Monday, April 17, 2023

Let's Talk About Geometry Again

Diagram showing what "trail" is on a bicycle
With the brief return of Winter here in Iowa and elsewhere in the Mid-West, there wasn't much riding being done. So, what better time is there to grab a hot cup of coffee or tea and ruminate on the finer details of bicycle design? 

So, with that said, here are some reasons for this post today to start out with. I have written a LOT about bicycle geometry in the past, specifically concerning geometry for gravel road/rough road riding. This all came out of a research I did in the late 2000's into what older ideas were for road bikes in terms of geometry. Scouring the internet for old ideas led me to thinking more critically about what would make my perfect gravel bike. Which leads me to....

This originally was all about what "I" wanted. I was not ever thinking about these geometry ideas for anyone else other than myself and a potential custom designed gravel going bike. Context: At the time I was using a Surly Karate Monkey as my main gravel bike. I knew it could be refined and made better to do what it was that I was falling in love with doing, namely "gravel grinding". Of course, there were others doing this as well, but at that time there were no options specifically designed for gravel, and the hope that there ever would be was not high. In fact, there may have been no notion at all that the cycling industry would ever take notice and do for us what they have done. So, keeping in mind that this was concerning my take for myself, and that any ideas that this "gravel thing" would take root were not very hopeful, I came up with a refined idea for what I thought would make a good gravel bike design on my own. 

The Raleigh Tamland Two ended up being the bike I would have designed.

Briefly I will then just say that due to a set of circumstances beginning in 2012 things turned out so that my design didn't have to be custom made. It ended up being (mostly) realized in the production of the 2014 Raleigh Tamland Two bike, which I then purchased. 

While it is true that the Tamland fit the mold of what I was after in a gravel bike, it was still based upon "my ideal" and not necessarily what a lot of other folks would think was, or would think of in the future as, "Gravel Bike Geometry". 

Much to my surprise then, the "gravel bike", as we have come to know it now, is pretty much an approximation of these ideas I put together back in the early "twenty-teens". Sure, there are variants, but the meat of what is used as geometry now for these bikes is pretty much based upon the same ideas I found back then. Note- I did not say, or ever would say "I invented gravel bike geometry". That would be preposterous. So, let's not be confused. I mined history for ideas that others came up with and by coincidence or influence, I do not know which, the cycling industry did a similar thing as well.

Now, on to something recent that appeared on social media that is relevant to this discussion....

Courtesy of Steve Garro's Facebook page

The above image, courtesy of Steve Garro's Facebook page, (he of Coconino Cycles), shows a page from a 1946 edition of "Bicycling" discussing the geometry and technical features of a frame from a "Willie Honeman", who was a three-time National Champion track cyclist and, apparently, he dabbled in frame making in the 1940's. This design being discussed is one that Mr. Honeman would have ridden on the board tracks in the late 1920's and early 1930's, but aparently was still relevant in the 40's as well.

You'll note, amongst other things, the odd nomenclature for frame parts, but what I wanted to draw our attention to was the geometry. This bike is what could be considered prototypical gravel bike geometry. Note- This is a board track bike design! In the notes on the frame, you'll see a recommendation for a slacker head tube angle for "a Road Machine to absorb some of the vibrations caused by bumpy roads." That angle range being listed as "20 or 22 degrees", which may be confusing until you realize that this is looking at the angle from 90° perpendicular to the ground to the centerline of the steer tube. The vertical line being "zero" degrees and adding degrees until you get to the steer tube angle. Reading it as we do now this would be 70° - 68°! 

A deep bottom bracket drop is also specified (Hangar drop) which turns out to be approximately 75mm. The chain stay is specified at 17" which is a bit more than 431mm. So, as I looked at this, I realized that these numbers, besides the surprisingly slack head angles recommended, were right in the same pocket I was thinking about back in 2010. 

Of course, one could argue that materials technology was part of the reason for those odd geometry numbers.  Also, you might say that this is a hold-over from earlier thoughts on rough road riding and track bikes, but here I'd have to think that while traditions may have been part of these choices, I would also assume that they did actually work in real-world applications. If they didn't, well one could assume that we'd have never heard about bikes like this. 

My main purpose here is to show that these ideas we are plumbing for gravel bikes today have deeper roots than we may have thought. This particular design offered by Mr. Honeman being but one example. 

I hope you find this as interesting as I did. I think it is fascinating to see that many ideas we have now have their roots in the past. We only refine them minutely and when materials technologies allow for things to actually be made that were designed and thought of back in the late 19th and early 20th Centuries.


teamdarb said...

So what are your thoughts on the traditional "Path Racer" geo for gravel?

Guitar Ted said...

@teamdarb - Traditional Path racer geo features little bottom bracket drop, so right there it is a no-go for my tastes. I find high bottom brackets to be rather unstable on looser gravel, and I am not a fan of that sort of thing myself.

teamdarb said...

GT, I totally forgot about the BB height. I have always thought the Path Racer geo to be akin to having full suspension...slack and long. The flex required to keep the power on the ground under a fixed drivetrain over rough road. But never thought about the BB height.