Do manufacturers take economy tyre pressures into account when measuring mpg?

The accuracy, or otherwise, of manufacturers' fuel consumption figures attracts regular correspondence but my question is slightly different. We have just taken delivery of a new Vauxhall that boasts start/stop functionality to boost economy. In addition, the handbook has two sets of recommended tyre pressures: rock-hard for 'economy' and approximately 30 per cent softer for 'comfort'. Do manufacturers take these two features into account when calculating their consumption figures?

Asked on 16 March 2013 by NH, via email

Answered by Honest John

Yes. They don't calculate them. They lab test them, so everything is optimised for the conditions in which the test takes place. For example, the 'cold start' has to be at between 20C and 30C. So every manufacturer heat-soaks the cars in the lab for 24 hours at 30C to minimise the cold running.

Tags: fuel economy tyre pressures real mpg

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