What is tyre graining? Who decides on F1's DRS zones? Ask Mark

Can you explain what tyre graining is and how it affects car performance? Is it different to tyre deg that we hear so much about?
Geoff Hill, Ealing

Hi Geoff. Tyre deg is just short-hand for ‘degradation’ of the tyre’s performance, i.e. how much lap time it loses as it is used. But there can be many reasons for that reduction in performance. Graining is one of those reasons. It happens when a localised part of the tyre’s contact patch is not flexible enough (because it is too cold or the compound is too hard) and so cannot sustain the loads on it and tears across the surface. This means that the contact patch is not being fully utilised because part of it is tearing. Typically as the tread wears down the graining will cure itself, as there is less leverage. Other causes of tyre deg are simple wear, blistering and heat-degradation.

Who gets to decide how many DRS zones a track has and where they are placed — and how can drivers like Fernando Alonso have them removed?
Duncan Stafford, Somerset

The FIA makes the detailed calculations but they are only ever estimations until the cars actually take to the track. If they are found to be too powerful they will be trimmed. Or in some cases if not powerful enough, they might be extended but that’s less common. If there is a safety issue they may be removed — and that was the case in Melbourne. Alonso made the point that the cars were very difficult to control there with DRS enabled and that if you went off it would be a big accident. It’s also probably true he benefited from the removal of that zone. But that doesn’t make the safety point invalid. There was general agreement that any accident there would be a big accident.

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