4X4 PRO­FES­SOR

Why does your ve­hi­cle need shock ab­sorbers, how do they work, and when do they need to be re­placed? We went in search of an­swers.

Go! Camp & Drive - - Contents - Text Cyril Klop­per Il­lus­tra­tions Do­minic Wien­and

Long ago, when peo­ple still drove around in ox wag­ons, sus­pen­sion was not that im­por­tant. But when the in­ter­nal com­bus­tion en­gine en­abled our an­ces­tors to whizz around at 60 km/h, even de­cent dirt roads be­came a bumpy, dis­agree­able or­deal. Out of sym­pa­thy for teeth and spines, the lab coats de­signed sus­pen­sion. But sus­pen­sion on its own isn’t enough to ab­sorb jolts; it can only store the en­ergy of a jolt by bounc­ing up and down. The clever guys had to come up with a plan to keep the buck­ing of an ag­i­tated sus­pen­sion sys­tem un­der con­trol. C.L. Horock de­signed the first hy­draulic shock ab­sorber in 1901, but it only damp­ened in one di­rec­tion. Me­chan­i­cal shock ab­sorbers like Gabriel Snub­ber’s de­vice that con­tained some type of belt coiled up in­side it was also pop­u­lar, but it was Mau­rice Houdaille’s 1908 patent on which the ma­jor­ity of mod­ern shock ab­sorbers are based. Houdaille’s con­cept really took off when Henry Ford used a ver­sion of it in his 1927 Ford Model A. How do shocks work? As the name im­plies, a shock ab­sorber ab­sorbs shock. But to put it more pre­cisely, a shock ab­sorber ab­sorbs the ki­netic en­ergy stored in the springs of your ve­hi­cle’s sus­pen­sion af­ter its wheels hit un­even­ness in the road. Your car’s sus­pen­sion stores ki­netic en­ergy by means of move­ment. When a wheel bounces, the springs of the sus­pen­sion are com­pressed, but all of that en­ergy needs to be re­leased some­how. The sus­pen­sion os­cil­lates un­til all of the en­ergy is spent – this may take a while. This is all well and good, but if the wheel re­peat­edly bounces, like on a dirt road, while the spring is still busy os­cil­lat­ing, the ve­hi­cle will even­tu­ally re­bound so er­rat­i­cally that your teeth will chat­ter and you’ll lose con­trol over your ve­hi­cle. This is where the shock ab­sorber comes into play. A shock ab­sorber damp­ens the move­ment of the sus­pen­sion. This damp­ens the re­bound and short­ens the os­cil­lat­ing pe­riod by con­vert­ing a large por­tion of the ki­netic en­ergy into heat. This heat is ab­sorbed through oil in­side the shock ab­sorber. When hot and com­pressed oil comes in con­tact with air, it starts to froth and bub­ble, re­duc­ing the shock ab­sorber’s ef­fec­tive­ness. Mod­ern shock ab­sorbers there­fore con­tain ni­tro­gen that sep­a­rates reg­u­lar air from the oil and also helps to cool down the shock ab­sorber a lot faster. >

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