The W in 91W after the size code indicates a speed rating. While these tires are proably Z rated (speeds in excess of 149MPH) in the tire size the W indicates that the tires are rated to a higher speed. W and X were added since there were no guidelines about how much over 149 Z rated tires were good for.
W indicates a top rated speed of 168MPH.
The "91" indicates load capacity per tire! You'll get about 1350lbs per tire.
Its the weight of the tire!
Where you hang the spare tire.
it is water resistant so yes you can surf with it buddy!
how much air is in the tire
It means an automobile tire if you're British.
low tire pressure in one tire
the size of the tire, the model, when it was made
it means flat tire.