[Editor’s Note: This article originally appeared in the November 2012 issue of Grassroots Motorsports.]
After I began my professional profession within the Touring Automobile class of the Pirelli World Problem (then often known as Velocity World Problem), I, like many drivers earlier than me, had visions of massive, highly effective GT automobiles dancing by my head—huge, 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. Effectively, as Peter Cunningham proved various instances 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 might 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 over time, I’ve discovered a factor or 10 about easy methods to drive them rapidly, however extra importantly, easy methods to set them as much as be pushed rapidly. I feel there are loads of drivers who say they don’t like racing front-wheel drive automobiles, however I feel that’s primarily as a result of they’ve by no means pushed a correctly arrange one. So let’s take a better have a look at what it takes to get one in all these “wrong-wheel drive” autos across the monitor rapidly.
Begin on the Steering Wheel
Entrance-wheel drive automobiles require a really completely different driving model than their rear-wheel drive counterparts. The primary 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 similar 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 motive 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 out there grip for cornering, it may possibly solely use 20 % for acceleration. Any greater than that 20 %, and the tire will go over its most out there grip and lose traction, with the consequence 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 vitally essential to reduce the quantity of steering enter as early within the nook as potential 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 implies 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 motive force to lower steering enter, which leads to extra grip for acceleration.
The easiest way 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 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 advantage 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 motive force to open the wheel far more at exit for higher grip and acceleration.
Now we’ve seen a little bit of what the motive force can do to assist negate a number of 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 monitor days a yr. Others are way 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 various methods to pores and skin a cat relating to automobile setup—excess of I’ve house 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 many others.). The extra parameters you’ll be able to modify (suspension pickup factors, roll facilities, customized uprights and management arms), the much less it’s important to “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 Vehicles 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 price. Extra importantly, it will increase spring price on the level of contact with the highway. This implies there isn’t any delay in spring response—not like suspension springs, which have to attend for a drive to journey by the suspension with the intention to reply. As well as, the elevated tire strain within the rear adjustments the form of the tire, making it rounder, which makes it journey extra on the middle of the tread, reducing the contact patch and reducing grip.
There are a few downsides to increased rear tire strain. As a consequence of decreased grip, increased pressures can have a destructive 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 nicely on your automobile.
Camber and Caster
One other easy, but efficient change that may be carried out to each avenue automobiles and monitor automobiles alike is growing destructive camber on the entrance wheels. Most automobiles run little or no destructive camber straight from the manufacturing unit. 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 drive on the inventory C30 suspension that we might find yourself with constructive camber on some corners though we began with greater than 3 levels of destructive camber.
On inventory front-wheel drive automobiles with out camber plates, a few levels of destructive camber is essentially the most you’ll be able to hope to get throughout the inventory shock mount. Including camber plates with a modified high mount ought to mean you can get a minimal of three levels of destructive camber, which is the beginning vary used on our production-based C30 race automobiles. Working camber in that vary will permit the tire to put utterly 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 destructive 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 even enhance exponentially with steering angle. Mainly, the extra you flip the steering wheel, the extra camber, and probably 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 all the time 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, in the event you take away an excessive amount of entrance wheel price, 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 reasonably than extra. That is very true on automobiles with MacPherson strut entrance suspensions.
The objective in eradicating or disconnecting the entrance bar is to load the surface entrance going right into a nook as a lot as potential by permitting higher weight switch throughout trail-braking. (See, now you want you hadn’t skimmed over that complete trail-braking part). Carried out appropriately, this weight switch has the additional advantage of taking weight totally 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 reduce in half, additional aiding rotation throughout cornering.
The objective with stiffening the rear bar is to switch weight to the surface because the automobile enters a nook. The issue with this weight switch is that it takes weight off the within tires, which is strictly what we’re in search of within the rear however precisely the other of what we want within the entrance. The objective with the large rear bar is to switch the vitality from the loaded exterior rear tire to the unloaded inside entrance, trying to maintain it planted and hopefully giving it extra grip each laterally and for ahead acceleration.
Irrespective of how a lot we attempt to preserve that unloaded, inside-front tire planted, nevertheless, it’ll nonetheless have much less grip than the surface, loaded tire. If we attempt to go to throttle at this level, that inside tire will rapidly exceed its most grip, lose traction and start to understeer (instantly adopted by a lot swearing coming from the motive force’s seat neighborhood). That is the place a limited-slip differential comes into play. The first objective 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 preserve that inside-front tire planted, whereas a contact of rear toe permits the motive force to play quick and unfastened with the automobile’s rear. Pictures Credit score: photosbyjuha.com
There are two important kinds 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 very best for daily-driver avenue automobiles that see some monitor day use. Gear diffs, nevertheless, have one shortcoming: If the within wheel utterly loses contact with the monitor 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 monitor rapidly. This makes plate diffs the clear winner when used for a full-time, devoted front-wheel drive monitor automobile.
The final alignment trick used to get a front-wheel drive automobile to play good is rear toe. Rear toe is without doubt one of 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 trying to move the entrance at each alternative. With sufficient rear toe, front-wheel drive race automobiles will get extraordinarily unfastened, which can deliver a smile to the face of any skilled front-wheel drive pilot.
Now that we’ve the automobile unfastened on nook entry, the driving model 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 return round, you catch it with the throttle. This model 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 must 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 might be going to throttle lengthy earlier than nook apex, growing the period of time the automobile is accelerating. Moreover, as a big proportion 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 carried out the inconceivable and gotten a front-wheel drive race automobile dealing with nicely, you’re free to tackle simpler assignments—like fixing the European debt disaster or resurrecting Lindsay Lohan’s appearing profession. Or perhaps it’s best to simply apply your trail-braking.
When carving round a cone, does your automobile resemble a canine lifting its hind leg to a hearth hydrant? In that case, your anti-roll bar setup is heading in the right direction. Pictures Credit score: Rupert Berrington
View feedback on the GRM boards
Folks all the time speak about caster and the way it provides camber as you flip… That is true nevertheless it additionally jacks the chassis in a foul means by transferring the surface 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 enhance it. I overlook the place I ran upon the dialogue… however there may be some sort of evaluation that was carried out in some unspecified time in the future to see why he may 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 possibly can extra simply sense the bounds of the automobile with much less caster, so whereas extra caster may in principle provide you with extra grip, the purpose at which traction is exceeded is completely different than the place you’re 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 destructive camber on flip in, as a result of steering axis inclination takes camber away.
Effectively, you possibly can in the event you had caster increased than the 10-15 levels of SAI your automobile might have.
Both means, the impact is barely noticable at excessive steering lock. When you find yourself driving heading in the right direction you’re hardly ever over 10 levels of steering angle and often underneath 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 way in which you stated it simply clicked with me.
I am considering that in the event you lower caster / reduce it, it might have the impact of retaining the chassis flatter when turning. Maybe jacking the rear inside up making it looser is why that is so frequent for individuals so as to add caster on a entrance wheel drive automobile? Typically talking it is going to really feel higher.
10/9/20 11:07 a.m.
I actually get pleasure from my R53 as a day by day runabout and occasional monitor automobile, however RWD will all the time be my go to for toys. It is simply the way in which 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 either side are equal. In autocross, extra caster does result in legitimate camber acquire because the steering inputs are a lot better on smaller, tighter course. The camber/toe feedback are dead-on although. The one vital disadvantage to the unfastened rear is throughout fast transitions (slalom) as native membership course designers appear to actually like them. If the rear is unfastened sufficient to nook nicely, it’s typically too unfastened for finest time in transitions. Street racing, the place slalom does not actually apply, extra caster is not almost as efficient. Suspension set is all the time a compromise with each setting, so it actually will depend on the motive force “really feel” for the given setup.
One other level to make is that skilled race automobiles must run with very, very agency/onerous suspension bushings, usually steel or Delrin® to be aggressive. They know one thing. Now, to make an fanatic’s competitors car extra in a position to preserve your required competitors alignment settings you should remedy that with efficiency suspension bushings. Efficiency urethane/polyurethane to the rescue! Pictured is an entire PROTHANE efficiency urethane suspension bushing package for a Honda Civic (on the left) and their stiffer than inventory rubber rear sway bar bushings (on the fitting). Keep in mind within the article, in regards to the rear sway bar being extra essential than the entrance? Additionally, utilizing them could be very near putting in a extra sturdy suspension. After all, each kind of car is completely different, however to take away the suspension slop/looseness total is fascinating!
This text has been my information for modifying, my Fiesta, good to see it out once more. Once 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 might 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.
It is a fairly subtle 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 parents 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 masses up, the within rear tire toes in. The earlier the automobile rotates, the earlier the throttle might be utilized.
In reply to Brock2 :
Nope. Toe in is extra steady underneath braking however that’s as a result of it stops the rear from transferring round. Toe out within the rear is what helps the automobile to rotate. In case your store is saying completely different then take your automobile to a different store
As somebody who spent 20 years driving as “proper wheel drive” purist, having not too long ago began driving/racing a fwd automobile, I’ll admit that I used to be fallacious and utterly agree with the opening of the article. Given I used to be by no means uncovered to something apart from sloppy econo-boxes, (nothing fallacious with econo-boxes), I had a powerful bias primarily based on issues I believed to be true, however by no means skilled firsthand.
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