Intriguing to see that, contrary to our tame DT guru ('brakes are for stopping, gears are for going'), the current AA mag says:
'anticipate braking and change down, so its done gently and with the aid of the engine - you can double the life of your brake pads and disks this way.'
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But surely it's much cheaper to replace your brake pads than your clutch
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You will only wear the clutch if you do not match engine speed to road speed when changing down.
Virtually all clutch wear should come ifrom starting from rest if you are driving correctly. If you wear the clutch out then blame your driving technoque, not the clutch.
Changing down gives you much better control over the vehicle.
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Also, on the same page:
'Remember that driven tyres will wear more quickly, so rotate front to back or vice versa when they are part worn to extract maximum mileage from all four.'
But the handbook for my motor (which has identical tyres all round) says, regarding changing wheels around:
'This practice is not recommended.'
Hrrrmmmph ...
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I don't swap my tyres round at all. If you do then both sets wear down to the same level at the same time. This means two things. The first that you have to replace all four at once, which is a bigger dent in the wallet. The second is that all four tyres have less grip. Better to have at least two reasonable treads.
Jonathan
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Colin,
My driven tyres don't wear more quickly. They last longer than the fronts.
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Rear-wheel drive evens out the wear, as the front does most of the braking.
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> you can double the life of your
> brake pads and disks this way.'
And half the life of your gearbox and engine...
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Transmission systems are not designed or suitable for retarding the speed of a vehicle - that is what the brakes, which give a balanced amount of retardation to each of the four wheels are for. Clutches and gearboxes are not wired to the brake lights so that vital signal to following drivers is also lost. The only safe way to slow a car without the brakes is to use natural engine braking is by lifting off the gas, then changing down once the appropriate speed is reached. This is what the AA probably meant.
Changing to a lower to allow the clutch, gearbox and drive shafts to provide the braking effect is going to prove very expensive in the long run.
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"Transmission systems are not designed or suitable for retarding the speed of a vehicle"
Eh? How do the gears know which way you're going? And what about reverse?
I use engine braking a lot (in conjunction with wheel brakes - that's what heeling and toeing is about, although I daresay that's frowned on now) and I've not worn out a clutch or broken a gearbox yet...
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Sorry James, heeling and towing is not using the transmission as a brake, it is used to do the exact opposite in fact. The method allows one to use the brake to slow while keeping the engine at a speed where the gears engage in synch with the road speed and protects the transmission from the sudden strain of trying to retard the momentum of the vehicle.
There seems to be a bit of confusion here as to the difference between changing down the gears to slow which is poor practice both from a safety and a mechanical point, and in using engine braking, which is using the natural drop in revs as one lifts off the gas to progressively lose speed.
If you doubt the negative effect of using the gears to slow, then buy yourself an ex driving school car where the transmission has been abused for most of it's life and the resulting driving experience will convince you of the need to treat the transmission system with respect.
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Strictly speaking, engine braking is anytime the engine is being driven by the wheels, i.e. whenever you lift off the accelerator when in gear. Braking at the same time simply increases the retardation. I think what is being described as engine braking in the original enquiry is effectively clutch braking, where the clutch is being used to match the engine revs to a lower gear, which never was a good idea. I blame synchromesh!
WRT driving school cars, they are abused in all sorts of ways, and I don't imagine that ordinary engine braking accounts for much of the damage.
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Also consider that using engine braking (and a change down) to retard the vehicle will only apply braking to the driven wheels.
This may upset the balance of the car more than applying the brakes on all four wheels.
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There must be a body of people who think engine braking is oK hence the manufacture and fitting of exhaust retarders, and electrical retarders in the transmission. For those who do not know, coaches and lorries use them, particularly for descents of long hills mountain passes etc. The exhaust type blocks the exhaust manifold so that a high pressure builds up in the engine causing excellent engine braking, and the electrical is a giant electromagnet in the transmission. They are used to prevent brakes overheating .
Regards
Mike
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Exhaust retarders and similar devices are fitted to prevent the speed increasing once the vehicle has been slowed with the brakes, in the same way that using a low gear on a descent helps to keep the speed of the vehicle in check. They are not designed to actually reduce the speed of the vehicle in the first instance.
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Intersting. I was taught to drive this way, but on a recent Advanced driver session I was told not to changem down, but to brake, and change straight into the gear required to start of again (I fin d this difficult - something about old dogs and new tricks).
However, a more interesting addendum is that a friend of mine is a driving examiner, and he says if you consistently change down and use engine braking, you will fail!
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Shows how much the AA knows. Can't even spell "discs". No wonder the car won't stop with floppies behind its wheels.
HJ
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Honest John wrote:
>
> Shows how much the AA knows.
You would also have a problem spelling, if you were P*ssed all the time, HJ!
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In contrast to Tony Capps, on an IAM session I was told to use a lower gear and control the car by the throttle and gears!
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Both are correct. It is possible to be in too high a gear for the road conditions but it is also necessary to use the brakes to slow your vehicle down below the comfortable range of your current gear.
The IAM (and the Police's Roadcraft) promote: Information, Position, Speed, Gear, and Acceleration (which can be positive or negative). Their associated books provide a wealth of useful information and advice on attitudes and skills for driving and biking on the road. Being able to stop in the distance seen to be clear became a popular expression.
An urban area with a limit of 30mph may require a lower gear as you may have to be comfortably in control of your vehicle to speeds of 15 or 20mph despite the fact that you may be driving at the posted limit. On the other hand, the limit may be 40 in which case, even though traffic conditions dictate 30mph, the next gear up will be more appropriate. It's all about reading the road and the surrounding conditions and taking the appropriate action (that's not a euphemism for going to war, the roads aren't that bad yet).
Additionally, application of the brakes (and therefore brake lights) alerts other road users that you're slowing down quickly (in addition to the fact that your car, in their eyes, is becoming suddenly larger).
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the AA having been going badly worng for ages, and its worse under centrica
same way they have been firmly in the pro-camera "hammer them for 5 mph too much" camp in the press the last few months
do not pay them, move and join another outfit!
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Automatics and how do they fit into this?
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Good point, Growler.
So far as I've seen, vehicles with auto or manual options all have the same brake systems ...
BTW, I once joined the AA. They gave me a bottle of scotch and a mask. :)
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Surely it's all about knowing your vehicle. On an empty road experiment with the effect of closing the throttle, get a feel for it an use that and anticipation to reduce the number of times you need to apply the brakes.
Some things - high compression, little residual fuelling (both diesel traits) and manual x/mission will give a high level of retardation by lifting off the accelerator.
With an auto presumably there will be a loss of whatever engine retardation there is in the torque converter, though that may be different in systems where the tc is capable of locking or in belt based systems?. Seriously bad practice to slow an auto by manually selecting low gear.
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This Old Dog has just aquired his first automatic. Can you explain why it's "Seriously bad practice to slow an auto by manually selecting low gear"?
I thought that, with the heaviness of an automatic, selecting a lower gear for descending a long hill would be a sensible precaution, and would prevent a long descent on the brakes, thereby avoiding any risk of the brakes overheating.
Is it just that auto boxes are not designed for enabling engine braking?
I find it hard to adjust to the new trick of letting the brakes do it all....
Advice really welcomed, please.
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From Supra MKIV manual:-
2 (SECOND): Use when the engine brake is required while travelling downhill.
L (LOW): Use when the engine brake is required while travelling down extreme slopes.
That's with fairly big brakes. Keeps them cool for any extreme demand, I take it
Regards, Tomo
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Thanks - confirms my instinct. I wonder why others say it's seriously bad practice? Obviously if one selects 2 or L at too fast a speed it's not going to do any good - but I would hope never to have to do that (just as one wouldn't manually change down into, say second, when going 50mph in an ordinary car down a steep hill!).
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Re my point about bad practice:-
This started as a discussion about relative merits of brakes and gears when slowing. The degree of speed loss from lifting off the accelerator wil vary with engine type etc.
What I meant about autos was that you will knacker an auto box by forcing the transmission lever into low ratios while still travelling at excessive speed. Same principle of course applies to manual boxes. Having first slowed down holding low gear is recomended for example long descents.
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Have you ever been driven by someone who uses the gearbox to slow down? It's so annoying, all that down-changing and the accompanying noise. My sister-in-law used to do this on the approach to red traffic lights, going from 4th through the gears to 1st before coming to a complete stop. It was made even worse because it was in a Vauxhall! (much whining etc)
It took more than a few subtle hints to tackle the issue.
Regards
Pat
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Thanks, Simon - that's reassuring, and accords with my practice.
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