The DeSalvo Custom Bike Project Part 2 – The Frame
Ashland, Oregon, 22 September 2013 – The DeSalvo Custom Bike Project Part 2 – The Frame
I fully intended for the next installment of the DeSalvo Custom Bike Project to deal with the mental flip-flopping associated with wheel selection. But other developments have moved that post to sometime in the future. Instead, it’s prime time to dive deep into the innumerable geometric design decisions of a custom bicycle.
If you walk into almost any bicycle shop you’ll find they usually sell two or more brands of bicycles. The number of brands is often predicated on the variety of customers that come through the shop. The often-beautiful carbon fiber designs are built to standard sizes based on the average rider’s height and inseam. The geometry of a particular model of bicycle is designed almost like an off-the-rack suit jacket; taller shoppers will need a jacket with longer arms and longer length to fit properly. A buyer can often have the jacket sleeves altered or the back taken in to make the jacket fit their body type. When complete the jacket will not be made precisely to the wearer’s measurements but it will be close enough for comfort.
With a standard set of bicycle frame sizes the bicycle dealer will pick the bicycle size that most closely fits your height and adjust the bike to your needs by changing the saddle height and distance from the handlebars, the height and distance of the handlebars from the saddle, and sometimes the length of the crank arms on the gears. These specifications are adjusted to fit your non-standard body measurements onto the standard sized bicycle. Similar to an off-the-rack suit jacket, the bike will not be made precisely for you but it should be close enough for comfort.
When you have a bicycle built to your requirements by a custom builder the angles, tube lengths, tube dimensions, and reach measurements are fully customizable. In my case, although I’m 5’ 10” tall, I have proportionally longer legs and a shorter torso than the average 32” inseam rider. My arms also measure slightly longer than the average 5’10” male.
As you might recall, back in February after meeting Mike DeSalvo and a few dozen other worthy builders I made the decision to commission Mike to build a bike as a testament of having survived fifty years of everyday life. I had considered buying a carbon fiber road bike from a reputable production manufacturer but I realized that for the price of a mid-tier production bike I could purchase a handmade custom frame and have something as unique and special as I am.
Just over a week ago, Mike sent me an email thanking me for my patience while he cleared up some other commitments before starting my frame. I’ll admit I worried he’d forgotten about me but I was also hoping he was trying to figure out how to make this bike special. Attached to his email was the first draft drawing of my bicycle frame with tube lengths and angles.
As I looked at the drawing I wondered how one even begins to process the information in a picture of a bicycle with some of the tube lengths and important angles identified. I’m sure plenty of people have simply conceded that they haven’t a clue what they’re expected to do with such an image and step blindly into production. What fun is that? Where’s the anxiety? Where are the planning and thinking and understanding that turn dreams into reality?
The closest I’ve been to being an engineer was during my college days when my roommate would be working on his homework as I looked over his shoulder. I remember reading a study question to calculate the velocity of a box falling off conveyor belt moving at X speed onto another conveyor belt moving at Y speed. My thought was as long as the box wasn’t moving fast enough to break the contents everything was good. Until now, I felt the same way about bicycle design. If it looks good and is relatively comfortable everything is good. And like most people my understanding of bicycle geometry is elementary at best. So how was I supposed to understand how the DeSalvo design would be different from my current bicycle?
Luckily there’s an App for that, or at least a website where anyone can go to dabble in basic bicycle design; BikeCad.ca is a great place for neophyte bicycle designers like myself to practice their bicycle design skills. The web-based version is free for anyone who signs up for an account. And if you’re looking to design bikes as a profession, a desktop version of the software is available for a reasonable fee. On a side note, the customer support, which I used because I forgot my password and then locked up my account, was responsive and very personal.
Once you’ve created an account, you use the web-based design tools to adjust tubing length, angles and component specifications while you design the bike of your dreams. Once you have the basic design down you can experiment with paint schemes, handlebars, components, saddles and wheels. I started by entering the basic measurements that Mike specified for my frame.
And after about an hour I had enough practice with the software to change the seat style, adjust the handlebars and component group so that I could compare the geometry of my current Cannondale CAAD9 to the new DeSalvo design. Although all of the features of the desktop version are not available online, there’s enough functionality to draft the basics geometry of any bike.
Some basic measurements seem to be well understood in bicycle design. Two of these are the head tube angle and the seat tube angle, with both being set at about 73 degrees give or take a point or less. Changing these further often results in a bike with a more compliant or comfortable ride such as on a touring or town bike. I think I’ll leave the explanation of the basics of bicycle frame sizing to Sheldon Brown so I can discuss the specifics of my build.
Mike DeSalvo has had some twenty years experience in the bike building business to hone his design and manufacturing skills. This is one of the many reasons I asked him to build my bike. I figure no matter how hard I try Mike won’t let me screw up his design enough to ruin my bike. And I found it was very helpful to use BikeCad to visualize the design and the variations in the measurements he was suggesting.
One of the specifications that interested me was Mike’s selection of 410mm for the chain stay length. The CAAD9 has 405mm chain stays, as do many mass-produced bicycles. The Colnago C59 Italia in a 56cm frame size has 412mm chain stays while the Specialized Roubaix, a bike described by reviewers as an endurance bike with a comfortable ride comes in at 415mm. Mike explained that his selection of 410mm chain stays was made because he feels this length helps with smooth shifting and adds a bit of cushion to the ride characteristics. The Specialized Roubaix is designed specifically to have a more compliant and comfortable ride characteristic, so comparing its chain stay length to other bikes clarifies how this affects its ride characteristic.
Another specification that the Mike mentioned was becoming more popular in the custom industry is a lowered bottom bracket drop. This is the measured vertical distance below a line drawn between the centers of the wheel hubs to the center of the cranks. Changes to the height of the bottom bracket can adjust the frame for a rider’s longer or shorter legs and also is considered to be a means of making a more stable bike during turns since, they say, the lower the bottom bracket is the lower the center of gravity the bike will have. The height of the bottom bracket seems to generate much debate on the Internet however. I’ve read posts from builders who say the drop of the bottom bracket has no effect on the ride and posts that say changes to the center of gravity are important to bike stability. After some discussion Mike and I settled on a 75mm bottom bracket drop; this is slightly lower than the standard on production road bikes but not as low as cyclocross bicycles that usually drop around 80mm. There is a calculable finite height (See Sheldon Brown’s link to a bottom bracket drop calculator) before the drop will interfere with pedaling during turns. I think for the sake of stability and my longer than average legs, 75mm is a solid choice.
The last item that required my attention was the height of the head tube. My CAAD9 has a 155mm head tube, but to compensate for the heightened saddle for my longer legs, the handlebars are raised on about 30mm of spacers on the fork tube to lift the bars to the proper height. Instead, the DeSalvo design will have a 170mm head tube to eliminate the need for the spacers.
I’ve realized I have less anxiety about the design process now as I consider all of the steps I took to better understand the design aesthetic of my DeSalvo frame. And I’m sure it helped having Greg take my measurements using three different builder’s planning forms. I’m not kidding; I wanted to make sure there were no glaring errors in the measurements. And we took my measurements on two separate occasions because after I saw the design drawing my stomach turned thinking we measured something wrong. But the truth is, like a poorly fitted jacket, my CAAD9 has not been fitted as well as it should have been when I purchased it. I’m relatively certain the DeSalvo will fit more like a Kilgour bespoke suit and less like an off-the-rack Hugo Boss, which is the real reason for having this bike custom built. There’s nothing like a good fitting suit and nothing more fun than riding a bike that fits well.
I think we’ve come to the part of this process where sometime this week, titanium pipe will be cut, filed, bent, and brazed into a bicycle frame. Now if I could only decide which wheels to order.
Thanks for reading.