Originally Posted by ThermionicScott

I agree with Road Fan, especially the last line. My '91 Bianchi came to me with a 40mm (yes!) stem, and I was able to ride it for a couple of years just fine before adopting more of a stretched-out position. I now use an 80mm stem on that bike, and have just moved up to a 90mm stem on my '87 Bianchi, after using an 80mm on that one for a couple of years.

While stem length does have a slight impact on the arc of the steering range, I wouldn't be surprised if it's actually the amount of weight over the front wheel that gives people the impression that longer stems lend more stability.