Deflationary thoughts

Having read Diesel Car for many years and also as a fan of the BMW marque, I thought I would write to refer to the comments on run flat tyres (RFT) in the Christmas edition. I personally have had no problems with RFTs, as BMWs are so well insulated for sound, but importantly there is no mention of a plan B or how an owner would then deal with having a flat tyre after replacing all of the run flat tyres, as you suggested. It should also be noted that BMW has told me in the past that their carís suspension is designed around the RFT tyre hardness and compensates somewhat for the harder tyre, and that to introduce standard tyres will give a spongy effect, which is not what the designer intended. On a similar subject on the opposite page, I would also suggest that the 5 Series M Sport is aimed at a different market to the 1, 2, and 3 Series models and the 5 Series M Sport suspension set-up is not nearly as harsh when comparing SE versions to M Sport on the 1, 2 and 3 where, having owned a 3 Series M Sport, I would agree that the ride is harsh. Looks aside, that’s probably why nearly all second-hand 5 Series examples are M Sport variants, as the articles states.

Jon Watkins, Bracknell

I much value your comments. I don’t know how much experience you have of different tyre brands and sizes (in terms of profile and wheel diameter) on your BMWs, but more recently there seems to have been a general (I mean with regard to all marques) trend towards better ride comfort with RFTs, but not necessarily to lower road noise levels. As you say, the problem of ripping a tyre on a rock maybe, or piece of road debris, rendering the tyre beyond even run-flat use, and certainly beyond repair, is rarely addressed by the supporters of RFTs. Also, of course, if you switch from RFTs to conventional tyres, you do need a spare ñ preferably a full-sized one, if it fits in the spare tyre well, which unfortunately it often does not with larger wheel sizes. A spare wheel well is often provided, but usually only for the space savers or the more modest wheel sizes that are generally favoured on BMWs in mainland Europe.

I am aware that BMW suggest that the handling of their RFT equipped cars can be compromised by switching to conventional tyres. I have never had the opportunity to ask a BMW person whether different suspension settings, and maybe bushes, are used in Europe where RFTs are often not standard, or whether the suspension settings are different on, for example, 2 Series cars, where conventional tyres are standard on some trim levels, and RFTs on others, or when RFTs are fitted with optional larger tyres.

I’m glad that you made your point though about the 5 Series in general, and the M Sport specifically, as I do now reflect that I had no negative feelings when I last tested a 520d with run-flats. So I do take on board your point about the M Sport 5 Series, although I must confess to something of an M Sport allergy, based mainly on my hate of big alloys and low profile tyres, and how M Sports are often driven! Regards,

Doc Diesel