CARE OF TIRES

Evening Post, Volume CVII, Issue 26, 31 January 1924, Page 15

CARE OF TIRES

The modern type of cord tire, the distinguishing feature of which is its straight thread construction, has almost entirely supplanted the tire with a casing of canvas or interwoven threads, Extended use proves that this has resulted in the production of a tire which is much better. able .to, withstand additional bending or flexing, and thus not only permits the use of the reduced inflation pressures wliich'are now current, but also' gives increased** resistance to damage by impact: blows, writes "The Motor.'',. ■■'■. , . ; ■ These ' attributes of the cord tire casing have caused the wear-resisting capacity of the rubber tread tc- be now of relatively greater importance to the user than hitherto, and it is becoming increasingly apparent that (leaving accidental damage out of the question) the limiting factor of cord tire performance to-day is not inability of the casing to resist the demands made upon it, but is more often determined by trie amount of wear obtainable from the rubber tread. : The evidence shown by the many experiences detailed in the correspondence columns of the technical Press clearly indicates that, in at least the- betterknown makes of cord tire, the tread rubber,is of a quality capable, of giving extraordinarily long mileages. On the other hand, it is manifest that there is an appreciable number of users whose experience of tvead wear, even with firstclass makes of tire, embodying a rubber tread presumably of the very best quality for the purpose, is not so fortunate in : obtaining satisfactory mileages on account of premature wearing out of the "actual tread.1 It is apparent that, contrary to popular yiews as to what should happen, excessive tread wear is more often produced by ,the smaller types o£ cat —especially two-seaters of the 10 h.p. to 12 h.p. class—and it is of interest to examine the reasons for this circumstance. The ideal condition producing minimum wear is»that the tread of the tire should have merely a rolling action upon the surface of the Toad, but in practice this cannot be obtained. There is always some very slight "slipping" action in the case of driving wheels (otherwise tire .treads would not wear out at all), but it is quite evident that all good makes of tires have treads which enable them easily to take carp of this normal factor and give long mileages. - '■ ■ . CAUSES OF PREMATURE' WEAR Premature and excessive wear is clearly a measure of some corresponding excessive increase o£ friction between tire and road, produced by abnormal wheelspin or slip of some nature, and, indeed, it will be-apparent that.no other cause is possible-. Examination of the conditions affecting the use of the modern"' small car in dicales'. that'- th ey have a. much.;gr.cater; tendency: tp produce, ex-1 cessive wheel-spin or slip than the liivgev and heavier types, and in connection with this one of the most iin- j portant factors is that :of the compava- ! tively small ear weight, relative to the power and efficiency of/ tho, engine; /.Experiment's conducted upon a typical aridr-populuT 11.9; h.p. two-seater model show-Wihat•'. the lignt weight- upon tho rear axle and the'Vample power,-avail-able ■ provide conditions in. -which at starting and during • acceleration wheel spin can be very easily; produced. Anyone can make this test by accelerating rather strongly on a smooth piece of road—and the black tire marks or tracks which are occasionally noted on tarred macadam are - often produced by this meaiis.' This is proof of excessive slip, leading to prematuro wearing out of the rulibed tread, although,, of course, the absence of such marks does not necessarily, indicate, absence oE heel-slip, as it is largely a matter of degree. Most users ot light cars have noted that their cars seem to run much better when heavily loaded—say, by carrying an extra passenger, or a considerable weight of luggage. This , improvement is almost entirely due to the fact that the increased weight gives better tire i'.dhesion and means that wheel-spin is practically absent. v Apart from spin i during acceleration, another important : effect of light weight is the tendency ;of the rear wheels to leave the ground, especially, when lightly loaded and run- , ning at speed over uneven roads, and it lis a familiar idea that light cars do I not. as a class, "hold the' road" so well as the heavier and larger cars. When the wheels leave the ground in ' this way they are instantly speeded up by the engine, and considerable slip, tnkes place when they again touch the 'road before they aro fully retarded to tho car speed. Here, again, tho better : road-hold ing capacity experienced by the addition of a further load checks this tendency in proportion- to tho weight added—and the wear of tires is reduced by their more uniform and nor- , mal progression. ; EFFECTS OF CARELESS DRIVING. I The next factor is that of driving ! methods. Inexpert handling of throt- ! tie, clutch, and brakes, together with running">at a higher speed than the road condition warrants, all tend to produce additional excessive wheel-spin and consequent tiro wear. Many drivers are quita unaware of their ability to do this, and it often explains why one driver never gels good tire wear,- whereas another, under the same conditions, obtains quito satisfactory • results. There is also another factor, ■Which, while not normally of great relative importance, may become so under certain conditions. This factor is that of the tread pattern of the tire being used. \ Some patterns, especially those not broj ken transversely, are easier to slip than j others in fore and aft direction. This {leads to excessive wear, Although tho ! pattern may be quite effective against side-slip. ' Nevertheless, if properly handled, and the causes of excessive wear are understood/they will, as a rule, give excellent service from tho point of view of tread wear. To sum ufi^. —(1) With the modern small car, by reason of the light axle weight and its comparatively high power, wheel-spin is easily produced by | unnecessarily rapid acceleration, and j this is a condition responsible for tiro I wear. : (2) For lbs same reason excessive wear may bo caused by wheel-spin due to the rear wheels leaving the ground when runnine; over uneven roads. (3) Additional weight or differences between the distribution of weieht on different cars, by increasing 'aclhesiop, have'si marked-effect in reduction of tread wear. (4) In all t«vi<. liiii especially curs ot li^ht weight. Hip matter of wear can be largely controlled by the driver, whon lu ceali-ies bow easy it. is for liim to produce ""heel-spin, aijd its effect when i VTmhicetl. . ' (51 Apui't from tlicsc factors, diffeil--j nicus in tire trend dcFtgti intiy niutcririlIly afffct the easr \vitli winch wliecl-'spm |cau bo produced under cei'tiiiu eemdi-

tions, and, therefore, the rate of -\vear in some gatterns may be more rapid. (6) In cases of excessive wear, wheel alignment is always important. It should be carefully checked and corrected by a competent engineer. (7) The sum total of all these factors may easily produce wide differences in the rate ."of tire wear experienced by different drivers, different cars, and different road .conditions. If unduly rapid wear is present, the point as to which factor is being unduly stressed is worth examination before blaming either cars or tires. „