August 1. 1921 



THE INDIA RUBBER WORLD 



811 



Dynamic Balance and Construction of the Pneumatic Tire^ 



By William Roberts^ 



IT has always been a puzzling problem to secure perfect running 

 balance of an automobile pneumatic tire. To combine long 

 life of bearings and accuracy of operation in any machine 

 where the speed of rotation is groat, the revolving parts must be 

 in perfect balance. Lack of running balance produces not only 



Machine 

 Operations 



B- Condi tfsn 

 l.-Stock 



k-Prop*rW,dftiond 



Z- Watch Scrap 

 y PI'tt undtr Brad 

 hf Ply ttihhtd wa/ 

 daKn-'NoWnnklt' 



■ i-F,r3t '!»y slihhrd 

 half ive^ or more 

 under B*ad on SS 

 and Q D. Tints 



■C-S.S, frimiTud half 

 irm op fact ofBtad 



O-O'n and t^ shtcfied 

 iraydorrn 

 i-BtadSttt;ng 



•k-Pignf Btad 



i- Locatinq Ring 



t-Proptrief ' 

 r-iPlitt ottr Btadififchtd 



n^down 



r-6-rrirr 



— A- rn'm at proptr 



plac* and Itart 



no rayijtd tdgt 



1. -Crossing Laps 



i^~ Not lOKttr than 



IV from Stod 



i-nidtttafLop''^' 



Finishing or Cov«r«rs 

 Operotions 

 \ Ctmtnting Tot of Btod- 

 h-fivst tt dry btfort 



•6 Optraton 

 VWosfy T,rts 

 \-Paddtng 



A- At Ctnttr 



t-Polttd 



IBtrtltd- 



\)-Bt,Sttrs 



\-Wast'id 

 KBrtaktr — 



A- In Ctnttr 



B- VLap 



C- l<v airmy from Spliu 

 ^-'l66aon5ifes.Vfrom- 



k-Rolltd 



Z-Pottrrttti >iPolttr and 



Stitcher 

 C-l^'Lop-oirsotra'iSdri 



D- Tnm at Tot 



VCotvr- SrdtftdHi Tntad 



ti-Plactbtt,^ttnSpli 

 iBneifnds :cs7tx 

 Z-lfotlwitt>FollPolttr 



^■Btitt Bdgts 



5id€ Walt- 



tv Place rigtit betxrten 



i-Dont strttch -aagt 



Z.-P0II mtti Foil itolltr ) 



to Ctiafing Sfnp and! 



trim mitt} Knife held \ 



atAi'AngleandBtvwIi 



^-Rolltifht^Polltrto 



Fig. 1. Str.\ight-Side Tire Construction — Machine and 

 Hand Operations 



a vibration of the unbalanced parts but of the whole machine. 

 For instance, if a tire is not balanced it will wear unevenly and 

 therefore reduce the mileage. 



MILEAGE OF TIRE REVOLUTIONS 



The following tabic wili sliuw tlie various tire sizes with the 



number of revolutions per mile and 3,500 miles. 



Size, Circumference Revolutions Revolutions 



Inches in Inches Per Mile Per 3,500 Miles 



26 81.7140 775.38 2,713,830 



28 88. 730. 2,520,000 



30 94.2856 672. 2,352,000 



31 97.4384 650.32 2,275,120 



32 100.5712 630. 2,205,000 



33 103.7140 610.91 2,138.185 



34 106.8568 592.94 2,075,290 



35 110. 576. 2,016,000 



36 113.1428 560. 1.960,000 



37 116.2856 544.86 1,907,000 



38 119.4284 530.52 1,856,820 



39 122.5712 516.92 1,809,220 



40 125.7140 504.79 1,766,765 



41 128.8568 491.70 1,720,950 



42 132. 480. 1,680,000 



43 135.1428 468.84 1,640.940 



THE EFFECT OF UNBALANCED TIRES 



At every revolution, when the heavy side of the tire comes in 

 contact with the road, it receives more wear besides transmitting 

 vibration to the running motor. If the fly-wheel or crank of an 

 automobile engine is badly "out of true" the whole car will shake. 

 Not only are vibrations unpleasant, but they are very destructive 

 to the engine, the bearings, the chassis and the joints. Sometimes 

 a tire delivers a mileage of 15.000 miles and to all appearances is 

 in good condition except that the breaker strip is l.eginning to 

 show. That tire has through some mishap, or just plain luck, 

 been in perfect running balance. 



Some tire manufacturers have tried to balance tires by drilling 

 holes in the bead and filling them with lead, but this has not proved 

 successful for two reasons. (1) When the inner tube is inserted, 

 the weight of the valve stem throws it out again. (2) It weakens 

 the strength of the bead and eventually the tire. 



•This article may not he reprinted without permission of the author, who 

 reserves all publication rights. 



^ Cansulting productiot- and efficiency engineer. 



Running balance is a subject of constantly growing importance. 

 E.xact symmetry of form is no guaranty of running balance. 



VARIABLES IN TIRE CONSTRUCTION 



From an engineering standpoint an endeavor will be made to 

 show where some variables in tlie construction of a tire might be 

 remedied. The construction of a straight-side tire, both the 

 machine and hand operations, is illustrated in Fig. 1. In the 

 machine operation, the stock required under A calls for proper 

 width and gage. The gage of the fabric after it has been fric- 

 tioncd and skim-coated should be constant with a variation of 

 aliout .002 to .003-inch. If the gage of the stock varies, it will 

 cause either buckles or shy sidewalls in the finished tire. Opera- 

 tion 3 is the first place where one of the largest variables in the 

 construction of a tire commences ; that is obtaining the correct 

 tension of the fabric as it is applied to the core. To keep this 

 tension constant is one of the greatest difficulties for the following 

 reasons. (1) Where the stock is lapped it is much stronger and 

 requires more tension so that the sides can be stitched down 

 properly without causing wrinkles. (2) When the operator 

 cuts off the correct length, he can give it only approximately 

 the same tension that it receives when it is directly applied with 

 the machine. 



PROPER BEAD LOCATION 



A great deal of care should be taken in the next operation, 4, 

 that of setting the bead. To eliminate a great deal of trouble in 

 mashed beads and imperfect tires, a device shown in Fig. 2 may 

 be employed with a great deal of success. This tire-building 

 template is used to inspect the proper location of the bead. The 

 "present method" shown in dotted lines is crude and frequently 

 results in faulty bead location. The template-gage, however, is 

 fool-proof and cannot be twisted in use, thus insuring proper bead 

 location. It makes possible the inspection of the bead location 

 after the next ply of fabric is stitched over it, thereby avoiding 

 dislocation of the bead and an imperfect tire. 



In applying the various plies of fabric, a great deal of care 

 should be taken to distribute crossing laps so as to balance the 

 tire, and as stated under number 7, the laps are not to cross 



i-Ply 



2-Ply 



FiG. 2. G.\GING Proper Location of Beads 

 Insert — Tire-Building Template 



lower than V/i inches from the bead. The reader will now begin 

 to see variables that occur in tire building and that this particular 

 case cannot be worked out with a positive result because the 

 manufacturer relies on the operator to use his sense of judgment. 

 Some of them should certainly receive credit as their judgment is 

 sometimes really uncanny. 



