I bought some new tubes last year - I think that they were michelin tubes - but I haven't put
them on yet (was waiting for the new tires) so I'm not sure 'bout the valve stem length.
I do know that these wheels pose a challenge in this area, and I asked the guys at Max
BMW about it. They weren't 100% confident, but these are now the only brand of tubes they sell...
I'll check them out and get back to you on this thread with a measurement.