Archive for June, 2007

Tyres Hang Around – PostScript

Sure old tyres are difficult to get rid of.

Those who read the article titled “Tyres Hang Around” are aware of the experiment that took place off the Florida coastline, where 700,000 tyres were dumped into the ocean to create an artificial reef. Well, it didn’t work, as Victorian authorities discovered to their cost with a similar trial at Geelong harbour.

But the Americans have seen the error of their ways, and are doing something about it. They sent down a team of military divers to return the tyres to the surface, for disposal by incineration. They only have 698,800 tyres to go! Seems getting them back is not quite as easy as dumping them overboard.

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June 20, 2007 at 9:00 am Leave a comment

V8 Supercars at Eastern Creek

Eastern Creek 1

CarbonBlack’s founder and Managing Director Jodi Stanton and Sunrise Sports Anchor Mark Beretta in the pits at the V8 Supercar race at Eastern Creek.

Jodi Stanton & Mark Beretta

Mark Skaife and a fan after a successful race on Monday

Mark Skaife and a fan

CarbonBlack’s Leisa Emberson and Jodi Stanton learn from the V8 expert Brian Lawrence of Stone Brothers Racing.

Leisa Brian Jodi

Channel 7

Channel 7

June 12, 2007 at 9:46 am Leave a comment

Stretch Limos

Makes you feel envious as they glide by, does it? It shouldn’t- just console yourself that they wear out their front tyres much faster then the long wheel base Fairlane or Mercedes that they were derived from.

You see, a car turns in a circle round an imaginary point some distance out from the side of the car. The rear wheels track following the fronts, the outer wheel on the circle travelling further than the inside wheel. The differential takes care of the difference. The front wheels behave differently. The inside front wheel turns in a tighter circle than the outside, because it is closer to the imaginary point, the “centre’ of the turn. The angle of the outer wheel is not as acute, because it travels in a wider circle. It’s 2 metres or so further away because of the width of the vehicle.

Now when the vehicle modifiers stitch in another two metres or so of bodywork, and a longer tailshaft and underpinnings, the relationship of the front wheels to this imaginary point is affected. The front wheel angles no longer match the designer’s intentions, and so the tyres “scrub” in ways that were never intended. They wear out fast.

This is why your front end mechanic doing an alignment checks the “toe out on turns” at full lock, to check that nothing has been bent. The steer angles of inside and outside are different at full lock.

limos and tyres

If you wish to see the differing angles, look at the front wheels of a forward control vehicle like a Toyota Hi-Ace, or a vehicle with the ability to do really tight turns. And if you customarily do very tight turns, such as garbage trucks manouvering, or hooning around the inside lane at roundabouts, then you have joined the stretch limo brigade, wearing out your tyres faster, because the imaginary point is now much closer than the designer engineer accommodated in his design.

June 11, 2007 at 8:02 am 1 comment

Extended Track Width

One of the limitations placed on modifying a vehicle’s suspension, is restricting the increase in track width to one inch (25.4 mm, so some States say 26 mm., some 25). They would, wouldn’t they! Can’t even agree on how to round out metric conversions.

So I’d better define track width first. It’s the measured distance from the centreline of the crown of one tyre, across the vehicle to the centreline of the other on the opposite side.
So why do they bother? As part of the program to discourage such modifications, State legislation prohibits tyres extending past the width of the body-work (though you can buy mudguard flares). Even with those, you might still get knocked back because of the fall-back position, which is to also legislate for track width limitations.

There is a sound reason for the limitation. The wheel is supported by two bearings on the axle. The inner bearing is load bearing (only), and is cylindrical in shape, whilst the outer bearing, which is tapered, is a thrust bearing. When the car is loaded up by either extra load, or cornering, the stresses on the wheel rise, and are transferred to the bearings. The outer bearing is designed to cope with sidethrust, the inner bearing with load carrying.

When the wheel track is widened, generally by fitting wider wheels and tyres, more load is transferred to the outer bearing, as the centre of the load is moved outboard. Wheel manufacturers can compensate for this by moving the centre disc of the wheel (the nave plate) further outboard, so that the extra width is carried inboard as well as outboard. These might be known as “deep dish wheels”.  It is possible to find wheels with the same hole spacing, which will fit on your hubs, but the offset may not be suitable for your car. Incidentally, the wheel is located on its “Bore Hole” the centre hole, and the wheel nuts are located on studs at a specified “Pitch Circle Diameter” (P.C.D.), which is what you find in wheel makers’ catalogues.

The life of the outer bearing is important. Should it collapse, then the car’s steering can be greatly affected, and it can lead to loss of steering control. Designers of front wheel drive cars are well aware of the risks, the front wheel drive is already “busy” steering and driving, so they applaud these limitations. A note of caution- if your FWD car’s drive joints screech when you corner hard, please get them replaced. If they collapse, you might end up in “big trouble”. How much trouble depends on the design of the front end.

June 1, 2007 at 7:18 am 1 comment