H is rated for 130mph, the stock 850 / 70 class top speed (controlled by ECU). Load factor on my S70T5 was 89. If you've upgraded the ECU, you'll have to upgrade the tires accordingly. You'll probably find the correct rating in the owner's manual...and any reputable tire retailer will have it in their database.

Here's an informative explanatory chart - http://www.tireguides.com/tip2.html

If you like to really fly around corners, higher rating such as V would be OK, especially for turbo but it will cost you more.

For the record, I just put Michelin Pilot XGT H4 on my car for $130/tire plus balancing - more comfortable and grippier than my previous sport tire (which were a CR best buy, hah! ). Michelin also catalogs Pilot XGT V4 (V-rated) tires.
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(98 S70 T5SE misc mods - mostly lighting - and red calipers) (92 940GLE)

If you are doing motocross, then get Z rating. If not, just mostly every day driveing, with "FUN" spurts, The H will be fine. Look at the Yokahamas... They are QUIET and perform just fine... And....have a 70K mileage warranty ( pro rated after 50 K).

if you have the turbo version, you need z rated tires...if non turbo, h rated will do.
regards