Tyre Tests Prove More M.P.G.
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Fuel Consumption Tests in Watford Area Show Advantages of Steel-cord Tyres
'CUM., consumption tests carried out last week by the Michelin Tyre Co., Ltd., showed that the fitting of Michelin " X" tyres to vehicles resulted in fuel consumption up to 14 per cent. better than that obtained with textile tyres. The ksts took place in the Watford area and considerable efforts were made by Michelin to ensure that figures obtained were completely accurate and the tests absolutely fair.
In order to show the improVement in fuel consumption with Michelin " X" tyres, three series of test runs were made using two 1960 Ford Anglia cars, two 1960 Morris LD 1-ton petrol-engined vans and two 1960 Thames Trader 5-ton oil-engined trucks. The vehicles were run in pairs, one close behind the other over a 654mile route, the commercial vehicles being fully laden. In each pair, one vehicle was fitted with textile tyres, the other with Michelin "X." For the second run, the wheels and tyres only from one vehicle were changed with those of the other and all vehicles again completed the same course. In this way each vehicle did one run with textile and one with " X" tyres.
Fuel Used Compared
This procedure was adopted so that the fuel consumption figures would not be affected by the probable varying mechanical conditions of the vehicles. In fact, in the assessment of performance, the actual fuel used by the vehicles when fitted with the "X" tyres was compared with the fuel used when textile tyres were fitted.
The results obtained showed that the improvement in fuel consumption when Michelin " X " tyres were fitted amounted to 12.25 per cent. on the Ford Anglias, 5.68 per cent, on the Morris vans and 14.14 per cent. on the Thames Traders.
There is no doubt that the results are completely truthful and accurate. Large c42 test tanks fitted to the rear of the vehicles provided the fuel supply and to obtain complete accuracy in the measurement of fuel used, the amount required to return the level of fuel in the test tank to that at the start of the run was obtained by weighing. The beam weighing machine used for this was extremely accurate.
• Tests Completely Fair
In addition to the efforts made to obtain precise fuel measurements, every precaution was taken to ensure that there could be no suggestion that the vehicles when fitted with Michelin " X " tyres had any advantage. The vehicles themselves were hired, with drivers, and every stage of the preparation of the vehicles and the measurement of fuel used was checked by R.A.C. observers, one of whom travelled in one of the vehicles on each test run.
A member of The Commercial Motor staff also acted as an observer on the tests of the Morris vans and his impressions were that the runs were of an identical nature and at no time did. the drivers attempt to spare the engines in order to obtain good fuel consumption figures. The course consisted of motorway work, country lanes, hill-climbs and town work, all of which were taken at the best possible speed.
On the changeover to " X " tyres, it appeared that the steering was lighter and that road shocks were not so heavily transmitted through the steering. They also gave the impression that there was much less resistance to roiling, although they did tend to pick up gravel or stones more easily.
While the tests were being carried out, a Press conference was held at which Mr. W. R. Good, head of the technical division of Michelin, spoke on the reasons why the fitting of "X" tyres produced fuel savings.
He said that the rolling resistance of a tyre is due to the distortion which i undergoes as it comes into contact witl the road surface. A proportion of thi energy used up in bringing about thi distortion fails to return as the tyn resumes its normal shape, but is convene( to heat and consequently wasted.
When a tyre with a number of textill plies is deflected, the rubber between thi plies is subjected to shear stress. As tls " X " tyre has only one steel-cord ply ji its casing there are no inter-ply stresses and the only heat generated is due to tfs bending of the one ply. Mr. Good aim said that because of the steel plies in the crown of the "X" tyre, a flat surface presented to the road surface, not a cum as in the case of a textile tyre. Thi results in less energy wasted at this poin also.
Details of the results of laboratory an -oad tests of a number of vehicles wen iiiven. The latter were carried out unde R.A.C. surveillance and showed improve ments of from 5 to 15 per cent. afte Michelin " X " tyres had been fitted Results were also given of improvement in fuel consumption obtained by a num ber of passenger and goods vehich operators when using "X " tyres. Fue savings of from 8.8 to 17 per cent, haNN been reported.
Laboratory Tests
Laboratory tests were said to have given results similar to those obtained or the road. To discover the rollim resistance of comparable tyres, the power required to keep a wheel rollim at a constant speed was measured, the wheel with the •test tyre being passe( against a drum at a definite and measur able load. At a speed of 47 m.p.h., i was found that an 8.25-20 l2-ply textile tyre had absorbed 3.12 b.h.p. for even ton of load imposed on it, compared witf 2.4 b.h.p. for a Michelin "X" tyre of the same size.
On a vehicle with six tyres, taking the tyre load at 1 ton 14 cwt. (the maximurr rating for this size of textile tyre), the "X" tyres would absorb 7.3 b.h.p. les! than the textiles.
An interesting comment by Mr. Good which he made when the results of the Watford tests became known, was that jr the ease of the Ford Anglias, the fue saving when taken over the normal life of a set of tyres was in fact equal to tht cost of a new set of tyres.