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Piston Slap: The Pandora’s Box of Vehicle Cowl Heights
Larry writes:
Over the last many years, I have noticed the size of tires on cars the public is offered just keeps increasing. When I was a teen, the most common [wheel and] tire size was 14” with some 13” and 15” tires. Now it seems like it most tires are in the 18” – 21” tires. Aside from giving the driver a higher elevation, I keep wondering if there is an advantage to this size increase.
These tires are expensive, and I don’t see that they last any longer, especially on electric cars. Tire disposal is a modern-day problem and just keeps getting more of a problem. So the question is, “Do these larger size tires offer a performance or longevity increase? Do they just pander to a sales program of increased performance or image?
(Personally, I drive a 1995 Nissan pickup, which to me is much easier to get into and out of because of the height. My other car is a 1995 Acura, which is harder to get into and out of because it is rather low, complicated by the fact that I am 81 y/o. My son drives a new SUV, and I have to climb up to get into it, which I do not like much.)
Sajeev answers:
Sadly, the ever-increasing wheel/tire sizes have nothing to do with their superior attributes. Along with your concerns about bigger tires, these bigger wheels increase unsprung weight and rotational mass, which negatively affect acceleration, braking, ride quality, and even fuel economy.
We likely see these negative effects as passenger car wheels go beyond 16 or 17 inches in diameter, and when trucks go above 18 or 19 inches. The only real benefit comes from the curb appeal of having a more desirable body-to-wheel ratio.
Tall bodies need tall wheels. Smaller wheels from a previous era would look “uncool” to the eyes of many motorists, as they make everything look like a Mitsubishi Mirage. That Mitsubishi has a sky-high roofline, a tall cowl (the metal part below the windshield), but only has 14 inches of wheel to mask all the mass.
Of course, this is fine for the Mirage, as it’s an honest little car for well under $20,000. But most of us want something nicer in our garages, and bigger wheels are necessary to complete the look.
The genesis of this trend needs to be discussed, as I wager it came from a singular design change over the last 15-20 years: a taller cowl to reduce head injuries for pedestrians living in Europe.
Join me as I attempt to dissect this change over time.
The Need For Pillowy Impacts
Again, the cowl is defined as the metal part of the body at the base of the windshield. As seen in my Vellum Venom design analysis of a 2016 Volvo V60 Polestar, all cars around 2010 needed higher hood lines to ensure pedestrians (generally adult-height pedestrians) are protected from hard underhood things, like intake manifolds, that won’t budge in the event a human comes into contact with the hood of a vehicle. Traumatic head injury is not to be trifled with, so the science and engineering behind this notion is admirable.
Before we proceed, I might be guilty of oversimplifying the problem of pedestrian safety, so if needed, please read this amended document from the United Nations to get a clearer perspective.
Higher hood lines could be implemented like that V60, which is a modern-day visual (if not functional) interpretation of a cowl induction hood seen on a 1970 Chevelle SS. You can also meet the law’s requirements by implementing hood poppers at the cowl, and several Lexus products did this in the past. Perhaps the poppers weren’t used industry-wide for good reason, as you see in the video below.
We might not know why, but most automakers merely raised the cowl height so there was more space between a “normal” hood and the engine at all times. But when that happened, every bodyline around the cowl is forced to adjust.
The Cowl Is The Problem
Changing the cowl creates a turning point for things like door height, A-pillar curvature, and the all-important hood height. And making those changes means you must adjust the heights of the front and the rear end of the vehicle to compensate. It’s a snowball effect, but not doing so ensures you make something like the quirky Fiat Multipla from 1998.
This older Fiat’s design isn’t based on the pedestrian safety laws that came a decade after its introduction. It is only included here to show how a tall cowl affects everything around it when you do not make adjustments to mask the increased height.
Europe’s Legislation Affects North America
Vehicles sold by Ford, GM, VW, BMW, Mercedes, etc. in Europe are not significantly different-looking from the ones sold in North American showrooms. Ford, for example, learned this the hard way, as altering cars like the original Ford Escort, Contour, and the 2008 Focus for North American tastes turned them into huge money pits for no good reason. (The original America-flavored Escort likely sold well enough to overcome the cost, but the Malaise Era was a unique moment in history for small cars.)
Detroit automakers also saw cash in platform consolidation. They killed off wholly American designs like the 1986-07 Ford Taurus (for the Ford Fusion). Then GM ended the W-body’s reign in favor of the Epsilon II global platform. Diving into the mechanics of lowering costs across a globalized company’s product portfolio is a bridge too far, but when it comes to homogenized cars, whatever they (Europe) get, we get it too.
Ram-ificiations From A Feedback Loop?
Here’s where things get spicy: Europeans don’t much care for our full-size trucks and SUVs. They are not sold in meaningful quantities in Europe, so that European tail only wags the North American dog. With no boundaries for where North American trucks can go to their wildly loyal base of customers, their cowl heights went higher and higher in the last 20 years to differentiate themselves from cars with taller cowl.
I wager this has turned into a feedback loop, forged by our need for trucks/SUVs/CUVs that must be cooler looking than a mundane family sedan. (Mission accomplished, as the sedan genre is a shadow of its former self.) As sedans got taller and puffier from the European mandate, CUVs had to beef up to look cooler than the cars they are based on. And when CUVs get cooler looking, SUVs need to get even taller and tougher looking. And when SUVs do this, full-size trucks must get downright macho…does my feedback loop analogy hold water with you yet?
Blindspot Widening
The elevated cowls of trucks from the last decade are so bad that options like bed and tailgate steps seem downright reasonable. That’s low-hanging fruit, but we all have larger side-view mirrors to reduce blind spots. There’s also a legitimate need for computers to help us park and to check for blind spots while changing lanes. The mandated backup camera in modern vehicles is a genuine lifesaver, considering how significantly rearward visibility has diminished in this time period.
We haven’t even discussed the unintended consequences of tall cowls affecting forward visibility. This has become a real threat with a real name: Frontover accidents. As “Mister Bear” in the video above proves, cowls are so tall that full-size truck and SUV pilots see essentially nothing directly in front of them. It’s gotten so out of hand that federal legislation was proposed to add sensors/cameras to the front of vehicles just like we have in the back.
That bill didn’t pass, as mandating more equipment (and cost) to a vehicle likely has a large number of detractors. No matter the politics, there are real consequences for having “much taller than European cowls” on North American trucks and SUVs.
Back To The Wheels
I apologize for the length of this answer, but I am pretty passionate about this problem. The only way to get smaller wheels is to give designers the freedom to lower the height of the cowl. That’s it…just lower the darn cowl already!
Europe’s intentions are worthy because saving adults from traumatic head injury must never be discounted. But North America has spent way too much time and money adjusting its trucks and SUVs to scale up in the process. The cost of blind-spot-reducing technology, the current danger of front-over accidents, and the degraded performance from huge wheels (alongside Larry’s issues mentioned at the beginning) have taken their toll. We have truly opened a Pandora’s box.
But much like the Greek artifact with the same name, this Pandora’s box likely has a vision of hope for the future. The only question to ask is, what does that future entail?
I look forward to reading your thoughts in the comments section.
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VERY interesting historical perspective. Like so many things, the compounding effect of one change leading to another flies under the radar until you look back in decades rather than years. I tend to move from car to truck to car to truck, and never really compared my trucks until I read your article. I pulled pictures of my ’78 Chevy Bonanza and put them next to my daily driver – a 2019 Nissan Titan.
The contrast was stunning. At the time, I thought the Bonanza was “big” compared to my Monte Carlo SS. In comparison to the Titan, it looks like a mid-size pickup from today. I have always felt that driving the Titan was akin to driving a bus. Now I know why!
Thanks for the continued eye-opening stories!!
The 20″ wheels on my 06 Magnum (factory SRT8 wheels) are actually lighter than the 16″wheels on my 49 International pickup, and about the same if not less than the 14″ wheels on my 68 Dart. Aluminum is great stuff.
Brakes are another big reason that wheel sizes have grown over the years. Many of the 79-91 Panthers were equipped with 14″ wheels. When the aero was introduced for 92 they came with 15″ to fit over the new front brakes. With the new brakes for 03 16″ became the minimum that would fit over the front brakes. That is something that has played out across many models.
Simply put the desire for better braking performance exceeded what could fit in those smaller wheels, leading to the increase in the base size wheels. Of course once those base size wheels got larger so did the optional wheels. Much easier to get someone to drop extra $$$$ on optional wheels when they are larger than the base model.
I’m not convinced that giving the designers the freedom to lower the cowl will result in smaller diameter rims. Look at 90% of the customs you see. The ‘bigger is better ‘ rule has more than likely been applied. It may have very well have been a starting point. Unfortunately even unmodified factory stock cars and trucks frequently fall victim to owners who must go up in size. They also never bother to consider how this will effect final gear ratio among other factors you mentioned. I’m all with you on ending this current craze. However how many customs and resto-mods has Hagerty featured with 20s on the front and 22s in the rear?. Any performance car produced today with a reasonable size wheel and tire combination would probably be viewed by most as being a low end model. Trucks perhaps more so. Designers can set trends but they’re also forced to follow them.
As a former factory rep for a very large car manufacturer I was told the reason for the bigger tires and wheels was to house larger brakes, which makes a lot of sense. This allows a bigger rotor and a bigger caliper. Both of which require bigger tires and wheels.
If the modern cars didn’t weigh so much, they wouldn’t need such big brakes. Maybe that’s another feedback loop?
This is one of my gripes with modern vehicles. Whether the dog is wagging the tail in terms of cowl height (and other) regulations, or the tail is wagging the dog in terms of desire for more monstrous appearing vehicles, we have certainly gotten to a point where all modern vehicles pretty much look the same – with the exception of exotics and a few ‘throwback’ sports cars.
The bigger wheels started with bigger brakes. Cars today often have brakes larger than old wheels were.
Next it was not so much cowl but more the side impact standards. When they went into effect car sides got taller. Cars like the Camaro and 300 are perfect examples.
To make these side profiles look in perspective the wheels grew. A 15 inch wheel on a 300 would have looked silly.
The cars and trucks really don’t sit higher. Some trucks may with an off road package but they generally use 17” tires.
As for cost my 20” are not any worse than any other tire. Generally the larger tires that cost more are performance tires and that is why they are more not size.
What it all comes down to is design by legislation. You have political folks making laws and they know nothing of car design or care what ghe effects are.
As for weight it depends on the wheel and tire. You can’t judge them by size.
Also the EV cars often sit taller with batteries under the floor. Again higher sides.
People generally like the larger look. Even my side says a truck on base wheels look silly.
Automakers would do smaller lighter and skinnier tires for more mpg but no one would buy them.
I’m really tired of this problem started and exacerbated by Gen X and their need to piss off their parents being my problem.
SUV’s hit their peak in the 1990’s when people born in the 1960’s were in their 30’s.
This isn’t a recent trend. Same with the death of your beloved stick shift. Corvettes in the mid 1980’s were made something in the order of 80% with an AUTO.
Remember the Isuzu Vehicross? That was touted as this revolutionary, wow, new, cool, funky design.
Now EVERY vehicle sold is a “Vehicross” CUV toy.
When I graduated from high school they’d just stopped selling the Ford Ranger because it was “too old, too small, not sold with “the latest tech.”
It was a small, old school Truck. And Auto Journo’s crapped all over it. Complained it wasn’t loaded and bloated.
I’m not falling for this nonsense. You demanded everything become safer, larger, loaded down with technology. That was 15 years ago.
Yes, the wheels are big because “Mike Jones rides on 22’s” and all our favorite Hip Hop artists had big rims on their cars. Trucks weren’t allowed to be small. Wheels needed to be big.
I drive a Crown Vic by the way.
The small truck died for two reasons. Low sales and little if any profits.
Before you blame an entire generation for their choices you also need to consider the economic side of things on the automakers side.
Your beloved Ranger shared parts with the RWD sedans of your era. It saved money and made them profitable. As cars went FWD and killed the RWD mid size cars these parts were no longer available in updated form. This is why the Ranger got old as it had no other cars to rob parts to provide scale.
The same happened to my Beloved GMC Canyon. GM tried to partner with Isuzu. But ended up with a truck that did not sell well and then Isuzu left the deal. Their truck soon died. Ford even partnered with Mazda but it it did not help.
Only Toyota and Nissan kept at it but they had a global market. They sold trucks that shared parts globally that Ford and GM did not.
GM took the risk and brought back the Mid Size truck to the American Market. Ford did their down under first waiting to see how the Colorado did. If offered with Options it makes money. If stripped down there is no money in it.
So to make a cheaper truck today Ford rebodied a cheap econo car as a truck. Even then they make little money but at least it shares engineering with the cheap eco car. But if you want to tow or anything else it take money.
Automakers would love to cover every base with the customer but todays economics prevent that. It is damn hard to make money on low end products and sadly prices are going to a point many can no longer afford a new car at over 50K plus.
Nothing is cheap anymore and the $9999 Ranger is just not possible to build and make any money with it.
Yes, the design feedback loop is real, but it isn’t the only, or even primary reason for taller vehicles. In terms of buying preferences, tastes were influenced by upsizing. Cowls got higher, window sills got higher, seating positions got higher, wheels got larger, brakes got bigger to deal with the increased weight, and so on such that people like and think they need a taller car so they can “see”. People used to complain that it was hard to back out of parking spaces when parked adjacent to a minivan or full size SUV. Now, everything is tall as heck, and wide, too. I drive a sedan and can’t see squat around the fatbutt Equinox in front of me, so I leave more following distance, which people happily exploit to change lanes. Between tall cars and tinted windows, it is very difficult to look ahead to read what traffic is doing, and I think that’s an overlooked aspect of driving safety.
I think the evolution of impact safety requirements is the primary driver of car enlargement. Several articles have been written suggesting cars got bigger because manufacturers exploited CAFE carve outs for SUVs and CUVs, but that’s hooey. The real culprit is impact requirements, especially the evolution of frontal and offset impact tests. The tall cowls, strong a-pillars and floors are needed to pass the partial-offset impact test in particular.
One last thought: I don’t like the move to blown 4-bangers and oversized cars, but that mess isn’t going away as long as target markets adopt and maintain tough impact standards and fuel economy or carbon regs. The forces influencing these design choices are much stronger than anyone’s preferences for smaller, lighter cars. Consumers have accepted high prices, good fuel economy and adequate power in trade for safe cars that sit relatively high, even with the packaging compromises. The US recently relaxed CAFE standards but with the exception of light trucks and large SUVs, most cars aren’t designed exclusively for the North American market. The requirements of scale in manufacturing and global branding mean we will continue to find mostly tall vehicles with small displacement powertrains in the showrooms for the imaginable future.
And one of the biggest reasons for turbocharged 2.0 liter engines? Lower taxes for engines that size in China:
https://cnevpost.com/2022/05/31/china-halves-purchase-tax-on-mainstream-ice-vehicles-for-rest-of-the-year/
Cylinder count is not a big deal if the engine is built right. Most semi truck run Turbo 4 and 6 cylinder. Many indy cars were turbo 4 cylinders for year
The deal is today to meet MPG regs they need smaller more power dense engine engines. I ran a 300 HP turbo ecotec for 10 years and never an issue.
Yes it is more design via goverment regulation but in this case they are not all bad. I ran 13 sec 1/4 miles and got over 30 MPG on the highway and 26 around town.
I had enough torque to spin the tires at 55 MPH. It would trigger the traction control.
Cowls getting higher, BMW kidney grills getting bigger, wheels getting bigger. Everything is getting bigger. I saw a GMC Canyon pickup go by and thought to myself that is a big truck and it is supposedly “midsize” but it seemed more full size large to larger than an F150 from 10+ years ago.
FWIW, I have owned the same brand and model of pickup for the past 25+ years, replacing them about every 4-5 years as they approached 100k miles. The biggest (no pun intended) thing I noticed was that as the wheels (and tires) got taller, they were able to transition road imperfections much easier with the larger diameter wheel/tire, and gave me a smoother ride than the smaller, earlier tire/wheel combinations because the taller tires rolled over the imperfection instead of rolling into the hole/expansion joint/etc. Keep in mind, that my trucks use the standard sized tires with a decent sidewall, not the low-profile tires seen mostly on aftermarket or performance wheels.
One more thing about tires that fill wheel wells. In some not all cases they can improve aero dynamics as the large wheel wells can act as a parachute and catch air. This is why the GM trucks now employ the air curtain and even the cut down on the front of the wheel well. It moves air out or around.
Another thing to is handling. Shorter side walls on the performance cars make for faster steering response and feel.