i recently blew a rear tire on my g37, when i bought a new one i bought the 245/40/19 94Y i noticed that the oem one is 94W , is this a concern mixing rear speed rating? since iam not downgrading the speed rating? btw the tires are exactly the same except for the different speed rating

THanks for the help

dunno if i post in the right section.

 

This won't be an issue at all.
Unless you were running your car at speeds in excess of 150 mph for long distances this is a non issue.

W has a speed rating of 168 mph
Y has a speed rating of 186 mph

 

If you'd have any issues it would be with handling. The lower sp rat tire wont respond as much as the higher. However, the effects should be minimal.

 

One thing to always keep in mind is that tires are speed tested brand new with ZERO CAMBER and 90-100% of max PSI.
Adding any negative camber changes the contact patch shape and load balance across the tire reducing the real world speed rating.

Don't count on a used W [168 mph] being safe at even 150 mph for long in hot weather with negative camber, ESPECIALLY more than -1.0 degrees.

Measure the inner tread vs outer tread temperature at even 100mph to see the situation.