Blog Fast Cars by Robert Pepper 14 September 2022
What are the driving technique differences between RWD and FWD?
Every car is different, be that say a Hyundai i20N vs an i30N, let alone that i20N vs a Lotus Elise. And so you need to adapt your driving style to suit, but how?
If you’re on your first few track days, and you’re not at the stage where you’re happy with a 1/10th second improvement on your PB (personal best), and not able to consistently lap within 0.5 seconds of your PB, then don’t worry about whether you’re driving a front, rear or all-drive car. What’s important when you start are the basics of racing lines, trailbraking, power delivery, load transfer, car control basics and more…those fundamentals don’t change from car to car at the novice level.
Once you are chasing tenths, and are consistently quick, then you can move onto the drivetrain-specific considerations, and here we’re going to look at FWD (front wheel drive) vs RWD (rear wheel drive), and assume both cars are identical save their drivetrain, and both are running engines around 100-200kW. We have to do this as the drivetrain differences are less than you may think; I’d say there’s more of a difference between a Porsche 911 and a Toyota 86 than a i20N and MX-5, even if the types of differences are different!
First off, let’s look at the differences in car characteristics between RWD and FWD. Obviously the rear wheels are driven in the RWD, and the front in the FWD. But the vehicle will also typically have a different weight distribution; a FWD may be 60/40% front/rear, and a RWD more like 50/50, or even 40/60 if it’s mid-engined; we’ll assume a front-engined RWD here. Therefore, the centre of gravity in the RWD will be more centrally located, further away from the front axle. The front-drive car has its propulsion point ahead of its centre of gravity, and the rear drive behind. All this affects manouverability and stability under braking and accelerating.
In a FWD car the rear wheels neither drive nor turn. All that is done by the front wheels, so there’s a lot more work to be done with the front tyres on a FWD car. This definitely leads to greater tyre wear on the front wheels for a FWD, but FWD cars usually have tyre-symmetrical layouts so you can swap tyres from front to rear – more powerful RWD cars often have a staggered layout where the front tyres are shorter, and narrower than the rear tyres.
Okay, so for FWD/RWD from a driving technique perspective let’s begin with acceleration. Off the line, the RWD will be typically quicker. The reason is that when a car accelerates, regardless of drivetain, there’s a load (not weight) shift towards the back, which increases grip of those tyres, and for a RWD, the rear tyres are driving so more grip. For FWD, you actually get a grip reduction on the drive wheels the harder you accelerate. So, first point is that you can launch a RWD harder than a FWD, and this is noticeable in first gear, possibly second, especially in the wet.
Now if you do get wheelspin in a FWD you just go slower, nothing much exciting happens. In a RWD, you can spin, particuarly if you have a limited-slip diff or locked axle. This is because the propulsion point of a RWD is behind the centre of gravity, so when the car steps out of line the deviation becomes worse, whereas the FWD “pulls straight”. So, you need to be good with opposite-lock corrections if there’s any wheelspin in a RWD.
FWD vehicles may also have torque steer, which you shouldn’t get in a RWD. So your steering will be more “pure” under power, and you need to absorb what the car is telling you and not assume it’s just torque steer which you can ignore.
Once you’re into third gear there’s no difference, just flat out. There won’t be any torque steer of note, and you’re unlikely to spin the rear wheels although it is possible in the wet.
Now we have arrived at Turn 1, so we are going to brake and downshift. Here we do have a difference. Firstly, you had better learn to heel’n’toe shift a RWD. The reason is that if you don’t, the extra engine braking of the downshift could overwhelm the traction of the rear tyres, and you can even spin. This is less of a problem for a FWD as there’s a load shift to the front so you’re less likely to lock up, and if you do, then you’ll just understeer on, unlikely to spin.
RWDs should be able to brake a fraction later than FWD, as because their weight is less biased to the front then the rear tyre are better able to contribute to the braking effort. However, the effect is small and would only be noticeable under controlled tests; drivers would just do what they normally do and brake late as possible.
What you will notice is turn-in under brakes. The FWD will get very light in the rear, often lifting an inside rear wheel. The RWD will not – again this comes back to weight distribution and centre of gravity location, plus suspension/chassis tune and setup. The FWD may well oversteer on entry, and you can, and should, use this to help rotate into the corner. The RWD will be harder to oversteer into the corner, but has an advantage on the exit we’ll get to. Now the above is a theory generalisation and the bigger factors are going to be tyre pressures, suspension setup front/rear and a host of other factors, so you could easily find your RWD loves to rotate under brakes and your FWD does not, depending on setup.
It is at this point we need to talk about oversteer recovery. In both cases, you want to look where you need to go, steer in that direction, and reduce or at least not increase the rear tyre load. The difference is that with FWD you can accelerate as that helps pull the car straight, and FWD acceleration demands no extra traction from the rear wheels – in fact, it adds grip to the rear. But in a RWD oversteer situation, do not accelerate – you’ll simply demand yet more traction from the rear tyres which they clearly don’t have as otherwise you wouldn’t be oversteering. All that is explained here:
Now we’re into mid-corner, and let’s assume it’s a big long sweeper, maybe third, fourth gear as otherwise there isn’t much of a mid-corner. At this point you’re using all the tyre’s grip for turning, you’re neither really accelerating nor braking. But what if you want to adjust your line, increase or decrease your corner radius? Well, you do that by slightly changing your throttle positon, not so much the steering; add throttle to increase radius, decrease for tighter. This works on both RWD and FWD, but in slightly different ways. When you’re in that big sweeper and increase throttle on a RWD, you’re asking more from the rear tyres so they may go into a slight exceeding of their grip level, which means slight oversteer. In a FWD, you’re asking more from the fronts, which means slight understeer. Now these situations could be reversed or masked depending on setup, how close you are to the grip limits, the nature of the corner…but think about it this way. Imagine you’re on a skidpan, holding a constant 50km/h radius arc. You hit the throttle in a FWD car…you’ll understeer as you overwhelm the front tyres. Hit the throttle in a RWD, you’ll oversteer thanks to overwhelming the rear tyres. Slowly increase the throttle in a RWD and you may just understeer a little. There’s a lot of ‘it depends’ here, because that’s the way car dynamics generally works.
Finally, we’re accelerating out of the corner and here is a significant FWD/RWD difference; with a RWD you may be able to slightly rotate the car under power which is an advantage, means you can tighten the exit arc. But taken to extremes, you can get power-on oversteer which is slow and requires a lift to correct. With a FWD, adding power usually means an element of understeer and running wide which could mean a lift to correct, but you won’t get oversteer. This all becomes much more apparent in a slow-speed, wet corner.
So, your driving line in FWD may need to allow for a wider arc on exit, and that planning starts from when you apply the brakes for a corner. This is particuarly important if you are driving an open-diff FWD (such things are a sin unto the god of racing) as you’re likely to get inside-wheel spin. On the other hand, a well set up FWD with a clever computer-controlled front diff can almost feel like a RWD under power. As ever, it’s all about driving to what you car can, and cannot do.
That’s a brief summary of RWD vs FWD; there certainly are differences, but they can be entirely masked by car setup, drivers naturally adjust anyway to a large extent, and the differences are only really applicable for drivers beyond novice levels.
Here’s a variation on the driveline theme; mid-engined RWD vs front-engined RWD:
And off-topic, but here’s an explanation of double vs single apexes: