Wheel / Tire advice on 19" rim replacing bad run flat

[Starman]

I have the 19' rims on my 35i (m sport adaptive suspension) and I bought it with Potenza 255/30 Run flats. I was actually shocked when I bought this thing that it had 30 series tires, I knew there would be a problem and now I have a rear passenger flat. I've never had run flat tires before.

Its too bad since these have a good 50% of their life yet (all front and rear matching).

If I need a new tire I need advice.

Im just not going to spend the money on new fronts and that drives me crazy since I obviously would prefer all tires to have the same rubber. But Ill replace the rear tires especially since with RWD the rear tires should matter the most.

I would much prefer to not go with run flats, this is garage car for me. If I bought normal tires probably in the ZR range for the rear, how bad is that going to be with front run flats.

The next obvious thing is replacing the 30 series tire with maybe a 40? Has anyone done this and not had any rubbing issues with these larger 19 inch rims?

Any advice would be appreciated. Tire brands? Its been a decade since I had a sports car like this and Im not up with all the modern info.

 

[jamie_z4]

I'd either go 265/30 or 255/35 to avoid issues with speedos and such, those sizes will under read slightly but negligablly, also wont look too baloony in comparison to the front.

 

[Starman]

I'd either go 265/30 or 255/35 to avoid issues with speedos and such, those sizes will under read slightly but negligablly, also wont look too baloony in comparison to the front.

Ive noticed that with my current setup of 19" 255/30's that my speedo is already reporting 5 mph slower at speeds of 60 mph. Meaning, when the speedo says I'm going 60, things like gps or street side police speed meters are telling me that Im going 55 (constantly)

 

[jamie_z4]

 

[Starman]

Well, not much advice came down so I'll update what I ended up doing for people in the future.

I replaced all the Bridgestone run flats with regular Michelin Pilot Sport 4S tires with the same factory specs (255/30 rear 19' and 225/35 front 19@). I went to 3 major tire vendors (Cosco, Les Shwab and Discount (American) Tires and none would install a 255/35 for me. Without a doubt I can tell you that it took 3 seconds of driving to tell the difference. I no longer feel like my back is breaking when I hit even the smallest of rough roads (it would actually pound the ground), the Z4 travels perfectly on rough road and handles absolutely better with the steering coming alive. It now feels like I'm in my old Honda S2000's. The braking even felt a hell of a lot better, I no longer had the feeling of it being squirrelly when at higher speeds breaking hard. The overall change is actually shocking to me.

 

[sw4nny]

The bridgestone runflats are shocking,at least they were a few years ago as i swopped to non rf a while back.
Your findings are of no surprise to me :driving:
I have just got refurbed wheels now with pirelli p zero run flats i will see how these go after a good few miles of testing as i have heard the run flats have been much improved over the years and i would prefer the run flats if the drive is not compromised.

 

[sars]

If I’d seen your post earlier my recommendation would have been the Michelin PS4 or the PS4S, great tyres. The PS4’s are marginally more comfort oriented than the PS4S’s

Interesting that the tyre fitters in your area won’t go away from OE tyre sizes, perhaps the US litigation culture means it’s not worth the risk for most, though seeing some of the wheels put on some cars over there, someone is clearly doing it :lol:

 

[Starman]

Interesting that the tyre fitters in your area won’t go away from OE tire sizes, perhaps the US litigation culture means it’s not worth the risk for most, though seeing some of the wheels put on some cars over there, someone is clearly doing it :lol:

Absolutely hit the nail on the head, its litigation. Another example, once they pulled my tire off and saw that the run flat was also comprised, they wouldn't even put it back on, I had to leave the car in the shop over night for them to get the new tires in.