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Understeer vs Oversteer: Which is Quicker?

There are 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 the three distinct traits at the limit - "understeer", "neutral", and "oversteer" - this way: Understeer is bad. Neutral is good. Oversteer is slow but fun. And 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. 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):

Limit understeer isn't a true or false deal, however. It isn't either present or absent. It's a range. You can make almost any car understeer or oversteer by provoking it. An F1 car couldn't go through a chicane at 200 mph. It will understeer. Turn the wheel at that speed for a sharp turn, and it will plow straight. 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.

Myth Busting

E46 BMW M3 at Atlantic Motorsport Park - Graham MacNeil ©

People usually associate road-going good RWD cars with oversteer (or at least neutral handling) such an MX-5, but that actually understeers at the limit. BMW M cars also understeer at the limit, a little more so than Miata's. 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 bean counters, saying 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 approached the limit of their cars in corner exit. As long as we're talking about RWD cars on track and there is enough power for the car to get out of its own way, that is generally true.

Grip Balance

C7 Corvette (Stingray) Grand Sport at Atlantic Motorsport Park - Graham MacNeil ©

Any 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 a turn, the car will naturally want to oversteer once you exceed grip in the back because it's the rear tires losing grip (holding/maintaining or controlling 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, you won't be able to put much power down before you go into a drift because suspension tuning put just as much grip up front as there is in the back (i.e. front and rear axles lose grip at roughly the same speed, hence the four wheel drift once you exceed the limit). That means if you are right up to the limit coming out of the turn, you have to be patient before you start to put a lot of power down. But if it is set up to have a little understeer dialed in at the limit, it is much easier to balance and control 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. How much exactly depends on the car (how much power it has, how forgiving it is, and how progressive it is at the limit) and the driver (comfort level/preference).

Perception of Grip Balance

S550 Mustang GT at Atlantic Motorsport Park - Kevin Doubleday ©

Most people who drive truly neutral RWD cars actually describe them as tail happy. Most people who drive RWD 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 are much easier to provoke into a slide once you go to the throttle. Cars that have a bit of understeer dialed in allow you to put more power down.

That little bit of understeer makes the cars approachable and stable, resulting in you being much more comfortable putting your foot down. 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 every corner of every lap, but chances are you can't do it perfectly.

This isn't about holding a slide or avoiding a crash after the back end has started to come around. Many seasoned drivers are good at that and a few are excellent. It is about keeping the 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. You don't have to just take my word for it.

Boris Said once told SAFEisFAST in an interview that "a car that has a little bit of understeer in it is a lot more consistent to drive than a car that has oversteer in it." He can claim three (3) 24-hours of Daytona wins, one 12 hours of Sebring, and even one 24 Hours Nurburgring, all in addition to countless poles and wins in NASCAR and IMSA races.

What About Maximizing Corner Speed?

Scion FR-S (Toyota 86) at ASCC autocross - Kevin Doubleday ©

So maximizing corner speed is useless? Everything we do to carry more speed into a turn are wrong? No, absolutely not. Everything is a balance, of course. The reality is that most cars come from the factory with too much understeer dialed in and you try to do things to make it turn better (square tire setups, suspension tuning, trail braking, etc.). That's why I said you want a little bit of understeer, not a car that plows into every corner screeching its front tires. Unfortunately, all else being equal (i.e. tires, weight, aerodynamics, suspension setup, etc.) max possible corner speed will be lower in a car with a little understeer dialed in vs one that is truly neutral at the limit 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.

F1 royalty Sir Jackie Stewart puts an emphasis on the importance of corner exit. When Captain Slow was sent to him to cut 20 seconds off his lap time (Top Gear Season 8 - Episode 5), Sir Jackie told him: "the exit of the corner is FAR more important than the entry of the corner, with regards to smoothness."

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 which is a very bad example because it has a lot of corners in a short distance (11 in 1.6 miles). 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 gain over 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 generally translates to a much higher speed gain at the corner entry of the next turn or at the end of a straight following that corner. And that gain is a lot more consistent for most drivers turn after turn and lap after lap, as we've established that most drivers including professional ones with multiple titles are more consistent in a car that has a bit of understeer dialed in

Rules Are Meant to Be Broken...

Mazda MX-5 (NA Miata) at Atlantic Motorsport Park - Kevin Doubleday ©

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 so the balance point will change (i.e. you generally will want less understeer on smaller technical tracks and a little more on high speed tracks). 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.

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