Understeer vs Oversteer: Which is faster?
It doesn't matter which side of the pond you're on. If you call yourself a petrol head or a gear head, you'll have no shortage of automotive journalists praising neutral handling balance, sliding a car half way around a track, and condemning understeer as the enemy of speed. It's not just journalists, either. Forums for all sorts of cars are filled with people who hate understeer and try their best at exorcising every last understeering demon out of their cars. But is understeer actually that bad?
Drifting vs Hot Laps
Everyone seems to categorize cars under "understeer", "neutral", and "oversteer". Since most people don't get to drive a multitude of different cars, let alone push them to their limits, most opinions are formed based on professional reviews. That's fine in general, but there is a distinction between "fun" and "fast". Drifting is a lot of fun, yet everyone knows that drifting is not the fastest way around a track. People don't seem to make that distinction when it comes to hot lapping, though.
Of course, terminal understeer is not the fastest way either, nor is it any fun (unlike drifting). But whenever someone thinks of any understeer, they think of something like this (fast forward to 2:35):
You can make almost any car understeer or oversteer by provoking it, though. An F1 car couldn't go through a chicane at 200 mph. It will understeer. Strictly speaking, a car is neutral if it goes into a four wheel slide as you start to exceed its limits without provoking either under- or oversteer. Otherwise, if the front end starts to go wide, the car understeers at the limit. If the rear end starts to slide, the car oversteers at the limit.
People usually associate road-going good RWD cars with oversteer such an MX-5, BMW M cars, etc. but those cars actually understeer at the limit. A magnificent, nearly faultless Cayman GT4 also understeers at the limit. In fact, the vast (vast) majority of mainstream production cars understeer at the limit, even the ones typically described as "neutral". Almost everyone will blame lawyers and say manufacturers consider understeer to be "safer", but it's not the only reason. It's also because you can go faster with a little bit of understeer...
It's true and I'm sorry, but most people who think they have to get rid of all understeer to go faster either drive low-power, momentum cars, or just haven't put their foot down hard enough on the go-fast pedal. This only applies to RWD cars on track and the reason is because of what I said a couple of paragraphs up. You can make almost any car oversteer (or understeer) by provoking it.
Now, a RWD car with a decent amount of power could easily be provoked into oversteer using a little more power than grip allows. That means that if you put your foot down in a RWD car going around the turn, the car will naturally want to slide once you exceed grip in the back (holding/maintaining that slide is much more dependent on proper suspension tuning, but initiating a slide is straight forward in any RWD car with good power).
If the car is set up to be neutral or - especially - "loose" (tail happy), you won't be able to put much power down, you'll just go into a drift. But if it is set up to be slightly on the understeer side, it is perfectly stable under power.
You can think of the grip balance as a sliding scale, not just singular isolated points. Zero - or neutral - is in the middle and understeer and oversteer are on either side. You'll find some people who say they can't stand understeer, the car needs to be tail happy. Then there are those who say they don't want the back end to ever come out. Both are fine if you are just out there to have fun and/or never push beyond your comfort zone. But what you want for speed is somewhere very close to zero (neutral) but towards the understeer side, say 10% towards understeer.
Perception of Grip Balance
Most people who drive truly neutral cars actually describe them as tail happy. Most people who drive cars that have a slight amount of understeer dialed in describe them as neutral. The reason being is simple. Cars that are truly neutral at the limit feel loose once you go to the throttle. Cars that have a bit of understeer dialed in feel neutral.
That little bit of understeer makes the cars approachable, stable, AND fast. Moreover, it makes it much easier to be consistent. I have no doubt there are people who will argue that and say they can hold a slide right at the edge of the limit every corner of every lap, but chances are, unless people associate your last name with multiple world F1 championships, you can't do it consistently.
This isn't about holding a slide or avoiding a crash after the back end has started to come around. Many (many) drivers are good at that. It is about keeping that car right at the edge of grip all the time OR bringing it back after it crossed the edge while losing the least amount of time. It is much easier to do that in a car with a bit of understeer dialed in than oversteer.
What about maximizing corner speed?
Everything is a balance, of course, That's why I said you want a little bit of understeer, not a car that plows into every corner screeching its front tires. All else being equal (i.e. tires, weight, aerodynamics, suspension setup, etc.) corner speed will come down as you go from neutral to understeer because your front tires will have less grip which means you can't turn as well. But the thing to remember is that corner exit matters more than corner entry when it comes to lap times.
If you think of the total time the car spends in the entry of a corner on a track, it's a fraction of the overall lap. It's less than a third, for instance, in my car on our local track. You stand to gain a whole lot more by maximizing the other two thirds of the lap. Moreover, focusing on the exit - meaning a little more stable/understeer to be able to put power down - pays huge dividends in speed by the time you get to the next corner.
You are not just looking at sacrificing, say, 1-2 mph in corner entry/mid corner to gain 1-2 mph over the rest of the lap, which would be a gain in itself since it's a longer portion of the lap. There's more to be had than that. A small sacrifice of 1-2 mph you lose in entry to optimize the exit could translate to a gain of 10+ mph higher speeds at the end of a straight following that corner because you can put power down that much better.
Rules are meant to be broken...
Now, there are exceptions to the above. Like I said, this mainly applies to RWD cars on track. I will discuss other drivetrain layouts (FWD and 4WD/AWD) in future posts, but the main thing to remember is that, even for RWD, as the course/circuit gets smaller and tighter, the benefit of maximizing speeds between corners and on the straights diminishes. That's because there just isn't enough room to build speed and you have to try as much as possible to maintain it.
The same is true for momentum cars, regardless of course length or size. Momentum cars just don't have enough power to build a lot of speed. Fast laps are done by minimizing braking and maximizing corner speed, meaning understeer will slow you down. But the majority of modern sports cars don't fall under that category. They're big, heavy, tall, and have plenty of power. They stand to gain a lot more by maximizing use of available power.