Au­to­mo­tive odd­i­ties in the form of Vernier gauges, tyre conic­ity and mag­netic fuel savers re­quire Garage­man’s ex­per­tise this month

Car (South Africa) - - TECH - BY: Garage­man

In the in­ter­ests of pro­tect­ing him from un­wanted fame, stalk­ers and the pa­parazzi, CAR can­not re­veal the true iden­tity of the re­source­ful Garage­man TYRE DE­FECT

In ear­lier days, many farms were con­nected by sin­gle tele­phone lines, with the re­sult that any­body could pick up the phone and lis­ten to their neigh­bour’s con­ver­sa­tion. Each farm had a dif­fer­ent ring code con­sist­ing of a com­bi­na­tion of long and short rings so that you knew when to an­swer. In any com­mu­nity, there were al­ways one or two peo­ple who lis­tened in all the time, so that they got to know every­body’s busi­ness. We all knew who the cul­prits were and some­times used their knowl­edge to our ad­van­tage.

At present, we have an even bet­ter sys­tem called Face­book. Su­san Houghton spends hours on it ev­ery day and, since many peo­ple add a com­ment ev­ery time a dog barks, she gets to know what’s go­ing on as well as what’s com­ing off. Con­se­quently if we wanted to hear any local news, we con­tact who we called “Ra­dio Houghton”.

When Ra­dio Houghton brought her 2014 Ford Fiesta in for a service the other day, she men­tioned the steer­ing pulls to one side. Hannes per­formed the usual service and then took the car for a spin. There was a strong pull to the right so he started to look for likely causes. A dif­fer­ence be­tween front-wheel right- and left-hand tyre pres­sures is by far the most likely cause but the pres­sures were nor­mal.

Hannes put the car on a lift and ex­am­ined the suspension arms for signs of dam­age. He then checked wheel-bear­ing play and was on the point of sug­gest­ing we send the car to a wheel-align­ment spe­cial­ist when the thought oc­curred to him that it might be a tyre de­fect. He in­spected the tread on both front tyres but could not see any dif­fer­ence in the pat­tern. Even­tu­ally, he came to me and asked to phone Ra­dio Houghton to check when the pulling first started.

She replied she’d been on a trip and the mileage was right to have the tyre po­si­tions ro­tated so she took it to a tyre shop and they ro­tated the wheels cross­wise front to rear. On the way home, she no­ticed the pulling but de­cided to bring the car to us in­stead of go­ing back. I told her if she men­tioned this to us it would have saved some work and time.

Hannes heard this news with joy, swapped the front wheels left to right and went for a drive. The car now pulled to the left, con­firm­ing the sus­pi­cion that formed in his mind. He ex­am­ined the left-hand wheel tread care­fully us­ing a Vernier gauge and pro­nounced the tyre was suf­fer­ing from conic­ity. This is a man­u­fac­tur­ing de­fect which re­sults in the tread be­ing moulded-in slightly to one side of the tyre, so that it is not sym­met­ri­cal with re­spect to the con­tact patch. This causes a pull if mounted on a front wheel but not if mounted at the rear, which is why the pull started only when the wheels were ro­tated. Tyre com­pa­nies will nor­mally re­place such rub­ber and I of­fered to ne­go­ti­ate with the com­pany con­cerned.


Do you know most or­di­nary (non-sci­en­tific) pocket cal­cu­la­tors some­times give the wrong an­swer? This is be­cause they’re not pro­grammed to cal­cu­late us­ing the se­quence we’re taught at school. It’s called BODMAS and is short for the se­quence bracket, of, di­vide, mul­ti­ply, add, sub­tract. If you use any other se­quence, the an­swer may be wrong. The chil­dren in our pri­mary school know this very well. One their best-loved teach­ers has men­tioned, preached, de­claimed, shouted and whis­pered “bodmas” so of­ten he’s now known as Mr Bodmas.

Bodmas seemed friendly and in­tel­li­gent but he suf­fered from a com­mon men­tal con­di­tion: gulli­bil­ity. He tended to be­lieve things just be­cause they were writ­ten down. Re­cently, he came across an ad­vert ex­plain­ing an en­gine’s com­bus­tion can be im­proved by fit­ting a pow­er­ful mag­net around the fuel -line. This would some­how line up the fuel mol­e­cules so that they burn faster and hence more ef­fi­ciently. He bought a mag­net and fit­ted it around the fuel line.

I bumped into him at a party and he soon started to rave about the mar­vel­lous mag­net baf­fling en­gi­neers. He fit­ted it a month ago and claimed his fuel con­sump­tion has im­proved by at least 15%. I played along, pre­tend­ing to be amazed, be­cause I be­lieve the best way to deal with non­sense is to suck all the in­for­ma­tion out of the talker and then de­liver the death­blow at the end.

I asked Bodmas to bring the car to the work­shop so that we could take a look at the mag­net and mea­sure the fuel con­sump­tion sci­en­tif­i­cally. When the car ar­rived, we all crowded around it while the bon­net was slowly be­ing opened by the ex­cited teacher. Our curiosity turned to mirth when we re­alised that the beau­ti­ful red cir­cu­lar mag­net was mounted around one of the heater hoses!

How come Bodmas mea­sured an im­prove­ment in fuel con­sump­tion? It’s hu­man na­ture to drive more se­dately, obey all traf­fic reg­u­la­tions and cruise ex­actly at 100 or 120 km/h when you’re test­ing some­thing. You will in­evitably get an im­prove­ment. A month later, when your old habits re­turn, the con­sump­tion re­verts to nor­mal.

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