At Interbike, I spoke with Mark in the Salsa booth, since we sell Salsa bikes and components at the shop. And we started talking about the Salsa Size-O-Matic II stem measuring tool kit. The Size-O-Matic II is an adjustable stem tool that you can use for determining a stem length and angle that feels most comfortable for your specific riding position.
To use the Size-O-Matic II, you attach it to your 1 1/8-inch steerer tube on your fork or to a provided 1-inch adapter, which fits in your traditional 1-inch head tube. It comes with shims (inserts of varying widths), so you can attach your current handle bars of 25.4, or 26.0, or 31.8 clamping diameter. By moving the stem fore and aft (back and forth) and incrementally tilting it up and down, you can better determine the length and angle of a handle bar stem that works for you.
For example, some customers with new race bikes are transitioning their older steel race bikes into commuter bikes. For that riding application, they want their handlebars raised higher, and they want to sit up a bit more, so they don't have their heads down in traffic. Other customers feel crunched up in the cockpits of their bikes, and they want a longer stem with a steeper angle, so they can effectively reduce their drag and comfortably stretch out while riding. The Size-O-Matic can give you a better idea of what a change to your current stem's length and angle might mean in terms of performance and comfort.
(FYI: Do not put the Size-O-Matic II on your bike and take a ride; let me say that again, in case I wasn't clear. Don't ride with it. The tool is marked in white print clearly to this effect for those who can't help but think, "Sweet. I am going to put this baby on my bike; take a ride, and really dial in my stem measurements." Remember: It is measuring tool only, not a proper and safe stem.)
First photo by Wheelgirl at Interbike, Vegas 2007. Second photo lifted from the web.
