I'm confused about sizing.

[CanucksTraveller]

Wait til you try to order Italian cycling shoes via mail order... then you'll be really confused as to how sizing works.
Italians apparently only have 3 toes per foot.

 

[smutchin]

The internet gives pretty good access to a proper 'dimensions' chart and most will show both ctc and ctc(virtual/horizontal) to inform the buyer's choice.

Assuming you can trust the manufacturer's figures - in my experience, there is plenty of variation, sometimes quite significant.

 

[youngoldbloke]

But I don't think many seat tubes extend much beyond the point they would have 'reached' with a conventional horizontal top tube so the length of seat tube above the seat tube / top tube junction is really a function of how 'slopey' the top tube is. But I hadn't thought of your 'space in the triangle' point. Which make/model had you in mind which has a lot of seat tube above the top tube junction?

Agreed but we've had the centre to top and centre to centre anomaly for half a century (at least). The internet gives pretty good access to a proper 'dimensions' chart and most will show both ctc and ctc(virtual/horizontal) to inform the buyer's choice.

The(horizontal/virtual) top tube dimension (ctc) has become the most important one, with the advent in the last 20 years of increasingly long seatposts combined with sloping top tubes.

Here's an example - not a lot of tube above the TT, but just how long is the seat tube C to C? As for more information available - same example - What is the actual (edit) top tube length? The virtual seat tube length? The geometry charts (not just Giant's) are generaly pretty unhelpful, and it is very difficult to compare one brand's frames with another's. As for scale drawings ...........
Ok - you can go to a dealer and sit on bikes you are interested in, but it's unusual for shops to have much choice in small or extra small framed bikes - if any.

 

[smutchin]

Here's an example - not a lot of tube above the TT, but just how long is the seat tube C to C? As for more information available - same example - What is the actual (edit) top tube length? The virtual seat tube length? The geometry charts (not just Giant's) are generaly pretty unhelpful, and it is very difficult to compare one brand's frames with another's. As for scale drawings ...........

Looking at that example, there's a lot of useful information there - including standover height, so you don't even need to make a guess about that based on how much seat post is above the top tube.

 

[youngoldbloke]

Looking at that example, there's a lot of useful information there - including standover height, so you don't even need to make a guess about that based on how much seat post is above the top tube.

Ok - might not be the best example - first I came across with obvious projection of the seat tube - but short of making a measured drawing or taking a tape measure to the shop I would still like to know exactly how long that seat tube is between the top tube and bottom bracket, and not just 'not very' .

 

[Red17]

I'm getting confused as well here - surely all depends on the height you set the saddle so all a manufacturer could give is a maximum / minimum range against the standard seat post extension

 

[cyberknight]

I'm getting confused as well here - surely all depends on the height you set the saddle so all a manufacturer could give is a maximum / minimum range against the standard seat post extension

As long as you can get the preferred saddle height its a start but if the frame is too large or small by too much your going to have to compromise a lot to get a good fit , my old commuter has a 56 cm top tube and i used a 80 mm stem although a 70 would have been better , new bike has a 54 cm TT but a really compact reach bar and i have a 110 mm stem on it ready to test .