Speed Secrets: FWD vs RWD

 

Some drivers think that a FWD car is not fun. I was driving a FWD Acura Integra in an endurance race. One of the team members had been driving RWD only and said, “This car is a blast to drive!” FWD can be a lot of fun, when set up correctly. If not, they can push like a dump truck with old front tires on a wet road (but then again, so can a RWD). 

 

What we are dealing with, ultimately, is getting the feeling in the steering wheel and the seat of our pants. So there are some things that you need to do if you want to be fast in a FWD car. You need to adapt your driving style to the FWD car. FWD and RWD cars require a few different techniques when driving them at the limit.

 

Let us take a look at what the platforms have in common. We are dealing with four tires (friction circle) and a platform that moves around as we use the pedals and steering wheel. Getting on the brake, the weight transfers forward and when we get on the accelerator, the rear compresses and the front lifts up. Therefore, the load goes off the front tires and goes to the rear. On most platforms, this is the perfect recipe to achieve understeer. This is the case with most FWD cars and lower-horsepower RWD cars. (The stickier the tire, the more this is evident in a low-horsepower RWD car).

 

Driving a FWD car: So we need to adjust our driving style to minimize the potential issue of understeer that a FWD car comes with. Trail braking, most times, is a must. We use it to keep the front-end down (load on the front tires) and lighten up the rear. Most race cars with FWD are set up loose to help rotation. Many different set-up approaches are used for this: stiff springs in the rear, heavy sway bar, high air pressure, toe out, etc.  (Sorry, different article. For this one, we will focus on how to drive the car). Our goal is to get the car rotated so we can get on the power while exiting the corner, and get on our going-forward-pedal right before the apex or at the apex, depending on the rotation. There are two ways of doing this: either late apex, getting the turning done using trail braking and a tighter radius in the beginning of the corner; or early apexing, sacrificing a tiny bit of mid-corner speed to achieve rotation (again while using trail braking). By using either technique, we straighten out the exit, which allows us to get on the power earlier (smoothly!). Patience is paramount with the throttle, as otherwise we will be inducing the all-feared understeer. And we all know that overworking the tire is going to make matters worse and the spiral has started… yikes!

As always, there are exceptions and sometimes this one example may work: I once drove a FWD car that was set up beautifully. When driving everything at the limit, the car had a slight understeer from apex out when off throttle (it should not have – remember more load on the tire, we should have more grip). However, when I cracked the throttle a tiny bit, the car pulled in and became neutral. WOW! What a feeling when altering your driving style and it works! My right foot had to do a lot of convincing of my brain, which was screaming, “No, not yet!”

So a couple of things happened there. The set-up on the differential made it pull in and also the tiny bit of throttle made the front tires more efficient (overloaded with no throttle and perfect with a little less load). Hard to overcome, as that is not what normally should happen when you drive a FWD car. And I am just talking maybe 5% throttle, as too much power will now overload the tire and you will lose lateral grip. The egg between your foot and the gas pedal is there and it has a very thin shell.

 

Driving a RWD car: Higher horsepower RWD cars can compensate for the understeer when picking up the throttle. You will now "overload" the rear tire, and thereby increase slip-angle, so the rear tire becomes less efficient (loses grip and makes the car continue to rotate mid-corner). When this is possible, we don’t need to concentrate on finalizing the car rotation, as power will give us the last bit of rotation, and not make the car understeer when getting on the gas. The laws of physics still apply and when we apply power, the weight will still shift back, leaving the front tires light. But, as I said, the throttle can now help compensate for weight transfer. This is so much fun. However, keep in mind you are going past the optimal slip angle of the tire, so don’t get greedy. If you do, you are “messing” with the friction circle, pulling our little friction ball a little closer to center. Although it may only slightly diminish the overall grip, you lose grip – you go slower. I know it is FUN going sideways and hanging the back end out. Heck, I did it for over fifty-one miles for the World Record and could not take the grin off my face, but it is not fast. Also, keep in mind that if you are sliding the rear tires, it generates heat, which makes the tire slide more. That darn spiral….

Fast is at the outer edge of the friction circle and sliding is not efficient; working the car at the peak of the slip angle curve is what you’re searching for. Back to basics and doing them well: proper late braking, sensitive brake release as you turn in, letting it roll, then picking up the throttle smoothly on exit. That’s having the ball at the outer edge of the friction circle all the time. The only time you can’t achieve this is when accelerating in a straight line… and when you find that car, it is very expensive, has a ton of horsepower, has very wide tires, and pounds your chest when it takes off down the drag strip!

Driving at the peak of the slip angle can at times can be hairy (learning how to be comfortable being uncomfortable – bet you have heard that before). But you will go faster than the driver who is a “spectator” favorite. It is, in my opinion, easier to drive a car past the peak of the slip angle and right on the edge, but that again is a whole another article. 

It all comes back to having good balance in the car, allowing the handling to be manipulated with the gas, brake, and the steering wheel. So much in driving at the limit is about these three inputs, and how they are used in concert. 

The biggest difference: The biggest difference between FWD and RWD is when you get into situations where you get oversteer or when a correction needs to take place.

In a FWD car, when getting to a slide, you would want to stay on the gas to pull yourself out of it. In a RWD car, when the back end comes out, you get off the gas for the tire to regain grip and correct with the steering. Going from a FWD car to RWD car can be detrimental if oversteer happens and your brain is trained to stay on the gas. Very exciting and possibly a very expensive outcome! Going from a RWD car (with RWD reaction when sliding) to a FWD car is not nearly as bad when getting into a slide. It’s always a huge benefit to have good car control when dancing with the car at the limit.

All-wheel-drive (AWD) shares a lot of the same characteristics with FWD. However, there are some very sophisticated differentials that have torque vectoring, which can make the car do amazing things and make it really neutral and a beauty to drive.

A lot of driving a race car is common sense – sometimes a sense that you don’t have time to consciously think about in mid-corner, but builds up with driving experience. The theory is simple and can be accomplished if you have a good sensitivity for what is happening with your car. Driving a car at the limit demands concentration, so you can always be ahead of what is going to happen next. Looking ahead, feeling the tires, proper brake release, and smooth application of power will suffer if you lose your concentration.

In the end, the biggest difference in driving the different platforms is your mind and being set and used to driving a certain platform a certain way. Not being willing to adapt will hold you back in your ability to make the transition. Just like half the field is out mentally when the rain starts to drop  – it is all about the mindset and listening to the car.

 

There are so many “it depends” when driving a car and each car has its own personality for how it needs to be driven. Hopefully, this will give you some different options and fuel for thought when jumping into different platforms, no matter what the drive is.

 

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