Traditional way to measure bike frame size? Pre-2000.

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LittleGreyCat
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Traditional way to measure bike frame size? Pre-2000.

Post by LittleGreyCat »

I drifted into looking at bikes for sale on eBay.
https://www.ebay.co.uk/itm/204352587330
Looks similar to my Univega Rover 3.5 from 1995.
The frame size is quoted at 21".
I think that this is the top tube length.
I went outside to measure my bike and I think that it is a 23" frame, assuming that you measure from the middle of the seat post to the middle of the head tube.

However my other two bikes don't quite fit this, perhaps?

My (very) old Dawes Galaxy seems to also be 23" but not quite 60 cms which I had in my head for some reason.

My Spa Wayfarer is allegedly 58 cms but I can't quite get it to measure this. Rough attempt indicates 57 cms.

So I am asking the collective minds to check if I have missed something.

[If I could find a similar all steel MTB to my Univega in better condition this might save me a refurb to get a base bike for an electric conversion.]
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mjr
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by mjr »

I thought the traditional way was from the centre of the seat cluster to the centre of the bottom bracket, see https://sheldonbrown.com/frame-sizing.html

I think a classic diamond frame would have seat tube length about the same as top tube length anyway, although Sheldon Brown disagrees on that.

With sloping top tubes, do you measure from where the seat cluster would be with a horizontal top tube, or some other tube, or between some other arbitrary points? I think there's manufacturers doing different things and it started well before 2000, probably late 1980s.
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tatanab
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by tatanab »

The traditional way before "compact" frames with sloping top tubes had nothing to do with the top tube.
British way - centre of the bottom bracket, along the seat tube to the top of the top tube (NOT the top of any protruding lug etc).
Continental way - centre of the bottom bracket along the seat tube to the centre of the top tube.

Sloping top tubes made things difficult. Modern generations consider the top tube length more important, perhaps because you can raise or lower a saddle more easily than fitting a longer/shorter handlebar stem.
Bmblbzzz
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Bmblbzzz »

mjr wrote: 1 Jun 2023, 1:37pm With sloping top tubes, do you measure from where the seat cluster would be with a horizontal top tube, or some other tube, or between some other arbitrary points? I think there's manufacturers doing different things and it started well before 2000, probably late 1980s.
Horizontally from the junction of top tube and head tube, IMO.
Nearholmer
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Nearholmer »

I think a classic diamond frame would have seat tube length about the same as top tube length anyway, although Sheldon Brown disagrees on that.
I’m sure you’re right about that, and that for the UK context SB is wrong.

Even now, a rough guide to ‘neutral’ frame geometry, not something stretched-out, or squashed-up, seems to be that the notional horizontal top-tube is the same as the notional seat tube measured from centre of bottom bracket, up the seat tube to where the top of the top tube would be , if it were horizontal, ‘square’ I’ve heard it called, although it isn’t.

But, that may always have been no more than a rough guide, because if you look at old pictures, or if you have older frames to hand, some bikes were built tall but short, and others low but long, by comparison with that ‘neutral’.
AndyK
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by AndyK »

tatanab wrote: 1 Jun 2023, 1:59pm The traditional way before "compact" frames with sloping top tubes had nothing to do with the top tube.
British way - centre of the bottom bracket, along the seat tube to the top of the top tube (NOT the top of any protruding lug etc).
Not quite. It was centre of the bottom bracket to the top of the seat tube. (I've just double-checked in Tony Oliver's Touring Bikes (1990).
Nearholmer
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Nearholmer »

On a very trad frame, the seat-tube barely protrudes above the line of the top of the top-tube, so the distinction is a bit meaningless n those cases, I think. The centre of the top of the seat tube is more or less level with the to of the top-tube.

I just had a look at how Pashley describe it, they being very trad, and this is one of their diagrams, where the red line is the one that defines “frame size”. It is indeed to the top of the seat tube, but can you see what I mean about how closely that matches the top of the top-tube? Maybe a quarter of an inch in it.

198A35CC-0EE9-43E8-824B-A569D603A3F7.jpeg


All of their trad-shaped frames are like this - seat tube ends effectively level with top of top-tube.
Last edited by Nearholmer on 1 Jun 2023, 8:35pm, edited 4 times in total.
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Mick F
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Mick F »

My Mercian Vincitore frame built specifically for me ........... delivered October 1986 ................ is 23.5inches as per my specifications.

This is 23.5 inches from centre of bottom bracket to top of seat lug.
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tatanab
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by tatanab »

AndyK wrote: 1 Jun 2023, 3:48pm
tatanab wrote: 1 Jun 2023, 1:59pm The traditional way before "compact" frames with sloping top tubes had nothing to do with the top tube.
British way - centre of the bottom bracket, along the seat tube to the top of the top tube (NOT the top of any protruding lug etc).
Not quite. It was centre of the bottom bracket to the top of the seat tube. (I've just double-checked in Tony Oliver's Touring Bikes (1990).
I would disagree a little because a seat tube can extend beyond the top of the top tube. This is why I wrote excluding any protruding lug etc. I think we both intend the same thing.
Bmblbzzz
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Bmblbzzz »

I'm a late convert, but the intricacies and variations exposed here persuade me of the value of stack and reach measurements; in that they measure size without being dependent on the geometry or configuration of tubes.

Which doesn't help the OP or anyone in a similar position, of course.
AndyK
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by AndyK »

tatanab wrote: 1 Jun 2023, 4:24pm
AndyK wrote: 1 Jun 2023, 3:48pm
tatanab wrote: 1 Jun 2023, 1:59pm The traditional way before "compact" frames with sloping top tubes had nothing to do with the top tube.
British way - centre of the bottom bracket, along the seat tube to the top of the top tube (NOT the top of any protruding lug etc).
Not quite. It was centre of the bottom bracket to the top of the seat tube. (I've just double-checked in Tony Oliver's Touring Bikes (1990).
I would disagree a little because a seat tube can extend beyond the top of the top tube. This is why I wrote excluding any protruding lug etc. I think we both intend the same thing.
The traditional British method included any protruding seat tube, right to the very top. That was what measuring "C-T" (centre-to-top) meant.
AndyK
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by AndyK »

Bmblbzzz wrote: 1 Jun 2023, 4:28pm I'm a late convert, but the intricacies and variations exposed here persuade me of the value of stack and reach measurements; in that they measure size without being dependent on the geometry or configuration of tubes.

Which doesn't help the OP or anyone in a similar position, of course.
Absolutely. A much better way. It's disappointing how many manufacturers still fail to quote them on their geometry tables.
Barrowman
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Barrowman »

What Tantanab said mostly but Andy K also not wrong :

Measurements were often quoted as 'centre to Centre' (Centre of the bottom bracket to centre of the seat lug bolt hole.)

OR

'Centre to top ' (bottom bracket again to top of the top tube / lug .) both measured up the seat tube.
drossall
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by drossall »

Agreed. In the UK, you'd tend to assume that a measurement was C-T unless told otherwise, but you did come across C-C measurements (generally, add about 1cm to get the C-T equivalent). Always a seat-tube measurement. Few frames had enough seat tube protuding above the top tube for that to make a difference, until the emergence of what were then called "funny bikes", in the late 80s and 90s. I would have expected most measurements to be to the level of the top of the top tube, as the odd millimetre or two of extra lug above made no real difference to fit. It's another matter if it's 4cm on a funny bike.

For a given frame size (i.e. seat tube height), top tube length could vary. On custom builds, that was rather the point - riders come in different proportions, and adjusting for that, while still building a bike that was good to ride, was one of the reasons to go to a good builder. Top tube length might be quoted as a secondary dimension therefore.

This system was completely fouled up by sloping top tubes. Measuring top-tube length as a substitute then became popular - and of course that is an important determinant of reach. I can't see the point of measuring along a sloping top tube though; it's the horizontal distance that matters. In practice, different manufacturers seem to do different things.

Whatever its limitations, a system that was universally comparable, as long as you remembered to check C-T or C-C, has been destroyed, and you cannot now reliably compare one bike brand with another, whatever measurement you use.
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Chris Jeggo
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Chris Jeggo »

So far, no-one has mentioned that seat tube length as measured from BB centre to seat tube top (including seat lug if necessary) is important in that it determines minimum saddle height, which is important with regard to leg geometry.
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