
Questions & Answers about taiyahaba ga hiroi.
It is a compound noun made from:
- タイヤ = tire
- 幅 = width
So タイヤ幅 means tire width as a single technical-style noun. Japanese often combines nouns this way.
A less compact version is タイヤの幅, which means the same thing but is phrased more explicitly as the width of the tire.
が marks タイヤ幅 as the thing that has the property 広い.
The basic pattern is:
X が 広い = X is wide
So in this sentence, タイヤ幅 is what is being described as wide.