Make Your Front-Wheel-Drive Car Faster | Advice From Pro Racer Robb Holland

[Editor's Note: This article originally appeared in the November 2012 issue of Grassroots Motorsports.]

When I started my pro career in the Touring Car class of the Pirelli World Challenge (then known as Speed World Challenge), I, like many drivers before me, had visions of big, powerful GT cars dancing through my head—big, powerful, rear-wheel drive GT cars to be precise. My thoughts were that all things being equal, a rear-wheel drive car will totally run circles around a front-wheel drive one, and of course, I wanted to be in the faster cars. Well, as Peter Cunningham proved more than a few times this year running his front-wheel drive Acura head-to-head with the rear-wheel drive Mustangs and Camaros in the WC GTS class, well-set up, well-driven front-wheel drive cars can be more than competitive with their rear-wheel drive counterparts. 

Photography Credit: Rupert Berrington

Part of the reason I still enjoy racing front-wheel drive cars is that over the years, I’ve learned a thing or 10 about how to drive them quickly, but more importantly, how to set them up to be driven quickly. I think there are a lot of drivers who say they don’t like racing front-wheel drive cars, but I think that’s mainly because they have never driven a properly set up one. So let’s take a closer look at what it takes to get one of these “wrong-wheel drive” vehicles around the track quickly.

Start at the Steering Wheel

Front-wheel drive cars require a very different driving style than their rear-wheel drive counterparts. The main thing for a driver to recognize is that in a front-wheel drive race car, the front tires are trying to do several jobs at the same time. Between dealing with braking, cornering and acceleration forces, the front tires really do have their hands full in any given corner. Unfortunately for the driver, tires are only able to do so many tasks at once before their limits are exceeded. For example, if a tire is using 80 percent of its maximum available grip for cornering, it can only use 20 percent for acceleration. Any more than that 20 percent, and the tire will go over its maximum available grip and lose traction, with the result being the dreaded “power-on” push that front-wheel drive cars are infamous for. 

Properly executed trail-braking shifts weight from the rear of the car to the front, increasing grip on turn-in. Photography Credit: Rupert Berrington

For that reason, it is very important to lessen the amount of steering input as early in the corner as possible before you start going to throttle, which will give the tire a bit more grip to work with for acceleration out of the corner. 

In short, it means that you want to get the car to rotate more in the earlier phases of cornering so at apex (before going to throttle), the car is pointed better down the following straightaway, allowing the driver to decrease steering input, which results in more grip for acceleration. 

The best way to accomplish this rotation is by decreasing the amount of rear grip in relation to the front (or by increasing front grip in relation to the rear) at corner entry—either through driver input, car setup or both.

Trail-Braking

A commonly used technique drivers use to induce the car into getting entry rotation is trail-braking: decreasing, or trailing off, brake pressure as the car approaches the apex of the corner. This technique allows the weight to remain transferred toward the front of the car at corner entry, which helps add grip to the front and has the added benefit of shifting weight off the rear. This transfer of weight to the front of the car should allow the rear to lose enough grip to have some rotation into the corner, thus allowing the driver to open the wheel much more at exit for better grip and acceleration.

Get Wrenchin’

Now we’ve seen a bit of what the driver can do to help negate some of the front-wheel drive disadvantages, but what can the car do to help in return? This is where car setup comes into play. There are several adjustments that can be made to assist in “loosening up” a front-wheel drive car and countering the terminal understeer they commonly exhibit. Some are fairly simple tweaks suited to cars that only see a few track days a year. Others are far more involved and only make sense for dedicated race cars. 

Photography Credit: photosbyjuha.com

The disclaimer here (before I get totally ripped on the GRM forums) is that there are many ways to skin a cat when it comes to car setup—far more than I have space here to go into. I’m going to slant my advice more toward stock, production front-wheel drive cars than specialized, highly modified front-wheel drive race cars (last-gen WC, WTCC, BTCC, etc.). The more parameters you can modify (suspension pickup points, roll centers, custom uprights and control arms), the less you have to “trick” the car into doing what you want.

Rear Tire Pressure

One of the simplest things to do to help get rotation in a front-wheel drive car is to increase rear tire pressure. On the Volvo C30 Touring Cars we ran in the Pirelli World Challenge last year, we had nearly a 10-psi spread between the front and rear of the Pirelli P Zero slicks. Increased pressure makes the tire stiffer, which in turn, increases effective spring rate. More importantly, it increases spring rate at the point of contact with the road. This means there is no delay in spring response—unlike suspension springs, which have to wait for a force to travel through the suspension in order to respond. In addition, the increased tire pressure in the rear changes the shape of the tire, making it rounder, which makes it ride more on the center of the tread, decreasing the contact patch and decreasing grip.

There are a couple of downsides to higher rear tire pressure. Due to reduced grip, higher pressures can have a negative effect on braking. In addition, too much pressure can result in making the tire too stiff and unpredictable (snap loose), so make small increases in pressure until you find that sweet spot that works well for your car. 

Camber and Caster

Another simple, yet effective change that can be done to both street cars and track cars alike is increasing negative camber on the front wheels. Most cars run very little negative camber straight from the factory. Once in a corner, the forces on the car are great enough to flex the suspension and substantially decrease the amount of camber on the wheel. Those bespoke Pirelli slicks we run put so much force on the stock C30 suspension that we would end up with positive camber on some corners even though we started with more than 3 degrees of negative camber.

On stock front-wheel drive cars without camber plates, a couple of degrees of negative camber is the most you can hope to get within the stock shock mount. Adding camber plates with a modified top mount should allow you to get a minimum of 3 degrees of negative camber, which is the starting range used on our production-based C30 race cars. Running camber in that range will allow the tire to lay completely flat in the corner, giving it the biggest contact patch and the maximum amount of grip.

Pumping up the rear rubber and hitting the front tires with more negative camber can boost your car’s cornering abilities, but don’t forget to modify that variable in the driver’s seat. Photography Credit: photosbyjuha.com

Caster seems to be the red-headed stepchild of suspension adjustments. Most conversations about front-wheel drive suspension engineering revolve around camber and shock adjustments, with little to no mention of caster. The reason caster is a highly effective adjustment on front-wheel drive race cars is that as caster is increased, camber will also increase exponentially with steering angle. Basically, the more you turn the steering wheel, the more camber, and potentially more grip, you get. 

And there was much rejoicing.

Anti-Roll Bars

Next in line are anti-roll bars. “Disconnect the front and stiffen the crap out of the rear” has always been the mantra for front-wheel drive set up, and for good reason: It works—kinda. Stiffening the rear bar does “trick” the car into rotation, but it also can result in a car that is not as evenly balanced as one that uses bars at both ends. That being said, if your car is suffering from terminal understeer, getting rid of the front bar will definitely help. On the flipside, if you remove too much front wheel rate, you can have issues with body roll to the point where you lose contact patch due to the camber change—resulting in less front traction rather than more. This is especially true on cars with MacPherson strut front suspensions.

The goal in removing or disconnecting the front bar is to load the outside front going into a corner as much as possible by allowing better weight transfer during trail-braking. (See, now you wish you hadn’t skimmed over that whole trail-braking section). Done correctly, this weight transfer has the added benefit of taking weight entirely off the inside rear tire, resulting in the classic three-wheel, “peeing dog” cornering stance that front-wheel drive cars are so well known for. Once that inside rear tire is off the ground, grip in the rear is effectively cut in half, further aiding rotation during cornering.

The goal with stiffening the rear bar is to transfer weight to the outside as the car enters a corner. The problem with this weight transfer is that it takes weight off the inside tires, which is exactly what we are looking for in the rear but exactly the opposite of what we need in the front. The goal with the big rear bar is to transfer the energy from the loaded outside rear tire to the unloaded inside front, attempting to keep it planted and hopefully giving it more grip both laterally and for forward acceleration.

Differential

No matter how much we try to keep that  unloaded, inside-front tire planted, however, it’ll still have less grip than the outside, loaded tire. If we try to go to throttle at this point, that inside tire will quickly exceed its maximum grip, lose traction and begin to understeer (immediately followed by much swearing coming from the driver’s seat vicinity). This is where a limited-slip differential comes into play. The primary goal of the diff in a front-wheel drive application is to apply power efficiently to both wheels, without excessive wheel spin from the less loaded, inside front wheel.

Installing a differential helps keep that inside-front tire planted, while a touch of rear toe allows the driver to play fast and loose with the car’s rear. Photography Credit: photosbyjuha.com

There are two main types of diffs used in front-wheel drive applications: gear and plate. Gear diffs are far smoother in operation than plate diffs and are substantially lower-maintenance, making them ideal for daily-driver street cars that see some track day use. Gear diffs, however, have one shortcoming: If the inside wheel completely loses contact with the track surface, a gear diff will behave similarly to an open diff and send more power to the unloaded wheel. This is great for smoky burnouts but not so great for getting around a track quickly. This makes plate diffs the clear winner when used for a full-time, dedicated front-wheel drive track car.

Rear Toe

The last alignment trick used to get a front-wheel drive car to play nice is rear toe. Rear toe is one of the most powerful alignment tools used to loosen up stubborn front-wheel drive race cars. As little as 1/16-inch toe out in the rear can get the rear end of your car looking to pass the front at every opportunity. With enough rear toe, front-wheel drive race cars will get extremely loose, which will bring a smile to the face of any experienced front-wheel drive pilot. 

Now that we have the car loose on corner entry, the driving style becomes what I like to call “pitch and catch.” You can pitch the car into the corner, and as the back end starts to come around, you catch it with the throttle. This style of driving has a couple of benefits. The first is that the car is rotating enough that it should be better pointed down the next straightaway, allowing us to open up the steering wheel and decrease the amount of grip the tires need to steer the car and allow more to be used for acceleration. 

Secondly, because we’re having to use the throttle to counteract the rotation of the car, we will be going to throttle long before corner apex, increasing the amount of time the car is accelerating. Additionally, as a large percentage of front-wheel-drive cars these days are turbocharged, going to throttle early helps the car build boost sooner, further helping exit speed out of the corner.

Go Forth

Now that you’ve done the impossible and gotten a front-wheel drive race car handling well, you’re free to take on easier assignments—like solving the European debt crisis or resurrecting Lindsay Lohan’s acting career. Or maybe you should just practice your trail-braking.

When carving around a cone, does your car resemble a dog lifting its hind leg to a fire hydrant? If so, your anti-roll bar setup is on the right track. Photography Credit: Rupert Berrington

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Comments
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flatlander937
flatlander937 HalfDork
10/7/20 9:40 a.m.

People always talk about caster and how it adds camber as you turn... This is true however it also jacks the chassis in a bad way by moving the outside tire upwards and the inside tire downwards which results in more body roll. 

Dick Shine used to say that caster was evil and to never increase it. I forget where I ran upon the discussion... but there is some kind of analysis that was done at some point to see why he might have thought this... And it had to do with the tire's "trail" and where it fell in relation to the contact patch causing a disconnect in steering feel as grip is exceeded. In a nutshell, you could more easily sense the limits of the car with less caster, so while more caster might in theory give you more grip, the point at which traction is exceeded is different than where you feel feedback in the wheel or some such. I wish I could find the discussion again.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
10/7/20 9:48 a.m.

In reply to flatlander937 :

Caster will never add negative camber on turn in, because steering axis inclination takes camber away.

 

Well, you could if you had caster higher than the 10-15 degrees of SAI your car may have.

 

Either way, the effect is only noticable at high steering lock.  When you are driving on course you are rarely over 10 degrees of steering angle and usually under 5.  Changing camber with caster adjustments is like shuffling the deck chairs on the Titanic, technically you are making a change but we're talking a tenth of a degree or so.

flatlander937
flatlander937 HalfDork
10/7/20 9:58 a.m.

In reply to Pete. (l33t FS) :

I want to say I've heard that before, but for some reason the way you said it just clicked with me.surprise

I'm thinking that if you decrease caster / minimize it, it would have the effect of keeping the chassis flatter when turning. Perhaps jacking the rear inside up making it looser is why this is so common for people to add caster on a front wheel drive car? Generally speaking it will feel better.

350z247
350z247 New Reader
10/9/20 11:07 a.m.

I really enjoy my R53 as a daily runabout and occasional track car, but RWD will always be my go to for toys. It's just the way God intended it.

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