Goodyear Wingfoot teams with Aussie Lightfoots
Helen and John Taylor, an Australian couple who have made a speciality of setting records for low fuel consumption in the USA, have done it again.
Converting their miles per American gallon to litres per hundred kilometres yields an astonishing 4.155 litres /100 km in their 2009 Volkswagen Jetta diesel.
This time they were riding on Goodyear Fuel Max tyres, and improved on their 2008 figure by a further 15.4%!
This consumption is more fuel-efficient than the most popular hybrid, and shows what can be done with modern diesel technology, careful preparation and fuel saving driving techniques.
Follow this link to learn more.
So how do they do it? Tyres obviously play a part, since Goodyear sponsored their 9000 mile circuit of the States. We are constantly told to maintain high air pressures if fuel savings are desired, but what are the limits? A tyre usually absorbs around 2 KW just rolling around under load at 120 km/h.
The safe maximum pressure of a tyre is shown on the sidewall, and for a passenger tyre is in the 36 (Standard Load)- 42 (Extra Load) p.s.i. range. It will not burst at 43 p.s.i., but a maximum is specified to maintain a margin of safety for tyre abuse such as potholes and rough edges. So economy drivers go to the limit, or beyond. A tyre with 15 p.s.i. pressure pulls nearly twice the rolling resistance as the same tyre at 33 p.s.i. at 120 km/h, the higher pressure giving a fuel consumption improvement of about 4%. Steel belt radials have the lowest rolling resistance, too.
Staying with tyre design, a narrow tread width, shallow tread pattern, and a rounded tread arc radius all contribute to lower rolling resistance, and with specially compounded tread rubber it is possible to design a tyre to maximise the reduction in a tyre’s contribution to fuel consumption.
Preparation of the vehicle using low friction lubricants, a well run-in engine, diesel fuel designed to give “more bang for the buck”, and other tricks of the trade are also used, such as refuelling at low ambient temperatures, like the middle of the night.
But driver’s skills are required to get good figures. Feather-footing, low top speeds, shift points carefully calibrated, travelling when wind speeds are low, smooth car surface with no unnecessary projections, climbing hills carefully (just making it over the top), and no air-conditioning are techniques used. Depending on the rules of the contest, in most cases coasting downhill, and drafting, is prohibited. In certified fuel economy runs conducted in Australia, an independent observer travels in the car to prevent this.
Want to know more on the tyre angle? In our All About Tyres section you will find Green Tyres are Black, David’s ten tyre tips, and Exploding Cylinders which will expand on rolling resistance and fuel consumption.