I recently received an email from a reader asking for clarification on the complicated rules about mounting speed-rated tires that differ from the OEM specification — and I found a complicated answer.
The question is: If a customer's vehicle comes OE with H-rated tires, but the customer doesn't want to spend the money to buy another H-rated tire, what are the dealer's liabilities when replacing with lower speed-rated tires?
A couple of tire makers I contacted suggested referring to the tire fitment guide recommendations.
Michelin North America Inc. recommends that the speed rating of the replacement tire be equal to or higher than that specified on vehicle placard.
I spoke with one of Michelin's tire experts who admitted that there are dealers out there who acquiesce to consumers' requests to downgrade the speed-rated tires on their vehicles and noted that speed indexes have been evolving very rapidly on tires, much more rapidly than speed limits on the road.
Some light truck tires may be S-rated (112 mph) or even R-rated (106 mph), but he advises against replacing R-, S-, T- (118 mph) or H- (130 mph) rated tires with a lower speed-rated tire.