Imperial All Season Driver is a allround tyre made in total of 134 sizes, ranging from R13 to R13 - this particular dimension is R19, which means it fits to a 19 inch/482.6mm diameter wheel. 245/40 R19 is 100mm wider than the narrowest dimension (145) and -30mm narrower than the widest one (215). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (245mm), which results in 98mm sidewall height. In 245/40 R19, there is only one possible speed index for Imperial All Season Driver - "Y", which is good for speeds up to 300 km/h.