Originally Posted by
ThermionicScott
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.
This is absolutely it, in my opinion. When I indulged myself with a custom bike, the only difference in fit between that and the Giant TCR I'd been riding was that my centre of gravity was moved slightly forward, with a 120mm stem instead of 100 mm. The new bike handles better as a result, but I think it's the weight distribution, little or nothing to do with the steering arc.