Bike Size

[Woz]

Would add my 2p worth. I would say the standard way of measuring was always centre-to-centre for both seat-tube and top-tube in inches.

No such concept of standover height, effective top-tube, forward reach etc. If you can, try to ascertain the angles to help. The market is mixed with older production bikes and many custom made bikes using dark art that may have been tweaked a little for the rider / for the purpose.

 

[Yorkshirelad92]

Here’a a question someone mentioned To check the head tube length as this if often indicates on frame size. I’m confuzzled as I’ve seen a few frame that look to have really short headtube yet advertised as a 54 or bigger.

 

[bikeworkshop]

Bike sizing is almost standardised but not quite.
The size (mostly) indicates intended rider height, and the frame length will (mostly) be standard.

Mtb frames have recently got longer at a given size.
This is due to longer travel suspension and the growth of bike parks.

Some Road bikes have developed a taller head tube - this is due to an influx of mammals and reaching into leisure markets.

But a faster bike might well have a lower front end at the same size, and different brands and regions have different standards, even with S,M,L

So if you have a bike you like riding, measure it up - or ask for advice in a shop that sells the style of bike you're interested in.
If you don't want to buy anything, offer to pay for the advice

 

[Jez Nemeth]

C-T-C, C to Top... As above, echo that good advice -faced with an unknown frame, safer to measure the whole thing comparing against measurements in the target area that will suit you

 

[non-fixie]

A website that may be of interest to you is this one: Geometrygeeks

Its database contains the measurements of many bikes and, with a bit of luck, it enables you to compare a bike you know and like to others.

It has certainly helped me to understand why I like some bikes better than others, even though they are the same "size" and also look very much alike.