im looking into Yokohama H4s OR V4s, or YK520's (235/45/17)...questions are:

1. what rate are the stock tires?
2. is it REALLY neccessary that i go with V rated over H or is there that much of a difference?

FYI: i wouldnt consider myself a 'spiritied' driver.

 

I don't know what the speed rating is for the stock tires but my guess would be V.

I wouldn't even consider H rated tires unless they are for winter use only because there is a huge difference IMO between V and H. When I first got my Integra GSR in high school I would rotate the same size winter (H rated) and summer tires (V rated) onto the same wheels and the difference was very noticeable. The main difference for me was the cornering. The H rated side walls just seemed to give up in any corner taken reasonably quickly where as the V rated sidewalls held their own much better. If you go on tirerack they even recommend using at least V rated if they are not snow tires for the TL. Even if you are not a "spirited driver" you would notice the difference in handling from an H to a V rated tire. By the way, speed rating is not the speed at which the tires break apart if you touch that speed briefly but rather the speed if maintained for some period of time that the tires will break apart at.

 

+1

My stock tires are v rated Michelins. I won't go lower than a v rated tire.

 

You cant compare V & H Summer to winter ... V to V summer to winter comparison will show the same type of symptoms.

H rated is 130 MPH and V is 149 MPH ... the bigger concern is the load rating ( Max weight the tire is designed to carry )

 

1. The stock tires are W-rated (168 mph) Bridgestone EL-42s or Michelin MXM4s.

2. The difference is that V-rated tires can take constant driving at 149 mph while the H-rated tires can take a constant speed of 130 mph. The TL's top speed is between 150 and 160 mph, which is why it comes with W-rated tires.

The speed rating shouldn't make a difference for us in the US unless we are [really!] speeding or putting the car on a racetrack. However, some tire places will put a lower speed rated tire than stock on cars; others won't.

 

Remember as was said already, the v rated tires will out handle the h rated tires as well, based on many factors, speed handling capability notwithstanding.