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If the tyres are lower profile than normal or just plain worn out, they go round more often per mile so record more 'miles' on the ododmeter, and the genuine mpg is less than you calculate. I wouldn't trust a mileage taken on the basis of one fill-up to better than 10% accuracy, when there could easily be uncertainties of 5% in the fuel and 5% in the distance (or even more). The difference in circumference between new tyres with full tread and the same ones worn out is about 3% - that's about 1 mpg 'gain' on old tyres. It's interesting to compare the vehicle analysis figures for a '69 Fastback FI auto by the Motor Industry Research Association:- Motorways at 68.1 mph 29.5 mpg (imp); 23.6 mpg (US) Main roads at 43.1 mph 34.1 mpg (imp) ; 27.3 mpg (US) Towns at 17.7 mph 26.3 mpg (imp); 21.0 mpg (US) A graph of steady speed fuel consumption (multiply by 0.8 for US mpg) has the following plotted points:- 25mph > 46 mpg (imp) / 36.8 mpg(US) 30 > 48 / 38.4 40 > 44 / 35.2 50 > 42 / 33.6 60 > 37 / 29.6 70 > 31 / 24.8 80 > 22 / 17.6 Bear in mind this is for an engine with just 5,500 miles on it at the start of the test, and an automatic one, too. They've corrected for speedo errors which were 4 to 5 mph high from 10 - 70 mph, 6mph high at 80mph and 8mph high at 90 mph. So at 40mph a journey takes twice as long as at 80mph, but costs half the fuel. Weren't we getting over 30 mpg (US) in the hills, Jim, and not much under 30 at lower altitudes in your '69 AT Square going to Parma? Dave. UK VW Type 3 & 4 Club http://www.hallvw.clara.co.uk/ ------ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org