If you’ve spent any time driving a car these days you will no doubt have encountered them, probably cursed them, and maybe even damaged your car on them. I’m talking about your and my favorite road feature, the speed bump. Or as the English call them, the sleeping policeman (a bit morbid if you ask me, but hey, they invented the language so I suppose they can call it what they want).
These speed-reduction devices seem to be popping up in more and more places these days, and if you live in India, they are absolutely everywhere — even in the middle of highways. In the U.S. and pretty much everywhere, residential areas seem to be the favorite places for them to breed; their rate of multiplication tends to match that of local residents.
In my years of driving I’ve noticed different ways people cross these dreaded things and I’ve boiled those methods down to three strategies:
1. Slow down and turn just before the bump to cross over diagonally
2. Maintain speed, and power through
3. Lower your speed and drive over slowly.
Let’s talk about each of these and then I’ll let you know which “speed bumper” I am and why.
Cross My Heart and Hope to Die
Let’s first talk about diagonal speed bump crossers. These are the folks who approach a speed bump and then at the last minute turn the wheel sharply so the car drives diagonally over the bump. Each wheel hits the bump separately and the car pitches sideways as each wheel goes over. If you had any coffee in your cupholder it has now drenched your center console. Or your passenger just whacked their head against the door glass and is now cursing you instead of the speed bump.
As each wheel drives over the speed bump it wants to lift the car. But the other three wheels are still on level ground and they don’t want to be picked up. Even though the suspension is designed to isolate the sheetmetal from the forces coming from the road, those forces still go into the body via the springs and dampers. This means the body of the car is fighting with the other three wheels as it tries to push down on some and lift the others. The result is that the body wants to twist out of shape and the only reason it doesn’t is because of the welds that hold it together and the stiffness of the metal it is made of.
If you’ve ever jacked up a corner of an older car you may have noticed it can be hard to open the doors. It’s the same thing. The body has been twisted out of its normal shape and the doors are now jammed shut. Put the car down and everything is fine again because the twist is gone. In the meantime, the welds of the body have been stressed and it is possible for some of them to just give up and pop open. What is more likely to happen, though, is that as the body is trying to twist, other parts that are connected to it — like the dashboard, or the seats, or the headliner — are also being asked to twist and the clips and bolts holding those things in place aren’t nearly as strong as a weld. Do this enough times and those little fasteners will start to loosen and create nasty squeaks and rattles.
The same twisting is also happening in your suspension. Much of the suspension doesn’t really care about this but most cars these days come equipped with anti-roll bars front and rear and these bars connect the left and right side suspension systems.
When one wheel goes up, the anti-roll bar has to twist, which stresses the bar itself but more importantly, it stresses the rubber bushings that hold the bar in place.
Damn the Torpedoes. Full Speed Ahead!
Some people believe when it comes to speed bumps that the accelerator is their best friend. The faster you go the less you feel them – Must be good, right? Well, not exactly. When your suspension comes up to a speed bump, it has to move up and out of the way to cross it. The faster you go, the faster the suspension has to get out of the way. This causes very high stresses in all the parts that make up the suspension and can seriously reduce the life of those parts, especially the dampers.
Dampers work by forcing hydraulic fluid through many tiny holes as the wheels move up and down. The movement of this fluid is how a damper absorbs energy, turning it into heat and slowing down the motion of the suspension. To get a better understanding of how a damper works, imagine jumping on a sealed plastic bottle filled with water. The fluid doesn’t compress, so — aside from the bottle changing shape a bit, your landing is going to feel really stiff. Now imagine poking a small hole in the bottle. When you jump on it, you’ll squeeze water through that hole and you’ll feel less resistance than with a sealed bottle. As you increase that hole size (or add more holes), the “damping” becomes less and less, and the bottle feels softer when you stomp on it — in other words, the bottle displaces more for a given input. If you remove the lid entirely or add a bunch of holes, and jump on the bottle, you’ll experience basically no damping — in other words, nothing will be there to resist your motion towards the ground.
Without dampers, your car would hit a bump, the springs would compress, and that potential energy in that now-compressed spring would push the wheel down (and thus, the body up), this would then stretch the spring, and that potential energy in a stretched spring would pull the wheel up (and to a lesser extent pull the body down). The spring is pushing and pulling the wheel/body, sending the car bouncing up and down along the road like a pogo stick, because there’s nothing to absorb that energy and turn it into heat. You may have seen older cars with worn out shocks bounce as they drive down the road; it’s a wonder those drivers don’t get seasick.
To get a feel for how driving fast over bumps could affect shock life, let’s continue our water bottle analogy. If the bottle only has a small hole and you stomp on it, what is likely to happen to that hole? If you guessed it would get bigger or just rip open, you are right. The same thing can happen to the damper but in this case it is the rubber seals keeping the hydraulic fluid inside that might rip open. Again, the faster you drive over the speed bump, the faster the damper has to move, and the more pressure you build up. The result is a greater chance that something will burst.
So for those who like to drive fast over speed bumps, you may not be feeling the bump, but your suspension sure is.
Slow and Steady Wins The Race
The last type of speed bumper is the one that slows down to a crawl and drives over the bump two wheels at a time. This method keeps the suspension in its more or less normal position because the body has time to move up with the bump. Since two wheels are going over the bump at the same time, neither the suspension nor the body is being asked to twist and since it is all happening slowly, the dampers don’t have to move and force fluid through those tiny holes at high speed.
By now I’m sure you’ve already guessed which type of speed bumper I am. I cringe every time I see someone fly over speed bumps at high speed. As a dynamics engineer, I can’t help but feel for the poor suspension being abused like that. And as someone who absolutely hates squeaks and rattles, I just can’t bring myself to cross them diagonally. Slow and Steady wins the race, in my book. Yes, this may seem like the obvious answer, but I figured I’d walk you through my thought process; it was just something I had to get off my chest.
So, which type of speed bumper are you? Cross my Heart and Hope to Die? Damn the Torpedoes, Full Speed Ahead? Or Slow and Steady Wins the Race? Let’s discuss.
I hit a surprise speed bump at night in my 2013 Charger going 40 MPH and thought that was the end of the car. Turns out everything was fine, so I think 40 MPH is probably the optimal speed.
I want to know about the one side over the bump and the other side through the gap option. Slowly.
This is what I do more often than not, position the car so only one side of tires go over/make contact with the bump and slowly. Car goes over quicker and with less jolt. That either means the other side goes in the gap between the speed bumps or the gutter depending on the bump. But I have been guilty of the diagonal way a fair bit too which I am no longer going to do after reading this article.
This method is the same as the sideways method except with half the number of cycles since only one set of wheels go over the bump. The amount of twisting is the same but the quantity is cut by half.
I worked out my speedbump-fu with an Econoline E-150, and it goes like this.
1) Approach at a bit more speed than you want to take the bump at. You’re feeling confident and alert.
2) Dab the brake before the bump, nice and smooth. This shifts the weight forward, loading up the front springs.
3) Just before the bump, release the brakes. The front springs push the weight up, and become unloaded them as they extend.
4) Bump. The wheels have much less load on them, so they bip over real gentle and easy. Nice move.
5) Continue with smooth motoring.
Get it wrong, and hit the bump with loaded up front springs, and you may not come back from that.
You should always be finished slowing down and off the brakes before you hit the bump though. If you’re still actively scrubbing off speed as you contact it, your front suspension is already compressed by the forward weight transfer.
I’m the “drive around them” type :p I live in the middle of nowhere, so you can (almost) always just drive around them… that said, I haven’t encounter many (any?) since I got the X4 and I image it will handle them better than any of my previous (much lower-riding) vehicles did.
Seriously, fuck speed bumps. Aside from doing a number on my (very) old Passat’s sump, they decrease air quality around those they’re designed to protect. And those they’re seeking to curb (pun semi-intended) just see them as a challenging obstacle to overcome.
Where I’m from, it’s not unusual to see brand new speed bumps installed on crumbling, potholed, washboard roads. Then, of course, the bumps themselves are not maintained, so potholes open either side of them, or the paint to demarcate them so drivers can actually SEE when to slow down has rubbed off and you end up taking it at cruising speed completely unintentionally.
Usually, they only come about because curtain twitchers want something to complain about behind their squinting windows.
I hate them and everything they stand for.
Depends on the car. I’ve found my 80 series much prefers the speed method. It has a ton of vertical travel and its more than robust enough to take the hit. If I get the speed right you hear more than you feel. The GX doesn’t love the speed approach but it does like crossing it up. Lots of suspension articulation and lightly damped suspension means it glides gently over the cross. Body on frame means the torsional loads aren’t too stressful.
An 80-series Land Cruiser? That’s cheating.
certainly feels like cheating.
My Raptor stays level if you hit them at 40+. It’s what it’s designed to do and I’m not apologizing to it.
Always wondered: with a special-purpose-built vehicle like that, do you even notice them if you go over them at say parking lot speed?
IMO speedbumps should enforce a “reasonable” speed, which is rarely the 3mph that seems necessary to go over one comfortably. Is it even possible to design a speed bump that would be comfortable at an appropriate speed but uncomfortable at a higher speed? Say 20mph is the goal, and 25+mph is to be discouraged?
All I want for Christmas is a Bose Active Suspension:
https://youtu.be/eSi6J-QK1lw
I had a chance to drive that car a few years ago and it was magical. It really is a shame they never were able to take it further.
GM has had Delphi active MagnaRide suspensions in their high end cars since the early 2000’s.
Let me add a caveat to this discussion. What we are talking about here is dumb suspensions, which are only designed with spring constant, vehicle mass, and suspension travel.
We have this wonderful new capacity with magnetorheological active suspensions with ground sensors, to see the height of the ground in front of the vehicle many thousands of times a second, and calculate how much resistance should be applied at that wheel, in order to maintain vehicle height, and thus avoid lifting that corner of the vehicle at all. This is limited by available suspension travel, and the computing power of the active suspension circuit of the ECU(s).
So, in a vehicle like that, unless it’s a particularly long bump, traveling at a normal rate of speed would get the car’s mass over the bump faster, and allow the suspension to anticipate and accomodate the road height deviation rapidly, without ‘upsetting the apple cart’.
So in an active suspension car, DON’T slow down.
I will need to change my method. I used to floor it and yell “Yeee–hawww” while my inner monologue was saying “Them Duke Boys were trying to….”
I guess my F150 Platinum 4×4 has a suspension designed for high speed over speed bumps. My old C6 Corvette did not. From the videos I see, I guess WRC cars would take the average speed bump at about 127 MPH.
You forgot the one-wheeler… find the gap and run one wheel in the gap and one on the bump… probably similar to the diagonal tho.
Your cars alignment says hi
No problem with lifetime alignment 🙂
I’ve been guilty of this one.
You are correct. That would be similar to the diagonal method but with fewer cycles since only one set of wheels go over the bump.
Hating the lurch forward as the back wheels ride over the hump, I actually give it a touch of gas once the fronts have cleared. Shifts weight backward, smoothing out the ride. Yeah, compresses the rear shocks more but, at that speed, there’s no way I’m doing any long term damage.
At work they installed really harsh rubber speed bumps. With just enough wide gap between them to fit a normal size car, so most of us just go down the center of the drive to avoid them.
I probably don’t slow down for them as much as I should, but I have started clutching in and coasting over them. If you try to go over them in gear with a manual, there’s a shudder as the driven wheels go over that can’t be good for engine mounts and such.
Full speed ahead. It’s fun to watch your passengers get pissed off when they are covered in food, drinks always good for a laugh. Besides shocks are cheap. I think there is a guy who specializes in buying shocks and other bits from junk yards….allows one to both save money and have lots of fun.
Yeah that’s funny, but even funnier is being in the back seat and dumping your drink out on the seats or floors beforehand so as not to get drenched and an insincere apology to the gentleman driving. Oops sorry I spilt my Eggnog, you’re going to want to clean that up quick quick or it’s going to stink forever.
My wife had surgery on her cervical spine recently and I gotta tell you… speed bumps stopped being funny then.
I like to play with weight transfer in my softly sprung Jeep. Right before my front wheels are about to hit the bump, I hit the gas pedal to transfer the weight to the rear and lighten up the front wheels. Then, I’ll let off before the rear wheels hit.
Came here to mention option D as well.
If you’re not treating speed bumps like monster truck hops, you’re not living your best life.
We also have a few “speed humps” in one part of town. They’re speed bump height, but a few feet long and with a more gradual approach and departure. You can catch great air on those with a well timed downshift.
The speed humps were a lot of fun when I had my Supermoto. Take-em or leave-em with my old Honda CB. Terrifying on my moped (mostly due to my weight, but partly due to the complete lack of damping).
I sometimes do the same thing, except I tap the brakes just before the bump and then catch it on the rebound as the nose is moving back up again.
Even better: weight transfer is pretty much the same no matter how softly sprung your car is. Your soft jeep is just rolling more in reaction to the weight transfer. So I think physics says your “gas the front wheels, brake the rears” method is the best way to hit a bump and spare the suspension, regardless of vehicle.
I do the same. Helps me practice weight transfer
I’m mostly curious as to whether speed bumps actually reduce the speed people on average, or if they just slow down to go over them and then accelerate as quickly as possible back up to whatever speed they were going before.
That’s what I tend to see, anecdotally …. people jam the brakes, go over, then jam the gas.
I’m guessing it burns extra fuel. (or uses up battery)
It’s not even anecdotal, it’s been studied. Speed bumps decrease safety in areas they’re installed, but busy bodies don’t care about data.
Just another driving thing to add to the list of things that are more dangerous but seem intuitively safer so we do them anyway.
I can’t reply to your other comment, but over half of children vs vehicle accidents is because their parents back over them in the driveway.
In all honesty I would be interested in seeing those studies. There is a campaign to get them added to my street and I would like to make sure this gets added to the discussion.
On my street there aren’t a lot of kids running around or dangers inherent to people speeding. But there is alternating parking, and during that time of day the honking from people driving like assholes and then getting pissed at people who are just trying not to get into a head-on collision is infuriating. Bring on the speedbumps.
I also kind of wonder how many fatalities with children in residential streets have anything to do with speed and everything to do with children running out in front of moving vehicles where you’re basically never going to be able to stop in time regardless.
Not exactly “studies” (I’d like to see them too) but this might be useful:
https://ww2.motorists.org/blog/how-to-fight-speed-bumps-humps-and-cushions-part-2/
To add to your discussion, speed humps slow down emergency vehicles too. I had to call an ambulance for a neighbour once and it was excruciating watching it slowly crawl over the humps (even though it was probably faster than I thought). Every second counts and there are far better methods for slowing vehicles.
Lets look at the data:
https://www.iris.unict.it/retrieve/handle/20.500.11769/371970/437278/Evaluation%20of%20the%20benefits%20of%20traffic%20calming%20on%20vehicle%20speed%20reduction.pdf
I have a head ache and couldn’t read the article. What is the 30 second cliff notes of it?
There are three different kinds of roadway modifications that work very well to calm traffic speeds and increase safety. Speed bumps are a primitive form of one of them, and they work OK, but not as well as some of the others.
But don’t say you cheated off me on the test, and no complaining if you don’t get full credit.
Speed bumps (and other “speed tables”, which includes things like rumble strips), chicanes, and making the road narrow all work to slow Italian drivers. For this crowd, I’d worry about chicanes being seen as a challenge, though.
The short summary is that going slow with both front wheels on the speed bump decreases twisting forces on your car frame and suspension, and going slow allows the fluid in your shocks to shift as designed, instead of bursting something. The analogy being if a water bottle has a small hole and you press on it, the water slowly comes out, but the bottle stays intact. If you speed across the speed bump it’s like stomping on the water bottle, which causes a rupture.
People get to know the bumps in their neighborhood and commute routes. some are small and can be almost ignored, but most probably need careful maneuvers to cross. when you encounter one by surprise, that’s when a trip to Midas gets on the schedule.
My High School had speed divot’s instead of bumps. Instead of coming up out of the flat pavement, they inverted them down into the roadway.
Going faster (or fast enough) meant you didn’t even drop in them…much.
Brilliant design choice for 18 yr olds driving themselves to school lulz
You obviously don’t have a lowered car. The angled approach is the only way to do it without massive scraping 😛
Otherwise bye-bye rockers…
I think this is where my habit for taking them at angle comes from; ONE time I took it slow and head on and kissed the rockers, luckily no damage. Learned my lesson there.
For some odd reason SoCal loves to have extremely high speed bumps and 12 inch high entrances at store entrances. Anything remotely close to a sedan has to take them sideways, otherwise you damage your front bumper/aero devices. I would attach Google Maps links of the store entrances but I think that requires manual approval.
LoL, no the suspension engineer doesn’t have a lowered car, Cause they know better!
Huibert, I cringed for you.
I’m not saying you’re wrong but custom car culture and motoring trends have always pushed OE’s to make things better. You being a VW guy should know that to the extreme. GTI’s, Raptors, Hellcats, GT3’s, slantnoses, Westfalia’s, screens, cd changers, Jeep dealer/MOPAR lift kits, I’d say the VW Thing was to directly compete with dune buggies, fog lights, etc… Even engineers are garage mechanics, ahem… David Tracy… They tinker and figure out a way to work it into production. I mean, look at the Big Three race teams in the 60’s, most started with the engineers asking themselves, “What if we put a big block in it?”.
Chassis engineer here, my Mustang is lowered.
There’s a large spectrum between factory, compromised ride height, and slammed on its nuts.
My car also happens to have a smorgasbord of geometry correction devices to go along with that lowering.
I have a hard time thinking that something like gently crossing a speed bump one wheel at a time would actually put enough stress on your car to damage something. I mean, I get the theoretical logic I just doubt that it matters in practice. Mind you, I go over then straight because why make life more complicated.
Its about cyclical loading. You twist the frame once, you’re fine. You twist it 10,000 times?
If you always go over them at an angle, you’re going to twist the frame 4 times per speed bump. In my local grocery store there are half a dozen speed bumps. If I’m going through there and hitting the speed bumps at an angle every time I’m now twisting my frame 24 times every time I go get groceries. 416 and 2/3 of a trip to the grocery store twists the frame 10,000 times
The above doesn’t even take into account pot holes and other such issues that are going to twist your frame independently of what you might experience in a parking lot.
Now, realistically you normally have to get an order of magnitude or two above 10,000 cycles to actually damage steel, but the rubber bushings and such? Those are designed to give and wear out. 100,000 cycles might start to be an accurate number.
Sorry, made a mistake. You enter the store to get groceries, that’s 24 twists, you leave that’s 24, so 48 twists per visit. That’s probably a little less than a year’s worth of grocery store runs to reach 10,000 twists.
This comment requires a soundtrack. I would suggest a classic by Chubby Checker.
David doesn’t understand that reference.
Which one? I’d go with “Let’s Twist Again”.
Yackity Sax for me.
But the car needs to be designed to handle cyclic twisting stress anyway. Because this type of stress happens any time you enter a driveway at an angle, which is most of the time, certainly when making a right turn into a driveway. There are also other road irregularities that cause this, like a depression formed in the road at an angle so that rain water drains properly. Those are all over the place where I live.
Chassis engineer here, my Mustang is lowered.
There’s a large spectrum between factory, compromised ride height, and slammed on its nuts.
My car also happens to have a smorgasbord of geometry correction devices to go along with that lowering.
This website needs a delete or edit button…
Sent this reply to another comment, hit reply on this comment, and it filled and sent this reply somehow to this comment as well.
I try to go around them if at all possible.
Sometimes there are strategically-placed gaps that allow you to do just that. They’re there so that first responders don’t have to slow to a crawl on their way through the speed bump.
Yes, I love the speed bump slalom courses!
I have not seen these speed bump gaps in my area. There is a gap near the curb for drainage, and I do see some people creep the one tire around that side as a habit. Never gaps spaced where both tires will go through gaps.
Doesn’t that just produce twisting forces on your car?
I can’t reply to your other comment, but over half of children vs vehicle accidents is because their parents back over them in the driveway.
When in doubt… Flat out!
Seek help.
I’m beyond nuts, I’m condiments!
I relish the thought
You mustard been thinking about that one a long time.
Mayo always have a good pun handy.
Yes. Make the suspension work so you don’t have to….