All About Tyres

     

Installing and Changing Tyres         

 

So you’ve tried fitting or changing one or more tyres before. The original brand, the mechanical condition of your vehicle plus other considerations will influence how many tyres you replace, and how long they will last! We’ve posted some articles below to provide some things to consider when it’s time to change your tyres.

 

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Installing a Tyre

If you have ever tried to fit a tyre yourself, you will know that it is not easy. This is because it is not the air pressure that holds a tyre on its rim - nor is it the safety humps on the rim ledge. Read more

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Original Equipment Tyres

Discover why YOUR tyre budget and tyre selection impacts on manufacturer budgets and production. The early bird does not always get the rubber worm. Find out why

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Alignment - Tell me a Story

Drive continuously on a straight road and your tyres will last almost forever…..but the reality of varied terrains and driving conditions means that correct alignment of your tyres should be a priority when new tyres are fitted. Read more

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Alignment

Discover why a mis-aligned set of tyres can play havoc with performance of your vehicle, as well as reduce the longevity of your tyres. Read more

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Installing a tyre

If you have ever tried to fit a tyre yourself, you will know that it is not easy.

 

This is because it is not the air pressure that holds a tyre on its rim - nor is it the safety humps on the rim ledge. It’s an interference fit between the beads and the rim that makes it stay there.

 

The mounted tyre rides over the safety humps, generally with a loud ‘pop’, slides up a tapered ledge, and stops when it hits the rim flange. During this fitting process, the rubber and fabric composite caught between the steel hoop built into the tyre, and the steel or alloy ledge built into the rim, is compressed. It requires localised force to break the seal caused by this compression.

 

Archimedes said ‘Give me a lever long enough and I will move the world’. Your tyre dealer uses a powered lever instead, called a tyre fitting machine. Air pressure is used to dislodge the beads into the wheel well, and then the steel hooped part of the tyre is levered over the rim flange. Lubricant is used to help the process, and also to stop the rubber bead tearing. If it does tear, the tyre may leak or bubble when refitted.

 

The choice of lubricant, as simple as soft soap, is basic. Once it has done its job, it should disappear. It’s biodegradable. This is because the part of the bead (the ledge) that sits on the rim is transmitting the power, steering, and braking forces to the road.

 

The ‘pop’ that you hear is caused by the tyre beads sliding over the humps once there is enough sideways force generated by the inflation pressure, to drive them over. It should happen between 12 and 25 p.s.i. of pressure. Then the beads slam up against the flange, are checked that they are centrally located using guide lines engraved in the sidewall, and pressure is adjusted to road service requirements.

 

You will also have been charged for a new tubeless valve. This is because the rubber ‘snap in’ valves flex during service. High-speed photos of long valves, or those with extensions to make them accessible when deep hub-caps are used, show them to bend right over and touch the rim at speed. Ultimately they will crack, or de-laminate from the brass core. Some alloy rims may require clamp in tubeless valves, due to service requirements, or the rim thickness at the valve hole. Since these don’t flex, they don’t have to be replaced every time new tyres are fitted, though they cost more.

 

But wait, there’s more. After fitting, the whole assembly is balanced statically (vertical plane), and dynamically (lateral plane) on a sophisticated machine, which process adds kilometres to the tyres performance, smooths the ride, lessens mechanical wear on your car’s suspension, and reduces the risk of flat spotting.

 

Finally your friendly tyre dealer will refit the wheel to the car, and replace the rub cap evenly, having kept it clean and unscored by dirt on the workshop floor. Cheap at half the price!

 

Original Equipment

Tyre manufacturers chase the business of having their tyres fitted to new cars very assiduously. Of course it helps if you own a large slice of the car company, as does one such company, but most compete strenuously for the business.

 

This because they know that further down the track, the car buyer will have to replace his tyres, and they can have a profound influence on his or her choice, particularly if the customer has ‘had a good run’. Besides, there is the compatability of the (probably) un-used spare with any other tyre, the calibration of the A.B.S. braking system, compatability with the inbuilt traction control sensors, and many other factors to be considered. To the customer, it might just get too hard, so they take the easy choice first.

 

Important to the tyre manufacturer is that the car company requirement helps build the volume of that sized tyre, which spreads the development costs over a greater number of units.

 

So when you come to replace your tyres, what do you do?

 

If you’ve been reading our panels of information, you know that there is a wide choice of tyres available on the Australian market. What do you do about the spare? Leave it there? If you do, the next time you have to replace tyres, it will be six years old, not three. You will be missing out on six years development and improvements in tyre design. It will be a little crazed in the sidewall rubber from the heat in the boot, and the rubber will be harder and less flexible. So it seems like a good idea to use it, by matching it with an equivalent tyre, if you can still buy one the same. Tyre fashion changes too, you know.

 

Is your car front wheel drive or rear wheel drive? If FWD, the front tyres wear out twice as fast as the rears, normally, because they are doing all the work- steering, braking, driving. The rears hold up the corner, and come along for the ride. So probably you are up for two new tyres on the front first.

 

A matched pair of tyres on the one axle won’t upset the calibration of your traction/braking systems. If one tyre is worn out, the other part worn, buy two, put the part worn tyre in the boot or the garage. It’s false economy to only put one new tyre on an axle when the other is almost worn out. The new tyre rides better, the drive system is balanced, and the alignment is as the designer intended. There is also less risk of punctures with new tyres.

 

If your car is rear wheel drive, dependent on the type of rear wheel suspension, and whether you have diligently rotated your tyres in either a 4 wheel or five wheel rotation (including the spare), you may find that you are up for five new tyres at once. Shock! Horror! That blows the budget!  Most of us leave the spare in the boot though. So wear is much more evenly balanced around the car, and it is likely that you have the choice of two or four tyres to be replaced immediately.

 

It would be a rarer circumstance where you replace only one tyre. That would likely be due to damage. If the remaining tyres ‘still have plenty of meat on them’, you could assume that one is the spare, so less worn, so match the new tyre with that on the same axle. The one that comes off goes in the boot, but pump it up first to close to the maximum so that you can forget it till you need it next. Everybody else does! Just be aware that it will probably be on a dark and stormy night in the rain, because that’s when you are most likely to get a puncture.

 

Alignment - Tell me a Story

Your worn tyres will tell an experienced tyre man a great deal about the mechanical condition of your car, and the way you drive it.

 

Tell-tales on a rear wheel drive are rear tyres worn in the crown (hard driving), rear tyres worn on the inside only (I.R.S. camber /load  relationship), and tyres worn scored or smooth-surfaced (jack rabbit starts or not).

 

Front wheel tyres worn excessively on the shoulders show up misalignment, fast cornering, and  underinflation. That’s just some of them.

 

Front wheel drive cars are different. The front tyres can wear nearly twice as fast as the rears, and can show wear in the crown, and excess wear on the shoulders, at the same time, for all the reasons listed above.

 

Yet the salesman will spend much more time trying to sell you the flavour of the month, and then recommend that you have a wheel alignment after new tyres are fitted.

 

What are the benefits? After all, alignment can cost quite a bit, and it might seem hard to justify. For the dealer, the installation is a big outlay in both equipment and training for the operator.

 

However, tyres are an expensive item, so here are some of the benefits:

  • The car is easier to drive and steer, so long trips are less tiring. 
  • Tyre Life is increased, particularly if the alignment on the previous set was out of whack.
  • Restoration of the steering angles designed into the car will make it handle the way the designer intended. 
  • You’ll get your money back in extended tread life, provided of course that you don’t indulge in the improved handling and cornering that results. 
  • Adjustment to your suspension camber can be made to suit the way you use your car. For example, suspension can be adjusted if the car has a high negative camber for fast cornering, but is used mainly on freeways. Aftermarket kits are readily available to permit these changes. 
  • If you’ve had a bingle, make sure that your car is completely aligned before you sign the release form from the panel works. 
  • If you have kerbed your front wheels badly, it will pay to have them checked.
  • After any front end work on steering or drive components, alignment is highly desirable. 
  • Ask the tyre salesman before he launches into his spiel, to assess the wear pattern on your tyres, and advise him how you actually use the car, before he makes a recommendation on the best tyre for YOU.

See also the following article on misalignment to the thrust line of the vehicle, particularly on front wheel drives.

 

Alignment

A vehicle has to track straight on a road that is crowned, or sloped, or flat. The whole vehicle. On some of these huge road trains, their trailers seemingly have a track of their own, whipping from side to side. Yet the modern B-Doubles travelling the major highways, track quite well.

 

They bear the fruits of a lot of research into vehicle alignment. The whole set-up has been laser aligned to make the trailer track properly. The settings may be different for vehicles that travel the flat roads from the eastern States to W.A.; or set so the trailer alignment counteracts the high crown of far N.Q. roads.

 

The Holden Kingswood, or any rear wheel drive car of that vintage, was not as critical in its alignment as the modern front wheel drive. The rear wheels thrust the car forward on the Kingswood, whereas the front wheels drag the car along in the FWD.

 

There are three major alignment factors - camber, castor, and toe in (or out). All affect tyre wear and handling. The settings are decided by the car engineers. For example, a Commodore SS has more negative camber than a Commodore Executive, or the tolerances may be set to the maximum on one, the minimum on the other, to improve one aspect of handling.

 

But there is a fourth setting. The thrust line and its alignment to the drive are more critical in a front wheel drive. If one REAR wheel is out of alignment, it can make the whole car travel crabwise down the road. You see the car drifting off one way or the other, while the unconscious driver is constantly correcting his steering. Once you become aware of this, it’s amazing how many cars you see tracking like that. So if your car has been clipped over one rear wheel, the mountings have been disturbed, or the car repaired after a smash, ask for a ‘full four wheel alignment to the thrust line.’

 

If the front tyres on your car (which has had its alignment checked) still wear unevenly on the outside of one front tyre, and the inside of the other, look to the rear end to see what is making it travel crabwise.

 

     
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