Originally Posted by
neo_pop_71
Hi
Sprayman,
My buddy
frantik is spot on about the twitchiness of a short stem if the frame has a long top tube. I'd like to add that if your frame has short chain stays, the shorter stays cancel out the twitchy steering. I've built a number of dirt drop conversions and all but one used a threaded headset and a tall quill stem. For the most recent build I was after the classic dirt drop feel but I wanted to do so with a more modern threadless set up. I went with an uncut threadless Soma Cross fork and a short Azonic stem to achieve the same height and reach of a Nitto Dirt Drop quill stem. The 1990 Nishiki Ariel frame I went with was perfect for the task because the virtual chains stays are very short. So, even though I have a stubby stem, I have no twitchiness in the steering. Going on the idea of shorter chain stays, I would for a late 80's to early 90's frame and avoid the early to mid-80's ATB/MTN frames that will have long chain stays and slack geometry. Compare the difference in distance behind the seat tube to the tire on the 1982 Stumpjumper I picked up awhile back with the 1990 Ariel I used on my dirt drop conversion... the gap is almost twice the size. All these characteristics combined are going to have a major impact on the steering and handling of the bike.
Many older mountain bikes have slack headtube angles, 70 degrees or even less. I don't see how you are going to get to 'twitchy' on these as opposed to a road bike with a 73 or 74 degree headtube. My Schwinn High Plains has a 70 degree headtube and even with a short, upright stem the thing steers like a truck. Unless you are using real short reach drop bars, your hands on drop bar hoods or in the drops will be at or beyond where they would have been with a stock stem and flat bars. It's the length of the reach on the bars plus the stem that matter. With my next conversion, I am looking for a bike with a 52 or 54 cm top tube. I have lots of choices for raising the seat and the bars.