[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 referred to as Pace World Problem), I, like many drivers earlier than me, had visions of massive, highly effective GT automobiles dancing by way of my head—large, highly effective, rear-wheel drive GT automobiles to be exact. My ideas had been that each 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 sooner automobiles. Nicely, as Peter Cunningham proved various instances this 12 months 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 the best way to drive them shortly, however extra importantly, the best way to set them as much as be pushed shortly. I believe there are a whole lot 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 one among these “wrong-wheel drive” automobiles across the observe shortly.
Begin on the Steering Wheel
Entrance-wheel drive automobiles require a really completely different driving fashion 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 try 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 palms full in any given nook. Sadly for the motive force, tires are solely ready to take action many duties directly earlier than their limits are exceeded. For instance, if a tire is utilizing 80 % of its most obtainable grip for cornering, it might solely use 20 % for acceleration. Any greater than that 20 %, and the tire will go over its most obtainable 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 purpose, it is vitally necessary to minimize 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.
Briefly, it implies that you wish 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 ends up in extra grip for acceleration.
The easiest way to perform this rotation is by lowering 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 way of driver enter, automobile setup or each.
A generally used approach drivers use to induce the automobile into getting entry rotation is trail-braking: lowering, 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 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 few 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 observe days a 12 months. 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 various methods to pores and skin a cat in the case 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 on.). The extra parameters you possibly can modify (suspension pickup factors, roll facilities, customized uprights and management arms), the much less it’s a must to “trick” the automobile into doing what you need.
Rear Tire Strain
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 12 months, 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 any delay in spring response—in contrast to suspension springs, which have to attend for a pressure to journey by way 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 journey extra on the middle of the tread, lowering the contact patch and lowering grip.
There are a few downsides to greater rear tire strain. As a result of lowered grip, greater pressures can have a damaging impact on braking. As well as, an excessive amount of strain may end up in making the tire too stiff and unpredictable (snap free), 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 executed to each avenue automobiles and observe automobiles alike is growing damaging camber on the entrance wheels. Most automobiles run little or no damaging 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 pressure on the inventory C30 suspension that we might find yourself with optimistic camber on some corners though we began with greater than 3 levels of damaging camber.
On inventory front-wheel drive automobiles with out camber plates, a few levels of damaging camber is probably the most you possibly can hope to get inside the inventory shock mount. Including camber plates with a modified high mount ought to help you get a minimal of three levels of damaging 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 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 damaging camber can enhance your automobile’s cornering skills, however don’t neglect 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 at all times been the mantra for front-wheel drive arrange, and for good purpose: It really works—kinda. Stiffening the rear bar does “trick” the automobile into rotation, nevertheless it additionally may end up in a automobile that’s not 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, if you happen to take away an excessive amount of entrance wheel fee, you possibly can 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 purpose in eradicating or disconnecting the entrance bar is to load the skin 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 entire trail-braking part). Executed appropriately, this weight switch has the additional benefit of taking weight completely off the within rear tire, ensuing within the traditional 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 purpose 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 on the lookout for within the rear however precisely the other of what we’d like within the entrance. The purpose with the massive rear bar is to switch the power from the loaded outdoors 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 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 motive force’s seat neighborhood). That is the place a limited-slip differential comes into play. The first purpose 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 free with the automobile’s rear. Pictures Credit score: photosbyjuha.com
There are two essential varieties of diffs utilized in front-wheel drive functions: gear and plate. Gear diffs are far smoother in operation than plate diffs and are considerably lower-maintenance, making them best for daily-driver avenue automobiles that see some observe day use. Gear diffs, nevertheless, have one shortcoming: If the within wheel utterly 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 likely 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 go the entrance at each alternative. With sufficient rear toe, front-wheel drive race automobiles will get extraordinarily free, which can convey a smile to the face of any skilled front-wheel drive pilot.
Now that we’ve the automobile free on nook entry, the driving fashion turns into what I wish to name “pitch and catch.” You may pitch the automobile into the nook, and because the again finish begins to come back round, you catch it with the throttle. This fashion of driving has a few advantages. The primary is that the automobile is rotating sufficient that it needs to 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 enhance sooner, additional serving to exit velocity out of the nook.
Now that you simply’ve executed the unattainable 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 performing profession. Or perhaps you must simply apply 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
Folks at all times discuss caster and the way it provides camber as you flip… That is true nevertheless it additionally jacks the chassis in a nasty method by shifting the skin tire upwards and the within tire downwards which ends up in extra physique roll.
Dick Shine used to say that caster was evil and to by no means enhance it. I neglect the place I ran upon the dialogue… however there may be some type of evaluation that was executed in some unspecified time in the future 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 might extra simply sense the boundaries of the automobile with much less caster, so whereas extra caster may in concept 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 damaging camber on flip in, as a result of steering axis inclination takes camber away.
Nicely, you might if you happen to had caster greater than the 10-15 levels of SAI your automobile could have.
Both method, the impact is simply noticable at excessive steering lock. If you end up 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 wish to say I’ve heard that earlier than, however for some purpose the way in which you stated it simply clicked with me.
I am pondering that if you happen to lower caster / reduce it, it could have the impact of retaining the chassis flatter when turning. Maybe jacking the rear inside up making it looser is why that is so widespread for individuals so as to add caster on a entrance wheel drive automobile? Typically talking it can really feel higher.
10/9/20 11:07 a.m.
I actually get pleasure from my R53 as a every day runabout and occasional observe automobile, however RWD will at all times 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 probably the most SOTP impact with extra (optimistic) caster is steering really feel because it pertains to the self-centering impact, if either side are equal. In autocross, further 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 important downside to the free rear is throughout fast transitions (slalom) as native membership course designers appear to essentially like them. If the rear is free sufficient to nook nicely, it’s typically too free for finest time in transitions. Street racing, the place slalom would 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 dependent upon 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/exhausting suspension bushings, typically steel or Delrin® to be aggressive. They know one thing. Now, to make an fanatic’s competitors automobile extra in a position to keep your required competitors alignment settings you have to clear up that with efficiency suspension bushings. Efficiency urethane/polyurethane to the rescue! Pictured is an entire 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 fitting). Bear in mind within the article, concerning the rear sway bar being extra necessary than the entrance? Additionally, utilizing them could be very near putting in a extra strong suspension. In fact, each sort of auto 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. 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 publish someplace, I would like to see a Section 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 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 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 secure beneath braking however that’s as a result of it stops the rear from shifting 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 just lately began driving/racing a fwd automobile, I’ll admit that I used to be mistaken 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 mistaken with econo-boxes), I had a robust bias based mostly on issues I believed to be true, however by no means skilled firsthand.
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