Beth W

I was looking at this listing today for a Raleigh ladies 3-speed bike, which is listed as being 21":

Vintage women's Raleigh 3-speed

I'm small -- 5'2" -- and my bikes are in the 16" range. My understanding is that a 21" bike would be for someone over 6' tall, which suggests to me (since this is a ladies bike and few women are that tall) that this is some different kind of measurement.

Can someone clarify this sizing for me? Thanks!

repechage

welcome.
The dimension is the same, the marketing is very different due to the rediscovery of sloping top tubes, and the attempt to have fewer sizes fit more people.
For someone of your height, in a classic and vintage style, most probably a suggested men's road bike would be in the 19" or 49-50 cm seat tube measure. For a ladies or mix tie, 19" most likely, 17" frames started becoming available in the later 70's from some makers for that frame style.
Modern sloping top tube road race looking bikes are a very different animal.

lostarchitect 

21" would generally refer to the seat tube size, from the center of the crank to the top of the seat tube. That would be probably for people in the neighborhood of 5'-7" or so, but it depends on leg length. It is probably a little bit big for you if you are 5'-2". It would be waaay too small for someone over 6'.

Are your 16" bikes mountain bikes? Sizing works differently with those. And older bikes in general tended to be sized larger than modern ones.

Oldpeddaller

A 21" traditional frame is quite a small frame. I'm guessing your 16" frames are on mountain bikes or similar 'non-traditional' hybrid bikes with top tubes that slope downwards towards the seat? Without getting too technical about bottom bracket height, geometry and angles - it's just a different system of sizing.

In traditional sizing, a 6 foot plus rider would usually need a frame in the 23.5 to 25 inch range, or bigger. I'd be very surprised if the 21" Raleigh did not fit you, in terms of height anyway. It would definitely be worth looking at and trying if it's the kind of bike you'd like.

A more important measurement than the height of the frame in my opinion, is reach. When sitting on the bike can you comfortably reach and turn the handlebars without stretching too far or moving off the seat? At the other extreme, if it's too short you might feel cramped up. Shouldn't be a problem with this bike as far as I can see from the photo.

Scooper

This may help. The frame sizes on the chart are in centimeters instead of inches, but you can convert centimeters to inches by dividing the size in centimeters by 2.54 (there are 2.54 centimeters per inch). For example, a 53 cm frame would be 53 ÷ 2.54 = 20.8". At 5' 2", a 21" frame would probably be a bit too big for you unless you have very long legs in proportion to your overall height.

Beth W

Thanks, @Stan, that was indeed useful. Now I know this bike would be too big for me and I won't be tempted to schlep to the East Bay for a bike that's inappropriate for San Francisco anyway. @lostarchitect, one of my bikes is a mountain bike while the other is a 1980s 10-speed, but yes, both have an angled top tube. The 16" (ish) measurement is the seat tube.

eschlwc

just based on the length of the head tube, the 21" bike advertised in the craigs ad looks larger than 21".

but i don't know step-thru frames all that well.

i'm almost 5'11", and all my bikes are 22" c-c.*

* c-c is the seat tube's center-to-center measurement, taken from the center of the crank dust cap, up the seat tube, to about the middle of the seat tube lug.