BMW 330i: Run-Flat Tires

In a nutshell, the RFTs on our 330i are not that brutal. The ride falls within the realm of what one might expect from an enthusiast-oriented German performance sedan with an advertised Sport suspension. Two "howevers" deserve mention:

(1) Our car has the optional 18-inch tires -the ones that come with the sport package. They are Bridgestone Potenza RE 050A summer (aka performance) tires. By almost all accounts on the boards, the 18" RE050A summer tires are the ones to get. It is the owners with 17" Bridgestone Turanza all-season run-flats who are complaining loudest of compressed vertebrae (joke). Because Germans don't use all-season tires back home, methinks the suspension was optimized to the 18" summer run-flats in this case. By no means do I mean that all-season tires generally ride worse than summer tires, because they usually don't. Handling and steering, well, yeah, usually.

(2) If I pay attention, the signature lack of "envelopment" that goes along with the mega-stiff RFT sidewalls is here. On our 330i, certain sharp pavement edges, such as bridge joins, asphalt lifted by tree roots, and the nastier sections of segmented LA freeway, hit a bit hard and sometimes ping. But our RE050A tires generally roll over asphalt without bringing too much of the surface texture inside.

In order to confirm this, I'm planning to do a back to back drive with another 330i that has had its RFTs replaced. Look for another blog in a week or two.

On a related note, our 2006 330i does have a ABS sensor-based Flat Tire Monitor. In fact, all BMWs that came from the factory with RFTs have such a monitor, necessary because RFTs don't look under inflated even if they dangerously are.

But you wouldn't know it unless; (a) you read a specific page in the manual, or; (b) you experienced a flat tire and saw the above warning. This outmoded system, not compliant with the new US FMVSS 138 regulation (that's Federal Motor Vehicle Safety Standards if you're curious - or even if you're not) has no "bulb check" function to illuminate the warning lamp briefly when you start the car, as not shown below...

If you start the engine and flick the multifunction switch up before you put the car in gear and start driving, you'll happen upon the initialization screen shown at the top of this blog. However, if you flick the switch once you've started moving, this screen is missing from the cycle. So if you never have a low tire on your 330i, and you never peruse this screen just after start-up, you may never know you have a low tire monitor.

New FMVSS 138 compliant systems, such as the direct measurement Tire Pressure Moinitor system found in the 2007 335i coupe, are required to have a three second bulb check of the dashboard warning lamp upon engine start. 

Dan Edmunds, Director of Vehicle Testing  @ 23,710 miles