Frame geometry, general design, and rider sizing.

[SkipdiverJohn]

I know I'm well out of touch with this, but back in the early 1980's when I first bought a "proper" adult gents bike, pretty much everything sold, irrespective of price, had round cross section tubing, a crossbar set parallel to the ground, 72 degree geometry, a fair amount of fork trail to give castor angle for predictable handling, and there was generous clearance between the tyres and the frame.
When you look at most modern bikes, you see a lot of differences. The most obvious one being the sloping crossbars, some being quite steeply raked. A lot of down tubes are oval or some variation of, in cross section, and frequently oversized. How long ago did the conventional frame layout go out of the window and why?
This brings me to sizing; using the conventional formulae for calculating ideal frame size from height/inside leg measurements, I should have a frame of around 23 1/2 inches. However, if you read manufacturers/retailers sizing guides nowadays, they typically suggest a frame size a couple of inches smaller. A smaller frame theoretically means a shorter frame, so the handlebars are then closer to the saddle. So I suppose my other question is, is ideal bike sizing different now for a given size adult, compared to the 1980's and earlier? I tend to see a lot of riders now on small frames with long seatpost saddles set very high, rather than the old rule of having the biggest frame you could comfortably straddle without inviting painful mishaps.

 

[Racing roadkill]

I know I'm well out of touch with this, but back in the early 1980's when I first bought a "proper" adult gents bike, pretty much everything sold, irrespective of price, had round cross section tubing, a crossbar set parallel to the ground, 72 degree geometry, a fair amount of fork trail to give castor angle for predictable handling, and there was generous clearance between the tyres and the frame.
When you look at most modern bikes, you see a lot of differences. The most obvious one being the sloping crossbars, some being quite steeply raked. A lot of down tubes are oval or some variation of, in cross section, and frequently oversized. How long ago did the conventional frame layout go out of the window and why?
This brings me to sizing; using the conventional formulae for calculating ideal frame size from height/inside leg measurements, I should have a frame of around 23 1/2 inches. However, if you read manufacturers/retailers sizing guides nowadays, they typically suggest a frame size a couple of inches smaller. A smaller frame theoretically means a shorter frame, so the handlebars are then closer to the saddle. So I suppose my other question is, is ideal bike sizing different now for a given size adult, compared to the 1980's and earlier? I tend to see a lot of riders now on small frames with long seatpost saddles set very high, rather than the old rule of having the biggest frame you could comfortably straddle without inviting painful mishaps.

There’s more choice with certain components now. Back in the 80s you’d probably have a threaded headset or a quill, and the stem length was whatever it was manufactured to be. You can mix and match components, to ‘fine tune’ your bikes settings much more readily now. So the frame size isn’t so much the lynchpin ‘driver’ of the consideration of bike fit, that it may have been years ago. There is a far greater degree of flexibility in designs now, and a greater choice.

 

[SkipdiverJohn]

Back in the 80s you’d probably have a threaded headset or a quill, and the stem length was whatever it was manufactured to be..

I thought ALL headsets were built like this! Even my skip salvaged "BSO's" which I would estimate are both under 15 years old, seem to have conventional stems/headsets. One is currently a bit of a sore point, as it's stubbornly resisting my attempts to get the stem out of the headset so I can strip and rebuild. Rubber mallet and penetrating fluid being applied regularly..

 

[MichaelW2]

You size a modern frame by length, not height. Modern frames are designed to offer the same length with more standover clearance, ie higher seatpost. You only use the old fashioned sizing method for old fashioned frames.
Smaller main triangles and fatter tubes give more stiffness, which is a good thing in large sizes but not in small ones.

 

[raleighnut]

Not sure what the angles are but this is a very short/steep frameset from probably the late 80s early 90s (I don't know the maker and it doesn't even have a frame number anywhere)

 

[SkipdiverJohn]

Not sure what the angles are but this is a very short/steep frameset from probably the late 80s early 90s (I don't know the maker and it doesn't even have a frame number anywhere)

I'd imagine that bike would have quite sharp handling, but be rather twitchy and unpredictable unless ridden on very smooth surfaces. I may be completely wrong, but the wheelbase looks very short and the forks don't have much trail.

 

[SkipdiverJohn]

Did someone say short wheelbase? 1939 Baines Flying Gate

What was the supposed advantage? Quicker handling maybe? I can't imagine it would have saved any weight, if anything there's probably more tubing in that frame than a conventional one.

 

[TheDoctor]

Possibly that it looked distinctive in a pre-advertising age of cyclesport?

 

[MichaelW2]

I'd imagine that bike would have quite sharp handling, but be rather twitchy and unpredictable unless ridden on very smooth surfaces. I may be completely wrong, but the wheelbase looks very short and the forks don't have much trail.

Looks like a custom bike for a very tall guy for time trial or triathlon use. It is hard to estimate how the bike will respond to steering just by eyeing the frame. It looks like it should be twitchy, but it may not be. The short wheelbase is a common "feature" on big bikes, being the same wheelbase as found on medium and small bikes, excepting a little variability over the front toeclip coverlap. Big bikes should have a more generous wheelbase to give the same rider feel, since the centre of gravity is higher. Of more concern then was rear triangle stiffness using the one size of rear stays that were available. Modern frames can use stays of any length and diameter but big frames still have short wheelbase and small frame usually have long wheelbase.

 

[raleighnut]

I'd imagine that bike would have quite sharp handling, but be rather twitchy and unpredictable unless ridden on very smooth surfaces. I may be completely wrong, but the wheelbase looks very short and the forks don't have much trail.

No, the handling is fast but not twitchy in fact it's quite stable mind you it is a Reynolds 653 tubeset so it's really stiff.