Tire Speed Rating Question

CapriRacer wrote:

Francesca Knowles wrote:
O.K...here's another poser- same subject, sort of.

Can anyone explain why Michelin Ribs, though "Q" (99 mph) rated if installed on pickups etc, are speed limited to 75 mph when installed on an RV/trailer?


See different specs at:

Ribs at Michelin Pickup page

Same tire at Michelin RV page

Thanks again...

I wonder if this is a difference in interpretation.

On the Pickup page, they don't specifically mention a maximum speed. It is only implied by the speed rating.

On the RV page, it is explicit. I wonder if Michelin feels the need to be explicit for RV's because of the fact that RV's tend to be use infrequently and tend to be loaded up pretty much all the time.

I don't see how the speed rating given at the pickup page could be more explicit- it clearly states speed rating as "Q"...which is 99mph.
The RV page effectively "derates" to 75 mph, but without calling attention to the fact that this contradicts the rating given on the tire. If assertions made from users on this site and others are any indicator, I'd bet that nine buyers out of ten are unaware of that derating when they choose these tires for a trailer.

It seems to me that it would be appropriate for Michelin to make a point of clearly notifying/warning buyers of that fact. This especially considering the emphasis given (again on the pickup page) that installers must clearly caution about derating if a customer mixes in a lower speed rated tire-?

Michelin Speed Rating Warning wrote:
When a customer requests a replacement tire with a lower speed rating than the original equipment tire, you must clearly communicate to him or her that the handling of the vehicle may be different, and that its maximum speed capability is limited to that of the lowest speed-rated tire on the vehicle.

Why no similar stern-caution-directive that the speed rating is automatically diminished to a mere ten mph above that of the lowly ST when the Rib goes on a trailer?