Quote:
Originally Posted by stickypaws
I pose my question again. BMW uses RFTs. They come on the car. I have to assume the chassis was designed with RFTs in mind. Why are they on the car?
|
BMW have used the statement "designed for run-flats" or something similar. I've come to the conclusion and from an engineering point of view, it's more like "compromised for run-flats". Nothing wrong with that in itself, as suspension and steering tuning and feel are a set of compromises anyway.
From my investigations (and experience) it is clear that the working parameters of the run-flat are to a much tighter envelope than conventional tyres. When we recall that a tyre is also a spring element in a suspension system, we have a different animal to deal with, at a basic level.
The performance is affected in a much more critical way to setting pressures, temperature, road surfaces and particularly to cambers and road crown. There seems to be issues when running on uneven surfaces where one side wall per tyre causes the 'cone effect' that takes away directional stability. Very understansdable as the tyre is not as flexible, cannot follow the road form as easily, and the slip angles are different than conventional tyres.
BMW have certainly improved things in six or so years, but are we really through the issues? That's why I suggest we could still have tyre performance in this steering debate. Why some won't find the critical areas where the envelope is pushed to the limits, others will be finding the limitations, but perhaps not thinking tyres are a part of the issue. I personally find there are similar problems for run-flats on a hydraulic assisted steering, so don't see it just as an EPS issue.
I'd love to take an F10/11 where I feel the steering slackness and try different wheel sets, including non run-flats and see how the steering changes.
HighlandPete