[Editor’s Note: This article originally appeared in the November 2012 issue of Grassroots Motorsports.]
Once I began my professional profession within the Touring Automotive class of the Pirelli World Problem (then generally known as Velocity World Problem), I, like many drivers earlier than me, had visions of massive, highly effective GT automobiles dancing by means of my head—massive, highly effective, rear-wheel drive GT automobiles to be exact. My ideas had been that every one issues being equal, a rear-wheel drive automobile will completely run circles round a front-wheel drive one, and naturally, I wished to be within the quicker automobiles. Nicely, as Peter Cunningham proved various occasions this yr operating his front-wheel drive Acura head-to-head with the rear-wheel drive Mustangs and Camaros within the WC GTS class, well-set up, well-driven front-wheel drive automobiles could be greater than aggressive with their rear-wheel drive counterparts.
Pictures Credit score: Rupert Berrington
A part of the explanation I nonetheless get pleasure from racing front-wheel drive automobiles is that through the years, I’ve discovered a factor or 10 about easy methods to drive them shortly, however extra importantly, easy methods to set them as much as be pushed shortly. I believe there are a variety of drivers who say they don’t like racing front-wheel drive automobiles, however I believe that’s primarily as a result of they’ve by no means pushed a correctly arrange one. So let’s take a better take a look at what it takes to get considered one of these “wrong-wheel drive” autos across the observe shortly.
Begin on the Steering Wheel
Entrance-wheel drive automobiles require a really completely different driving type than their rear-wheel drive counterparts. The principle factor for a driver to acknowledge is that in a front-wheel drive race automobile, the entrance tires are attempting to do a number of jobs on the identical time. Between coping with braking, cornering and acceleration forces, the entrance tires actually do have their arms full in any given nook. Sadly for the driving force, tires are solely ready to take action many duties without delay earlier than their limits are exceeded. For instance, if a tire is utilizing 80 % of its most accessible grip for cornering, it might solely use 20 % for acceleration. Any greater than that 20 %, and the tire will go over its most accessible grip and lose traction, with the outcome being the dreaded “power-on” push that front-wheel drive automobiles are notorious for.
Correctly executed trail-braking shifts weight from the rear of the automobile to the entrance, growing grip on turn-in. Pictures Credit score: Rupert Berrington
For that cause, it is extremely essential to reduce the quantity of steering enter as early within the nook as attainable earlier than you begin going to throttle, which can give the tire a bit extra grip to work with for acceleration out of the nook.
In brief, it signifies that you need to get the automobile to rotate extra within the earlier phases of cornering so at apex (earlier than going to throttle), the automobile is pointed higher down the next straightaway, permitting the driving force to lower steering enter, which leads to extra grip for acceleration.
One of the best ways to perform this rotation is by reducing the quantity of rear grip in relation to the entrance (or by growing entrance grip in relation to the rear) at nook entry—both by means of driver enter, automobile setup or each.
A generally used method drivers use to induce the automobile into getting entry rotation is trail-braking: reducing, or trailing off, brake strain because the automobile approaches the apex of the nook. This system permits the load to stay transferred towards the entrance of the automobile at nook entry, which helps add grip to the entrance and has the additional benefit of shifting weight off the rear. This switch of weight to the entrance of the automobile ought to permit the rear to lose sufficient grip to have some rotation into the nook, thus permitting the driving force to open the wheel rather more at exit for higher grip and acceleration.
Now we’ve seen a little bit of what the driving force can do to assist negate among the front-wheel drive disadvantages, however what can the automobile do to assist in return? That is the place automobile setup comes into play. There are a number of changes that may be made to help in “loosening up” a front-wheel drive automobile and countering the terminal understeer they generally exhibit. Some are pretty easy tweaks suited to automobiles that solely see just a few observe days a yr. Others are much more concerned and solely make sense for devoted race automobiles.
Pictures Credit score: photosbyjuha.com
The disclaimer right here (earlier than I get completely ripped on the GRM boards) is that there are lots of methods to pores and skin a cat on the subject of automobile setup—way over I’ve area right here to enter. I’m going to slant my recommendation extra towards inventory, manufacturing front-wheel drive automobiles than specialised, extremely modified front-wheel drive race automobiles (last-gen WC, WTCC, BTCC, and so forth.). The extra parameters you’ll be able to modify (suspension pickup factors, roll facilities, customized uprights and management arms), the much less you must “trick” the automobile into doing what you need.
Rear Tire Stress
One of many easiest issues to do to assist get rotation in a front-wheel drive automobile is to extend rear tire strain. On the Volvo C30 Touring Automobiles we ran within the Pirelli World Problem final yr, we had almost a 10-psi unfold between the entrance and rear of the Pirelli P Zero slicks. Elevated strain makes the tire stiffer, which in flip, will increase efficient spring fee. Extra importantly, it will increase spring fee on the level of contact with the highway. This implies there isn’t a delay in spring response—in contrast to suspension springs, which have to attend for a power to journey by means of the suspension with a view to reply. As well as, the elevated tire strain within the rear modifications the form of the tire, making it rounder, which makes it experience extra on the middle of the tread, reducing the contact patch and reducing grip.
There are a few downsides to larger rear tire strain. On account of lowered grip, larger pressures can have a detrimental impact on braking. As well as, an excessive amount of strain may end up in making the tire too stiff and unpredictable (snap unfastened), so make small will increase in strain till you discover that candy spot that works properly in your automobile.
Camber and Caster
One other easy, but efficient change that may be finished to each avenue automobiles and observe automobiles alike is growing detrimental camber on the entrance wheels. Most automobiles run little or no detrimental camber straight from the manufacturing facility. As soon as in a nook, the forces on the automobile are nice sufficient to flex the suspension and considerably lower the quantity of camber on the wheel. These bespoke Pirelli slicks we run put a lot power on the inventory C30 suspension that we’d find yourself with constructive camber on some corners regardless that we began with greater than 3 levels of detrimental camber.
On inventory front-wheel drive automobiles with out camber plates, a few levels of detrimental camber is essentially the most you’ll be able to hope to get throughout the inventory shock mount. Including camber plates with a modified prime mount ought to will let you get a minimal of three levels of detrimental camber, which is the beginning vary used on our production-based C30 race automobiles. Operating camber in that vary will permit the tire to put fully flat within the nook, giving it the most important contact patch and the utmost quantity of grip.
Pumping up the rear rubber and hitting the entrance tires with extra detrimental camber can increase your automobile’s cornering talents, however don’t overlook to switch that variable within the driver’s seat. Pictures Credit score: photosbyjuha.com
Caster appears to be the red-headed stepchild of suspension changes. Most conversations about front-wheel drive suspension engineering revolve round camber and shock changes, with little to no point out of caster. The explanation caster is a extremely efficient adjustment on front-wheel drive race automobiles is that as caster is elevated, camber may also improve exponentially with steering angle. Principally, the extra you flip the steering wheel, the extra camber, and doubtlessly extra grip, you get.
And there was a lot rejoicing.
Subsequent in line are anti-roll bars. “Disconnect the entrance and stiffen the crap out of the rear” has at all times been the mantra for front-wheel drive arrange, and for good cause: It really works—kinda. Stiffening the rear bar does “trick” the automobile into rotation, but it surely additionally may end up in a automobile that isn’t as evenly balanced as one which makes use of bars at each ends. That being stated, in case your automobile is affected by terminal understeer, eliminating the entrance bar will certainly assist. On the flipside, when you take away an excessive amount of entrance wheel fee, you’ll be able to have points with physique roll to the purpose the place you lose contact patch as a result of camber change—leading to much less entrance traction slightly than extra. That is very true on automobiles with MacPherson strut entrance suspensions.
The aim in eradicating or disconnecting the entrance bar is to load the skin entrance going right into a nook as a lot as attainable by permitting higher weight switch throughout trail-braking. (See, now you want you hadn’t skimmed over that complete trail-braking part). Accomplished accurately, this weight switch has the additional benefit of taking weight completely off the within rear tire, ensuing within the basic three-wheel, “peeing canine” cornering stance that front-wheel drive automobiles are so well-known for. As soon as that inside rear tire is off the bottom, grip within the rear is successfully minimize in half, additional aiding rotation throughout cornering.
The aim with stiffening the rear bar is to switch weight to the skin because the automobile enters a nook. The issue with this weight switch is that it takes weight off the within tires, which is precisely what we’re searching for within the rear however precisely the alternative of what we’d like within the entrance. The aim with the large rear bar is to switch the power from the loaded outdoors rear tire to the unloaded inside entrance, making an attempt to maintain it planted and hopefully giving it extra grip each laterally and for ahead acceleration.
Regardless of how a lot we attempt to maintain that unloaded, inside-front tire planted, nevertheless, it’ll nonetheless have much less grip than the skin, loaded tire. If we attempt to go to throttle at this level, that inside tire will shortly exceed its most grip, lose traction and start to understeer (instantly adopted by a lot swearing coming from the driving force’s seat neighborhood). That is the place a limited-slip differential comes into play. The first aim of the diff in a front-wheel drive software is to use energy effectively to each wheels, with out extreme wheel spin from the much less loaded, inside entrance wheel.
Putting in a differential helps maintain that inside-front tire planted, whereas a contact of rear toe permits the driving force to play quick and unfastened with the automobile’s rear. Pictures Credit score: photosbyjuha.com
There are two essential forms of diffs utilized in front-wheel drive purposes: gear and plate. Gear diffs are far smoother in operation than plate diffs and are considerably lower-maintenance, making them ultimate for daily-driver avenue automobiles that see some observe day use. Gear diffs, nevertheless, have one shortcoming: If the within wheel fully loses contact with the observe floor, a gear diff will behave equally to an open diff and ship extra energy to the unloaded wheel. That is nice for smoky burnouts however not so nice for getting round a observe shortly. This makes plate diffs the clear winner when used for a full-time, devoted front-wheel drive observe automobile.
The final alignment trick used to get a front-wheel drive automobile to play good is rear toe. Rear toe is among the strongest alignment instruments used to loosen up cussed front-wheel drive race automobiles. As little as 1/16-inch toe out within the rear can get the rear finish of your automobile seeking to move the entrance at each alternative. With sufficient rear toe, front-wheel drive race automobiles will get extraordinarily unfastened, which can convey a smile to the face of any skilled front-wheel drive pilot.
Now that we’ve got the automobile unfastened on nook entry, the driving type turns into what I wish to name “pitch and catch.” You possibly can pitch the automobile into the nook, and because the again finish begins to come back round, you catch it with the throttle. This type of driving has a few advantages. The primary is that the automobile is rotating sufficient that it must be higher pointed down the following straightaway, permitting us to open up the steering wheel and reduce the quantity of grip the tires have to steer the automobile and permit extra for use for acceleration.
Secondly, as a result of we’re having to make use of the throttle to counteract the rotation of the automobile, we will likely be going to throttle lengthy earlier than nook apex, growing the period of time the automobile is accelerating. Moreover, as a big share of front-wheel-drive automobiles today are turbocharged, going to throttle early helps the automobile construct increase sooner, additional serving to exit pace out of the nook.
Now that you just’ve finished the unimaginable and gotten a front-wheel drive race automobile dealing with properly, you’re free to tackle simpler assignments—like fixing the European debt disaster or resurrecting Lindsay Lohan’s appearing profession. Or possibly it is best to simply observe your trail-braking.
When carving round a cone, does your automobile resemble a canine lifting its hind leg to a hearth hydrant? If that’s the case, your anti-roll bar setup is heading in the right direction. Pictures Credit score: Rupert Berrington
Individuals at all times speak about caster and the way it provides camber as you flip… That is true nevertheless it additionally jacks the chassis in a foul manner by shifting the skin tire upwards and the within tire downwards which leads to extra physique roll.
Dick Shine used to say that caster was evil and to by no means improve it. I overlook the place I ran upon the dialogue… however there’s some type of evaluation that was finished sooner or later to see why he might need thought this… And it needed to do with the tire’s “path” and the place it fell in relation to the contact patch inflicting a disconnect in steering really feel as grip is exceeded. In a nutshell, you could possibly extra simply sense the bounds of the automobile with much less caster, so whereas extra caster may in principle offer you extra grip, the purpose at which traction is exceeded is completely different than the place you are feeling suggestions within the wheel or some such. I want I might discover the dialogue once more.
In reply to flatlander937 :
Caster won’t ever add detrimental camber on flip in, as a result of steering axis inclination takes camber away.
Nicely, you could possibly when you had caster larger than the 10-15 levels of SAI your automobile might have.
Both manner, the impact is simply noticable at excessive steering lock. When you’re driving on target you might be hardly ever over 10 levels of steering angle and often beneath 5. Altering camber with caster changes is like shuffling the deck chairs on the Titanic, technically you make a change however we’re speaking a tenth of a level or so.
In reply to Pete. (l33t FS) :
I need to say I’ve heard that earlier than, however for some cause the best way you stated it simply clicked with me.
I am considering that when you lower caster / reduce it, it might have the impact of preserving the chassis flatter when turning. Maybe jacking the rear inside up making it looser is why that is so frequent for folks so as to add caster on a entrance wheel drive automobile? Typically talking it should really feel higher.
10/9/20 11:07 a.m.
I actually get pleasure from my R53 as a each day runabout and occasional observe automobile, however RWD will at all times be my go to for toys. It is simply the best way God meant it.
I’ve auto-crossed FWD for many years and essentially the most SOTP impact with extra (constructive) caster is steering really feel because it pertains to the self-centering impact, if each side are equal. In autocross, further caster does result in legitimate camber acquire because the steering inputs are a lot higher on smaller, tighter course. The camber/toe feedback are dead-on although. The one important downside to the unfastened rear is throughout speedy transitions (slalom) as native membership course designers appear to actually like them. If the rear is unfastened sufficient to nook properly, it’s usually too unfastened for finest time in transitions. Highway racing, the place slalom does not actually apply, further caster is not almost as efficient. Suspension set is at all times a compromise with each setting, so it actually is determined by the driving force “really feel” for the given setup.
One other level to make is that skilled race automobiles need to run with very, very agency/arduous suspension bushings, typically steel or Delrin® to be aggressive. They know one thing. Now, to make an fanatic’s competitors automobile extra capable of keep your required competitors alignment settings you want to remedy that with efficiency suspension bushings. Efficiency urethane/polyurethane to the rescue! Pictured is a whole PROTHANE efficiency urethane suspension bushing equipment for a Honda Civic (on the left) and their stiffer than inventory rubber rear sway bar bushings (on the precise). Bear in mind within the article, concerning the rear sway bar being extra essential than the entrance? Additionally, utilizing them may be very near putting in a extra sturdy suspension. In fact, each kind of auto is completely different, however to take away the suspension slop/looseness general is fascinating!
This text has been my information for modifying, my Fiesta, good to see it out once more. Whenever you do ALL of this, after which decrease the automobile and stiffen the suspension and improve the brakes, no bar up entrance is no-bueno. My larger entrance bar was from a GRM article or put up someplace, I would like to see a Part II follow-up article on what occurs after you do what’s on this article.
2/17/22 12:02 p.m.
This can be a fairly refined FWD arrange story and dialog however I did have one query. I too have been racing FWD’s for a few years and early on, the oldsters that did my preliminary alignments, a race store in LA, set the entrance toe out, and the rear in, not a Robb suggests, rear out.
My understanding was the rear toe-in steered higher into the nook very like the Honda Passive rear steering, because the suspension hundreds up, the within rear tire toes in. The earlier the automobile rotates, the earlier the throttle could be utilized.
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