531 ST Frame Sizing

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pwa
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Re: 531 ST Frame Sizing

Postby pwa » 2 Sep 2016, 10:54am

Binkyboy wrote:"Can anybody with more experience than me on Touring Frames explain why most 531st frames are either 22 inch or 23 inch? Most what I'd call racing frames seemed to go 22 1/2 and 23 1/2 etc. Is it a European influence? From memory all my bikes have been going up on the 1/2 inch as far as I can remember. I currently ride a 22 1/2 inch 531 steel racing bike frame with the stem and saddle level (bad back) I'm 5'10" with a 32" inside leg. The stem and seat post are showing approx a few inches so in theory I could go to a 23 inch. I'd welcome any thoughts on this please."

The frame size is determined by the builder, based on
a) what the customer specifies (and that could be down to the nearest mm if needs be, because they are cut to suit,
b) the most common heights of typical buyers, if he is building for stock. Hence the preponderance of mid size frames.

In the good old days, the frame size (as measured up the length of the seat tube from centre of BB to top of seat lug) was your inside leg length, without shoes, less 10". This allowed for crank length and seat pin and saddle height.
I'm 6ft and, using the above formula, where my inside leg length is 34", the frame size is 24", and that's what all my traditional steel frames have been.

The modern "compact" frames with sloping top tubes, are anyone's guess!


But even with the traditional arrangement you would still be taking pot luck about reach to the bars unless you did more research. With sloping top tubes, reach to the bars is effectively the determining factor. Seat tube length is something you don't have to consider. I find it easier to accurately reproduce my ideal set-up on a semi-compact frame. So long as the published geometry is correct.

Binkyboy
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Re: 531 ST Frame Sizing

Postby Binkyboy » 2 Sep 2016, 7:58pm

"But even with the traditional arrangement you would still be taking pot luck about reach to the bars unless you did more research. With sloping top tubes, reach to the bars is effectively the determining factor. Seat tube length is something you don't have to consider. I find it easier to accurately reproduce my ideal set-up on a semi-compact frame. So long as the published geometry is correct."

I thought we were talking about seat heights....
Reach is another can of worms, but cheaper to get right by swapping the stem.

Roadster
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Re: 531 ST Frame Sizing

Postby Roadster » 2 Sep 2016, 11:48pm

Yes, you bought a frame or, much more commonly, a complete bike "off-the-peg" and its size was specified by the length of the seat tube.
Other dimensions were determined solely by the manufacturer but not in a haphazard way: such decisions were taken carefully and based on decades of accumulated wisdom and experience.
This saved you from taking pot luck and was to your benefit, because he invariably knew an awful lot more about bicycle design than you did.

pwa
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Re: 531 ST Frame Sizing

Postby pwa » 3 Sep 2016, 1:27pm

Roadster wrote:Yes, you bought a frame or, much more commonly, a complete bike "off-the-peg" and its size was specified by the length of the seat tube.
Other dimensions were determined solely by the manufacturer but not in a haphazard way: such decisions were taken carefully and based on decades of accumulated wisdom and experience.
This saved you from taking pot luck and was to your benefit, because he invariably knew an awful lot more about bicycle design than you did.


But even then, as I'm sure you will agree, it is best to be armed with a full set of accurate measurements for the new frame and to be able to compare those to a frame you already have. Buying a frame purely on the basis that "it is 24" and I always have 24" is surely too crude.

It seems to me that a semi compact frame removes one possible problem by lowering the "seat lug" out of the way, meaning that the user is very unlikely to find they cannot get the saddle low enough. The only remaining height issue (regarding fit) is the top of the head tube.

Brucey
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Re: 531 ST Frame Sizing

Postby Brucey » 3 Sep 2016, 1:35pm

Roadster wrote:....This saved you from taking pot luck and was to your benefit, because he invariably knew an awful lot more about bicycle design than you did.


you have point but there appears to be an implicit assumption that

a) everyone would be aiming for the same riding position and/or
b) that everyone has similar bodily proportions at any given height/leg length.

Also it should be noted that if it were really true, then (say) all OTP touring bikes from the big manufacturers would presumably have shared a common geometry; this was no more true then than it is now IMHO.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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NATURAL ANKLING
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Re: 531 ST Frame Sizing

Postby NATURAL ANKLING » 3 Sep 2016, 1:37pm

Hi,
I have a 15" 700c road frame hanging up in the spare room, no idea what it would handle like, women specific geometry, well that's what is says on the frame.
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.

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meic
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Re: 531 ST Frame Sizing

Postby meic » 3 Sep 2016, 1:39pm

and to be able to compare those to a frame you already have. Buying a frame purely on the basis that "it is 24" and I always have 24" is surely too crude.


My original bikes had their geometry arrived on by chance, I was just as ignorant back then as I am now. The bikes that I have may not be the same as each other.
The saddle height is one thing that I know must be a certain figure and I even know what that figure is.

Handlebar height is something that I dont believe will ever be too high for me, so unless it is a custom build, I tend to find these two have eliminated the need for any further consideration as no other choices are left to be made.
Yma o Hyd

pwa
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Re: 531 ST Frame Sizing

Postby pwa » 3 Sep 2016, 1:48pm

I had a few frames with horizontal top tubes that I never got fully comfortable on because my upper body is long and made me want a longish top tube, but that seemed to give me off-the -peg frames on which the headset was a touch too high for me to get the bars as low as I wanted. I find with semi-compact frames and Aheadsets (and their spacers) I can buy a frame and set things up exactly right. I never managed that with the traditional system.

A figure which is not always given, and which is essential for me, is Front Centres. That is how I know whether I can fit guards without catching my toes.

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meic
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Re: 531 ST Frame Sizing

Postby meic » 3 Sep 2016, 1:55pm

Front centres was on my checklist too. Top tube height wasnt as I didnt have a clue about what would be best for me. I think that I would like longer top tubes for no better reason than I FEEL long stems "corrupt" steering and any bars should rotate around the axis of the headset bearings, rather than offset a long way ahead of them.
Yma o Hyd

Roadster
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Re: 531 ST Frame Sizing

Postby Roadster » 3 Sep 2016, 6:26pm

I don't disagree with any of your objections to off-the-peg frame sizing based solely on seat tube length. All I'm saying is, that's the way it was and it was close enough to be acceptable for the vast majority of buyers, otherwise you're talking custom/bespoke.

Quality touring frames built with 531ST by different makers were not, of course, all exactly the same but nor were they all totally different from each other: on the contrary, they were more similar compared to other styles of bicycle than they were varied. For example, most had 72 deg. parallel angles, a longish (~41.5") wheelbase and similar (~2.25") fork offset: if they were presented in the same livery, it would take a more expert eye than the average touring cyclist's to discern the differences between them.

Provided the length of its seat tube was appropriate for the length of your leg, you didn't complain that your frame didn't fit or presume to question its proportions. You trusted the integrity and reputation of the builder and just changed the other components or adjusted their positions until you were as comfortable as possible on it.

Brucey
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Re: 531 ST Frame Sizing

Postby Brucey » 3 Sep 2016, 10:35pm

then as now you would find touring frames with seat angles that varied from about 71.5 to 73 degrees and top tubes that varied by about 1" in length, all at 'the same frame size'.

This can mean that (with a given stem length/saddle position wrt the BB) your hands can be about 2" different in distance from the saddle, which is a 'chalk and cheese' fit, pretty much beyond what can easily be adjusted for using changes in stem length.

The idea that there ever was a Halcyon time when you 'just bought a bike of a given size and some clever chap had designed it so it would always fit you with just a stem swap' simply doesn't bear close scrutiny.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Roadster
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Re: 531 ST Frame Sizing

Postby Roadster » 4 Sep 2016, 2:09pm

No, that idea doesn't bear close scrutiny but then I didn't actually say there was a "Halcyon time" when every designer was clever and every bike bought in that way "would always fit you with just a stem swap". Those are your own words you're sarcastically "quoting", not mine, but in the interests of fairness let's also look at how much close scrutiny some of your ideas simply bear.

"About 71.5 degrees" sounds a lot like 72 degrees to me except for being slightly on the slack side, and I'd be interested to hear of some examples of 531ST frames (touring by definition) with steeper angles. Back in the 70s, I had an MKM 531 machine with 73 deg. angles and the shorter wheelbase, closer clearances and less fork rake that typically accompanied them. This geometry made for an extremely lively and exciting ride but also made it totally unsuitable for loaded touring. A few not-so-clever chaps may have made touring bikes like that but how many knowledgeable tourists actually bought them?

I agree that a 1" difference in top tube length can mean a 2" difference between hands and saddle, but dispute that this was "pretty much beyond what can easily be adjusted for using changes in stem length". Stems were available in lengths ranging from 70mm to 140mm and a 70mm difference is greater than 2" - in fact, it's almost 3". In practice, however, extremes of stem-length would have been indicative of the wrong choice of frame-size, not its proportions per se, and the obvious remedy was to choose the next size larger or smaller instead.

Brucey
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Re: 531 ST Frame Sizing

Postby Brucey » 5 Sep 2016, 7:43am

no sarcasm intended.

There have been (and still are) lots of touring frames built with 73 degree angles, including some that claimed not to be. I can't speak for how knowledgeable those who purchased them might be.

Starting with a mid-length stem, to accommodate a 2" error in reach would require at least a 4" range of stem lengths.

Most cyclists would -for various reasons- try to avoid using extreme stem lengths in any event.

R2 -and many others here- make a persuasive argument that you can fit well onto, or even get much of the benefit of a custom fitted frame, by carefully choosing an OTP frame. But to extend that argument to 'get one with a given length of seat tube and you will fit it OK' isn't true now and never has been.

cheers
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Roadster
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Re: 531 ST Frame Sizing

Postby Roadster » 5 Sep 2016, 3:18pm

Once again you are reading things into my posts which simply aren't there. I haven't in any way extended that argument to say that 'if you get an off-the-peg frame with a given length of seat tube, you will fit it OK'.
What I have said is that the method was "close enough to be acceptable for the vast majority of buyers, otherwise you're talking custom/bespoke". And a good job it was too, because you had no control whatsoever over the angles and relative tube-lengths of a 531st frame bought off-the-peg - that's what "off-the-peg" means.
Frankly, you are putting words into my mouth and then disputing them merely for argument's sake.

With regard to frame angles, we're not talking here about any old touring frames but specifically about those built with 531st tubing, and you haven't given a single example of one with 73 degree angles never mind "lots" of them. Are you seriously suggesting that reputable frame-builders in 531st were a disparate bunch of individuals still making it all up as they went along, cooking up their own idiosyncratic designs without regard for convention, tradition, their customers' requirements and the efforts of their rivals?
Personally, I don't believe that to have been the case and you're not convincing me otherwise. I think that a process of continuous refinement over the previous half-century had resulted in a considerable degree of standardization and conformity in the design of the high-quality touring bicycle, due partly to experience of what worked and what didn't and partly to the demands and expectations of the market. That's why they could be (and still are) manufactured, marketed and sold off-the-peg without controversy... until now, that is.

Brucey
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Re: 531 ST Frame Sizing

Postby Brucey » 5 Sep 2016, 5:24pm

as I pointed out above, many people find that OTP frames vary enough that they can fit themselves to a specific OTP frame very well and to others not at all. You don't appear to acknowledge this possibility, but 'twas ever thus.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~