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

General cycling advice ( NOT technical ! )
rareposter
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by rareposter »

Chris Jeggo wrote: 2 Jun 2023, 12:28am 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.
Yes and no in the way that you can get non-traditional frames (folding bikes, cargo bikes etc) that are one-size-fits-all. My e-cargo bike has a very slack seat angle so putting the saddle up also moves it back quite a long way so the effective frame size gets bigger overall. Means that one utility bike can fit pretty much everyone in the family with the simple movement of a seatpost.

But yes, on "regular" bikes, the sheer range of build options and design means it's getting more difficult to directly compare one bike with another and that's before you get into the wild inconsistencies of metric and imperial within bike measurements!
Barrowman
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Barrowman »

Chris

I did mention Centre to top .......

Of course a more useful reference is 'stand over' height. (Which only applies to a bike with a top tube as opposed to Mixte etc) . Which risking stating the obvious, is how high off the ground the top tube is and refers to being able to stop and stand astride the machine without 'discomfort' . :oops: .
Useful to know if the frame you are looking at has a higher than usual bottom bracket.
Measurement 3 in Nearholmers illustration.
This doesn't consider top tube length of course.

'Funny frames? I give you Paris Galibier, Sun Manx TT. Not 80's or 90's .
In fact if memory serves my 1890's Hurtu has a sloping top tube .
What goes around comes around ! :D
Nearholmer
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Nearholmer »

Yes and no in the way that you can get non-traditional frames (folding bikes, cargo bikes etc) that are one-size-fits-all.
Yes, although my experience is that they are more”one size fits nobody”.

I was using a Pashley Parabike, which can theoretically be made to fit anyone up to 33” leg, as a shopping bike for five years, and although it was comfortable as in smoothing out all the bumps, I could never really get it to work properly for me, despite it having a huge range of adjustment to all parts. Essentially, the frame was too small for me, so despite it being possible to get all the contact points right, it handled very strangely. My son is a couple of inches shorter than me, but he didn’t like it because it was too ‘stodgy’, and my youngest daughter found it too heavy …….. so not a great success overall. Good job I only paid £100 for it!

I really wanted to like it, it’s a quirky and ingenious design, but in the end I got fed up with it and donated it to the bike charity, who hopefully found someone who could get the best from it.
tatanab
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by tatanab »

Something different -------- a lugless frame. I say this is 22" since it measured to the top of the top tube. If the whole length of the seat tube was the size measurement it would be 22 1/2". Just teasing since of course the frame was ordered as a 22". Honestly, just teasing.
stube.jpg
Barrowman
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Barrowman »

Is this a rabbit hole ? :shock:

Lots of Rabbiting going on :lol:

Wonder if anyone else realises that isn't a bike in your picture, Tantanab ?
LittleGreyCat
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by LittleGreyCat »

Thanks all.

Crank to top of seatpost on the Spa is 58mm which is what I ordered.

Univega is either 22" to crossbar or 22.5" to seatpost clamp.

Dawes Galaxy is 26" which is a relief because I had that figure nagging me in the back of my head.

All 3 have much the same geometry.

This also confirms that the Univega Rover 330 on eBay (up thread) is a size smaller than mine.
gregoryoftours
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by gregoryoftours »

I'm not aware of any bike where the stated frame size related to the top tube or effective top tube measurement. It's always seat tube, either centre to centre, centre to top of top tube, or often center to top of seat tube for a lot of modern bikes (which often isn't very helpful)
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andrew_s
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by andrew_s »

With modern bikes, seat tube length isn't a useful measure when selecting a frame size, other than to provide a label for the different sizes of a frame model.
That's why it's normal to provide frame geometry tables & diagrams.

Back in the day, frames were all of a pretty standard design, with horizontal top tubes and top tube and seat tube lengths much the same, so you could buy a frame on seat tube length without bothering about geometry tables. All you had to worry about was whether the measurement was UK standard BB centre to top of seat tube/lug, or Euro standard BB Centre to top tube centre. Whether the size was in inches or centimetres was a pretty good pointer, and it only made about 1 cm or half an inch difference anyway.
Bmblbzzz
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Bmblbzzz »

In those traditional schemes, how was the seat tube measured on a bike with a non-straight tube? For instance the Paris Galibier mentioned above.
tatanab
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by tatanab »

The same way a top tube is measured on a sloping top tube frame. i.e the "imaginary or effective tube length". Flying Gate being an extreme example.
DSC00586.JPG
Bmblbzzz
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Bmblbzzz »

How very sensible!
mattsccm
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by mattsccm »

I wouldn't be assuming that any British framme is "square" . I have two Raleighs. Both badged "Competetion" from the factory which I know is untrue but that's a different story. Both have identical top tubes but one is a 21" frame and the other a 23".
rareposter
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by rareposter »

Bmblbzzz wrote: 3 Jun 2023, 10:13am In those traditional schemes, how was the seat tube measured on a bike with a non-straight tube? For instance the Paris Galibier mentioned above.
Varies.
When I got my first compact road frame, it was described as measuring up the seat-tube and then continuing up the seatpost to where a horizontal top tube would have intersected - this gave an "effective" seat-tube length; even though the actual frame itself only measured about 54cm to where the dropped top tube intersected, it was in fact a 61cm effective.

The reach (usually quoted from centre of seatpost to centre of bars) became a more pertinent measurement with compact frames. Note that "reach" back then is not the same as "reach (and stack)" now:

Image
Bmblbzzz
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Bmblbzzz »

rareposter wrote: 3 Jun 2023, 2:32pm
Bmblbzzz wrote: 3 Jun 2023, 10:13am In those traditional schemes, how was the seat tube measured on a bike with a non-straight tube? For instance the Paris Galibier mentioned above.
Varies.
When I got my first compact road frame, it was described as measuring up the seat-tube and then continuing up the seatpost to where a horizontal top tube would have intersected - this gave an "effective" seat-tube length; even though the actual frame itself only measured about 54cm to where the dropped top tube intersected, it was in fact a 61cm effective.
Sure, but my question was about frames where the seat tube does not go in a straight line from BB to intersection with the top tube (or to seatpost clamp or the relevant lug, etc, depending on frame construction). For instance a time trial bike with extremely short chainstays, where the seat tube goes almost vertically up from the BB to clear the back wheel then does a bend to a more 'normal' angle.
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Mick F
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Re: Traditional way to measure bike frame size? Pre-2000.

Post by Mick F »

The question is regarding "traditional".

As I said, my 1986 Mercian is 23.5 inches
(as designed ................... and specified by me)
.......... is from the BB centre to the top of the seat lug.
Mick F. Cornwall
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