Just what does it do?
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04/28/2014 07: 00 AM
Correctly while using parking brake.
The parking brake in your car is merely that – a parking brake. Not much of a handbrake. No e-brake. Not an emergency brake. In fact, in the event of an emergency, the last control in the car that you want to touch will be the parking brake. Locking the back wheels at any speed will result in a spin.
Once I moved to america I was appalled at the amount of people (read : it is apparently everyone) don’t know the standard things about the parking brake. Like the reasons you use it when you’re stopped at an intersection.
If someone rear-ends you in an intersection, and also you only have your foot around the regular brake, two things can happen, I’ll let you know why -. Which means that (2) you will either run into the vehicle in front, or worse – roll to the intersection into oncoming or crossing traffic, (1) you are going to jerk your foot from the brake due to the rear impact.
– if you have the parking brake on, your foot coming off the brakes makes no difference, and the distance you will be pushed will be considerably reduced, and as an added bonus, you won’t roll anywhere.
When I moved to the united states and had to stay a driving test, the examiner thought I was bit funny inside the head to make use of the parking brake at every intersection, until I explained these to him, at which point he explained I’d never heard of that before. And then he was not just a driving instructor – he was a tester/examiner! Explains a great deal about how people drive around here.
I went on to explain to him why I always waited to make across traffic with my wheels straight too. It’s the same principal. As well as your wheels are turned, you’ll be shunted across the road into oncoming traffic, when someone runs into you from behind. At least when the wheels are straight you’ll go basically straight ahead. Again – total confusion from the examiner.
Here’s another tip for automatic gearboxes – the pawl that drops in to the notch externally of the main clutch housing when you placed the car in Park will not be very strong. Certainly not strong enough to hold the car stationary on anything other than level ground. Sure – you only throw the car in park when on hills and everywhere, but that is slowly eating away the edge of that particular notch then one day, the parking pawl will slip out and your car will require off with the gear shifter firmly in P. So here’s the tip : utilize the parking brake every time your park – it reduces the probability of the P setting inside the gearbox stopping on you 1 day.
What’s worrying about all of this was illustrated when we went along to a ‘new owners’ evening at the dealership where we bought our car. It absolutely was one of those freebies to explain the nuances of this particular brand, with free drinks and snacks, with the hope that we’d buy accessories or something. Anyway, one driver asked when should I take advantage of the emergency brake? (aagh – it’s not just a fucking EMERGENCY brake! ) The expert through the dealership said – verbatim – Never – I don’t know why they even bother putting them in cars anymore.
Apart from your car’s tyres and seats, the suspension is the prime mechanism that separates your bum (arse for the American) from the road. It also prevents your car from shaking itself to pieces. No matter how smooth you think the highway is, it’s a bad, bad place to propel over a huge amount of metal at high speed. So, we rely upon suspension. People who travel on underground trains wish that those vehicles relied on suspension too, but they don’t and that’s why the ride is so harsh. Actually it’s harsh because underground trains have zero lateral suspension to speak of. So, so does the entire train, and it’s passengers, as the rails deviate side-to-side slightly. In a car, the rubber with your tyre is great for this little problem, while all the other suspension parts do the rest.
In it’s most basic form, suspension is made up of two basic components:
These come in three types. These are coil springs, torsion bars and leaf springs. Coil springs are what many people are familiar with, and are actually coiled torsion bars. Leaf springs are what you would find on many American cars up to about 1985 and almost all heavy-duty vehicles. They appear like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring. The torsion bar naturally is a bizarre little contraption which gives coiled-spring-like performance depending on the twisting properties of a steel bar. It’s used in the suspension of VW Karmann and Beetles Ghias, air-cooled Porsches (356 and 911 until 1989 after they went to springs), and the rear suspension of Peugeot 205s amongst other cars. As an alternative to having a coiled spring, the axle is attached to one end of the steel shaft. The other end is slotted into a tube and held there by splines. It twists the shaft along it’s length, which in turn resist, as the suspension moves. Now image that same shaft but instead of being straight, it’s coiled up. You’re actually inducing a twisting in the shaft, all the way down the coil, as you press on the top of the coil. Believe me, that’s what is happening, though i know it’s hard to visualise. There’s an entire section further down the page specifically on torsion bars and progressive springs.
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These dampen the vertical motion induced by driving your car along a rough surface and so should technically be referred to by their proper name – dampers. When your car only had springs, it would boat and wallow along the road until you got physically sick and had to have out. It might be a travelling deathtrap until the incessant vibration caused it to collapse.
Shock absorbers (dampers) perform two functions. As mentioned above, they absorb any larger-than-average bumps in the road so that the upward velocity in the wheel over the bump isn’t transmitted on the car chassis. But secondly, they maintain the suspension at as full a travel as possible to the given road conditions – they make your wheels planted on the road.
You desire more technical terms? Technically they are velocity-sensitive hydraulic damping devices – in other words, the faster they move, the more resistance there is certainly to that movement. They work in conjunction with the springs. The spring allows the wheel to go by the road, moving up and down. The kinetic energy of that moving unsprung mass is transmitted to the damper where it is dissipated. The damper performs this by forcing gas or oil via a constriction valve (a small hole). Adjustable shock absorbers let you change the size of this constriction, and thus control the rate of damping. The lesser the constriction, the stiffer the suspension. Phew! ….so you thought they merely leaked oil didn’t you?
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A contemporary coil-over-oil unit
coilover car suspension
The photo here shows a typical modern coil-over-oil unit. This is an all-in-one system that carries the two spring and also the shock absorber. The type illustrated here is very likely to be an aftermarket item – it’s unlikely you’d get this amount of adjustment in your regular passenger car. The adjustable spring plate enables you to make the springs looser and stiffer, whilst the adjustable damping valve can be used to adjust the rebound damping of the shocks. More sophisticated units have adjustable compression damping as well as a remote reservoir. When you don’t typically get this measure of engineering on car suspension, most motorbikes do have preload, spring and rebound tension adjustment. See the section later on within this page in regards to the ins and outs of complex suspension units.
These are the basic rubber grommets which separate most of the areas of your suspension from one another. They’re used at the link of an A-Arm with the subframe. They’re used on anti-roll bar mountings and links. They’re used all over the place, and from the factory, I can almost guarantee they’re made of rubber. Rubber doesn’t last. It perishes inside the cold and splits inside the heat. Perished, split rubber was what brought the Challenger space shuttle down. It’s extremely important for your car’s handling, in addition to your own safety, that these small things are in good condition, even though this is just one of those little parts which hardly anyone pays any attention to. My advice? Replace them with polyurethane or polygraphite bushes – they are hard-wearing and last a heck of your lot longer. If you’re into presenting your car at shows, they appear better than the naff little black rubber jobs, and. Like all suspension-related items though, bushes really are a tradeoff between performance and comfort. The harder the bush compound, the less comfort in the cabin. You pays your money and makes your decision.
Suspension bushings are an essential part of your suspension system when you have an off-road vehicle similar to a Jeep Wrangler.
In their infinite wisdom, auto producers have lay out to baffle us together with the sheer a few different types of suspension available for both front and rear axles. The main groupings are independent and dependent suspension types but this naming convention really only applies to traditional or analogue suspension systems. Even independent systems are typically joined across the car by an anti-roll bar and so are not truly independent.
From about 2006 onwards, the concept of fully independent suspension systems did start to appear on cars where the anti-roll bar was replaced by sophisticated computer software associated with some form of electronically-controlled suspension. Start to see the section afterwards dealing with digital suspension systems for more information.
When you know of any not listed here, e-mail me and let me know – I would like this page to get as complete as possible.
Front suspension – dependent systems
So-called as the front wheel’s suspension systems are physically linked. For everyday use, they are, within a word, shite. I hate to be offensive, but they are. There is only one form of dependent system you need to know about. It is basically a solid bar under the front of the car, kept in place by leaf springs and shock absorbers. If you discover a car with one of these you should sell it off to a museum, though it’s still common to find these on trucks. They haven’t been applied to mainstream cars for years for 3 main reasons:
Shimmy – since the wheels are physically linked, the beam can be set into oscillation if one wheel hits a bump and the other doesn’t. It sets up a gyroscopic torque about the steering axis which starts to turn the axle left-to-right. This in turn feeds back to amplify the original motion, because of the axle’s inertia.
Weight – or maybe more specifically unsprung weight. Solid front axles weigh a great deal and either need sturdy, heavy leaf springs or heavy suspension linkages to have their wheels on your way.
Alignment – simply put, you can’t adjust the alignment of wheels on a rigid axis. From your factory, they’re perfectly set, but if the beam gets even slightly distorted, you can’t adjust the wheels to make up.
I frequently get pulled-up on the above mentioned statements from people jumping to defend solid-axle suspension. They generally send me pictures similar to this and claim it’s the very best suspension system for off-road use. I actually have to admit, for off-road stuff, it probably is pretty good. But let’s be realistic; how many individuals with these vehicles ever go off-road? The nearest they come to getting maximum wheel deflection is when the mother double-parks the thing with one wheel on the kerb during the school-run…….