Tyres and their Energy ratings

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   I know talked about tyres a million times on here but I'm looking at getting a couple of new boots for my E60 to wear at the front.

245/40/R18 93Y  currently shod with Dunlop SP Sport 01 Runflats.  These type were fitted by BMW when it rolled of the production line nearly 10 years ago.

From a browse on the old t'interweb, I've learnt that tyres now have an energy rating A to G, just like the do when you buy a fridge!

This covers rolling resistance (fuel economy basically), wet braking (the important bit!) and sound.

Now wet braking is improtant to me as is quietness.  Fuel isn't, which is why I drive a V8!  For every 3dB more the tyre is, it is twice as noisy, so a tyre with a rating of 72dB is twice as noisy as a tyre with a rating of 69dB in theory!

Rolling resistance, the difference between A rating and G rating is 6 litres of fuel per 625 miles or for ease of sums 1 litre per hundred miles.

Wet braking, the difference between A rating and G rating is 18m, approx. 3m per energy rating band.

So I could buy a Dunlop SP Sport 01 Runflats for £159 which has a rolling resistance rating of E, wet braking rating of B and noise level of 69dB.

Or I could buy a Conti Sport Contact 5 for £189 which has a rolling resistance rating of C, wet braking rating of B and a noise level of 72dB.  This tyre has the best rolling resistance rating of runflats in this size

Translating all the above and throwing in the price of fuel.  I would need to drive over 7,000 miles more with the Conti than the Dunlop to achieve a saving in fuel.  In theory I wouldn't stop any better and the car would be noiser.  Probably only get 30,000 miles out of the fronts on my car anyway.  So another 7k is pie in the sky I would think.

So why should I buy the more expensive Conti?

Proves that these figures are fairly meaningless when you do some sums!