
  #1  
Onyxaxe
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Please help me understand sloping top tube frame sizing.

I've searched til I'm blue in the face. Maybe I just don't get it. I'm looking to buy a Dawes SST. I'm hoping this will be my first road bike but I'm confused as to how the sloping top tube affects the size frame I should get.

Female, 5'8" barefoot.
33.5" inseam (measured barefoot with the book and all).
Arms L 27", R 28"
Torso 25 1/4

Is this the right bike for me? If you have another suggestion please keep it around the same price range. I'm most confused about the top tube sizing.

BTW: The town I live in is relatively flat so I am looking for a singlespeed for ease of maintenance and lightweight.
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Old 01-23-12, 04:25 PM
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wearyourtruth
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what that bike is doing is providing a slightly more upright riding position. what that means is that your saddle is not as high in proportion to your bars, bringing your torso more upright. note the difference between these two bikes in regards to the saddle/bar heights.


in the first one (the dawes SST steel) the saddle is at almost the same height, and there is plenty of room to lower it below the bar height if you desire. the second one (dawes SST AL) the saddle is above the bars, and if you lowered it as far as you could, you would still be just level with the bars.

i think this would be a great bike for you, as a woman. women-specific frames have (along with other things) moved into sloping top tubes, because women's pelvises are built differently than men's. as a result of this difference, a woman's pelvis wants to naturally sit more perpendicular (to the ground) than a man's when on a bike. this may or may not be true for you, as everyone is built a little differently. but you can always move your saddle higher if you need to, but you are limited by how much you can lower it by the seat tube.

at 5' 8" i would think you would fit best on the 54cm.

in before the "i should probably double-check your inseam" comments.
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Old 01-23-12, 05:58 PM
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Thanks, everything you stated made a lot of sense to me and I feel better about it. In saying that did you advice the 54 because you think the 56 would be too much of a stretch?. I do have freakishy long legs........ I was torn between the 54 and 56. I'm confused about how the toptube applies to height and arm length. All I understand is standover height, and I didn't get all my answers answered from Sheldon Brown unfortunately. This may be the first time.
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Old 01-23-12, 06:18 PM
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The main difference between the 2 frame styles is standover height. As a normal frame's top tube doesnt rise, the standover height is best measured according to the seat tube length. If you're suited to a 56 seat tube length on a normal frame, thats the size you would buy. On a sloping frame however, due to the top tube sloping upwards you'd need to go a size or 2 down and go for a 54 maybe as the middle of the toptube would be higher up than the seatube therefore increasing standover height.
However, any cyclist who knows anything will advise you to go to a bike shop and try the bike out for size first as what may look good on paper may not necessarily be good in realistic terms.
Smaller frames are also a bit easier to handle so worth bearing in mind
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Old 01-23-12, 06:51 PM
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Okay thanks . It makes sense now.
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Old 02-27-12, 01:43 PM
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Curious about the SST AL, did you end up getting it?
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Old 03-13-12, 10:49 PM
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Sorry for the late response . I haven't purchased either one as of now. Are you considering it?
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Old 03-14-12, 08:58 AM
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Yup, got one. Pretty solid deal. Nothing spectacular, but a good bike.
We have almost identical heights and inseams, but I haven't measured my arms or torso. I got the 56 and the stock stem was a bit too long for me, I have a 100mm stem right now, but will likely put a 90mm stem on soon and it should be perfect.
One of these might work for you: https://www.bikesdirect.com/products/...ift2_track.htm
Or you could try a LBS.
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Old 03-19-12, 10:12 PM
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Good to know. Thanks a lot .
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Old 03-19-12, 11:22 PM
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Originally Posted by wearyourtruth View Post
what that bike is doing is providing a slightly more upright riding position. what that means is that your saddle is not as high in proportion to your bars, bringing your torso more upright. note the difference between these two bikes in regards to the saddle/bar heights.


in the first one (the dawes SST steel) the saddle is at almost the same height, and there is plenty of room to lower it below the bar height if you desire. the second one (dawes SST AL) the saddle is above the bars, and if you lowered it as far as you could, you would still be just level with the bars.

i think this would be a great bike for you, as a woman. women-specific frames have (along with other things) moved into sloping top tubes, because women's pelvises are built differently than men's. as a result of this difference, a woman's pelvis wants to naturally sit more perpendicular (to the ground) than a man's when on a bike. this may or may not be true for you, as everyone is built a little differently. but you can always move your saddle higher if you need to, but you are limited by how much you can lower it by the seat tube.

at 5' 8" i would think you would fit best on the 54cm.

in before the "i should probably double-check your inseam" comments.
Wut?
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Old 03-19-12, 11:34 PM
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Sloping top tubes do not raise the bar height. The slope of the top tube has NOTHING to do with bar height. The head tube and stem set the bar height. The seat tube and seat post set the saddle height. Did you notice how top tube has nothing to do with any of those? All the top tube does is connect the head tube to the seat tube. It could be horizontal, sloping to the left, or sloping to the right.

Sloping top tubes are a result of modern compact geometries. This means that your bars and saddle height will be where they need to be for your application (commuting, racing) but you'll use more seatpost to raise your saddle.




Women do not use bikes with sloping top tubes because of their hips. Women-specific designs have shorter top tubes than a normal bike of the same make/model this is because, like the OP, they often have proportionately longer legs and shorter torsos than men.

These ladies seem pretty low to me:

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Old 03-19-12, 11:36 PM
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Watch this...


LOOK MA...NO TOP TUBE




But, there are both a head tube and a seat tube
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Old 03-20-12, 12:24 AM
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Originally Posted by carleton View Post
Aw, look at the wittle front wheel.

Also, those bars look like airplane wings.
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Old 03-20-12, 07:28 AM
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a sloping top tube can raise bar height, ie specialized roubaix. it allows for trendy amounts of seatpost showing and steerer not showing despite an absurdly tall headtube and a total lack of fitness, but thats via the secondary effect of increasing the headtube length ceiling. by itself, slope changes nothing.
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Old 03-20-12, 09:36 AM
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Originally Posted by adriano View Post
a sloping top tube can raise bar height, ie specialized roubaix. it allows for trendy amounts of seatpost showing and steerer not showing despite an absurdly tall headtube and a total lack of fitness, but thats via the secondary effect of increasing the headtube length ceiling. by itself, slope changes nothing.
Yeah, my Tarmac has a super tall head tube. I have to run a -17 130mm stem with no stack (very similar to the photo below). Look pro...but really isn't.

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Old 03-20-12, 10:17 AM
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and the roubaix averages plus 40mm on the same size tarmac. mind asplode.
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Old 03-26-12, 10:43 PM
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Thank you for the wealth of info and pics Carleton. 2 more questions, do I need to get a sloping top tube?. Like a lot of members I've found I find straight top tubes more visually appealing. What would I possibly need to do on a more traditional frame to get it to be more comfortable for my short torso?. Sorry I'm a noob and trying to learn lol.
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Old 03-26-12, 10:52 PM
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Not Carleton, but there's no reason you need a sloping top tube if you can find a traditional-style frame that fits. Lots of women used road bikes before the sloping-top-tube thing took over.
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Old 03-27-12, 12:04 AM
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Originally Posted by Onyxaxe View Post
Thank you for the wealth of info and pics Carleton. 2 more questions, do I need to get a sloping top tube?. Like a lot of members I've found I find straight top tubes more visually appealing. What would I possibly need to do on a more traditional frame to get it to be more comfortable for my short torso?. Sorry I'm a noob and trying to learn lol.
Choose a frame based on the top tube length, then use a slightly longer seatpost than normal (like 2cm). You may have to run an upward stem, but that's normal.
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Old 03-27-12, 12:16 AM
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Originally Posted by adriano View Post
and the roubaix averages plus 40mm on the same size tarmac. mind asplode.
I use a 20degree 100mm stem with no stack on my secteur. Same geo as roubaix.
as Carleton said "Look pro...but really isn't."
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Old 03-27-12, 12:42 AM
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Originally Posted by carleton View Post
Choose a frame based on the top tube length, then use a slightly longer seatpost than normal (like 2cm). You may have to run an upward stem, but that's normal.
Awesome. Thank you very much.
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Old 08-16-14, 10:33 PM
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To revive an old thread:

Smaller is better these days for BOTH male and female riders. I fit a M bike with sloping top tube geometry. The fit is simply more precise and I need very few adjustments made to fit to the bike.

Its clear that compact and semi-compact frame sizes are here to stay. More riders can fit the same bike in fewer sizing increments than on traditional frame bikes.
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