Run down your
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tyre costs by Tim Hoare US course for operators shows how to cut lown tyre wear and stay on the right side 4 the law YRES are round, black and made of ibber; they wear out too quickly and, ith the £100 truck tyre only just around e corner, they cost too much. These e the views of most operators but, with little knowledge and care, rapid wear id other tyre problems can be avoided id money saved.
1 recently attended a two-day tyre )preciation course organized for !hide operators and their staffs by tyre istributors, Associated Tyre lecialists. The course (between six and have been run for operators each year nee 1971) are really a spin-off from the ie-day courses ATS runs at its traing school at Aldershot for its own :ters employed at the company's 345 re fitting depots.
Training manager John Lee reckons at there is more confusion among )erators concerning plating regulaails and correct wheel fitment than iything else. The course, however, !gins with a description of the different pes, and relative advantages, of tyre onstruction.
According to tests carried out in the nited States some years ago wear rates comparable conditions between ossply, textile radial and steel radial tyres are in the ratio of I to 1.6 to 2. in other words a steel radial should wear at half the rate of a crossply tyre in identical conditions. The many more Plies required in the construction of walls of a crossply tyre provide far more rigidity than in a radial and so, unlike a radial, there is little "give" when cornering so that grip and cornering power depend far more on the tread pattern. In contrast the radial, textile or steel, has far more supple side walls.
Don't mix 'em
It is well known (at least it should be) that it is illegal to mix crossply and radials on the same axle and to have crossply tyres on the rear of the vehicle when radials are fitted to the front axle. Another point, however, is that although it is not illegal to mix textile and steel radials it is unwise to do so, particularly on a two-axle bogie. This is because of the different rolling diameters of the two types of tyre for the same nominal size. Therefore, if seven steel radials and one textile radial are fitted to the same bogie, don't be surprized if the textile, with its larger diameter wears out abnormally quickly. The effects of incorrect inflation pressures and overloading can be quite dramatic often inside the tyre rather than visibly outside. In normal circumstances with the correct pressure and load, a radial tyre will quickly reach 1750 F, because of the high internal friction and distortion forces imposed. Underinflation or overloading will increase this temperature considerably and since much of the manufacturing process is carried out at only 3000 F the effects can be imagined.
Recutting is also something which should be seriously considered — but rarely is. It can be quite easily carried out by the operator's own staff and since the equipment required costs in the region of £60 to £70 the money saved by extending tyre wear can be considerable. The secret is to not let the tyre wear down, before recutting, to less than 3mm of tread depth. This leaves plenty of tread depth to guide the cutting tool when increasing the depth by about 6 mm.
Remember also that it is illegal to recut or regroove any tyre fitted to commercial vehicles of less than 2.5 tons unladen weight. It is also illegal to re-cut tyres of less than 16 in diameter (exclud ing electric vehicle tyres, which may be re-cut whatever their diameter).
A frequent cause of excessive tyre wear is, of course, misalignment. However, wear on the front tyres does not always mean that there is an alignment fault on the front alone, Very often the cause of the trouble can be found at the rear of the vehicle. In fact a large part of the ATS course for its own fitters is concerned with diagnosing suspension faults. Worn spring shackles, particularly on tandem bogies, can cause accelerated wear on the front axles. Another obvious cause of excessive wear in this connection is a distorted or twisted chassis frame.
Down-plating
As far as plating regulations are concerned it is possible (although not encouraged by the DoE) to down-plate a vehicle. This may be possible when it is known that a particular vehicle is to run regularly below its orginal plated gross vehicle weight. The operator can then inform the DoE at the vehicle's annual test and have the weight adjusted downwards as required. The alterations would then be written onto the vehicle's new DoE plate.
Having done this the vehicle can be fitted with lighter tyre equipment. As an example, an operator hauling a light but bulky commodity may, instead of using the 1000-20 tyres with a I6-ply rating normally required for the vehicle, have 900-20 PR 12 (12-ply rating) tyres fitted. If the operator requires he can have the vehicle replated back to its original weight at the next test, provided he has the original tyre equipment refitted.
Tyre size can be changed on plated vehicles, but only if it is of equivalent carrying capacity or to a larger size and provided that the wheel is suitable and that the pressures are correct for the axle loading.
A trap which can exist for operators is that of wheel size particularly if, as has been the case in the past, a new vehicle is equipped with different size wheels front and rear. For example, many 16-tonners have been equipped with 7in rims fitted to the rear and 7.5 in rims fitted to the front. If a spare is specified then a 7in rim would normally be supplied. If the vehicle then has to have a front wheel and tyre assembly changed, then the chances are that the 7 in spare rim will be fitted making the vehicle illegal. The load on a 7in rim must not exceed 2.625 tons or 5.25 tons per axle — illegal for a 6-ton front axle. On the rear, of course, the four 7in rims are perfectly legal, having a total capacity of 10.5 tons within the 10-ton axle limit.
Identification of wheel rim dimensions is not made easy by the small marks stamped on to the wheel showing dimensions. Usually the only way of checking is by means of calipers.
Prime targets
Care should also be taken to have a close look at any vehicle known to have had a tyre replaced, especially if the work was carried out some distance from the vehicle's home depot. It is a well known fact that a "foreign" vehicle is a prime target for any old tyre that's lying around and which the tyre factor has been unable to get rid of locally.
Remember, too, that tyres may not have in them any cut or damage which exposes any body ply or which exposes 10 per cent of the section width, whichever is the greater. A tyre must not have any lump or bulge in it which is caused by partial casing failure or separation. A slight lump, however, which is caused by a properly carried out repair is permissible. Part of the ATS course consists of visit to a local transport cafe, with th trainees inspecting each vehicle in di park for tyre defects. The drivers at quite co-operative, once they realize it not a group of "men from the ministry that is so interested in their vehicle tyres. As most of the drivers are regulai they now know what to expect.
Included in this most useful course a complete set of notes, specificatior and data sheets for all makes and typt of tyre. Although ATS is a wholl owned subsidiary of Michelin the con pany lays no emphasis on this — quil the reverse in fact — and makes it clei that it is in business to sell any make tyre.
The course is free to operators an includes accommodation and meal The only cost to the operator is that g getting staff to Aldershot. Follow-up encouraged and if required the dal sheets provided during the course can t automatically updated as necessary.