Originally Posted by
Wilfred Laurier
Did you put sealant (like slime or something) in your tube? Because, generally speaking, tubes don't come from the factory with sealant. Maybe a very lopsided tube, but even that shouldn't result in 'steering instability'.
The idea of an aerodynamic anomaly is possible. have been running 35mm wide tires on 14mm wide rims on the front of my bike, and the turbulent air going around the pronounced 'omega' shape can be felt, I am sure. However, since the original tires were only 28mm, this might be a bit of a stretch.
ANother possibility is that the particular rotating mass of that tire helped your bike find its resonant frequency, and changing to a lighter (or heavier) tire, or a smaller diameter tire (which effects the 'trail') moved the bike away from the resonant frequency. This is assuming that your 'steering instability' was similar to whatis known as 'speed wobbles'.
Regarding slime in the tire tube, they were the tubes that came with the bike. It is purely speculation on my part that the shop might have added slime to seal a leaky tube rather than replace it.
Regarding speed wobbles, it wasn't as though the steering was oscillating. It wanted to turn hard to one side or the other. This is probably an indication of an aerodynamic problem. The thing I don't understand about this is that it was a relatively small change going from 28 mm tires to 25 mm tires. I might be mistaken about the actual width of the original tires. I discarded them a long time ago. I found a pdf of a 1994 catalog online that shows the stock tire width as 28 mm.