Dave Moulton

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« The New Normal | Main | Measuring Frames »
Monday
Jan152018

My Design Philosophy Explained

I look at frame specs of all the major bicycle manufactures today, and they all follow each other within certain parameters. Of course the UCI (The governing body of the sport of cycle racing.) lays out certain rules and regulations pertaining to the design of a racing bicycle. However, within these UCI rules there is a pretty wide scope for any individual to do something a little different.

Most take the safe approach and follow what their competitors are doing. It has always been that way, framebuilders do whatever is easiest for them, and bike riders make do with whatever is available. When I got into cycling in the early 1950s, the standard frame of the day was 73 head and 71 seat angle.

Sitting back that far was totally unsuited to my short stature of 5’ 6” (167 cm.) I got into framebuilding trying to build a better frame for myself. I found as soon as I made an effort, I would slide forward onto the tip of the saddle. This was not only extremely uncomfortable, it had the effect of my saddle being too low. The answer seemed simple to me. Make the top tube shorter, and the seat angle steeper, thus moving the saddle forward to where my backside wanted it to be.

Why were seat angles so shallow in the 1950s and before that? It was a throwback to the “Ordinary,” the high-wheeler that was the forerunner of the chain driven bicycle. In 1950 the chain driven bike was only 65 years old. There were still people around that had actually ridden the old high-wheeler.

By the 1960s the parallel angle frame came into vogue. By making the seat and head tube the same angle, the same size top tube could be used over several sizes, tubes could be pre-mitered, and simple frame assembly jigs could be used, thus speeding up production.

First came the 72/72 degree frame, followed a short time later by 73/73 degree angles. The reason being, people were not ready to jump from a 71 seat angle to a 73. 72 parallel was a good compromise. When people found that worked, it was an easier sell to the 73 degree parallel. 73 degrees was a better head angle anyway. That had been established as far back as the 1930s, and is still the standard today, for a road frame.

In the 1970s most Italian builders, and many English builders switched to 73 degree seat with a 75 degree head angle. No one was going back to a 71 seat angle, but having that 2 degree difference in the angle, and with the two tubes getting further away from each other as the frame got taller, was an advantage for the framebuilder. The top tube automatically became longer for the larger frames.

The selling point was, ‘Steeper head angle makes a livelier handling bike.’ It did indeed. Lively to the point of being dangerous for an inexperienced rider. I did not follow this trend, but instead made the top tube shorter. For example a 54 cm. frame (C to T) had a 54 cm. (C to C.) top tube.

A 55 cm. frame had a 54.5 cm. top tube, and a 56 cm. frame had a 55 cm. top tube, and so on. As the seat tube increased by one centimeter, the top tube only increased by half a centimeter.

This simple formula meant that by increasing the handlebar stem length to compensate for the decreasing top tube. It meant the front part of the handlebars was always in the same position directly above the front hub and the point where the tire contacts the road.  This was the case throughout the range of sizes. (See top of page drawing.)

When sprinting out of the saddle, there is always a certain amount of “Throwing” the bike from side to side. If the rider’s weight is directly above the tire’s point if contact, the wheel will remain straight. If the rider’s weight is ahead or behind this point of contact, any sideways movement could translate into the front wheel steering this way and that. I found with this set up, the 73 degree head angle can feel just as lively in a sprint, as the steeper angle, but without the “Squirrely” feel of the steeper bike.

Except for my very smallest size frames, 51 cm. and below. Which had a 72 degree head angle, and 38 mm. fork rake, all other sizes had a 73 degree head angle with 35mm. fork rake. This ensured the same handling characteristics for all sizes.

Above: A small 19" (49 cm.) frame, built in England in 1977. the differance in seat and head tube angles can clearly be seen. However, for a rider of small stature the riding position is more balanced than it would be if the frame were built with a shallower seat angle and a longer top tube.  

The seat angle varied from 76 degrees for the smallest frames, gradually decreasing, 75, 74, to 73 degrees for the largest sizes. This was often a hard sell to a market that had always heard 73 degree seat angles.  

What I had, (And still have today.) is a “Niche” following. I gradually built a network of bike dealers, who once they, or their employees had ridden my bikes, they were sold. It was then an easy sale to their customers, because they truly believed in the product. The proof can also be seen in the number of “Original” owners on my Registry website.

Will my ideas ever become “Mainstream.” I very much doubt it. Frames today either pop out of a mold, or they are welded steel or aluminum. There are no restrictions what-so-ever on angles or tube lengths, but most stick to the tried and safe 73/73. Any slight variation on this I feel is not done to improve handling or ride qualities, but rather to keep a balanced look throughout the range of sizes.  

Large corporations have to sell a lot of product to survive, and you can’t sell a lot of product in a “Niche” market.

 

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Reader Comments (19)

I particularly enjoy your posts about bike fit and frame geometry. The 49cm frame shown certainly has the steep seat tube, would that be 76 degrees? The mudguard appears to barely clear the down tube, would there be a fair amount of toe overlap on this frame? In practice this of course isn't a huge issue, you get used to it.

I think your design philosophy is very practical and well thought out. A lot of shorter riders would be much happier if more frame builders followed it.

January 17, 2018 | Unregistered CommenterKeith Gaunt

Are bicycles designed to become obsolete, planned obsolescence, in our modern age?
Like pretty much every other consumer product.

When you were making frames, what drove progress: racers, regular riders, you the builder? Bikes didn’t change much in all those decades. The biggest change I noticed was racers going to smaller frames, with more seatpost showing, around the start of the 80’s.

So what, or who drove change in bikes during your era? And what is motivating today’s designs: the rider, racers, the company building bikes, the investors, or is it the general economic atmosphere we live in?

January 18, 2018 | Unregistered CommenterSteve

Steve,
All good and valid points.
Growing up in England we always wanted to emulate the European pros. All that gradually changed when America became interested in cycling. Gradually bikes moved away from what the European pros used. America has never cared what the pros use or did anyway.
First came the BMX bike, (Kids pretending to be Moto-Cross riders.) Followed by the Mountain Bike, which lead to Index Shifting, and Tee Shirt sizing. Now we have disc brakes which the pros don't even want, or need, but it will be forced on them.
The top three bike brands in the world are now American. However the bicycle is such a simple machine I wonder how much more built in obsolescence can it stand?
Dave

January 18, 2018 | Registered CommenterDave Moulton

I was so overjoyed while reading this post! These are the kind of "secret knowledge" that I love. Thank you, Dave!

January 18, 2018 | Unregistered CommenterAlexander López

Great explanation!

So, considering "the market" and how frame dimensions stay within easily marketable confines, can you explain your logic behind your "shorter than the market fork rakes vs. head angles?

The "standard" was a typical 73 degree head angle/45mm fork rake. It's migrated to a 73/43 standard and I get that. But you built with considerably shorter rake/higher trail figures. Why?

January 18, 2018 | Unregistered CommenterPeter W. Polack

Peter.
It was the “Sweet Spot” I arrived at after years of experimentations. Not only my own experience but feedback from top International Class riders. The way my bikes felt and handled was my biggest selling point in the UK. It was why someone would choose mine over the competition. When I came to the US all that was forgotten, it was all about aesthetics. The paint and how the bike looked.
Occasionally I will hear from someone who says something like, “I rode down such and such mountain. My Fuso felt like it was on rails. I left everyone behind.” Etc, etc.
Dave.

January 19, 2018 | Registered CommenterDave Moulton

Dave

Curious what rake you typically ran with the 73-degree head tube. The 73-head angle/43 fork rake Peter mentions is 58mm of trail, close to the 60mm that I've always heard was "neutral steering." I have a track bike with 73 head angle/35mm rake that is *very* twitchy on the road.

January 19, 2018 | Unregistered CommenterEd

Ed;

Dave's 52cm and larger frames had a 73 degree head angle and 1 3/8 (or 35mm) of rake. That's wildly out of the norm but from his comments above, it must be fine. I'd love to try out that combination. I have to admit, from an aesthetic standpoint, the shorter fork rake does LOOK attractive!

January 19, 2018 | Unregistered CommenterPeter W. Polack

Peter

Thanks! That geometry makes for a lively road bike. I do have a steel Murray-Serotta criterium bike that has 75 head angle with 35mm rake, and that is definitely responsive. The 73/35 combo on a road bike must be super responsive.

January 20, 2018 | Unregistered CommenterEd

Ed, I think you've got it backwards.

A 73/35 combination will result in 66mm of trail, vastly higher than your 75/35 pairing, which would result in 53mm of trail. Less trail means a more responsive steering experience, although responsive is probably not the right word- It would require more frequent input to keep riding a straight line.

January 20, 2018 | Unregistered CommenterPeter W. Polack

Peter,
I'm thinking more of what I know on track bikes, where you typically see steep head angles and short rake. My primary track bike is a 74.5/30 combo for 63mm trail, and feels quite lively on the track. But then again the banked track is, in essence, a simulated straight line. A track makes a bike feel sluggish when slight steering input slowly takes you off your line (usually uptrack) but is slow to correct, and that seems to happen when trail is lower, when on the road the sensation may be different - the track makes it feel inverse, maybe?
But it's interesting that gravel bikes seem to be running geometries with slack head angles and long rake to create stability, even if the trail calculates to neutral. Trek's gravel bike runs with 72 head, 48mm rake, but comes out to exactly the same trail as my aforementioned track bike, although I suspect handling would feel very different - no one would like run gravel geometry on a criterium bike.
Anyway, this minutiae is fun to discuss - Dave, I appreciate it when you write about these little technical elements!

January 21, 2018 | Unregistered CommenterEd

Dave has a good post about bicycle trail and handling here.

http://davesbikeblog.squarespace.com/blog/2010/6/3/the-ideal-handling-bicycle.html

January 21, 2018 | Unregistered CommenterJim W

Hi Dave!
(just for the record, i've read 99% of your blog. why?! because i like it so much)

You say:
"if the rider’s weight is directly above the tire’s point of contact ..."

In my opinion... even the famous Caleb Ewan's extreme position cannot reach that... The rider’s weight will never reach that, it will always be behind front wheel's point of contact. The center mass of the rider will always be somewhere between the wheels. It's simply impossible that the rider’s weight (center mass) to be over the front wheel's point of contact - not to mention in front of it.

I think it has to do with the way you control the bike, the front wheel, and a lot has to do with the way you load the front wheel via entire arm placement... (and this is so subjective) like the relation between arm and torso and/or the relation between arm and rider's center mass.

About frame size... now most most of the frame are like this: the bigger the frame the slacker the seat angle and the steeper the head angle. A interesting exception (very famous-top bike) is the BMC, with constant 73.5 seat angle and constant 72.5 head angle (only the smaller size has a slacker head angle) and they are having this approach for a very long time (probably from their beginning).

Thank you for reading!
Best regards,
Mircea

January 29, 2018 | Unregistered CommenterMircea Andrei Ghinea

Mircea,
Of course you are right, but I wasn't expecting any one to take my statement literally. I meant the riders hands are as close as possible over the wheel center. If we split hairs even further, on the lever hoods the rider's hands a just ahead, and on the drops just behind wheel center.
I appreciate your interest.
Dave

January 29, 2018 | Registered CommenterDave Moulton

Dave, my pleasure ;-)

About the steeper seat angle as the frame goes smaller (what you experienced and what happens in general with most manufacturers), i think it is mainly because of one thing: the crank length... The smaller rider has longer cranks proportionally speaking - yup, those 170 mm cranks are long for a smaller rider although, as a number, that is smaller than 172,5 or 175. In bio-mechanics the number itself does not matter. All that matters is the relation between the levers, meaning the proportions... When similar force over the pedals is taken as reference, the longer the cranks the more the rider has to place the saddle (pelvis) more forwards - and this is what actually happens with smaller riders.

Another thingy that, in cycling, in general, people do not think <proportions> is the UCI rule of minimum 5 cm saddle setback... The smaller rider is in disadvantage with this rule because, for his/her body, the saddle feels (is) more rearwards... Why? simply because the angle of the line that starts from the bottom bracket and ends at the hip joint is slacker... The taller rider has that line steeper... which brings an advantage - better aero position and better loading of the pedals.

Best regards from Bucharest,
Mircea

February 2, 2018 | Unregistered CommenterMircea Andrei Ghinea

What does C to C and C to T mean?

February 6, 2018 | Unregistered CommenterAaron

Aaron, read the previous article, Measuring Frames, link at the top.

February 6, 2018 | Unregistered CommenterJohn B

That's a great read Dave. New to the hobby and its good read some knowledge on these frame designs.

February 14, 2018 | Unregistered CommenterAFE

America has never cared what the pros use or did anyway.
Time to alert the marketing departments of most bicycle manufacturers.
And the enthusiast magazines.

March 3, 2018 | Unregistered CommenterNAHBS visitor

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