Show ORIGIN OE WHEEL WOBBLE FOR SCIENTISTS Vibration of f Front Axle Coupled With High Speed and Unequal Road Surface Make I Front Wheels po Do a a Shimmy The subject of or wheel wobble or shimmy which ha attracted much attention since 4 the iho he advent advent of of t bal bal- balloon balloon bal balloon loon tires lire caused a Ion len gan fand gand lively discussion at al th the recent meeting In Detroit of or the Society of or Automo Automo- Automotive the tive Engineers No Xo positive of at the problem problem problem lem seems to h have e been reached and many maw divergent reasons for tor or the cause were presented There was a sharp difference of j opinIon the between the passenger ear car engineers and those of at the tire In- In Industry In Industry many man of the tho former aC according cording to Automotive Industries beIng Inclined to saddle balloon tires for tor much of or the blame while the lire engineers pointed Out that shimmy or wheel vibration was a question for tor technical discussion oon long before the he advent of ot low pres sure low sure zure tires BOUNCE It n B B Da Day of the 1110 research divI- divI divIsIon divi division sion slon of ot the Goodyear Tiro and Rubber company compan after explaining various tests testa stated that thai axle bounce Is a resonance effect be- be between be bc between tween the thea with Jh lh th lr weights and the bodY lody springs with their loads Each front wheel Is a hammerhead that t strikes down against the lire tire and then upward against tho I springs The ThO pact impact agaInst I the he springs moves move tilt th car body When the impulses pro pro- pro bounding of the axle at- at attain at attain tam tain to a period that synchronizes with the n natural tural period of the body and lb Its It springs a resonance condItion is reached In which the action Is III very severe This action will be bo maintained as ap as long as tile the car speed peed Is ya maintained KEEP SPEED DOWN V The sate safe sane sano and and unfailing remedy tor for speed high shimmying Is to drive within the lea legal lecal speed limIt sal said l Prof Prot-n Prot n H A A A of the engineering experIment station of ot university recently re- re re recently who Is to making an e extensive invest in Into the causes caucus for tor forI I shimmying and lis 1 With the tho advent adent ot of tho tho low low- pressure low pressure tire lire and nd the th brake says the university professor sor the motor cur car has developed some new steps that were never planned for tor It The problem or Of wheel wheel front vibration Is of recent origIn It Is la confronting the the au- au automobile au automobile Industry at a time time when riding comfort and safety at high speed were supposedly assured TIre manufacturers have respond respond- responded ed to the popular demand fo for tor com coin comfort comfort fort by producing a tire suitable for tor low Inflation pressures This the lire could absorb SI a a bump the of a paving brick without a qui qui- quiver qui quiver ver r I WIlY WHY NOT ORE Every Ever effort was waa made to pro pro- provIde provide pro provide vide comfort com Cart and safety independent Independent dent of road conditions But thle refinements In themselves automatically to enforce the tho speed sped laws la When the smooth road In- In Invited in invited a 0 a burst of ot speed something seemed to seize the front wheels and to demonstrate how rapidly It could turn them from left loft to right I and then back again When when lIen we study the phenomenon phenomenon phenomenon non non of or speed high shimmying wt wo I begin to wonder why cars ha have never shimmied before The causes have always been present in Und kind I It if not In degree The fhe mechanical improvements In toe latest auto auto- automobiles automobiles automobiles mobiles have however not onlY made tho shimmying forces morl more potent potent but have ha removed much much- much Of much ot the opposition offered them by bythe bythe the earlier cars care ORIGIN OF OP The rhe origin of ot the seems seem to lie in inthe the front axle Sup Sup- Supported Supported Sup Supported ported between the tires below And the springs above the axle is 8 set ao setin l lIn In motion by every Inequality of othe tho he road surface It If one wheel strikes a Email small bump the axle be- be begins begins be begins gins to see saw up and down This Vibration Induces a peculiar mo- mo molion motion mo motion tion lion of ot the wheels 18 which chanS changes direction with every onry reversal of the axle motion mallon The Tho The action Is 1 necessarily quite rapid In a developed well shim shim- shimmy shimmy shimmy my the wheels reverse about fifteen fifteen teen times per second There seems to be be a rate however be- be beyond be beyond yond which the wheels wheel do not re- re respond respond re respond spond to the axle vibrations and when this rate Is la exceeded the cardoes car cardoes cardoes does not shimmy The frequency with which the axle vibrates vibrate le- le depends de depends upon three factors thu factors weight of the axle the air pres- pres sure Kure In the tires and and the stiffness of th the springs A heavy axle loW air pressure and soft springs all the Ih frequency y of ot vibration It la is evident evident thep theA then that hat the means intended Int nd d t to make the car safe and le may defeat feat their own purposes tI by Ty bringing the vibration rate within the range that will promote shimmying |