Part 6: Blueprint

April 1, 2007
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The blueprint phase of the process has got to be one of the coolest and informative of all the steps. It’s here that I found out about how all the aspects of geometry effect the bike’s handling, and also how Carl proposed to alleviate some of the concerns I have with the current bike set-up. Here’s a walkthrough of some of the important design considerations and how they pertained to my specific situation. You’re will vary based on your needs.

Here’s an image of the actual blueprint:

(click for full size image)

Bottom Bracket Height: I was told that my current bottom bracket drop (measured as a straight line from wheel dropout to wheel dropout, and then dropping a line to the center of the bottom bracket) was about 67mm. This is a normal feature of a “crit bike” as cornering clearance becomes more important than overall stability. For a road racing frame, it’s pretty normal for the drop to be around 70-80mm, but for a crit bike, closer to 65mm is the norm. Based on my emphasis on wanting to be a better descender again, Carl decided to drop me down to 80mm’s. Basically, this keeps the frame within a standard range of normalcy, but gives me the greatest amount of control over the bike. If you think about what the bottom bracket height does to the bike, the lower the BB, the lower your overall center of gravity. Additionally, as a lever in a corner, a lower BB will put your outside pedal further “out” and allow you to carve better corners. I asked Carl if this was going to be scraping my pedals in the corners, but since I only do that rarely in races, it’s not a real concern.

Saddle to Bar Drop: Basically, I’m not 20 years old anymore, and the 13CM drop from the saddle to the bars had to go. I’ve been having more and more problems with my lower back as I get older, and I wanted a bike that would last me into my mid-40’s. Carl basically decided to build me a bike with 8cm of drop which is still pretty aggressive, but not insanely so. This really dictated the head tube length along with my choice of the Chris King headset so he knows the total stack height. However, we’ll be putting in 2cm of spacers between the headset and the stem, so my starting drop will actually be 6cm. I’ll lower it if I feel it’s necessary.

Top Tube Length: Carl is putting me on a 56.5cm top tube which is longer than want I’m currently on. I was really surprised at this having stated early on that I know I’m too “stretched out.” This combined with the 10cm stem and I’m a good centimeter forward of where I am with the Wilier. Based on my body measurements, Carl basically wanted me more in front of the bike. His theory is that my weight ratio is shifted too far back and having insufficient weight over the front wheel is compromising my handling abilities. What has happened, is that either after a crash or with the acquisition of the Wilier, I positioned myself more rearward and that has resulted in a loss of overall stability. Additionally, my tendency to be lower up front actually shifts more weight over the rear wheel. Bringing the bar forward should bring me back into a more neutral and stable position. Note that Carl wants me on a 10-11cm stem. He called 9 and 12cm stems “extremes.”

Overall Saddle and Bar Position: This is really a combination of the saddle to bar drop and the top tube length discussions. Overall, my concern about being “too stretched out” is being alleviated by a combination of Carl putting me 1cm more forward, but also 5cm higher. My back will feel better, the reach is probably going to be better, and I’ll be more over the front wheel giving me that stability I’m craving.

Wheelbase: Carl’s standard for a wheelbase seems to be around 100cm (he said “right around 100 is good”). I’m going to be at 99.8cm. This gives me a good neutral bike that can still be very aggressive and quick to accelerate. There really isn’t much science to the wheelbase, but it does have an impact on the overall ride. Since the front triangle is determined by the angles of the seat tube and head tube was well as the top tube length, there isn’t much you can do to wheelbase on the front end. For the rear triangle, Carl is putting a 41.5cm chainstay on for me. This is a factor of the seat tube angle and the fact that I have a 80mm BB drop. The 41.5cm chainstays will give me decent clearance if I ever want to put 25mm tires on, and are still short enough to be very responsive.

 

It’s also useful to view a comparison of what the blueprint looks like compared to my current bike set-up. While we didn’t add all of the tubes, the orange shaded areas are the curret BB and handlebar. Note that the current BB is a bit higher than the one Carl is proposing, and the current bars are a bit rearward and much lower than Carl’s proposal as noted earlier.

(click for full size image)

What’s great about this second blueprint is that when I told Carl on the phone that I was having a hard time visualizing what the proposal looked like compared to my current set-up, he had this second picture made and e-mailed to me within minutes while we were still on the phone. (color addition is mine)

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