The other day I became concious of the fact that I declutch when I go over a speed bump (there are some quite harsh ones at our local ASDA). It got me thinking whether or not this practice is beneficial/detrimental to the car (gearbox etc.) or whether it doesn't really matter either way... I have also noticed that I fully declutch even when I begin to brake.....maybe I am just weird?
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You shouldnt declutch at speed humps. The secret is to slow down just before the hump, then accelerate at the hump so the nose goes higher and takes the weight off the front suspension.
Then when the rear wheels are just about to hit the hump brake slightly to transfer weight from the back to the front and hence taking the load off the rear suspension as it goes over.
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That makes for very smooth progress in a C5 on speed humps.
You should only declutch when coming to a standstill and revs cannot go any lower in that gear. Take a peek at Roadcraft book, it is interesting reading.
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RF's advice exacerbates the effect of the bump - ie the nose rises as it hits the bump, and accelerating will make it rise further. v.v. at the rear. I have been advised the exact opposite - brake slightly as the front wheels hit the bump, so that the rebound from the bump is counteracted by the car's weight being shifted forwards by the braking. Then accelerate as the rear wheels hit, to keep the tail down. That way the ride stays level (ish) and the suspension does its job.
I have tried both, and the second method works better in my opinion.
It may depend on the car - I have a big car with soft suspension and high-profile tyres.
As for declutching, I admit my natural inclination has always been to declutch. I can't say why, but to me it just "feels" right. Again, experience shows that, for me, it gives the smoother ride.
I don't doubt that for smaller cars with harder suspension and low profile tyres, different tactics are called for.
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"accelerate as the rear wheels hit, to keep the tail down"
"As for declutching, I admit my natural inclination has always been to declutch. I can't say why, but to me it just "feels" right. Again, experience shows that, for me, it gives the smoother ride"
How do you accellerate when you have de-clutched?
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Not sure that I agree with you here Cliff.
Surely as you hit the bump this compresses the suspension, if you're braking at the time, this will also compress, so that is what will exacerbate the effect.
Perhaps the reason you are finding this method doesn't work for you is that you are accelerating to soon? You need to have a slight acceleration as you hit the bump, to lift the nose and de-compress the suspension, not before you hit it, which would just result in you going to fast when you get to it.
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Would agree with Renault Family method,
When negotiating an obstacle like a horizontal tree trunk on a trail M/bike the method is Just brfore front tyre hits the trunk stand on the footpegs and lean forward to compress the front forks then when the tyre makes contact open throttle and transfer weight back,the front end will clear the log and the rear wheel clinb over easily,in other words using weight trasfer to help the suspension which could take the shock off the cars suspension by braking then accelerating.Just a thought.
ndbw
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You're not weird Jamz. My dear old Dad was taught by the Army (circa 1940) to declutch when starting the car and also when going over over level crossings or other bumpy sections etc. Speed bumps are just a modern manifestation of such annoyances. He was told it took the strain off the drive components. No doubt suspensions have improved somewhat since then but I don't see why that advice shouldn't hold true.
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Terry
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Hitting a speed-bump will cause a rapid, if brief, deceleration of the car, depending on the bump. When my car decelerates rapidly, I don't want the wheels and engine connected as there's then a strain on the driveshaft. The engine is trying to pull the car forward, and the car is trying not to go. Something's going to give sooner or later, so I'd rather disconnect them.
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Good point, E34. Along similar lines, I've wondered whether doing an emergency stop in a car with automatic transmission causes similar strains on the box. Although I suspect modern autos are smart enough to compensate. Would be interested if anyone knows though...
Ed.
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I drive an auto box. My tactic is to wince a little, whilst slightly tensing my buttocks to give the illusion of reducing my body weight, every time I hit one.
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Slightly digressing, but regarding edisdead's point about emergency stopping in an auto:
I never felt entirely safe in my mother's automatic, since I had no control over the clutch, what was to stop the car declutching and leaving me with a heightened possibility of locking up?
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I drive a manual and I tend to declutch, which means I can only tense my right buttock; this sometimes results in slight vearing to the right...
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I de-clutch on the motorbike when going over speed bumps.
I can then rev the engine and annoy the H*ll out of the silly twits who put up with them being installed outside their houses on what used to be a smooth-running and safe road.
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>>I can then rev the engine and annoy the H*ll out of the silly twits who put up with them being installed outside their houses on what used to be a smooth-running and safe road.
It isnt their fault.its the ones that do 60mph in a 30 limit that forced them to be installed.so that I think unfair.(now I know why bikers do it)
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Was mech1
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Perhaps it's having your arms shaken and the pain of your back being compressed, (having had a muscular problem since my teens), however slowly one goes over the things, that makes one a little short tempered.
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I de-clutch on the motorbike when going over speed bumps. I can then rev the engine and annoy the H*ll out of the silly twits who put up with them being installed outside their houses on what used to be a smooth-running and safe road.
I'm gobsmacked you actually think like this! I've got them outside mine and it might come as a bit of a surprise to you to know I had (or have)no choice in the matter! You might want to try being a bit more considerate intead of acting like a "silly twit"
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There loads of speed bumps around near where I live in Northampton, If im in my own car I just drive between the stupid things & you dont feel a thing.
If im in the works van it doesnt really matter, the wheels go either side of the bump, lol
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Yes, hitting the bump compresses the suspension, so does braking slightly. I'm not trying to stop the suspension from compressing - that is its job - I am trying to keep the car level and reduce the pitching that makes bumps so uncomfortable. So I try to let the suspension soak up all the tendency for the front to rise.
I think the explanation about not straining the transmission makes sense. On thinking about it I think I declutch to let the front wheels go over, then re-engage to accelerate a bit as the back wheels hit.
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is it not, perhaps, simpler and less damaging to approach and mount these obstructions at a very slow pace?
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is it not, perhaps, simpler and less damaging to approach and mount these obstructions at a very slow pace?
The basic questions seems to be whether they should be designed to be transversed at the posted speed limit and if only designed for a lower speed then whether the posted speed limit should be reduced accordingly.
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The basic questions seems to be whether they should be designed to be transversed at the posted speed limit and if only designed for a lower speed then whether the posted speed limit should be reduced accordingly.
Could there be a potential court case against one's local authority if one was driving within the posted speed-limit but damaged one's suspension on a deliberately-placed obstacle?
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I go along with the school of thought that declutching over railway lines or in fact any severe bumps will minimise shock to the drivetrain components, and is therefore a good idea.
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L'escargot by name, but not by nature.
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> I have also noticed that I fully declutch even when I begin to brake.....maybe I am just weird?
No, just not been taught properly.
My wife also used to use the clutch as a "speed control device".
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Disengaging the clutch other than when changing gear or stopping is surely bad driving? Coasting in neutral while on a driving test would result in a fail I suspect. Instruction I've had from various sources over the years is never to coast.
At speed bumps I all but stop to select 1st and then drive over them slowly. My car has very firm suspension so this is the only method that works for me.
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Coasting in neutral while on a driving test would result in a fail I suspect.
True, or at least was when I took my test 9 years ago. Coasting either in neutral or with the clutch depressed is a major fault and therefore an automatic fail.
If you're moving along with no gear engaged then you are not in total control of the vehicle.
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>> Coasting in neutral while on a driving test >> would result in a fail I suspect. True, or at least was when I took my test 9 years ago. Coasting either in neutral or with the clutch depressed is a major fault and therefore an automatic fail. If you're moving along with no gear engaged then you are not in total control of the vehicle.
My instructor taught me to declutch for cattle grids and level crossings back in the darke olde dayes of 1987.
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My instructor taught me to declutch for cattle grids and level crossings back in the darke olde dayes of 1987.
I must admit, I came across neither while on driving lessons or test, so can't comment.
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My instructor taught me to declutch for cattle grids and level crossings back in the darke olde dayes of 1987.
Ditto, so did mine.
IIRC, there were no speed bumps around back then to bother worrying about whether to declutch or not.
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> I have also noticed that I fully declutch even when I begin to brake.....maybe I am just weird? No, just not been taught properly.
Or may have been taught properly, but then subsequently acquired a bad habit.
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L'escargot by name, but not by nature.
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Or may have been taught properly, but then subsequently acquired a bad habit.
Indeed. Which possibly now needs to be "un-learnt".
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Driving instruction and tests are only intended to cover ordinary situations, and I suspect speed bumps were pretty unusual when most of us learned to drive.
What I do remember from BSM driving lessons years ago was that the rules need not apply in exceptional situations, and one mark of an experienced and sensible driver is recognising those occasions.
I recall the first time my instructor directed me down an unadopted road full of potholes. He congratulated me for instinctively weaving about so as to avoid the suspension-jangling ruts. Yet if you asked "is it OK to weave about all over the road?" of course the answer would normally be NO.
Likewise declutching. Of course it is wrong, normally, to coast. But a good driver will recognise those few occasions when not doing so imposes strain on the transmission. He is in tune with the car.
My mother passed her test despite having swerved onto the pavement. Wrong? No, not on that occasion - a lorry had pulled over without looking and if she hadn't driven onto the pavement she and the examiner would have been crushed against a wall.
There are no absolute rules - only guidelines.
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Declutching when you begin to brake is wrong - you should declutch just as you come to a standstill, when the engine revs can no longer match the speed of the car in the lowest gear.
As for declutching over speedbumps - WHY do you do it? Is it to reduce speed, or to reduce strain on the drivetrain?
Personally, I drop down to 2nd or 1st, and 'drive' over the hump. My instructor always told me to keep the clutch engaged except when changing gear - keeping the car in control at all times and not 'coasting'.
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