Speedbumps . . . how hard on your car?

Factual Questions
1

I noticed that people who work in my building swing their cars far out of the way to avoid speedbumps (on levels where there are no cars parked yet, allowing them the room to do so). I’m assuming they are avoiding the speed bumps to avoid uneccessary wear and tear on their vehicle. But then I thought . . . how harmful is a speedbump at say . . . 15 mph? I just don’t see the point. I don’t think you can accelerate get fast enough in my small parking lot to do any amount of damage to your car by going over the speed bumps.

And who knows, maybe these people are simply trying to avoid having their cd skip, or enjoy defying authority by purposely not driving over the bump, or just find bumps unpleasant altogether. But assuming they avoid the bumps to avoid car damage, are they wasting they’re time? Has anyone here signigicantly damaged a vehicle on a speed bump?

2

In Belfast some speed bumps are a smooth hump of tarmac, others are angular and made of blocks, you can see scars from vehicles that weren’t expecting such a sharp up and down (like I did when I drove in the city first :mad: )

There are also problems for cars with low suspension, especially when its an ordinary family saloon or small hatchback with the full on body kit that includes skirts etc. They tend to scrap their noses when a speed bump is on a road that slopes down onto another road. Which is why some super cars have adjustable suspension to let them lift their nose to avoid the ground.

Anecdotal, perhaps you’re more interested in the impact on a car’s suspension, in which case I defer to more knowledgeable types :slight_smile:

3

I’ve always been convinced that the addition of speed bumps to my high school parking lot is what caused the demise of the tie rod on my 1987 Taurus.

Then again, you can be sure I wasn’t taking the speed bumps at “speed bump speed” when I was in high school.

4

There’s a couple ways to look at it.

Technically, any time your car does anything, there’s wear and tear. Your shocks can go up and down, say, x million times before they need replacing. Going over speed bumps makes them go up and down, so technically speed bumps increase the wear and tear on your car. However, in the grand scheme of things, even if you go over speed bumps every day, the long term effect will be minimal.

Of course, if you hit the speed bump fast enough, something can bend, or an alignment bolt can break lose. This won’t be a gradual thing… stuff either breaks or it doesn’t. You’d have to be going pretty fast for this to happen, but if you like to drive fast, and you’re careless, every time you hit that bump is another chance for something to break.
That all being said, I imagine the real reason people avoid them is the same reason I do - driving over bumps is noisy and unpleasant… the wheel jerks around, your stomach sloshes… it’s just not fun.

5

Go slow over them. If you go fast enough, your suspension may absorb much of the jolt, but it’s taking 2 hard and fast hits to do that.

6

The environmental nazis complain about large SUVs, as do many others, but the reality is that speedbumps are most often found in residential areas, and its no real surprise that SUVs are commonly used for transporting the children to school, where the speed bumps are most often installed.

So the safety nazis complain about cars speeding in residential areas, and the environmental nazis complain about the SUVs, you’d think maybe one would inform the other that there’s a coinnection here, get rid of the bumps and maybe folk would not be so inclined to drive SUVs.

There are other ways to discourage speeding that do not cause so much discomfort to drivers, and so much hassle for bike riders.

This especially applies in the UK.

7

[QUOTE=casdave]
…get rid of the bumps and maybe folk would not be so inclined to drive SUVs…
[/QUOTE]

I’ve never heard speed bumps cited as a reason to buy an SUV.

I go around speed bumps when I can so I can go faster through an empty parking lot.

8

There are speed bumps and speed humps and the latter are much less nasty. My car (a Civic) will sometimes bottom out on an especially sharp bump and I hate them. Humps don’t bother me at all. But I notice that drivers piloting SUVs hardly slow at all.

Put up speed limit signs and make speeding an executable offense, I say.

9

[QUOTE=casdave]
So the safety nazis complain about cars speeding in residential areas, and the environmental nazis complain about the SUVs, you’d think maybe one would inform the other that there’s a coinnection here, get rid of the bumps and maybe folk would not be so inclined to drive SUVs.
[/QUOTE]

Nawwww. The slowest people I see going over the speed bumps in my apartement are all on SUVs.

10

[QUOTE=garygnu]
I’ve never heard speed bumps cited as a reason to buy an SUV.

[/QUOTE]

Although I did not wind up getting an “SUV”, last time I was shopping for a car I was considering a Jeep Cherokee Classic almost entirely because of speed bumps. I wound up getting a Sebring Convertible and just had my transmission pan replaced two weeks ago because I didn’t see a speedbump and severely dented the pan. I wish I had a Jeep.

11

Just a pet peeve of mine but why do they show commercials of the latest/greatest super/heavy duty pickup trucks climbing mountains of cinder blocks and doing 55 down some dusty horse trail and then when I get behind one on NoName Residential Blvd. they like to slow to a crawl whenever they go over train tracks??

12

How about the people who aim so that they miss one side of the bump only? Can that possibly be better than going over with two wheels?

13

[QUOTE=SmackFu]
How about the people who aim so that they miss one side of the bump only? Can that possibly be better than going over with two wheels?
[/QUOTE]

I find that it is a much much smother ride than going over with all four wheels.

14

Yes, there is a decided difference between the speed “humps” and speed “bumps.” The humps are reasonable, just a mild mound of concrete or asphalt. The modern “bumps” that I’ve seen are bolted in to the road and are almost shaped like rail-road ties. Those are excessive, in my opinion. I could see those doing some damage.

15

Most cars are better off going over with two wheels on the same axle at the same time) If the car has an anti roll bar (most do now), a one wheel hit over a speed bump is going to be a bigger jolt, because the roll bar will work to resist the action created by the one wheel coming up.

Taking a bump with one side of the car is helpful if there is a clearance issue only, to prevent the front from nose diving into the pavement, such as on an entrance to a raised surface.

16

[QUOTE=casdave]
The environmental nazis complain about large SUVs, as do many others, but the reality is that speedbumps are most often found in residential areas, and its no real surprise that SUVs are commonly used for transporting the children to school, where the speed bumps are most often installed.

So the safety nazis complain about cars speeding in residential areas, and the environmental nazis complain about the SUVs, you’d think maybe one would inform the other that there’s a coinnection here, get rid of the bumps and maybe folk would not be so inclined to drive SUVs.

There are other ways to discourage speeding that do not cause so much discomfort to drivers, and so much hassle for bike riders.

This especially applies in the UK.
[/QUOTE]

You mean you have Americanoid suburban developments whose residents often drive big SUVs? At your gas prices? Yikes!!!

17

[QUOTE=steronz]
Of course, if you hit the speed bump fast enough, something can bend, or an alignment bolt can break lose. This won’t be a gradual thing… stuff either breaks or it doesn’t.
[/QUOTE]
Not true. Any time you load a mechanical joint or linkage in tension you get mechanical fatigue. This is true even if the loading is well within the nominal structural limits of the element. Fatigue is often difficult to characterize, but is usually considered a stochastic process for the purposes of analysis, i.e. a bolt subjected to so-and-so many actions at a given stress level has a failure level of such-and-such. (The actual mechanims of fatigue, and the factors that predominate vary with material and loading scenerio, and are only moderately understood. The most common treatment of fatigue models it as small crack propogation, but this isn’t the only way a part can fatigue, and in addition to tensile stresses you can also get fatigue from thermal stresses, aging, corrosion-related stress cracking, et cetera.) You also have bearing wear, which is a tribology (lubrication) issue and is even more complicated, but suffice it to say that you get a certain number of cycles for a given load level before the part gets out of spec and starts behaving anomolously.

So, any time your suspension sees an abnormal load (anything but driving over smooth pavement) you’re doing additional “fatigue damage” to the components. How well it is able to withstand this additional load (within the anticipated lifespan of the car) depends on how “overengineered” it is. Some manufacturers like Volvo and Subaru are noted for the long-term survivability of their vehicles (under normal driving) to a point that you can get several hundred thousand miles of reliability out of original structural components. Other manufacturers (coughGMcough) still seem to adhere to 60-80k miles before components start to wear out an require replacement.

Going slow over speed bumps will help lower the stress by not imparting such a rapid impulse, and thus reducing the stress levels on the components–which is, in fact, the purpose of the bump. However, I’ve noted that some recent bumps are sharp enough (in vehicle dynamics speak, the impingment angle is very high) and they cause a sharp, jarring motion even at very modest (5mph) speeds. Driving around these bumps is definitely recommended where it is safe and legal to do so. If you are going to hit a bump, though, it’s better to hit it straight on, with both wheels contacting the bump at the same time, rather than one after the other. This doesn’t matter so much with fully independent suspension (on the front wheels on virtually all cars) but on back wheels that are connected by an anti-sway bar or multi-link/passive steer you’ll be putting extra force on both wheels and the linkage by hitting with only one wheel.

On the notion of SUVs being better for speed bumps: Large SUVs have more unsprung weight (i.e. more weight in the stuff that is not supported on springs). This is generally bad for high speed dynamics, but in the case of rough surfaces it means that the unsprung mass absorbs more of the impulse, making the resultant forces on the suspension lower and better distributed. This is why many true off-road vehicles still have otherwise obsolete live rear axles and leaf spring suspension; not only is it a cheaper, proven design, but it also helps eat up vibration and jerk from uneven surfaces. Of course, it also makes road handling crappy, but that’s your trade. (Some modern SUVs–not made by the Big Three–have independent suspension, which demonstrates that it can be done, but at higher cost, and still with some tradeoffs in complexity and NVH.) Large SUVs also give higher ground clearance, although many do not offer as much as you expect. The Ford Explorer has barely more ground clearance than a Subaru Forester or Volvo V70XC, despite the larger tires and poorer onroad handling characteristics.

I’d say that we wouldn’t need speedbumps if people wouldn’t speed in pedestrian-intense areas, but frankly they don’t seem to stop people anyway. At the school across the street from me, parents drop off their kids (most driving gignormous SUVs) and then roar away at 40mph, loudly slamming speedbump after speedbump. I guess it’s okay if it’s someone else’s child at risk. :rolleyes:

Stranger

18

There is another reason why SUVs work better over UK speed bumps.

SUVs tend to have a wider track than normal cars, and so they can straddle compeltey across the speed bump without even touching it.

These bumps are made to a certain width so that bikes canget inside, and buses can and wagons can straddle them.

It is noticeable that SUVs hardly slow down at all for these types of traffic calming measures, the smaller the car, the more it has to slow down, the lower the car, the more is must slow down, SUVs have the advantage on both these aspects.

19

I have an RSX, which had stiffer, lowered springs when I bought it (around 3/4"), and if I go over any speed bump at 5mph or faster, it bottoms out. I hate it. I also have a Jeep Wrangler, with a 4" suspension lift(with stiff springs), and going over any bump faster than 5 mph is also extremely uncomfortable. The Jeep is actually better if I am going 25 and happen to dont see it, then I just skip over it. The RSX does not have that option.

20

Depends on the speed bumps and the vehicle. I always-always-always hate going over speed bumps in my Expedition. I actually have to slow down and crawl over the damned things so that I’m not bounced all over the place. In any car – from a push, land-boat Lincoln to a sporty Zephyr to a lowly Mondeo – I’ve always found it a lot easier and more comfortable to ignore the speed bumps altogether and pretend they weren’t there. The opposite of a speed bump (a speed dip?) isn’t so easy, though. Also there are more and more “modern” speed bumps to which my philosophy doesn’t apply; those things hurt if you don’t slow down!