FWD FTW

If you look at the YSAR Library, you will find a short description of The Front-Wheel Driving High-Performance Advantage by Jack Doo. When I read it, I remember thinking “oh, that’s cool”, but none of the content really struck me as “FWD is actually better than RWD”. Given my recent experiments in RWD vs. FWD, I have come away with the following provocative thought.

For 99% of YSAR readers, FWD is faster than RWD

Primary Disadvantages

First off, let’s look at why that might not be true.

  • 0-60 and 1/4 mile: RWD wins
  • 60-0: RWD wins
  • 0-100-0: RWD wins
  • Skid Pad: RWD wins

FWD vehicles have a disadvantage in a straight line. As soon as they accelerate, weight shifts to the rear, away from the drive wheels. At low speeds where gearing allows high acceleration, FWD vehicles spin their tires. For the drag strip, you want as much weight over the drive wheels as possible. So in order for FWD to have good off-the-line acceleration, it needs extra weight over the front wheels.

FWD vehicles are also worse at braking. When you double the load on a tire, it doesn’t produce double the grip. Not quite. The best situation for braking is to have 50/50 weight distribution during braking. This might be 40/60 static weight distribution like a RR layout. FWD vehicles might be at something like 80/20 during braking, which is pretty terrible.

For cornering, the best weight distribution is closer to 50/50 because all 4 tires are contributing to grip. FWD vehicles are much farther away from 50/50 than RWD vehicles, and so they also lose on the skid pad.

Since race tracks are composed of straights and corners, in theory RWD should be superior to FWD.

In theory, theory and practice are the same. In practice, they are not. — Albert Einstein

Primary Advantages

Common knowledge says there is one place where FWD has an advantage: rain. Why exactly does FWD win in the rain? If you look at the RWD advantages above, all of them should hold true in the rain. It’s not like rain changes the coefficient of friction differently for RWD and FWD. Both are lowered the same amount. So why is FWD faster in the rain? Maybe it isn’t. But if it is, why doesn’t this lead to FWD being generally faster under all conditions?

I think what all of this boils down to is the following truths (which are true because some Internet expert named Ian said so).

  1. Cars are driven by humans
  2. It’s better to turn when slow than fast

In order to drive a vehicle at the limit of adhesion, the driver must have confidence in their car and their abilities to drive the car. It doesn’t matter what potential a car has if a driver is unable to extract it. I see this all the time in data. One driver gets 0.2G more grip than the other driver in every corner. Both are driving what they perceive to be the limit. Neither is driving the true limit. They are driving their own limits. A car that inspires confidence allows a driver to get closer to the actual limit. Why does FWD inspire confidence? Because RWD may break loose on acceleration and cause a spin. Fear of spinning turns out to be one of the biggest problems of high performance driving.

To explain the next FWD advantage, I want you to imagine a completely different scenario. You’ve probably seen kids riding on skateboard ramps. I used to do that when I was younger. A skateboarder goes up one side, turns, and goes to the other side. This is repeated back and forth often with tricks in the air. Now imagine if you wanted to turn on the flat bottom of the ramp and go back up the side you just descended. Well, it would be impossible. While you could turn on the flat bottom, you probably wouldn’t have enough grip to conserve the momentum to return back up the ramp.

Here’s another imperfect analogy. Imagine you’re dogfighting in WW2. You can try to out-turn your opponent in a horizontal plane or perform yo-yo’s in the vertical plane. A yo-yo is a maneuver where the plane flies nearly straight up, turns at very low speed, and reverses direction back down. This can be repeated over and over much like riding a skateboard ramp. All of the turning is done at the top of the yo-yo. If you tried to turn at the bottom of the dive, you would lose all of your momentum and would be unable to get altitude again. A dogfighter who has an altitude advantage can keep that by bouncing an opponent all day. But if said dogfighter tries to make a flat turn at the bottom, the advantage is forever lost and now it’s an equal fight.

Cornering a car is like skateboarding on a ramp or performing a yo-yo in a plane. You know that saying “in slow, out fast”? Yes, you’ve heard that a thousand times. There is a slow part of the corner and there is a fast part of the corner. The slow part is where you want to do your turning, not the fast part.

A FWD car uses its front wheels for acceleration and its rear tires for grip. Because the rear tires have only one job, grip, they aren’t going to slide out under acceleration the way RWD does. This is where FWD vehicles give a driver confidence. A FWD driver knows that as soon as they add throttle, they can pull themselves out of a slide. This means they can enter a corner with more rotation. In other words, FWD gives the driver confidence to rotate more when going slowly. As described in the analogies above, turning while going slow is much better than turning while going fast. FWD also gives the driver confidence to accelerate in the 2nd half of the corner because the rear wheels aren’t going to lose traction and cause a spin. Let’s summarize.

  • FWD is better in the early part of a corner where rotation happens
  • FWD is better in the late part of the corner where acceleration happens

So what happens to the non-expert RWD driver? First off, they enter the corner well under the limit because they’re worried about oversteering and spinning. Since they are going slow, they are invited to add throttle in the mid-corner. If they add a little throttle, they understeer as the front tires unload and search for traction. If they add a lot of throttle, they oversteer as the rear tires fail to simultaneously balance lateral and longitudinal grip. The RWD driver ends up spending a lot of time at partial throttle because the rear tires are being asked to turn and accelerate at the same time.

For the sake of equality, let’s imagine what happens to the non-expert FWD driver. They too enter the corner under the limit. But they enter faster because they aren’t as worried about spinning. Entering faster is somewhat paradoxical because the FWD vehicle actually is worse at braking. In the mid-corner, they too are invited to add throttle, but this just causes a little understeer, which the driver mitigates by lifting a little. Lifting also helps rotate the car and so it practically turns itself through the corner. In the second half of the corner, the FWD driver only has one job: add the right amount of throttle that tracks out to the exit. There is no sawing at the wheel.

Summary

The FWD advantages aren’t so much physical advantages of the car as they are mental advantages to non-professional drivers. Driving a race car at the limit is difficult, dangerous, and nerve-wracking. Getting the most out of a car really means getting the most out of yourself. And that really comes down to your skill and your confidence in your skill. It is my contention that you will get more out of yourself driving FWD than RWD. I think this is true in the real world and in simulation. Does that mean you should give up RWD in favor of FWD? No, you should drive both. The skillset required to drive FWD is different than RWD, but there is a huge overlap. Ultimately, as you improve as a driver, the FWD advantages diminish, and maybe one day you’re faster in RWD. That hasn’t happened to me yet.

Postscript

My brother called me to remind me that FWD loses at Pineview (his local track) every time. There are caveats to the FWD advantage. If you’re not in danger of spinning or crashing, there will be no FWD advantage. In high grip situations, RWD should win. Heck, RWD should win all of the time, even in the rain. It just doesn’t be we suck at racing.

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