How Drivetrain Layouts Effect Performance

fwd

Though racing has its textbook rules, the real world requires consideration given to the different layouts and their own specific requirements, idiosyncrasies and strong points. Four wheel-drive, for instance, has obvious merits in the dirt, but on the racing circuit, the layout lends to good exits and poor entries with regards to cornering. Therefore, a certain line and braking technique is required to get the most out of these cars. While many of the upcoming platforms can obviously have their weight re-distributed and their suspension adjusted to change the vehicle dynamics, there are some basic truths with each platform that any astute road racer ought to become familiar with. For the sake of keeping things comprehensible, let’s begin with some of the simpler, more common platforms.

FR

Front-engine, rear wheel-drive, or FR, is a layout used in most low- and mid-range sports cars, older sedans and even a few economy cars from yesteryear. The packaging and inherent handling balance present with this layout made it a big hit with automakers and enthusiasts alike. Just about every successful drift car utilizes this layout, and more often than not, the budget track car is an FR.

With the majority of the vehicle’s weight sitting over the front axle, FR provides for good cornering speeds and a certain amount of ease behind the wheel. With the bulk of mass in front of the driver and closer to the front axle, the rear end has less to do with rotating the car while cornering. What this means is that while the car might be slightly less likely to change direction in the corner, when it begins to slide, it is still quite manageable thanks to a relatively large “window” between sliding and spinning. Without much weight over the rear axle, the platform is less capable when asked to put the power down, but it makes up for some of its shortcomings with throttle-adjustable angle and a relatively-benign character.

brz

FF

Front-engine, front wheel-drive is a layout more common with today’s offering of compact cars than ever before. With a good deal of weight sitting over the driven wheels, FFs have advantages in low grip situations. For this reason, they’re quite popular on the rally stage.
They also have certain limitations – like the tendency to understeer on-throttle. Because the driven wheels are also the steering wheels, the tires tend to get overloaded since sharing those two responsibilities puts lots of stress on them. For this reason, it’s good to use a bit of trail-braking to help tuck the nose into the apex and ensure a clean line out of the corner. Turning in later usually helps since a sharper entry will help ensure a smooth exit.

4WD

Four wheel-drive has made a great name for itself because it puts power down really effectively. However, depending on whether the layout features a full-time 4WD or a selective 4WD, the influence of driven front wheels can upset the cornering balance, much like a FWD car. To capitalize on the immense corner-exit traction available, a 4WD should be slowed to ensure the apex is met with the car reasonably straight. This doesn’t mean over-slowing the car on the way in, but it does mean putting an emphasis on the second half of the corner and changing the line to minimize the understeer. Extending the braking zone slightly to make a sharper turn covers a bit more ground, but it also “lengthens” the exit – and firing out of corners is what 4WD does best.

sub

MR

For those with a little more money to burn, some seriously exciting handling can be had. Generally speaking, mid-engined cars drive the rear wheels only. Due to the bulk of the weight centered more towards the center of the car, the amount of traction available on exit is stellar. Because the engine is moved towards the rear, this encourages a bit of yaw, or sideways-slip.

The yaw will help rotate the car into the corner and, with the weight more evenly distributed across all four wheels, will provide a very impressive amount of grip through the middle of the corner. The downside to this layout is that extra yaw in effect will make the car more nervous and finicky on the limit: going from a drift to a spin more quickly than other layouts. Only smaller angles are achievable while going sideways, and maintaining that slide requires a very light touch. Basically, a MR car is more sensitive to weight transfers and as a result can be daunting to drive if the fundamentals aren’t fully understood.

RR

Rear-engine, rear wheel-drive is still an exceptionally popular layout today. As championed by the Porsche 911, RR boasts immense traction and requires some interesting driving styles. Rear-engined cars tend to understeer in slower corners, thanks to the bulk of the weight sitting over the rear axle, leaving the front tires light and unresponsive. This understeer, combined with stellar rear grip, requires a line much like that of 4WD. In quicker corners, they are very sensitive to we ight changes, encouraging a long, steady throttle application without any lifting. However, that hefty rear end allows for some big, controllable drifts to be had, and like an FR car, can be slid very effectively out of the corner. The difference being that, with an RR, a bit of oversteer doesn’t necessarily mean a slower exit – the rear grip can still generate acceleration while spinning the tires.

Like the MR car, having the majority of the weight behind the driver gives this layout stellar braking performance. Since weight is transferred forwards during braking, the front tires aren’t easily overloaded thanks to a lighter front end while static. In effect, the weight is spread more evenly over all four tires during the braking phase with a RR car. This trounces most front-engined cars which can overload the front tires due to the weight imposed on them by motor and the act of braking.

Layouts in Racing

Once, when watching an American LeMans Series race from a few years back, I was fortunate enough to witness a battle between a 911 RSR, a Corvette C6R and a 458GT. The 911 RSR, being a rear-engined, rear wheel-drive car, showed great poise out of the corner but was slightly slower on the way in. This allowed for it to shine in the longer, straighter sections. The front-engined, rear wheel-drive Corvette C6R, interestingly, showed great entry speed and would always have a slight advantage in the tighter corners. The mid-engined 458 GT’s advantage was that it had no handicap – it worked well everywhere. Though this sounds too simplistic when talking about sophisticated racing cars, the merits were true and visible to anyone willing to watch. All of the drivers were familiar with these nuances and likely tuned some of the excessive traits out by fettling with the suspension and weight distribution, but nonetheless, they still had to contend with the laws of physics.

About Tommy Parry 101 Articles
Tommy Parry has been racing and writing about racing cars for the past seven years. As an automotive enthusiast from a young age, Tommy worked jobs revolving around cars throughout high school and tried his hand on the race track on his twentieth birthday. After winning his first outdoor kart race, he began working as an apprentice mechanic to amateur racers in the Bay Area to sharpen his mechanical understanding. He has worked as a trackday instructor and automotive writer since 2012 and continues to race karts, formula cars, sedans and rally cars in the San Francisco region.
Copyright © 2005-2017 RacingJunk.com All Rights Reserved.

Designated trademarks and brands are the property of their respective owners. Use of this Web site constitutes acceptance of the RacingJunk.com
Terms of Use, Classifieds Disclaimer, Privacy Policy, and Cookie Policy