This is just a quick guide to what the numbers and letters stand for,

it's not a full explanation but covers most of the tyres I sell on eBay.

I have kept this as basic as possible so as not to confuse people,

205  40  17  ZR  (84W) 

The first part *205* is the width of the tyre.

The higher the number the wider the tyre, they range from 165 ( Old Fiesta ) to 265 ( Porsche )  

The second part *40* is the profile of the tyre.

Profile is the hight of the sidewall or when your car is parked or the distance between the road and the bottom edge of the wheel, a standard profile is 80 (  Old Fiesta ) and anything less than 80 ( 35 Porsche ) is classed as low profile.  

The third part *17* is the size of the wheel in Inches.

Most cars have between 13" ( Old Fiesta ) and 18" ( Porsche )  wheels, the higher the number the bigger the wheels

The fourth part *ZR* is the speed rating.

The Z means the tyre can be used at speeds over 150mph and the R means Radial ( most car tyres used today are Radial) , speed ratings range from TR ( 118 mph ) to YR ( 186 mph ) .

The last part *(84W)* is the load index and true speed rating.

The 84 is the load index and they range from 80 to 100 , an 80 would be suitable for a small light car and a 100 would be suitable for a big heavy car. the W ( 168 mph ) is the maximum speed the tyre can be used at. The reason for this letter is that Z means over 150mph but has no maximum speed, the W or Y is the true Maximum speed.