Originally Posted by
barnabaas
So what's the difference between outside width of a wheel and inside width? My understanding is the outside width would allow you to run a wider tire - but depending on the inside width that would either make the tire bulge out more or less? Can someone explain how those two relate to each other??
Inside (inner) rim width is what matters in terms of how wide a tire can safely be fitted and how wide any given tire will be stretched.
Outside width is really only a concern for aerodynamics and fitting brakes.
Conventional wisdom states that a wide tire on a narrow inside width rim will push the tire into a light bulb shape. This is can lead to the tire folding over in turns and unpredictable or unsafe handling. The graphic below illustrates the idea.
Some claim to have felt this behavior. I'm not saying they didn't but wonder if they are using very wide tires on very narrow wheels at low pressures. I have not noticed anything like this with 13.2 mm inside width Wabi Sub 15's and 25 mm Vittoria Rubino tires at 90 PSI.