Tyre Size
In truth you are unlikely to notice the difference between the two unless your running a very fast pace on track. I wouldn't bother drawing any conclusions between the tyre diameter differences between a 200/55 and 190/55. There is just too much variation between tyre manufacturers when it comes to rolling circumferences etc. For example a Metzeler 200/55 will physically differ in size to a Bridgestone 200/55 and so on, let alone that of a 190/55. The point is the measurements for a 200/55 tyre from one brand may be similar to a 190/55 of another, but completely different to a 200/55 from another.