In the first of a series of blog postings from our local garage, a mechanic explains why speed humps are bad news for motorists.I'm not a big fan of road humps, or sleeping policeman, call them what you will. To my mind their disadvantages outweigh their advantages.
After human error - misfuelling, flat batteries, running dry - they're the most common reason why customers bring their cars into my shop.
There's nothing wrong with speed limits in built-up areas. You don't want people driving like maniacs past school gates. But are road humps the best way to keep speed down? Idiots will be idiots. Someone who's going to drive at 30mph in a 20 zone is likely to try and drive at 30 over speed bumps and bust their suspension in the process. And then come crying to me.
Speed bumps are a hindrance to the emergency services, skilled drivers who need to drive quickly, appropriately, to get to a scene. You've probably seen those speed bumps with gaps in them which are meant to help fire engines and ambulances through. But, in truth, they're pretty indiscriminate - they let Transit vans, Range Rovers and Audi Q7s through as well.
We're supposed to be living in greener times. But speed bumps aren't green, they encourage inefficient driving. Every time you use apply a brake you are wasting fuel. There's one or two cars, like the Toyota Prius, that use regenerative braking - storing the potential energy in a battery - but they're the exception not the rule.
Smooth driving is the key to fuel economy and a healthy engine. If you think ahead, and drive at the appropriate speed for the conditions, you shouldn't need to touch your brakes that often. All that speeding-up and slowing-down for speed humps, it's such a waste.
They also do my customers some harm. I know a chap, retired gentleman, he spent his redundancy on a BMW M5. On the whole cars are getting sportier in feel. And that means tauter, stiffer suspensions. Get yourself a Q-car (a wolf in sheep's clothing like an M5 or a Subaru Impreza Turbo) and you've got something that will go like the proverbial mess off a stick, but it's not going to smooth the road out like a limousine.
After a few visits to the osteopath he decided to trade down to something a little more cosseting.
The most common faults that I see as a result of hitting speed bumps too quickly is damage to the suspension parts and cracked sumps. What you've got to remember is that you get four knocks when you hit a bump at speed: the first impact when the front wheels hit and you get a bottoming-out, the knock to the suspension as it jolts upwards and then a second bottoming-out with the rear wheels and a subsequent knock.
A third of cars fail their MOTs because of damage to their suspension. I'd reckon most of that damage will come from hitting speed bumps, or misjudging the kerb when driving into a driveway.
Cracked sumps can be messy. The sump is a pan beneath the engine that stores the used oil before it's pumped back into the engine. There are two types of sump: dry sumps are external. Crack this and you'll drop oil around the place but it can easily be replaced. It's not a big job but it's not something you want to happen if you can avoid it.
A wet sump is actually in the bottom of the engine. Crack this and you'll drop oil around the place and you've got a potentially expensive repair job.
You can fit rubbers to protect suspensions from damage caused by speed bumps. To my mind they're a waste of money. My advice would be to take speed bumps as slowly as you can. If the road has a downhill gradient, coast in a low gear to save fuel. Much as I like getting work, it's better for your car, and for your pocket, not to hit speed bumps in the first place.
Yes - but far short of actgual damage even careful driving over these speed bumps can easily ruin wheel alignment causing excessive tyre wear and bills in excess of £100 to correct the alignment. I am aware that some grages, especially those retailing tyres will claim to check and correct wheel alignment for a more modest charge but none to my knowledge do all four wheels let alone reach manufacturers recommended standard. Can you advise on the best way to cross speed bumps without causing damage? I have heard that it is best to drive one wheel over the centre of the "split" type which usuually means driving to the centrew of the road. Advice welcomed!
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I believe that trying to straddle the split bumps is best - driving in such a way that the wheels straddle the highest part of the bump - the rise isn't so high and it isn't such a shock to the shock absorbers. Of course, there should be enough clearance to get the sump over the bump with you - as he implies, the sump won't do you much good if it's lying in the road behind you.
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A good article - I always wondered about the waste of fuel and increased exhaust fumes by all traffic calming methods. However forget the damage to cars, what about damage to drivers and passengers? Many humps even when driven at far below the speed limit will still give a nasty jolt. The worst are the acute rubber ones (our local hospital removed them) which jolt badly even if driven at snails' pace! How many people with back or spinal problems have suffered? Perhaps if a few Councils were sued by those injured then we might get some comon sense!
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There atre split spped bumps outside a school near where I live. Drivers concentrate on going over the low part of the speed bump, not giving a second thought to on-comming traffic or the kids who are crossing the road. Put speed bumps in if you must but put make them a bit lower and all the way across the road.
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I had to do an emergency braking in the wet, but because the suspension alignment has been damaged by speed humps i just slid. Speed humps cause accidents on other roads.
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The hazard of motoring sites like this is that they are invariably likely to attract a caucus of contributors with a skewed (say petrol-head tending) point of view. The reality is that there is a much broader spectrum of opinion across the motoring (and rest of the) public than will find expression here. Speed tables and similar devices are a good way of controlling speed in urban areas. They are relatively cheap and successful in slowing nearly all motorists to a speed appropriate in the locations where they are installed. Importantly many more people than hitherto now understand that pedestrian/vehicle collisions may be survivable at speeds of 30mph or less, whereas death is likely above that speed. There is great national concern that a disproportionate amount of our near 3000 a year road deaths occur to pedestrians (and particularly children) in our towns and cities. These are deaths that can be avoided if we keep our unnecessary speed down. Automatronic vehicle control will be introduced over time, and this clearly will help greatly to reduce casualties. Until then we shall continue to rely on relatively crude devices like speed cushions in our towns and cities.
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I've go to say that even if you go over these 'speed bumps' at 10MPH or less they will still put stress onto suspension components that, in normal driving, should not be there. Folk who go fast on these roads will ,for the most, still go fast where as the rest of us who do try to keep to the speed limits have to put up with this lump in the road. I read somewhere that the max height for a speed bump should be no more than 4" high which maybe makes most of today's bumps illegal. As for the folk that still go over them at speed then complain about damage to their cars, what do you expect??
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Copied from a newspaper artical........ The Department for Transport confirmed that the humps were too high. A spokesman said yesterday: "The legal limit for road humps is a maximum of 100mm." (which is about 4") So, get out there with your rulers & get measuring! (some councils may come up with the excuse that 'the road either side of the bump may have subsided!) I'm all for lowering speeds around town but I'm not up for damage being caused to my carin the process!
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not to mention the damage done to the exhaust my friends car used to s@#$%e on the bumps because it was only a little car, and i have had to change my exhaust twice as there are speed bumps everywhere around where i live and have to drive over these everyday
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Most of the problems in the motoring scene are caused firstly by lack of foresight by councils and the government and also the cost of everything we are a cost cutting society and do not value the individual, and ltes face who listens even to the best advice. kensax
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