A car tyre must be inflated to work properly. Should you suffer a puncture, you can change the wheel concerned. Here's how to do so in safety…
When
When to change a wheel becomes pretty obvious. A heavy pulling at the steering wheel and/or squirmy handling with assorted noises is usually sufficient to let you know a car tyre has deflated.
Where
Where to undertake a tyre change may seem obvious but this isn't necessarily so. The first and most important rule is to never, ever try to change a car tyre by a busy carriageway, be it a on a motorway hard shoulder or at the side of an A-road. Why? Quite simply, it is hugely unsafe.
So, what if you're caught out, on a busy road? Sometimes, it's possible to coax your car to a quieter location. Bear in mind that you'll need to find a level, firm surface to work on. If the car tyre has deflated fully, just pull up and call out the cavalry. The breakdown service will do the rest, after your mobile phone, or a roadside phone, has done its lifesaving bit.
How to prepare
A spot of preparation makes changing a flat car tyre much easier. Pull up in your chosen spot, apply the car's handbrake, put the car into gear (or 'park'), switch on the hazard lights and set up the car's warning triangle. This should be placed 45 metres (147 feet) behind the car.
The next stage in dealing with a flat car tyre is to have any passengers leave the car and stand well away from it, and from passing traffic. Then, it's time to extract the spare wheel, jack and tools – your car's handbook will tell you where they are to be found.
Jacking the Car
This step in the proceedings involves safety procedures, to which you must pay attention. First, you have to chock the wheel diagonally opposite to the one with the flat car tyre. No chock to hand? Then find a stone, brick or any other piece of debris that'll do the job.
Time for your car to go up in the world. There'll be a specific place under which the car jack must be placed. Once again, the handbook will tell you where this is. Do not improvise; only the proper jacking point will do. With the jack placed correctly, wind it up until it's bearing enough of the car's weight to not move.
Loosening the wheel nuts or bolts holding the wheel with the flat tyre comes next. These are always undone anticlockwise, with the wheelbrace that is in the toolkit. You may have to undo a locking wheel nut too – there's a key device for that.
Now, wheel fastenings can be very tight. Use the wheel brace so you'll be applying downward pressure (far less injurious if the tool slips). Loosen the fastenings first; the wheel can't turn because it's still on the ground.
Now, you can jack the car up. Do this steadily, until there is daylight between the flat car tyre and the roadside surface.
Changing the Wheel
Unscrew the fastenings completely one by one, removing the uppermost one last. You may need to 'persuade' the offending wheel to come off but be careful – over enthusiasm could cause the car to fall. For this reason, never let any part of you go between the car and the ground.
A car tyre and wheel combination can be heavy. Make sure that when lifting one, you’re on a firm footing with a straight back. Fit the spare wheel, securing it with the topmost fastening. Then, refit the remaining fastenings, tightening them only enough to seat the wheel firmly on the hub. Lower the car until the tyre is on the ground, and tighten the fastenings in a diagonal pattern. Now, you can stow the deflated wheel and tyre, put your tools away and continue your journey.
Finished?
Not quite, there are a couple of post-wheel change necessities. You need to get to a tyre bay, to have the wheel tightened to a specific torque – a repair on the flat car tyre is often possible. If you need to continue on the spare, you have to be sure that the car tyre on the spare wheel you've used is at the correct pressure. Finally, if the spare tyre is a space saver, there'll be limitations concerning speed and distance. The car handbook will show you what applies.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
Wednesday, 7 March 2012
Under Control. How Computers Help Car Tyres
'If in doubt, blame the computer' is an office standby. When it comes to car tyres, there are plenty of instances when it would be appropriate to say, 'Thank the computer'. Several computer-controlled systems optimize car tyre performance these days. Let's pick our way through the acronyms and look at some such systems.
ABS a.k.a. the Anti-Lock Braking System has its roots in aircraft technology. Gabriel Voisin, a French aeronautical and automotive engineer came up with it as far back as 1929. Forty-two years later, 'Sure Brake' appeared on the 1971 Chrysler Imperial. It's now hard to find a single car tyre whose stopping power isn't maximised by ABS. Here's how it works.
Enter the ECU, or Electronic Control Unit, which is what is in charge of ABS. Imagine a car tyre is rotating more slowly than its fellows. A wheel speed sensor detects this, and tells the ECU. The ECU, in turn, opens a hydraulic valve to divert brake fluid pressure away from the locking wheel, until the tyre in question speeds up again. The system can do this at up to 20 times per second. The result? On a wheel that isn't quite locking, the car tyre is gripping at maximum efficiency. A locked wheel offers virtually no grip, while a wheel nearly at locking point can still offer steering and braking force.
EBD (or EBFD) is a refinement of ABS. This acronym stands for Electronic Brake Force Distribution. On the old, 'classic' Mini, for example, there used to be a mechanical inertia valve, which would reduce braking force to stop the rear tyres locking under heavy braking. EBD does the same thing, far faster, far more accurately and in relation to each car tyre simultaneously.
Strange as it may sound, ABS can help a car tyre achieve maximum traction under acceleration. TCS – the Traction Control System – uses the ABS's wheel speed sensors to detect if a car tyre on a driven wheel is spinning (i.e. not gripping). The TCS applies braking force to the spinning wheel for a few milliseconds. In more sophisticated TCS systems, the throttle can be cut briefly, preventing wheel spin.
Speaking of sophisticated systems, we can now look at ESC (Electronic Stability Control). This again is ABS-related. In ESC (or DSC – Dynamic Stability Control), two further sensors play a role. One detects the angle of the steering wheel, while its gyroscopic stablemate checks this angle against the car's direction of travel. Should the figures not add up, the system applies braking force to individual wheels. Once again, each car tyre is maintained at its optimum level of efficiency in any given circumstance, by the application of very short pulses of braking pressure, and/or throttle input, as appropriate.
Here's where further refinement steps in, and where we become awash with acronyms. It's probably best to think of the refinements under the ACC (Adaptive Chassis Control) banner. Often using a button, with markings such as 'Comfort', 'Sport' and even 'Race', a car driver can dial in all manner of changes to how his car responds. While the stiffness of physical springs can't be changed electronically, the firmness of the suspension can, by the actuation of electronic tweaks to suspension damper rates. While the car tyres don't change, that which controls them can. It's possible for driving force to be distributed according to car tyre grip across an axle and, in some cases, between the front and rear wheels.
The bottom line about these immensely clever, capable systems is that they use car tyre grip as a benchmark. When the car tyres are offering optimum grip, tyre performance – and therefore the performance of the car – is necessarily optimized.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
ABS a.k.a. the Anti-Lock Braking System has its roots in aircraft technology. Gabriel Voisin, a French aeronautical and automotive engineer came up with it as far back as 1929. Forty-two years later, 'Sure Brake' appeared on the 1971 Chrysler Imperial. It's now hard to find a single car tyre whose stopping power isn't maximised by ABS. Here's how it works.
Enter the ECU, or Electronic Control Unit, which is what is in charge of ABS. Imagine a car tyre is rotating more slowly than its fellows. A wheel speed sensor detects this, and tells the ECU. The ECU, in turn, opens a hydraulic valve to divert brake fluid pressure away from the locking wheel, until the tyre in question speeds up again. The system can do this at up to 20 times per second. The result? On a wheel that isn't quite locking, the car tyre is gripping at maximum efficiency. A locked wheel offers virtually no grip, while a wheel nearly at locking point can still offer steering and braking force.
EBD (or EBFD) is a refinement of ABS. This acronym stands for Electronic Brake Force Distribution. On the old, 'classic' Mini, for example, there used to be a mechanical inertia valve, which would reduce braking force to stop the rear tyres locking under heavy braking. EBD does the same thing, far faster, far more accurately and in relation to each car tyre simultaneously.
Strange as it may sound, ABS can help a car tyre achieve maximum traction under acceleration. TCS – the Traction Control System – uses the ABS's wheel speed sensors to detect if a car tyre on a driven wheel is spinning (i.e. not gripping). The TCS applies braking force to the spinning wheel for a few milliseconds. In more sophisticated TCS systems, the throttle can be cut briefly, preventing wheel spin.
Speaking of sophisticated systems, we can now look at ESC (Electronic Stability Control). This again is ABS-related. In ESC (or DSC – Dynamic Stability Control), two further sensors play a role. One detects the angle of the steering wheel, while its gyroscopic stablemate checks this angle against the car's direction of travel. Should the figures not add up, the system applies braking force to individual wheels. Once again, each car tyre is maintained at its optimum level of efficiency in any given circumstance, by the application of very short pulses of braking pressure, and/or throttle input, as appropriate.
Here's where further refinement steps in, and where we become awash with acronyms. It's probably best to think of the refinements under the ACC (Adaptive Chassis Control) banner. Often using a button, with markings such as 'Comfort', 'Sport' and even 'Race', a car driver can dial in all manner of changes to how his car responds. While the stiffness of physical springs can't be changed electronically, the firmness of the suspension can, by the actuation of electronic tweaks to suspension damper rates. While the car tyres don't change, that which controls them can. It's possible for driving force to be distributed according to car tyre grip across an axle and, in some cases, between the front and rear wheels.
The bottom line about these immensely clever, capable systems is that they use car tyre grip as a benchmark. When the car tyres are offering optimum grip, tyre performance – and therefore the performance of the car – is necessarily optimized.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
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