Are centering rings really necessary? It is supposed to be to make sure that the rim is centered, but don't the lug nuts do that job?

 

yes, the lug nuts do that job, if your rims and hubs are "lugcentric" which the s2000 isn't.

 

I used to use them, but I always had problems with my Integra. The plastic ones would always melt, and the aluminum ones would always corrode stuck onto the wheel AND the hub. It was not a pretty sight.

Yes, they should be necessary, but really I've never had problems running without them. If you want to be extra anal, just torque your wheels in stages. I'll give the lug nuts more opportunity to properly centre the wheel between them.

 

Hub centric rings are for ease of mounting the wheel to the hub. The rings serve NO purpose when the lugs are torqued. The friction between the wheel and hub mounting surface keep the wheel from becoming un-centered.
Chris