- Hero image by Matt Parsons. All pictures below were taken from the open-access Internet.

Limits of horsepower: front-wheel-drive cars

19w ago

21.7K

In a world of automotive business we – as consumers – are often being elegantly cheated. Manufacturers offer us engineering solutions which are dubious or even useless. For example, the engine power measured in the hundreds of bhp.

Reading Jeremy Clarskon's book “Born to be riled” from 1999 I was hit by the following:

“Saab once said that it is ‘undesirable’ to feed more than 170 horsepower through the front wheels. Odd then, that its top models are now putting out more than 220 horsepower. This means the front wheels have to deliver that to the road, while dealing with the burden of steering too. Anyone who’s accelerated hard in a powerful front-wheel drive car will have felt what’s called torque steer, as the steering wheel squirms from left to right. It’s horrid.”

As you can see, the 170 bhp limit for the front wheel drive seemed to be reasonable for the late 1990s. Otherwise stress, inefficiency and danger. In around ten years Clarkson met the Saab chaps again and voiced another number in his “Don't stop me now” book:

“Engineers at Saab once told me that the most power you could realistically entrust to a front-wheel-drive car is 220 bhp. A point they proved recently by launching an unwieldy 250-bhp front-driver called the Hot Aero.”

Clarkson also added:

“And yet here’s Autodelta putting 328 bhp through those front wheels. Are they mad? Do they want to kill only their customers, or are they after people coming the other way as well? Driving a front-wheel-drive hatchback with 328 bhp is like playing Russian roulette with a fully loaded gun. It’s like trying to fly a helicopter gunship while drunk: you’re going to crash, and you’re going to die.”

These quotes lead me to a straightforward hypothesis: it is stupid to buy a front-wheel-drive car with stables more than 220 horses. Even if the manufacturer tells you they handle as fluffy ponies. Especially if the manufacturer tells you so!

Now, is my hypothesis correct? Let us check!

And let me start with ponies.

Way back in the late 18th century James Watt decided to improve the steam engine and help the miners. He did that successfully and launched a marketing campaign to sell his new engine. He promised that the engine would complete the work of multiple horses. The reasoning for this promise was set by observing the efficiency of ponies.

Imagine a pony hauling coal carts out of a mine using a winch. Watt calculated that one pony could haul one cart filled with 220lb of coal (~100 kg) 100 feet up (~ 30 meters) a mineshaft in one minute. This is 22,000 lb-ft per minute. Watt incorrectly assumed then that a regular horse must be at least two times stronger than the pony and declared: one horsepower equals to 33,000 lb-ft per minute. The number was not very scientific, but hit the target. Watt's engines became popular and the humanity started measuring power in hp.

By the way, according to my humble and – very likely – unprofessional calculations, it should take 221,6 seconds (~3,7 minutes) for the 1200 kg city-car with a 1 bhp engine to reach 60 kmh (the maximum legal speed in my city). However, the 1 bhp car will very unlikely crumble anywhere above the 30 kmh as any further acceleration will be killed by the air resistance.

So, the car should definitely have more than 1 bhp. But how much more?

Before we move to this, let me drop a word about the front-wheel-drive (FWD) cars, the heroes of this article. Wouldn't it be more rational to mass-produce the rear-wheel-drives (RWD) only?

Nope.

FWD cars are considered to be the optimal choice for a daily commuting. They are usually cheaper to produce and, thus, more affordable new. They offer more space in the cabin and boot as mechanicals take up less room. They have less drivetrain power loss due to the integrated transaxle (in other words, the propelling wheels get above 5% more hp than the ones in the RWD cars). Heavier front makes the FWD cars behave more confidently in slippery situations, such as driving through the mud, gravel, snow or puddles. Also, handling characteristics make it easier to control the FWD in every city-occuring situation.

Speaking of handling characteristics. The FWD cars have a stability advantage over the RWD as the front wheels are responsible for the propulsion. In other words, the traction is applied in front of the vehicle's centre of gravity, what can be compared to your pulling a shopping trolley. It is comparatively easy to pull it as you can steer the trolley with one hand and make it smoothly roll wherever you go. Oppositely, if you push the trolley from behind, you are likely to hold it with both hands and use more power to set the direction. The latter is comparable to how the traction is applied in the RWD cars.

However, tricky things with the FWD start happening on a speed. The things outlined by Clarkson above. The FWD cars usually have a heavy front – carrying engine and transmission – which makes them prone to understeer. In other words, when cornering on a speed, the bonnet drags you into a ravine or to the opposite lane. Apart from this, the front wheels are “overloaded” with work: they propel, turn and break. This overload usually ends up with a torque steer: the front wheels start rotating the steering wheel without your engagement because they “suffer” from the uneven traction. Also, if you floor the car on cornering, the front wheels will do everything to straigthen themselves up. Because the physics of grip. Finally, when you floor the car from a still, it will have extra troubles to get to a speed. When any car accelerates, its weight shifts onto the rear wheels. In the FWD case, the running wheels lose traction and you get spins, squeaks and torque steer. On the contrary, RWD cars use the weight shift as a major advantage.

But again – and this is important – the drawbacks of the FWD cars reveal themselves only at high speeds or during ruthless accelerations.

Does this mean than that the FWD can not be fast-and-fun?

Nope. They can.

In the 1960s, the Mini became a serious rival to Ford and Renault in the rally crosses. The Mini's ability to pull itself through corners and bypass the “column” of the RWD cars which were drifting around the same corners made this underdog a biting one. The Mini Copper S won Monte Carlo three times in (almost) a row: 1964, 1965 and 1967!

Another example is the escaping successes of the Gang des Traction Avant in France in the late 1940s. These notorious chaps used the Citroën 11CV, the first mass-produced FWD, to run away from the police, who were driving the big RWD cars. The FWD vehicle provided the gangsters with a huge advantage on the twisty and bumpy French post-WW2 roads. Because the Traction Avant – literally "improved traction". Gangsters had been successful up to the moment when the police also bought a bunch of similar Citroëns and levelled their chances up.

Speaking honestly, it is only on the straight-lined asphalt when the RWD cars clearly demonstrate their superiority over the FWD. But, speaking even more honestly, the FWD have never been about the speed, but the nimbleness. This is where their fun resides.

Now, returning to the number of horsepower the FWD cars can painlessly handle. Initially, I wanted to use some formulae and address the issue in hard numbers. But I am not that good in physics. Therefore, I will take more descriptive-and-analytic approach.

Two things should be kept in mind when discussing the FWD power limits: the laws of physics (addressed above) and the common sense.

The FWD cars' poor performance on speed can be improved with a proper engineering. However, this will require inventing super-differentials, hyper-gearboxes, ultra-grippy-tyres, mega-hard-suspension and cosmo-advanced-traction-controls. If successful, you will end up with the over-engineering: solving the problems which do not exist in the RWD cars for the sake of solving these problems. Investing a lot of money, energy, resources and skills in making the FWD a little bit faster, but never as fast as the comparable RWD.

The 2010 Focus RS500 stabled 350 bhp and did 0-100 kmh in around 5,6 seconds. The same year's BMW M3 coupé did the same 0-100 kmh in around 4,8 seconds, which is an eternity faster! It also comfortably stabled 414 bhp, what also is an eternity more. Think about how much extra engineering you would need for the RS500 to get at least to the 5-second threshold. By the time you are at that point, with all the over-engineering, it would appear dumb to keep the car FWD. This partially explains why the 2018 RS500 comes with the all-wheel-drive system and does 0-100 in around 4,1 seconds. Propelled by the similar 350 bhp engine.

Here you have another example. The 2018 Seat Leon Cupra R with 306 bhp does 0-100 kmh in around 5,8 seconds. The 2018 Seat Leon FR with 190 bhp (two-litre engine) does the same 0-100 kmh in around 7,5 seconds. The FR is significantly cheaper than the Cupra R (£25,680 with maximum available options against £36,000 for the “bare” Cupra R). The basic 2018 BMW F30 330i (two-litre engine) with 248 bhp does 0-100 kmh in around 5,9 seconds. So, comparable to the fastest Cupra R! The basic 2018 BMW F30 320i with 180 bhp does 0-100 kmh in 7,1 seconds. Faster than the FR, which is more powerful! The BMW prices are comparable to Seat's.

Therefore, it looks unreasonable to buy the 2018 Cupra R or 2010 RS500 for the sake of being invincible on the street-lights. Because BMWs are faster anyway. It is even more unreasonable to boy-tune the 1990s Hondas as they will not likely go faster! They have no traction control to harness the super-natural power!

All this leads me to the conclusion that yes, the FWD cars with more than 220 bhp are a waste of money. Primarily, they are over-expensive due to being over-engineered. The latter achievement, unfortunately, does not fully eliminate all the FWD physical flaws. It also look useless for daily driving as you will never fully engage the engineering sophistication within the legal speed limits. Feeding horses to old FWD relics is not only stupid, but also dangerous. Secondly, the FWD cars will very likely be slower than the comparable RWD or AWD on the asphalt track. And even if they get to the high speeds, the threat of an understeer or the “rude” intrusion of electronics will not make your driving joyful (unless this is what you want to experience or you know how to tame the understeer).

Do you agree?

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And here is a video-lesson how the Saab 900 was sketched:

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P.S. Matt Parsons can be reached here: www.behance.net/Matthew_Parsons_SA

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