Sizing

Ok, this may sound dumb:

I usually ride convention steelies 53/4 seat ct-ct 54.5 top.

Lookng at modern darn frames, there seems to be certain brands where a small is 53 ish top tube ( equivalent horizontal ) then a big jump to 55/56 top in a medium.

So what's best, a 53 with a massive stem or 55/6 with a stubby one?

sage wisdom appreciated!

It's so difficult to determine modern frame sizes without trying them first. My old steel Peugeot is a 56cm frame and is a perfect fit for me at 5'7".
I have several modern frames ranging from XS to S to 50cm to M and they all fit. The XS frame did require a slightly longer stem and 20 degrees layback seatpost but it is now one of my favourite bikes to ride as the whole package works perfectly for me. I would never buy a modern frame unless I had tried it out for size first

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Choose another make!

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Its funny you should bring this up, the 'old' sizing question! I'm just thinking about buying a new Cube Agree GTC. Now my size 'traditionally' in old school, retro, vintage steel is 23". From everything I've read, I need a 56cm (57cm if you can find one) frame in modern day measurements!

Confusing isn't it :facepalm:

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Robbied196":2f1m3clx said:

Confusing isn't it :facepalm:

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No.

Sizing of bikes by seat tube length is daft, always has been.

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mattr":2yzf17e9 said:

Robbied196":2yzf17e9 said:

Confusing isn't it :facepalm:

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No.

Sizing of bikes by seat tube length is daft, always has been.

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I think very frame builder in the country would argue that point

The top tube and seat tube are always going to be the determining factor for frame size.

Just ask Dave...

http://www.daveyatescycles.co.uk/custom ... ons-38.php

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Cube sizing is odd , I'm 5'8 and ride a 54 but need a 56 in cube and 48 in bottecchia !!

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Ps this thread is about TOP TUBE size equivalent horizontal , seat tube pretty irrelavent in sloping geo. Trying to find a logical way around small frame with long stem and setback seat post vs long tt with short stem and inline seat post where there is no in between size.

Modern frames also seem to have ridiculously long head tubes. I think this is probably for the people just taking up the sport who want a drop bar bike but still a relatively upright position. I've sized down on a frame just to get a head tube of my preferred length : 130 to 140 mm. My modern Bob Jackson has 135mm and a single 5mm spacer, with an ahead stem in a 21.5" size 545mm seat tube and top tube, 73 degrees parallel, classic geometry. My 1998 Merckx Corsa Extra has a 130mm head tube, quill stem, 560mm seat tube and top tube but slacker head angle and tighter seat angle so they feel pretty much the same.

The top tube length is the most important as it's the only measurement you cannot alter easily on a modern bike. In my opinion (and it's only an opinion) a road bikes requires a 100 to 120mm stem to handle "properly" - I have a 110mm on the BJ and a 105mm on the Merckx, which does give you 20mm leeway.

On a mountain bike it's a different story - 50 to 70mm stem and a long top tube gives a much better handling bike in the rough stuff than old school MTB geometry.

There are other ways of measuring now, which also take into account the seat and head tube angle called stack and reach but I haven't calculated these for any of my bikes.

I'd buy a different brand! If it's a carbon monocoque frame then they're all quite similar, anyway.

Robbied196":iih7s48t said:

mattr":iih7s48t said:

Robbied196":iih7s48t said:

Confusing isn't it :facepalm:

Click to expand...

No.

Sizing of bikes by seat tube length is daft, always has been.

Click to expand...

I think very frame builder in the country would argue that point

The top tube and seat tube are always going to be the determining factor for frame size.

Click to expand...

They can argue all they want, but in sizing terms, the seat tube is only there to provide something for the seat post (which is infinitely adjustable) to slide into. The angle at which it is inclined is far far more important than how long it is. And even that isn't massively important.

bikenrrd":iih7s48t said:

Modern frames also seem to have ridiculously long head tubes.

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Yup, i've noticed this too, some manufacturers have too and are addressing it by having race, sportive and comfort geometries on different bikes. Not all tho. Unfortunately.

bikenrrd":iih7s48t said:

There are other ways of measuring now, which also take into account the seat and head tube angle called stack and reach but I haven't calculated these for any of my bikes.

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Stack and reach have been kicking round for maybe 15 years, its simply the vertical (stack) and horizontal (reach) dimensions from bottom bracket to top of the headtube. Every other contact point on a bike is easily adjustable, these two points aren't

bikenrrd":iih7s48t said:

I'd buy a different brand! If it's a carbon monocoque frame then they're all quite similar, anyway.

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May i just LRQ (Laugh Really Quietly) to myself at this. If you are buying cookie cutter frames, yes they are quite similar (or in many cases identical bar the paint) if you are buying anything remotely top end the geometry can vary wildly.