The previous post ended with a hitch in the design for my new bike, a custom Ti touring bike from Seven Cycles.
Warning: there is going to be lots of nerdy talk about tubes and stays. Gear heads will love it, others maybe not so much.
As I mentioned in the previous post, I had ridden a demo bike which was a bit too big for me. Therefore I was sensitized, perhaps overly-sensitized, to standover height. Standover height is the height of the top tube when you are standing with both feet flat on the ground. Too high, and it is mighty uncomfortable. A low standover height is more comfortable when you are stopped. My current bike, a carbon fiber Giant TCR, has a sloping top tube, which gives a very generous standover height, so I am spoiled.
This being a custom bike, you can ask for a design that provides a lower standover height. Which I did, and Seven delivered, at a cost. The cost was two-fold (neither of which was monetary). First, it resulted in a smaller main triangle, which limited room for the water bottles, so that the 2nd bottle would have to be smaller than normal. Second, and almost as important, there would be no room for the integrated rack mounting points on the seat stays. That would require attaching the rear rack to a bracket on the seat tube, which works, but is neither as strong nor as convenient nor as elegant as the integrated mounts (or so I believed).
So I re-thought the standover issue. My current bike has a 71 cm standover height, which as I have said, is very low. The standover height called for in the design presented to me was 71.6. Hannah had measured my inseam, but I don’t have that number. I remeasured my inseam at home and got 79 cm. I realized I could easily live with a 75 cm standover height. So I called Hannah to talk about it.
It turns out that the standover height proposed by Seven before my request for a lower top tube was only 73 cm, which I could very easily live with. And, that would restore room for two full size water bottles and the rack mounting points. So on the Tuesday before Thanksgiving, I told Hannah to revert to the 73 cm standover height.
The new design came through the following Monday. (Pretty good service, especially over a holiday weekend.) It had a suitable standover height at 73.6, restored the space for two full size water bottles, and had a clean, strong design. However, there was still no room for the rack mounts on the seat stays. To get that would require a standover height of 77.9 cm, which is clearly too high for me.
I suggested to Hannah that maybe Seven could modify the design a bit by
- keeping the top tube exactly as it is in both angle and length
- extending the seat tube 3 inches or so (~80 cm),
- extending the seat stays to attach further up the seat tube
That would provide the length of seat stay I was looking for without raising the standover height. I’m not a mechanical engineer, let alone a bike designer, but it looked reasonable to me. (Hey, what could go wrong?)
Her response was music to my ears: let me put you in touch directly with the designer at Seven who is responsible for your bike. (That is what you get when you buy a custom bike.)
A few days later, I was on the phone with Liam at Seven, a delightful chap with some sort of Brit accent. He seemed almost as enthusiastic about my bike as I am. We talked about the trade-offs in my design idea, especially considering that this is a particularly high stress area on a bike, especially with a loaded rack. Not impossible, but not trivial either.
So I asked about seat collars with integrated rack mounting holes. I hadn’t known such things existed until Hannah sent me a link. (The last several racks I’ve attached to bikes were all painfully inelegant and difficult to attach and get right.) Liam was very confident that the right seat collar would work perfectly well, so that solved the standover problem.
My next concern was Toe Overlap. This is the very real, and often painful, situation where your toe hits your front wheel if you turn too sharply. Many performance bikes achieve their snappy handling with a short wheelbase, but that also makes toe overlap an issue. On the other hand, a touring bike, with its longer wheelbase, should not encounter this. In fact, that was one of the questions on the fitting survey: will you tolerate any toe overlap. So of course I said “No!”. Yet here it was on the spec sheet – Toe Overlap: Yes. Along with some blather about Estimated Front Center, whatever the hell that is.
Liam patiently and clearly explained that Estimated Front Center is the distance from the center of the bottom bracket to the center of the front wheel hub. In other words, it is the dimension that directly predicts toe overlap. So I measured the distance on my TCR – it was 58.4 cm. On the new bike it would be 61.3 cm, almost an inch longer than my current bike. And toe overlap has never been a problem on my current bike, even though technically it could happen. One more problem solved. (All this assumes the tire/wheel combination is the same size on both bikes. That is almost true – the new bike will have the same size wheels but slightly larger tires.)
I then asked Liam some questions I have wondered about since my earliest nerd cycling days in high school. Like, exactly how do they make tubes which are perfectly cylindrical on the outside, but have thicker walls near the ends and a thinner wall in the middle. These are known as double butted, and are the hallmark of many high end steel and Ti bikes. (Turns out that Seven makes their own butted tubes, and they do it by removing material from within the tube.) I can’t wait for my factory tour!
With that, I was ready to pull the trigger. On Sunday evening, I sent an email to Hannah giving her approval to commence building my bike frame. In 6 to 8 weeks, or so they promise, I will have my frame, painted yellow, with fork, stem, seat post and seat post collar. I can hardly wait!
[There will be more blog posts about the gory details, but the long story short is that the frame will then go to the Bikeway Source here in Bedford, to be built into a complete bike.]