I am contemplating going to a 215/45/17 Michelin A/S 3+ tire on a set of wheels I will be swapping to. I am struggling with the question of load/speed rating though. That tire is available in both an 87V rating and a 91W rating. The original spec 205/45/17 tires in that model are at an 84 (W or V) rating. The load ratings for these are as follows:

84W = 1102lbs
91W = 1356lbs
87V = 1201lbs

Obviously both of the larger size tires exceed the load rating of the original size. My quandary is around what I should get and what effect that would have? I absolutely do not track the car and it is my daily driver. I also live in Seattle where the roads are less than smooth shall we say. Right now I have a set of 205/45/17 Potenza RE960AS RFT's mounted and the ride is pretty rough for my liking. The switch to a non-RFT should result in a considerably more comfortable ride. What I don't want is to select a tire that would negate some of that comfort advantage for no real benefit.

So which tire should I go for? The 91W's are actually cheaper than the 87V's in the plus size so, if the load rating is immaterial, I would go with those. Or should I stop messing with the setup and go with the OEM size?

In case anyone is curious, the plan for the wheels is I will be mounting the tires to a set of OEM Mazda MX-5 wheels which are lighter than the JCW R112's I have now. I am having the center bore of the MX-5 wheels opened up to the Mini required 56.1mm so they should bolt right up. This assumes they clear the JCW brakes but if they don't I will throw in a small spacer.

 

The load index is just an upper limit for weight on the tire. As long as the vehicle weight is less than the load index, you're good to go.


Which Miata wheel style did you end up with?

 

Good to know. That is what I figured. I will likely end up with the 215/45's in the 91W rating as those end up being the cheapest.

The same ones you have. I actually picked up the 8mm spacers needed to mount them up without machining but I decided I wanted to see if I could get them mounted without spacers. I found a machine shop local that can open up the center bores for $50 per wheel. I am having the tires dismounted on Monday and will get them machined shortly after. Following that the new TPMS sensors go on and the new tires. Then the moment of truth to see if they clear the JCW calipers.

 

Is there a difference in tire diameter?

 

Yes, there is a minor increase in diameter going to the 215/45's over the 205/45's (~1.2%). It is common upgrade folks do though.