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JCL · #9 08-18-2006, 03:46 PM

These runflats are referred to a 4th generation by BMW. That means that the harshness, which has been an issue on early run-flats, is likely diminished even further than on the E90.

Bridgestone is the OE supplier for the 5, 6, 7, Z4, and E90, so it is probably a Bridgestone, and the shot of the pre-production model supports that.

Bridgestone isn't listing these tires on their website yet, which doesn't bode well. No-one needs one yet, but they are obviously a new product. With the Z4, no tire distributor had them in stock for some time after the vehicle was released, and the only place to get a replacement tire was from BMW, at BMW prices.

These tires don't have a support ring as is mentioned above. They rely on a stiff sidewall to support the vehicle. That is one reason for the special rim with the retaining lip on the inside. It doesn't require special mounting/demounting equipment, but it makes it more difficult to mount the tire due to the combination of very stiff low profile sidewall, and modified rim.

On the Z4, it is possible to mount regular (non-RFT) on the same design of rim, so I presume that will be possible with the E70 but it remains to be seen. Fitting non-RFTs is a common upgrade on the Z4 boards, but then with the very low profile and sport suspension that vehicle can be a little harsh anyways, and the tires don't help much. The X has the advantage of that 'road-hugging weight', to quote an old non-BMW advertisement. Without any real data, we are going to have to wait and see how early adopters like it. I just think that there is a potential risk for people not being able to buy a replacement; remember that after a flat, the tire usually needs to be replaced (at least if you have driven on it). The internal cracking that shows up is the sign that it can't be patched, even if the hole is in a safe part of the tread.

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