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Monday
Mar122012

Frame Design: Then and Now

The above picture is me riding in the British National 12 Hour TT Championship in 1953; dating the picture is the spare tubular tire worn around my shoulders as the pros did in that era.

My bike frame size back then was 22 inch; (56cm.) compare that to the 51cm. I rode at the end of my racing career in the early 1980s, and still ride today. That is a whapping 5cm or 2 inches smaller.

If I rode a 56cm. frame today it would way too big for me, and yet looking at the above picture my bike looks fine and not too large at all. So what happened; did I shrink over the years? I was certainly a lot slimmer back in my youth, but my legs are pretty much the same length as they are now.

A clue is in the amount of seat post showing; about 2.5 inches (6.3cm.) in the above picture; I have 4.5 inches (11.4cm.) on my current bike. This accounts for the 2 inch (50cm.) difference in frame size.

The reason my 1953 bike does not appear too big for me is because it wasn’t; it was a totally different design than today’s frame. My bottom bracket height was only 9.25 inches; (23.5cm.) today’s bike has a BB height of 10.625 inches (27cm.)

I would also point out that all racing cyclists in the 1950s, including the pros, pedaled much lower gears, sat more upright, and rode with their saddles set lower by today’s standard.

See picture of Fausto Coppi on right.

I can remember that my bottom bracket was low enough that I could lower my heel and actually touch the ground.

Our cycling shoes had real leather soles, and had steel tips on the heels to prevent wear when walking.

While out training after dark, and coasting down hill; we would sometimes lower our heel so the steel tip made contact with the road, sending out a shower of sparks. A pretty spectacular visual effect, especially if several riders did it together.

When you lower the bottom bracket on a frame you also lower everything above it, the top tube and the height of the saddle from the ground. You do not necessarily lower the saddle in relation to the pedals. That will be whatever the rider sets it at.

However, the handlebars are not lowered by as much. The reason being that the size of the front wheel and therefore the length of the front fork are constant no matter what frame size. Above the front fork there is a head tube and head bearings. 

It would be impossible to build a 51cm. frame with a nine and a quarter inch BB height, because with a level top tube there would be no room for a head tube; which is why I rode a much larger frame back then. Or not so much a larger frame, but one with a lower BB and a longer seat tube.

Over the years the bottom bracket height on racing frames has increased; not because striking a pedal on the ground was an issue. (I never found it to be a problem.) But rather one of making the BB higher makes the chainstays and down tube shorter, and therefore makes a stiffer frame.

Also probably the main factor driving frame design is the change in riding positions of today’s racing cyclists, over those of their predecessors in the 1950s. I have already mentioned the 50s riders sat more upright because the handlebars were higher in relation to the saddle.

Today’s racing bicycle has a large saddle to handlebar height difference; which is how most racing frames sold today are designed. However, the majority of the frames are bought by non raciing leisure riders; using them purely for exercise and pleasure riding. Many of them like myself are older, and are not flexible enough to get down in those horizontal, low tuck racing positions.

Today’s frame design with its sloping top tube does not restrict a frame designer/builder like the level top tube did. No matter what the BB height and seat tube length, the head tube can be any length. So anyone having a frame built for leisure riding by an independent builder might consider lowering the BB height.

I did this when drawing up the specs for my New Fuso that Russ Denny is building for me. This is probably the last frame I will ever need. I designed it with an 8.5cm. drop; which is a 10 inch. (25.3cm.) BB height.  (Drawing below.)

This does two things; by sitting closer to the ground it will be easier to put my foot down when stopping. But more importantly, a lower bottom bracket means the saddle is lower in relation to both the ground and the handlebars.

Not the other way round of having the seat high to begin with, then raising the handlebars to achieve the desired position.

I have come to realize, the racing position of the 1950s is probably the ideal leisure riding position for today. I will have my frame built lug-less; (Welded.) this means there is no restriction on angles, and because the modern design has a sloping top tube it is no longer necessary that I go to a larger frame.

 

                         

Reader Comments (13)

Well Done Dave ! At last someone has realised that there is another group of genuine cyclists to cater for. Not twenty year old racers, not women, but veteran male cyclists. As you pointed out, we do have our own specific needs, so thank goodness you've identified them. However, I pity the poor pensioners like me who can't afford a nice new custom frame from yourself. Do you think the Scottish Government would allow doctors to write a prescription for a new frame, as it would in the long run cost the health service less ? Or should I just sell my wife's kidney ?

March 12, 2012 | Unregistered Commenterthehandlebarcode

Did you just create a new frame design business for yourself? Charge a couple hundred bucks to have a frame designed by Dave Moulton and farm out the manufacturing to the builder of your choice.

March 12, 2012 | Unregistered Commentertzilinski

Dave, you don't say how you measured those frames. Traditionally, when a frame size was given in inches, it was from the centre of the bottom bracket to the top of the seat lug. When we started specifying frame sizes in metric, it was from centre to centre of the tube intersections. Now, with today's funny frames with sloping top tubes, it's apples and oranges all over again.

March 12, 2012 | Unregistered CommenterJohn B

I know Russ Denny would not have a problem building a frame I designed, and I would be happy to do that if it was requested; (A lot less than $200 BTW.) but I would not feel comfortable asking other framebuilders to do it without an OK from them first. I know I didn’t like it when someone asked me to build a frame that they, or someone else had designed.

Traditionally, English framebuilders measured center to top, Italian builders center to center. When I came to America I switched from inches to centimeters because that’s what everyone talked in the US, but I still measured C to T. Oddly Masi measured C to T also.
It only becomes a problem when people buy and sell frames; a seller lists by one method and the buyer assumes it is the other. Someone gets a frame that is off by 2 cm. either too big or too small. Today it seems frames come in T-shirt sizes, S,M and L.
Dave

March 12, 2012 | Registered CommenterDave Moulton

Very Pretty Dave. But please make Russ paints the fork. I am glad he is keeping your legend alive! BTW is Russ using your same painting technique with 8 coats or so of clear-coat and a ton of wet sanding as to minimize the decal relief?

March 12, 2012 | Unregistered CommenterJack Gabus

Lugless...welded? Lugless frames were traditionally fillet-brazed. I have 3 so made, 2 by Dave Yates and one by Jack Taylor. Perhaps you could bring your readers up to date on the difference between the old and new methods of building lugless, Dave?

March 12, 2012 | Unregistered CommenterMartin Hayman

I can't wait to see your new bike build!

March 13, 2012 | Unregistered CommenterAnthony Lim

I think it also has to do with fashion. In the 50s/60s the fashion was for larger frames/less seat pin. This started to reverse in the Merckx era and continued through the 80s to today's sloping top tube era where it is ALL seat pin.

March 14, 2012 | Unregistered CommenterJW

I too look forward to seeing your new FUSO... pics please!

March 15, 2012 | Unregistered CommenterJack

Interesting post. I'd agree, most recreational riders would do much better using the old school style fit. As would many "serious" riders, if they would ever admit it.

Grant Petersen/Rivendell fit philosophy (along with some others) falls along the old school thinking - bigger frame, higher 'bars, lower bottom bracket.

My first serious road bike, back in the early '80s, had a 58cm frame. I later moved to a 56cm and continue to ride that size today. Now 50 years old and not quite as flexible as I used to be, may bump up to a 57 or 58cm eventually.

I'm also curious to check out future posts on your new Fuso. Should be great,

March 18, 2012 | Unregistered CommenterDan O

Interesting about BB height and stiffness. But: is the minimal difference in chainstay length the real reason for the impression of greater stiffness with less BB drop? In your picture above, the downward pressure from your left foot includes a component torquing your frame to your left; this is compensated by the forces you apply to the handlebars. The needed handlebar forces are far less than the pedal force because the lever system pivot is at ground level and the BB height is far less than the height of the bars. The higher the BB, the greater the opposing force needed at the bars to keep the frame vertical. This could create an impression of increased stiffness even if the frame were totally rigid! Your thoughts?

The modern fashion for higher BBs is not such a great idea if the increased stiffness is only subjective, since energy losses due to frame distortion dissipated as heat may be minimal and may be almost completely unaffected. The choice could depend instead on whether a rider prefers to exert large upper body forces with small lateral excursions of the handlebars (which would favor a high BB) or vice versa. I think I appreciate a low BB for this reason, but as you say they are hard to find (unless one shells out for custom…or maybe a new FUSO)
Wonderful blog! Cheers from a fellow expat in San Diego
Don

October 11, 2013 | Unregistered CommenterDon MacLeod

A correction to my last comment, after a bit more rumination on O level physics: in the simplest case (bike vertical), handlebar forces will not depend on bottom bracket height, but only on the lateral pedal spacing in relation to handlebar width. If all your weight is on the left pedal and the right pedal is not pulling up or pushing down at all, there will be no net weight or lifting at the bars. But to keep from falling over, the rocking moment exerted by your weight on the left pedal has to be opposed at the handlebars by pulling on the left bar and pushing, equally, on the right bar). To cancel the rocking moment created at the pedal about the line of contact with the ground, the upper body push and pull would each need to be half your body weight divided by the ratio of bar width to pedal spacing, or about a third or a quarter of body weight. But of course the bike does rock significantly during pedaling out of the saddle, and bottom bracket height will then come into the picture in the way that I suggested.

October 12, 2013 | Unregistered CommenterDon MacLeod

Great point!
Dave, agree with you totally, lower BB can have a lower centre of gravity, good for turning at high speed.

November 3, 2014 | Unregistered CommenterJeff

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