Bicycle Frame Geometry

This is an interesting exercise in bicycle frame fit and why one size fits all frame geometry, doesn’t!


The crimson and white frame is one I built for a customer in 1987 that I was given back a few years ago. Ishiwata 019 tubing. Suntour Superbe Pro equipped.
The white and green frame is my own bike from 1989, probably my favourite from all the frames I built for myself, which is why I kept it. Tange Prestige Superlite tubing. Shimano Dura-Ace 8 speed STI equipped.
The red, white and green bike is a custom built (American) Serotta made for an employee at the factory in about 1987. Columbus “Squadra Corse” tubing. Campagnolo Super Record equipped. All weigh between 20 and 21 pounds depending on the wheels. The lighter Prestige frame is offset by the heavier components. They all have different ride characteristics due to tubing, bottom bracket height, seat stay design etc.


Having returned to cycling about 18 months ago I usually ride twice a week, the same ride every time, about 35km with 450m of vertical change – up and down Peats Ridge Rd.
I’ve been gradually getting faster with average speeds between 28 and 29 km/h over the last couple of months. I generally ride “my” bike, although sometimes on the Serotta, and for the first time the crimson one twice this week. All are 58 cm seat tubes, with 175 mm cranks and bar reach all set up the same.
The Serotta is maybe fractionally slower on the rides, it’s only slight, maybe 0.1 to 0.2 km/h average so not conclusive really, but both rides on the crimson bike were about 2.5 km/h slower than both rides the previous week on “my” bike and slower than I’ve done in over 12 months. If anything weather conditions were better this week (less wind). Not only slower, I felt more fatigued during and after and less able to push myself on it or stay on top of the gears and keep the bike rolling over the small hills.
During the second ride I suspected the seat was low so on return I checked all three bikes, no difference in seat height or bar reach, so that killed that theory. I then checked the set back of the seat behind the bottom bracket, “my” bike and the Serotta are the same (I already knew this, the Serotta could have been built for me, it’s basically identical in fit) but the crimson bike has the seat 22mm further forward – it was built for someone else and I knew it had a steeper seat tube than mine. The guy was my height but had shorter thighs. The simple solution could be to push the seat right back in the clamp, but that would require a lot shorter handlebar stem which in turn would change the whole balance and steering of the bike.


What all this indicates is that custom built frames that fit the rider properly bring out far better performances than one size fits all off the shelf frames, which is what I always said.
If I were younger and fitter like I was 30 years ago the differences may not have been so pronounced, but I always maintained that all other things being equal the guy who was best set up would be the freshest at the end of a 200km race, potentially making the difference between winning or otherwise. Correct frame fit starts with the seat tube angle, every other angle and dimension builds on that.


As an aside I’m probably going to build myself a new frame later this year, it’ll be the first one in over 20 years, but will definitely be retro. My son has also requested a frame, but his will be up to date in terms of componentry so will need a lot of different details in the build, and my grandson has requested a mountain bike frame. Busy, busy!

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