As a Chassis engineer, most of the work we do is out of sight of the consumer. Steering, suspension, and most of the braking system lives happily underneath the car where they are only open to scrutiny by mechanics and that tow truck guy who rolls your car back onto its feet after your foolish arse put it upside down in a ditch.
There are some exception, of course. Wheels are the first to come to mind, along with the brake calipers (assuming the wheel styling is open enough between the spokes). But there is one design feature that shows up on some cars that, although not something designed by chassis engineers, is influenced entirely by them.
I’m talking about those little bumps you see on some rear fender flares.
What the hell are those things, anyway? Why are they there? And why do only some cars have them?
They come in a variety of sizes and shapes. The one above is on a Lexus NX300H, and happens to be fairly prominent. Here’s one on a Toyota Corolla.
It’s a bit more subtle. But in some cases, they can be quite large — some may say gaudy, like these on an Infiniti QX60:
The best job I’ve seen in a while of hiding this feature can be seen on this Porsche Macan:
Whether gaudy and obtrusive, or small and subtle, each company clearly went through a lot of trouble to put these features there, so there must be a very good reason for it, right?
Yes there is.
In order to sell cars in Europe, manufacturers must meet certain homologation rules, and one of these is European Union Commission Regulation 1009/2010, more recently replaced by 2019/2144. This rule, in part, states that in an area marked by a line 30 degrees forward of the tire center to a line 50 degrees behind the tire center (the image above shows this visually), no part of the tire may protrude farther outboard than the body. In other words, there must be something on the body that extends further outboard than the tire within this 80-degree wedge shape.
The reason the standard exists is to protect pedestrians from accidentally brushing up against a moving car and coming into contact with a rotating tire.
Unfortunately, the styling of some vehicles does not naturally provide for the necessary tire coverage. The designers (and possibly aerodynamicists) may want to taper the rear part of the body more aggressively, which may mean that the sheetmetal near the back of the 50 degree portion may end up inboard of where it needs to be to meet the ECE requirement.
Designers resolve this by adding a small bump as part of the fender flare, or in the case of the Porsche, what appears to be a black extension of the wheelhouse liner that sticks out past the sheet metal. The more the body tapers, of course, the larger the bump may need to be.
In my years of designing suspensions, the way we would ensure we meet the requirement was to draw the 30/50 degree wedge in our CAD system and lay it flush with the outside of the tire profile. Something like this:
We would then move it 5 mm outboard and provide this to the design studio. The 5 mm was added to account for production variability. The design that engineers work to in CAD assumes all parts are made to their exact dimensions, but that is never the case. No production process is perfectly exact, and the parts that come out of it are always slightly different from the design. Some will be slightly smaller, and some will be slightly bigger. It’s known as “process variability,” and the trick is to keep it as small as possible so that each part is very, very close to being perfect.
However, if we look at all the parts that make up a car body and all the parts that make up a suspension and put them together, even small variations in the sizes of those parts can add up to a large overall difference from car to car. During a production build, some cars may have the tire sitting very close to the edge of the fender while in other cars it may be farther away. We need to ensure that all the cars built meet the standard because the European Union may check ANY car. You have no idea which car they may choose, and they may choose several.
Moving the wedge plane outboard 5 mm ensures that all cars will meet the standard and there is no chance of a failure, no matter which car the commission chooses to check.
Once the design studio receives the 5mm-displaced wedge from the chassis team, designers then need to ensure that some portion of the bodywork extends at least to this wedge or beyond. Of course, this doesn’t always fit with the design the studio has in mind, and designers don’t always like what they have to do to make it all work. I spoke to our own Adrian Clarke and here is what he had to say about the matter:
I hated these bloody things! They were always a pain in the ass. There’s lot’s of things to consider when you’re trying to work out wheels and tires: is the profile of the tire correct to protect the alloy wheel? Have we left enough clearance for snow chains where those are a legal requirement? Also what is the shape of the rear of the car doing? Do we need one of those little trim pieces? How small can we make it?
Unfortunately, the EU gets the last word on this and so, designers and chassis engineers have to design the car to meet the requirement, or you don’t get to sell your car.
So now that you know what these things are and what they’re for, you can see if your own car has them and/or which cars in the parking lot have them. And if you’ve never noticed them before, you’re going to see them everywhere now and it’s going to bug the crap out of you. You’re welcome!
Bro truck guy isn’t going to care about this rule.
Could you not simply move the wheel inboard by a centimetre or two and call it good?
For years I thought it had something to do with flinging rainwater or wind to clean the tail lights, absurd as it sounds. Glad to know the truth, great work!
Can anyone explain the purpose of the small rectangular shapes that disrupt the curve of the plastic wheel arch trim on various JLR products?
I think they first appeared on the Evoque, as well as the Discovery Sport. Right at the top of the wheel arch, the trim broadens to incorporate a squared-off rectangle. For no reason at all, as far as I can see.
They don’t widen the body and they’re certainly not attractive. Anyone know why they’re there?
Also why no car comes from the factory with the proper stance. Spacers required on almost everything these days.
What are you talking about? You think the wheels need to be further outboard? The wheels are literally within 5mm(1/4″) of being flush with the fender. Literally any amount of wheels spacer would be moving the wheels out of the fenders.
As opposed to anything more than 30 years old, which really did require spacers to get the visually right stance. A lot of 70s-90s cars require a 3″ spacer or more if you want the tires/wheels to be flush with the fender.
It’s very subtle, I’m not asking for wheels to be comically pushed out – most only need 10-15 mm to look right.
It’s a very slight flaw in all modern cars that just happens to be very noticeable (and frustrating) to me
So you want the tires to be 5-10mm sticking out of the fenders?
they’re not sticking out with such minimal spacers, majority of cars have way more than 5mm of being flush with wheel well (more like 20-30mm).
Exactly, it may look flush to you but most stock vehicles are at least 10mm inboard if not more.
A 10mm spacer is all I need on my car to make the wheels flush with the bodywork. My car also doesn’t have those little protrusions, the wheels sit pretty far inboard stock.
true, had to install 10-15mm spacer on all cars I’ve owned recently (Lancer, Honda Accord, Mercedes C, S550 Mustang), just to make wheels sit flush.
I think ‘proper stance’ will change over time. Older cars always had the wheels way more inboard, yet in the time most people were ok with it. If we today say that we think the stance is wrong for older cars, we look at it with todays eyes, not with the seventies eyes. Personal example, I drive my DS for 24 years now. In the beginning I thought the wheels were big, now they seem comically small (15 inch). They are so much inboard that the rear fender completely covers the rear wheel, yet doesn’t seem strange to me. Okay, maybe not the best example 😉
I also think older designs were better suited to have the wheels more inboard. Look at a mark I VW Golf, even the standard base version with the smallest wheels looks fine. Yet a modern Audi or Skoda Station only looks the business if you seriously upgrade the wheels.
Since the auto designers know about this requirement, why not include it in the design phase instead of sticking ugly bits on the night before the project is due?
Most of the ‘solutions’ to this issue just look so ugly.
Because there are lots of things to take into account, and the BIW is one of the first things to get signed off.
looks like this piece of plastic is just a safety buffer. Probably perfectly fine without it but what happens if 1,000 cars (or more) have one buck toothed wheel sticking out and the whole weight of the EU bureaucracy wants to turn it into a federal case and fines fines everywhere. Or you just slap a piece of plastic on it and call it good.
Tolerance stack up must get fun with so many parts on a car.
Tyre to wheel to brake disc to hub to suspension bush to suspension arm (often several arms with some adjustable ones) to another bush to subframe (often made of several parts, all with tolerances) to floor pan to inner fender to outer fender to the weird triangle trim. 5mm can get eaten up really easily.
I’ve only ever done tolerance stacks on engines, nice tight tolerances and lots of machined faces. I want nothing to do with body panels.
A GD&T nightmare.
All those surface tolerances on the body panels!
Yes, flexible, complex body panels. And add further complexity if the design datum isn’t the mounting point that your assembly progresses through
Also body on frame can add a bunch of sloppiness. I once had a 2001 Explorer that one rear tire was 5/8″ closer to the fender than the other side.
Another reason it’s astonishing how cheap cars are, especially compared to much simpler boats subject to a tiny fraction of the regulations, far more lax acceptable standards for build quality, buying engines and drives off the shelf from other manufacturers, and often leaving rigging to outside parties. And forget about RVs!
So it’s a shin guard – that’s cricket!
Huh. Pedestrian safety. My assumption was, particularly for pickups, that the fenders had to stick out past the tire so anything kicked up by the tires would go into the wheel well, rather than any chance of going straight back in general direction of the windshield of the car behind you.
Which makes me so mad when I see vehicles whose aftermarket tire setups do go past the fenders. Who’s passing their inspections?
I mean, over half of the states in the US have no inspections. So that accounts for a lot.
Damn, I didn’t know it was that bad.
Nonetheless…I’m also a PA resident, and even though only some counties do emissions inspections, they all do visual inspections.
I mean, I think it’s a good thing that more states don’t have inspections. Because even in rust belt states like Michigan, data shows that safety inspections are almost completely ineffective. There is no significant improvement in safety.
Which actually really makes sense. When ~99% of all crashes are caused by driver error, only ~1% are caused by unsafe vehicles or anything else. Meaning that even a perfect inspection system would net less than a 1% reduction in crashes.
Really weird that PA has areas with no emissions but a safety inspection. Most of the US is the other way around.
So, while I’m not exactly in favor of inspections, I think it’s important to note that the final analysis is going to be a little more complicated than simply “99% of crashes are caused by driver error”. While yes, very few crashes are caused because a control arm rusted through, non-compliant vehicle modifications can have substantial impact on safety and act as a contributing factor.
Very simple example – if a vehicle (say, an F-350) is lifted 8 inches, and the driver hits a pedestrian in a sidewalk while illegally turning right on red, the proximate factor for the crash is driver error, but a contributing factor to the severity of the accident is the increased ride height and contact zone. Similarly, putting 6 inch spikes on wheels isn’t going to cause many crashes, but certainly could make things worse or escalate an otherwise benign situation.
A good inspection regime would likely catch those modifications, and the net result is increased safety. Also, in real terms, not relative, a 1% decrease in crashes is a massive number of crashes, even if only maybe 0.5% get prevented.
Now, do I think that state inspections would actually solve this, instead of rapidly devolving into the hot mess of corporate kickbacks and corruption that plague the towing (and repair) industries already? Eh, maybe, maybe not.
But I’ll say I’m pretty damn tired of nearly being run over by a lifted brodozer turning right on red and not being able to see me because of the stupid lift, than having to dodge the wheels that are 6″ offset from the body right after.
My coworker (Hyundai dealership) saw one on a Tucson and thought the wheel well liner was sticking out. He tried to grab it, was utterly perplexed, and I pointed it out on the other dozen in a line.
He doesn’t work here anymore but I’m sending this to him pronto because it amuses me how upset he was at their presence.
The best solution I’ve seen is on the EX30, while the worst execution gotta be the EQC.. but in general I think they all look bad.
If they’re there only to satisfy a law, I don’t get why they don’t make these detachable so owners can just chuck them into the garbage.
Unfortunately, that would add extra cost (a separate part, fasteners, and assembly time) plus it would need to be designed in such a way that there would be no visible holes when it is removed.
Because the law doesn’t change when a car is delivered.
That is true, but the law applies to the car as delivered. It is perfectly legal for the customer to remove it. Just look at all the jacked-up trucks running around. None of them meet bumper height requirements anymore.
Yeah, but that’s also not endorsed by the manufacturer. I can’t imagine a regulator being all that thrilled if stuff was built to satisfy the law being designed to be tossed out – and that could easily prompt a revised regulation if someone catches on.
Bugatti doesn’t mind…
America Ruined The Bugatti Chiron With These Bumper Pads (motor1.com)
The airbag warnings on sun visors are supposed to be not-removable. But on my old conversion van and some Wranglers, they’re just stickers you can take off fairly easily.
Meanwhile I don’t know what black magic they are on my Prius but my attempt to remove it by ironing ruined the thing and I had to pay $130 (just the part!) for a replacement visor to look nice again.
Would love to remove the warnings but I have no idea how they’re so well-attached/integrated and I couldn’t find “replacement” covers, at least not ones for the exact same model.
I removed the visors in my BMW, soaked paper towels in IPA, let those sit on the hideous yellow warnings (F30, nothing fancy, some cheap plastic coverings on the visors) and the labels got all wrinkly after an hour or so and I was able to scrub them off.
If you look hard enough you can tell something was there, but I don’t even notice that anymore. Kinda mad my partner had his totaled X3 towed away before I could swap visors with it, because his could slide where the 3ers did not.
Back in my yout, in the days of drag styled cars with skinny front, huge rear wheel/tire combinations, the local police were quite zealous about checking that the rear tires were entirely covered by the fender. Failure to meet the requirement yielded a ticket and impound until the vehicle met regulations. The used to stop you, and using a tape measure and yardstick check clearances. There was also a min/max front/rear bumper regulation that was also rigorously enforced. We were pretty dumb back in those days.
I have read that in Pennsylvania a trooper can require you to park on level ground, and then will hold a quarter flat against the edge of the fender and let it drop. If it touches anything before the ground, you’re busted.
Yeah, I wish they would start enforcing bumper and headlight maximum height rules around here.
Im surprised that there aren’t more pickups launching each other woth the tires sticking out.
The law doesn’t change when a car is delivered. However, car manufacturers and car owners have completely separate sets of laws, and consumers are legally permitted to do many, many modifications that manufacturers cannot legally do.
They’re especially prominent (and a separate, taped on piece that sits in an indent) on the BRZ/GR86 and I figured they were for the stated purpose when looking at the how the tires sit, but didn’t know it was specifically the EU market. Other option was maybe as a trip strip to help reattach airflow against the sides (like on the corners of many tail lights), but I figured they were on the small side for that in an area of turbulence.
I idly assumed they were for getting another fractional mpg out of vehicles
I seem to be popping up more in other people’s articles than my own recently.
The more Adrian the better.
We are patiently waiting for your next submission.
I’ve been busy (extra teaching), and ill. Stuff is coming, I promise.
Figured real life was getting in your face. I can always go through your back catalog. Am part way through Torch’s stuff and have veered into some strange surreal revelations.
I thought it was for this reason, was not disappointed in myself
The Winnebago F17 finds this to be very comical.
Question : Are Europeans that bad of pedestrians that they are constantly being hit by cars? Or are Europeans the worst drivers ever and are constantly being hit by cars? Either way, so many rules due to pedestrians
The issue isn’t bad drivers but small streets and close quarters in cities that put pedestrians much closer to cars than what we are used to.
Because people actually walk in Europe rather than jump in the Canyonero just to drive half a mile.
I am telling on myself, and I’m genuinely sorry to be part of the problem, but when it gets over 90 deg, and hasn’t been under 80 for weeks, I just can’t do it. I live in my own darkened house with a sheen of sweat for 5 months a year; I have to stop automotive and other project work because I’ll ruin them with sweat. Running dripping rivulets of sweat.
Driving makes it worse still, I know. I at least use the motorcycle for every single thing that I can; I picked up two gallons of water and a gallon of coolant on it. In the summer that just means I arrive damp instead of soaked, which is the best I can offer.
Ah sweet, sweet contrition.
I just visited London, Paris and Rome a few weeks ago. The city streets are much tighter as are, more importantly, the parking spaces. Cars will barely clear the walls through a tiny ally and the chances to rub a pedestrian in that scenario are quite high.
I was absolutely shocked walking around through Italy that cars drove on what I thought were pedestrian walkways. NOPE! That is a street!
Interesting! Thanks for the insight all.
Its because in Europe we care about pedestrians.
In America we call those “points”:
https://m.youtube.com/watch?v=F2GEKV1dOgY
Witnessed a bicyclist get run over by an articulated dump truck in an intersection in the downtown core a few years back. The truck was turning a corner and didn’t have those side panels designed to prevent pedestrians and cycles from getting under the truck. The panels may have prevented her death.
Mystery solved! I always assumed it was for minor aero purposes, but now I know the more boring(factual) reason these exist. Thanks Huibert.
I too, thought this was aero related!
Same here. My car has so many little aero protrusions and vents and whatnot I just assumed this was yet another.
Actually is due to aero and the need to wedge the rear of the car which leads to the need of this feature, also usually the design part of the project dislikes the other solution (different front and rear tracks).
Thank you, never knew, just called them the rubbin’ nubbin’.
And now that’s what I’m gonna call ’em!