I have a frame sizing chart on my website; it was formulated about 30 years ago from actual customer measurements and the frames that I built for them. Apart from a few minor updates, it has remained basically the same.I am of the opinion that while bicycle frame design has changed, and to some degree riding styles change; human bodies remain the same. Therefore, the basic frame fit issues are the same as they have always been.
One question I find people are asking more and more is “How much handlebar drop should I have?” In other words the difference in height between the saddle and the top of the handlebars.
When I retired from framebuilding in 1993 handlebar drop was not even in the equation. The reason being that top tubes were level and the quill stem was placed at a height where the top of the handlebars were about 7cm. above the head bearing. (See picture above.)
The stem could easily be adjusted up or down a centimeter or so either way, and assuming the rider was on the correct size frame the difference between the seat and handlebar height was automatic. Head tube length had absolutely no bearing on anything.
It didn’t matter who built the frame or how the frame angles differed there was always the constant of the level top tube. If a rider switched from one 56-centimeter frame to another 56 from a different manufacturer, the handlebar drop remained the same. In fact the term handlebar drop was not even used.
All this has changed now with compact frames with sloping top tubes; the manufacturer can make the head tube as long or as short as they wish, thus effecting the saddle/ handlebar height difference. Adding to the problem, the new threadless steerers and stems are not as easily adjusted for height as the old quill stems.
Manufacturers are already listing their frames by virtual sizes rather than the actual seat tube length. I think they should also give the virtual top head bearing height. In other words, how much higher or lower is the head bearing compared to a level top tube frame?
Below is a preliminary handlebar drop column added to my frame size chart. I no longer have the luxury of actual customer measurements in front of me. I had to rely on memory and my gut feeling to come up with these numbers.
You will not find compact frames in all these sizes, but if for example, your size is a 57cm. but you can only find a 56 or a 58, set the reach and drop as you would for a 57.Your input is appreciated, how does this compare with what you are riding? Bear in mind this is for a racing position; adjust accordingly if you want something for a more leisurely style of riding. Please post a comment or email me direct, dave[AT]ProdigalChild[DOT]net
6 comments:
Most of my bikes are 20 years or older and I don't have one of the new frames. Some of my bike friends have these frames and their drops are near the top of the head tube and/or have the multiple position stems. Obviously this raises and changes the position of the back. Either way, the issue of drop becomes a "sensitive" one and therefore gets frequent adjustments and analysis. It truly has become part of the "fitting" process which is well marketed.
My setup is 10cm drop on 52cm frames, what I've used for a long time. I remember just dropping quill stems as low as they can go since starting racing in '79.
I never thought about "drop", but the almost flat back position looked like the Europeans; and you felt like a racer.
It's something I got used to.
We didn't have studies to confirm whether it really was efficient, it just felt like it.
Nowadays, my bars and seat are almost level, with only a couple of cm drop on my road bikes. That's just me, though.
I don't really like a lot of drop on my personal road racing bikes. A few cm at most. I am flexible and could certainly race with a bigger drop but, I spend a lot of time in the handlebar drops and find it really comfortable.
I am in this 55cm top tube vortex! Most of the fancy carbon race bikes I sell in my shop either have a 54 or 56+cm top tube. I must choose a frame based on either a 120cm stem with too much drop or a 90cm stem with acceptable drop. The bigger bike has a taller headtube and my post will "show" a little less creating less drop.
But, I default to the 54cm toptube bike and leave more headtube on the fork than I find aesthetically pleasing.
The point? I dunno. I size people for "modern" frames starting with the tt. I'm going to print out your chart Dave and see if I come up with anything.
Your charts for both handlebar drop and frame sizing seem to be just about spot on for what I've come to prefer riding after a year and a half.
I've got a modern 52 x 53.7 (st x tt) sloping frame, and an older bike from '85 that is 51 x 51. The modern frame seems too long, even with a 90mm stem. The '85 bike is pretty much spot on but has a reach from saddle tip to bar tops that is nearly 3cm shorter than the modern bike.
I run the same 4-5cm handlebar drop on both bikes but don't mind an extra 1cm drop (for 6cm) on the '85 bike.
Your sizing recommendations seem too small to me. I am only 5'7" (170cm) tall with an inseam of maybe 31" or 32", yet I have ridden 54 or 55 cm frames all my adult life. Typically the seatpost will be at or near its maximum extension or I have to buy a longer one. My favourite racing bike has a 55 cm top tube and an 11.5 cm stem and I hate it when a bike comes equiped with a stem less than 10 cm.
If I rode a smaller frame, the stem would have to be unacceptably long and the handlebars would be too low. On most of the bikes I ride they are nonetheless three or more inches below the saddle, but I have come to the opinion that it is more comfortable to gain an aerodynamic crouch by increasing reach and keeping the handlebars high--almost level with the saddle--than it is to get the same effect by simply lowering the bars. I had a touring/cross bike that I had set up this way and it felt wonderful.
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