What may cause a tire that is worn on both outside shoulders?

Worn tires on both outside shoulders are often indicative of underinflation. When a tire is underinflated, it cannot maintain its proper shape and pressure while in contact with the road. This causes more of the tire's surface area to make contact with the pavement, particularly at the outer edges of the tire. As a result, the outside shoulders experience increased wear compared to the center of the tread, which leads to the uneven wear pattern observed.

In contrast, overinflation typically leads to accelerated wear in the center of the tire tread rather than the shoulders, as the increased pressure causes the tire to bulge and reduce contact at the outer edges. Positive caster and positive camber can affect tire wear as well but would not specifically result in wear patterns on both outside shoulders. Caster influences stability and steering, while camber affects how tires sit relative to the road surface, impacting even wear across the tread rather than concentrating wear on the outside shoulders.