Super Singles Promise Doubled Mileage
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Bulmer's Experieno with Goodyears on a Foden-York Outfit
SEVERAL references have been made from time to time in the pages of this journal to applications of Goodyear Super Single low-profile tyres, but so far these have mainly been with regard to rigid vehicles. Considerable interest has, however, been aroused by these tyres among operators of articulated vehicles, and one of the earliest users of Super Singles on a semi-trailer was the cider firm of H. P. Bulmer and Co. Ltd., Hereford.
.Bulmer's have been operating a York-Boalloy tandemaxle semi-trailer van for about nine months (at the time of writing), equipped with 18-19-5 (16-ply) Super Singles, and over this period the semi-trailer has covered a little more than 39,000 miles, with every indication that the tyre life is going to be double that of the 9-00-20 (12-ply) conventional twinned tyres normally used on this type of
vehicle, An extremely important saving in weight has resulted from the use of this Goodyear equipment also, this being no less than 5 cwt. in the case of the semi-trailer alone. When I visited Bulmer's transport department at the beginning of June. a Foden tractive unit with Super Single tyres at the driving axle had just been delivered for use in conjunction with the van semi-trailer, and the weight saving in the case of the Foden was 2-5 cwt., giving an overall weight reduction for the complete outfit of 7-5 cwt., the unladen weight of the outfit with six Super Single tyres and two conventional 9-00-20 (12-ply) tyres totalling 9 tons 17-5 cwt, While I was at Bulmer's I watched a Goodyear engineer measure the tread depth remaining on three of the Super Single tyres of the semi-trailer bogie. When new the tread depth was 0.625 in., and in the case of one tyre (after 39,000 miles, remember) there was 0-344 in. of tread left, whilst the other two tyres had 0-44 in. of tread left: the fourth tyre was not measured as this had only been put into service recently, following the puncturing of the original tyre. However, taking the three measurable tyres, the average wear was only 35 per cent of the available tread depth, indicating that a clear 100,000 miles should be obtainable before the tyres have to be removed. Mr. Terry Goldrick, Bulmer's deputy transport manager, told me that the average mileage obtained from twin 9-00-20 (12-ply) on equivalent vehicles was 50,000 to 55,000, from which it is fair to assume that the Super Single life is going to be twice that of twinned tyres in this particular application, which involves trunk operation over reasonably well-surfaced main roads.
These, then, are the two main advantages of the use of such equipment over conventional tyres—reduced weight and longer life. There are, however, other less obvious advantages. For one thing, the Super Single tyre, by virtue of its construction, has a lower "spring rate" than a conventional tyre, thus the low-profile tyre contributes towards a better ride. Referring to actual figures, a Super Single tyre deflects tin, when subjected to a vertical loading of 6,600 lb., whereas to obtain the equivalent deflection with twin 9.00-20 tyres the loading has to be 10,000 lb. This arises partly from the fact that, for the same loads, a Super Single has to be inflated to only 75 p.s.i., whereas twin 9-00s require a pressure of 85/90 p.s.i. Another advantage is that a Super Single tyre is appreciably narrower than the twinned tyres it replaces, and this results in more of the brake drum being exposed to the air stream, with subsequent likelihood of fade resistance being improved.
Goodyear claim also that the rolling resistance of these low-profile tyres is less than that of twins, so fuel consumption should be improved. 1 have had no means of verifying this, however, as Bulmer's do not take individual fuel records, but Mr. Goldrick told me that his overall records would have shown up any significant change in fuelconsumption rate in the case of his semi-trailer with Super Single tyres, and as no such change has occurred, it can be assumed that the tyres are neither wasting nor saving fuel to any marked degree. Were there several SuperSingled vehicles in the fleet, a clearer picture would probably arise.
Another change occasioned by replacement of conventional tyres by tow-profiles concerns frame height. When 18-19-5 equipment is used in place of 9.00-20 twins the vehicle height is increased by about 0.5 in., which is hardly of consequence. However, a number of operators of articulated vehicles—and particularly tankers—fit single 14.00-20 tyres on the driving and semi-trailer axles, and when Super Singles replace these a height reduction of 2.25 in. or so takes place, whilst there is still a weight saving of more than 1 cwt. in the case of a tractive unit and tandem-axle semi-trailer.
So far as the Bultner's artic is concerned, the outfit is used on regular, runs between Hereford and London, the journey time in each direction being approximately 5 hr. 30 min. The vehicles used on this service gross 24 tons on the way up to London and between 16 and 17 tons on the return journey, and each semi-trailer makes one journey a day, .although the tractive units do two. The Foden tractive unit is the only one in the fleet to have Super Singles on the driving axle, and the 16-ply equipment at present fitted is not exactly correct for this application in that each tyre has a nominal load rating of 4 tons 0-5 cwt. and therefore is going to be slightly overloaded if the total driving-axle load is 9 tons. Thus, ideally, 18-ply Super Singles should be used, each of which would have a rating of 4 tons 10 cwt., but as these tubeless tyres are of nylon construction, the comparatively small overload is not important. Another factor concerning driving-wheel applications is that within the next three months Super Singles designed specially for such use will be made available: these will have a tread depth of 0.875 in. instead of the present 0.625 in.
The Super Single tyres on the Bulmer semi-trailer were fitted as conversions, and in such circumstances the cost to the operator is about 5 per cent greater than the cost of two 9.00-20 tyre assemblies, the wheels •being included in both cases. When it comes to supplying these low profile tyres as original equipment, Goodyear are reluctant to discuss cost. As the tyres and rims are at present being imported from the U.S.A., they carry a 27-5 per cent import
duty, and additional expense stems from the need to weld English-type centres into the American rims. This cost problem should be ameliorated within the next 12 months, however, as it is planned that Super Singles will be made in the U.K. before the beginning of 1965.
So far Mr. Goldrick is well satisfied with Goodyear Super Single tyres, and the only trouble he has experienced has been two punctures, each of which—fortunately occurred near a Bulmer's depot. The first tyre to be damaged was returned to Goodyear's Wolverhampton plant for repair, but the second was repaired by Bulmer's
themselves, using the normal tubeless-tyre plugging method. This question of punctures does raise the point of the diffi
culty of man-handling an 18-19-5 Super Single tyre and the wheel, the total weight of which is 281 lb. At present Goodyear make arrangements with their customers for replacement Super Singles to be made available in different parts of the country where vehicles equipped with them are likely to be operated, but eventually, of course, operators or manufacturers will have to effect structural arrangements on their vehicles to make it as simple as possible for a damaged Super Single to be carried: it is not necessary to have a spare Super Single on a vehicle, as a conventional tyre can take twice its normal capacity in an emergency for a short distance at low speeds.
Bulmer's drivers who have handled the semi-trailer fitted with Super Singles have commented favourably upon its handling when compared with semi-trailers equipped with twins. I drove the new Foden outfit with Super Singles at the driving and semi-trailer axles, and immediately
afterwards drove a conventionally tyred Foden outfit: it was difficult to detect any substantial difference in the general standard of ride and handling, but there was no doubt that the Super Singles gave a less harsh cab ride over small bumps as a result of their ability to absorb
high-frequency shocks, J.F.M.