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“Without heart, we would be mere machines”

 

I have a car with lots of grunt.  Fat, wide low profile tyres.  Impressive engine.  Low slung suspension.  And heavy steering that leaves me in no doubt of the weight of the metal that I am dragging around the tarmac.

I developed a rotary cuff shoulder injury about four months ago, coupled with lateral epicondylitis or tennis elbow.  Expensive weeks of physiotherapy and deep massages and anti-inflammatory drugs, along with a depressing inability to do almost anything, have helped to heal me, but it is my car, more than anything, that aggravates the injury and may even have contributed to it in the first place.

BMW have introduced run flat tyres to all their new models of car (save for the M series).  The run flat tyres cost more than ordinary tyres, do not last as long, produce a harder ride, and are much more sensitive to any small drop in pressure.  The horrible truth is that you may have allowed all your tyres to drop in pressure as seasons change, but you will not notice any difference as the tyre wall will not begin to bulge and collapse as it would on a conventional tyre.  There is no “give” in the side wall, so this is a theoretical impossibility.  Instead, what will happen is that the base of the tyre, so essential for road holding, will become concave, lifting up in the centre.  Only the outside edges of the tyre will be in contact with the road.  Eventually this will become obvious as the tyre wears at the edges but not in the centre.

 

 

Run-flats have two main advantages.  Safety (in the effect of a puncture) and weight (no need for a spare).  In the event of a puncture, you can generally continue driving to your destination at a moderate speed (no more than 50mph) without damaging the vehicle or its wheels.
See this video of a Mini with holes drilled in its runflats:
Disadvantages of the tyres are as follows:
(a) that they produce a harder ride, less forgiving of potholes (but your car’s suspension may have been set up to allow for this)
(b) that they cost more to replace
(c) that they need replacing more often, and it may well cause problems if one tyre is replaced and not others
(d) that you cannot check visually whether tyre pressure is down
(e) that the car’s mechanism for checking loss of pressure is activiated by a loss of pressure in one tyre, not all tyres, so is useful for detecting a puncture, but not more general loss of pressure throughout all tyres
(f) complaints of expensive alloy wheels cracking as they absorb the strain – and not when the runflats are being runflat either
I was told that the decision to put runflats on all BMWs was driven by the American market.
Blow-outs are very rare.  It is far more common for a tyre to be punctured and lose pressure slowly.  The first recourse is to re-inflate the tyre and see what happens.  The second port of call is the AA or the RAC. There is no possibility that I could change a tyre on my car, even if it were not fitted with runflats …
It would be rare for a British driver not to have membership of our “Fourth Emergency Service”  (my membership is a “free” additional benefit of my bank account) and my experience of the assistance of road-side recovery services is that they arrive quickly, change the tyre efficiently, and charge you nothing for their time.  It would be rare to have to wait longer than one hour, given the coverage these organisations have of our small country, and that most of us spent most of our time driving not far from centres of population.  Most of our cars nowadays are fitted with lightweight temporary spare wheels, technically illegal, but safe enough to get us to one of the many tyre dealers.  No need for a BMW dealership and no need for the pressure detection system to be re-initialised.
There is always a trade off between security and freedom, and BMW have not got it right with the run flat set up on the 320d.
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