Tires: Speed Ratings, speed capability, transition point

Question
My Dad has a 2000 Ford Focus ZTS. One of the front tires has a bulge that is making it vibrate. Ford indicates the speed rating must be S or T.  The tires on there now are H. How important is it to have the recommended speed rating? If we replace the 2 front tires only, do we need to match the H rating on the others? Should we replace all 4 tires with the proper speed rating? The tires still have 7/32 of tread so we don't want to replace them all if we don't have to.  Thanks!

Answer
Sonny,

H rated tires are more speed capability than S or T rated tires and this is good.

It is not a good idea to mix tires of different speed ratings, especially where H rated to S or T is concerned.  This is a transition point and tires contructions in this are are completely different between the 2.

So get another H rated tire.

Hope this helps.