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Old 02-25-13, 07:24 PM
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When trying to fit drop bars on a bike designed for flat bars, you generally need to make some kind of accommodation. It's easiest to figure this out if you have a bike that fits. It's also easier to get a frame designed for drop bars if that's what you want. You're not likely to find a frame that you can switch back and forth between flat bars and drop bars without a lot of compromise somewhere.

There are also some other considerations.

Your saddle position relative to the bottom bracket should be independent of seat tube angle from bike to bike. When you switch to a frame with a steeper seat tube angle, you'll need to move the saddle back farther than you would on a frame with a slacker seat tube. As a result, even though the actual top tube (and listed effective top tube length) is shorter on a frame with a steeper seat tube angle, it may not fit that way. When comparing frames, add about 1 cm to the effective top tube length for each additional degree of seat tube angle. Head tube angle has a small enough effect to be ignored for fitting purposes.

Handlebar height also has a big effect on bike fit in terms of reach. As the bars get higher, you don't need to lean as much to reach them. Or to look at it another way, if you lean the same amount, the distance from your shoulder to the bars decreases as the bars come up. When looking at frames, the head tube length, fork length and bottom bracket drop all impact the way that a given effective top tube length feels. Many companies will give you a handy figure labeled 'stack' which is the horizontal difference from the bottom bracket to the plane at the top of the head tube. A stem with lots of rise will also produce an effect like this.

So, getting back to the Karate Monkey, if you were going to use flat bars an 18" KM would probably be just about right for you. If you are going to use drop bars, even a 16" Karate Monkey will probably be a little too long.

I would suggest that if you want to use drop bars (but keep all your components), you look into something like the Disc Trucker or Soma Double Cross.
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