So what does 265/75R15 actually mean?
The ‘R15’ is the diameter of the tyre rim in inches. R15 = 15 inch rims (R stands for Radial)
The 265 is the width of the tyre in millimetres = 265mm.
The 75 is the height of the tyre from the rim to the tread, expressed as a percentage of the width.
So the height of the tyre = 75% of the 265mm width = 198mm
In Mike Reynold’s ‘Tire Work’ eBook he recommends using, for the first two courses of tyres, 235/75R16.
So now you know what that actually means!
In fact he discusses using R16’s for the first three courses and then dropping down to R15’s for the next seven courses, going from 235 R15’s (courses 4&5) to 225 R15’s (6&7), then 215 R15’s (8&9), finishing with 205 R15’s. R14 could even be used for the final course.
Obviously consistency is one of the most important factors as a uniform course of tyres is where the integrity of the monolith wall comes from. You will get quite adept at scanning tyre piles for the right size of tyre, not to mention having a strong opinion about which brands pound easier than others (Yokohamas v Bridgestones!). Sorting tyres into their sizes helps for the staging as well.