Steering Explained (for Dummies Like Me!)
Some people might have deja vu about this article that I totally did not post here long ago.
Oversteer and understeer are different than steering feel and precision. The latter is due to hydraulic power assisted steering (HPAS) or electric power assisted steering (EPAS). HPAS gives more feel, but EPAS is cheaper to produce and allows a car to steer itself.
The 997 had some of the best steering feel besides the E46 3 Series because it was HPAS. The 991, however, has EPAS. Mind you, the EPAS on the 991 and 991.2 is quite good. On BMWs, however, it isn’t quite as good. In fact, every time I drive or talk about my mom’s 330i, I cannot help but make some sort of comment about how numb and artificial the steering is. No steering feel whatsoever. The reason why I like the 570S and 600LT over the 991 911 Turbo/Turbo S comes down to the fact that I’d rather have McLaren’s HPAS over Porsche’s EPAS.
If we went to a track, with me in a 600LT and you were in a 911 Turbo, you’d cream me on the straights but I’d get you in the corners...not because the McLaren necessarily handles better (although mid engine is generally more balanced than front or rear engined), but mostly because the steering feel would help me not overdrive the tires and spin out.
A 600LT McLaren
Understeer basically means that, upon corner entry, the car’s nose has a hard time rotating in the direction of travel that you point the wheel (basically, it keeps trying to go straight as you attempt to turn). Simple physics is usually to blame. Either having too much weight or too little weight over the front end increases the chance of you running into this problem.
This VW Beetle is proned to understeer if it does not have rear wheel steering because of all the weight over the rear axle.
Basically, in cars with FWD, where the engine, transmission, and driven wheels are in the front (usually the engine ends up sitting in front of the front axle), placing a YUGE amount weight on the nose of the car. Due to the laws of inertia, the more massive (heavier) the front of the car is, the more likely it is to resist turn in and consequently understeer. This is why FWD based AWD systems usually compensate by having a torque vectoring rear diff that can send power to either of the rear wheels (such systems can be found on the Focus RS and Audi S cars with the Sport Differential). This increases the force applied on turn in and thus allows you to overcome the inertia resulting from all the weight over the nose.
Audis (like this RS 3) are known to understeer because of their traditionaly nose-heavy FWD-based natures
However, mid (and rear) engined cars are also prone to understeer, especially in slick conditions. They usually have almost no weight over the front wheels, meaning that they don’t have as much force pushing the front wheels into the pavement, meaning that the front wheels start to slide upon corner entry and consequently the car understeers. Manufacturers take different approaches to deal with this. Audi and Lamborghini give their R8 and Huracans lots of downforce over the front end, very grippy Michelin Pilot Sport Cup tires for their performance models, and AWD (which both allows the car to grip better due by nature of being AWD and by adding weight over the nose). McLaren tends to use extremely lightweight materials to balance the weight of the rest of the car, active aerodynamics to push the car into the ground, and super sticky Super Trofeo tires—pretty much the most grippy street tires you can fit to a road car. Porsche (as you know) uses rear wheel steering and also offers grippy tires and AWD. The 911 is prone to understeer because there’s basically no weight over the front of the car because all the weight is in the back, behind the rear axle (this is pretty much the opposite of the FWD-based Audi, yet has the exact same result: understeer!). By fitting rear wheel steering to the 911, Porsche can overcome the inertia generated at the rear of the car that makes the car continue straight instead of corner. If you want to understand understeer, just hop in a Porsche 911 WITHOUT rear wheel steering and chuck it into a corner. Then, hop in one WITH rear wheel steering and chuck it into the same corner. The latter will turn in as soon as you flick the wheel, while the former might plow straight before turning in, which is understeer.
Mid engined cars (like this Audi R8 V10 quattro) are proned to understeer on loose surfaces due to the lack of grip (and weight) at the front of the car.
Oversteer is easy to explain. When someone (either intentionally or unintentionally) causes the back tires to lose contact with the road and slide, this is called oversteer. Another good word for oversteer is drifting. Cars with RWD or RWD based AWD platforms normally are more inclined to oversteer because more torque is generated at the rear of the car, pushing it into the corner.
This is oversteer in the F90 M5
So, to recap: hydraulic power assisted steering (HPAS) and electric power assisted steering (EPAS) affect steering feel, whereas oversteer and understeer concern how a car corners (especially on turn in).