Challenges When Racing a Street Vehicle - 928 Motorsports, LLC When Racing a... · Challenges When Taking a Vehicle ... own Carl Fausett of 928 Motorsports, LLC ... drag racing and

Challenges When Taking a Vehicle Designed for

Street Use and Forcing it to Go Racing Or

“How will the stock (name your vehicle here) will be destroyed by racing”

Table of Contents

Session I Street Cars Racing

Weight and Weight Distribution

Sprung and Unsprung weight; Acceleration Chart; Polar Moments

Chassis Flexing

Framed Vehicles; Unibody Vehicles; The Convertible; The Roll Cage

Braking

Lockup; Threshold braking; Pedal Effort; Brake Pedal Location;

Calipers: Construction; Calipers: Location; Rotor Selection;

Rotor Weight; Drilled, Dimpled, or Grooved; Fluids; Brake Pads;

Compliance in the System; Brake Bias; Air Ducts and Cooling

Suspension and Steering

Center of Gravity; Roll Center; Ride Height; Track; Rubber Bushings;

Springs; Snubbers; Swaybars and Their Mounts; Mount Failures;

Shocks; Power Steering; Alignment; Camber and the Race Car; Caster;

Toe; Bump Steer; Ackerman Angles

Copyright 2012, 928 Motorsports, LLC All Rights Reserved

On Nov 15, 2012 a joint SAE (Society of Automotive Engineers) and PCA (Porsche Club of America) conference on "Challenges when Racing A Street Vehicle" was held in Chicago Illinois with the featured speaker, our own Carl Fausett of 928 Motorsports, LLC® About 110 attendees came to hear Carl's lecture on how race stresses on stock parts create failure and how to build your street car into a racer in such a way as to avoid those failures.

The lecture lasted for 2 hours, and is the first in a series of two lectures on this topic.

“Let me open by introducing you – the audience – to each other. Half of you are Porsche enthusiasts and passionate followers of sports cars. The other half are members of the Society of Automotive Engineers. I’m going to try to hit the middle-ground between your two interests. My best hope is not to educate you, but rather to enlighten you to a situation that you may not have previously been aware of regards racing a production street vehicle.

In the first session, I’ll cover Vehicle Weight and Weight Distribution; Chassis Flexing; Braking; and Suspension and Steering

In the second session, I’ll cover the Engine; Exhaust Systems, and The Drivetrain. (This session is not included herein and is available as a separate download)

Assumptions

When I mention “racing” I am focused on road racing, track and closed course racing. Autocross, SOLO 1, and DE days do apply, but to a lesser extent because of the brevity of the event. This information will not apply to drag racing and land speed racing as their needs are unique to their sports.

When I mention “car” I’m speaking of production street sedans. Fords, Chevy’s, Corvettes and Mitta’s, BMW’s, and yes, Porsches.

When I mention “brakes” disc brakes are assumed. Nobody should be racing drum brakes in this day-and-age.

When I mention “transmission” I’ll be talking about manual transmissions.


The title: “Forcing it to go racing” sounds aggressive. Make no mistake; it is an aggressive and forceful act to take a vehicle designed for street use and subject it to racing loads.

By no means is this an all-inclusive list or a thorough discussion of any one topic as time won’t permit it. But we will overview each of these items, and in the end, I think you will better understand how ill-equipped for racing the standard street vehicle is.

This means opportunity in after-market parts and services (like our host facility here) and spawns experts in a wide variety of niches.

Why do people take their street car and go racing?

1) because they are trying to learn to handle their cars better at its limits (The DE Day concept from Dr. Ferdinand Porsche) or it’s just because…

2) that’s the car they have. “Run what you brung” Hell. I road-raced and stock-car raced BUICKS, because that’s what I had.

Later, I would start to race a Porsche 928. “Why in heavens name would you take a 928, a touring car, to the race track? Because it’s what I had.

And later it would podium at Pikes Peak twice in the Open Division, and set the world 928 land speed record at the Bonneville Salt Flats.

These, plus wins in PCA, MC, and NASA wheel-to-wheel racing, demonstrates that it can be done.


Vehicle Weight and Weight Distribution

Weight is all bad in a road racer—it adversely effects acceleration, braking and cornering. Weight is a penalty in all directions, all the time.

Weight-removal is a constant project. You can’t say you’ve “done it” because it is never done. As you replace a clutch— it is time to consider an aluminum flywheel. As you replace an exhaust, it is time to consider lightweight thin-wall tubing. When you add a roll cage, consider chrome moly instead of steel tubing.

It’s getting better, should you select a more modern production car to race. Now that fuel economy is at the front of the consumer’s mind, modern street cars are becoming much more weight conscience. But even then the factory still makes decisions based on production-scale numbers and cost of manufacturing – and the individual racer does not have to. And, if you have selected an older model to take racing, the opportunities to lighten the car are even more numerous. So- we find amble places to “disagree” with the factory in weight and weight distribution.

Some weight is easier to remove than others—some of these ideas take no more than time and yield good results. Other weight-saving ideas cost money (like lowering your unsprung weight).

Here are just a few ideas on how to lighten your production car that cost nothing but your time:


Then there are those things that may cost you a little money. Here a just a few ideas:

Replacing the alternator with a newer, smaller and lighter one…

...and the same with the starter

Flywheels, front and rear suspension, seats, hatch glass, and many more.


Sprung and Unsprung Weight

Generally speaking, unsprung weight is worse to carry than sprung weight. That means that when you make your choice of wheels, tires, brake rotors, calipers, springs and shocks (all forms of unsprung weight) you should carefully consider weight as a criterion for these parts as well as the other factors. Lowering unsprung weight yields double and triple advantages. But remember—weight anywhere harms your acceleration and braking anyway. It all has to go.

The Relationship between Acceleration and Weight The conventional wisdom is that you gain the equivalent of 1 HP for every 11 pounds of weight you remove from the car. Remove 55 pounds—it’s like 5 extra HP in your engine. A good rule of thumb—but I am afraid it isn’t quite that simple. Factors like air density, rolling resistance, gear ratio, inclination in the road surface, Coefficient of Drag (Cd) all play a part in

increasing or decreasing that ratio.

This chart gives you some idea – but it is only 3-dimensional. To do the job right, it really needs to be 4 dimensional. Note it factors acceleration on a vehicle already at 150 MPH.

Plus, the weight of the vehicle itself skews the acceleration-to-weight ratios because taking 10 pounds out of a 2800 pound race car impacts the results a lot more than 10 pounds out of a 3600 pound car.

Also the velocity of the vehicle at time of acceleration and the HP of the vehicle affect these ratios even more. But, keep the 11:1 ratio in your mind, its good enough to give you the right idea most of the time.

Polar Moments Where the factory put the weight will not be where the racer wants it. Again, the OEM’s plan for the vehicle dictated where certain components had to be placed. Luggage space, rear-seat leg-room, etc. But the racer is free from many of these constraints, and can move the weight in toward the axis of rotation, (relocating the battery, moving the engine back, moving the driver’s seat laterally toward the centerline, etc. Even changing the size and location of the gas tank (at 6.1 pounds per gallon, it adds up! ) – why carry a 20 gallon gas tank and the attendant problems with free surface flow mid-corner, when we only need 10 gallons perhaps for a 30 minute race? The weight savings alone is 10 X 6.1 lbs per Gallon = 61 pounds!


Chassis Flexing

The two major types we are likely to encounter in most production sedans is either framed or unibody chassis.

Framed vehicles – represent a unique set of challenges in racing, as the frame (depending on the car) is often nearly a 2-dimensional element, and therefore easily twisted. They work rather well for drag racing, where the forces are in line with the frame rails, but once we take them road racing and subject them to loads to the left and right of center, they twist like a pretzel.

Unibody vehicles – can be somewhat stiffer than framed vehicles provided they are built right. They benefit from the triangulation from corner to corner that the ladder framed vehicles just do not have. This allows them to resist some torsion in the chassis itself. Enough, at least, for the stresses that a street vehicle might encounter.

Why do we care? Because as the frame twists and distorts we loose all our suspension geometries. We cannot hold camber mid-corner, which means we also are loosing our toe settings. Mid-corner, our camber and toe settings are who-knows-what, and the car will be at best difficult to drive fast, and at worst, dangerous.

The special case of the convertible unibody vehicle – without a way to tie the A-Pillars to the B and C pillars (because they don’t exist) the convertible struggles to acquire rigidity where it can. Look at this picture. Note the beefy lower side rails and exceptionally tall bolsters on each side of the driveshaft hump in the floor. That’s all they can do to provide stiffness to this chassis.

It can be augmented somewhat by very strong doors, connecting front and back through beefy door latches and hinges, but that’s it. It is not uncommon for convertibles to actually weigh more than the matching sedan because of all the metal added to attempt to locate stiffness in the bottom only. And you will usually observe that Porsche Caymen’s will out-corner Boxsters for this same reason. They’re stiffer.


The Roll Cage – is a case of a fortunate coincidence. Intended as a safety device, it also provides incredible rigidity to the race car, allowing us to hold our suspension settings under all forces from all

vectors. But we must be clear – we are talking about a roll CAGE not a roll BAR.

A roll bar. They have only two or four attachments points to the car, and cannot do much to prevent twisting of the frame.

On a roll cage, the more attachment points and the further away they are from each other, the better.

The best will have a contiguous main hoop behind the driver’s head and another over the driver’s knees, plus a “halo hoop” overhead. It’s tying-in the halo hoop to the corners of the car that provides the best triangulation and stiffness.

Note that after the roll cage is installed, lightening of the Unibody can be performed where structures in the Unibody exhibit unnecessary redundancies. Get a good set of rotary broaches (best) or at least a quality set of hole saws and have at it. It adds up!

Frame Conclusion: So the answer on racing a street vehicle is: 1) select a sedan, not a convertible, and 2) if you are serious about your lap times, put a complete roll cage in it to eliminate twisting and flexing of the stock chassis.

Racing a street vehicle without taking these steps invites frustration with low lap times, and, where mid-corner toe out and camber loss occurs because of frame flexing – creates the opportunity for serious accidents.


Braking

Of course, the manufacturer of our stock car was counting on several criterion when he designed the brakes for his automobile, criterion that we are going to change. For example, the designer of the car was planning on 2 or 4 persons in the vehicle, plus luggage.

When we race, we won’t have that. Further, they were counting on the whole car being heavier and we have been lightening it every chance we can.

So, at first blush, it looks like things are going our way. By lightening the car the stock brake system is going to be better than we need! Not so fast. (pardon the pun)

While initially there is some truth to this, it’s about the only good news from the braking system. Things that we will change when racing include far more frequent threshold braking stops than the designer ever contemplated and less time between these “panic stops”.

Let me explain: what they call “Panic stops” in street use we just call “threshold braking”. Where they assume you will have a very infrequent panic stop, we will be deliberately trying to threshold brake several times on every lap. So, as racers, our time between braking events is much less and we need much faster system recovery times. The driver will also find he/she is battling exhaustion if we don’t give them some help with pedal effort.

When discussing brake upgrades you will hear the word “gain” a lot. There are mechanical gains like the lever-action right at the brake pedal, and again at the effective radius of the pad and rotor. There are hydraulic gains too, like those between master cylinder diameter and caliper piston diameters. The amount of

gain in the system will determine the brake pedal effort, travel, feel, and effectiveness of the system as a whole.

Most drivers believe that if you are going twice as fast (100 MPH rather than 50) you will need twice the braking effort to stop the vehicle. Not so. If you double the speed, you square the amount of brake energy needed to stop the car! That’s 4 times as much! (The formula is mv 2 )

Pedal effort – the consumer wants little pedal effort and does not car about pedal “feel”. The racer will tolerate more pedal effort in order to acquire some pedal feel so he can do threshold braking and trail braking as needed. He needs and wants feedback. Pam, our virtual grocery getter, wants no such feedback from her brake pedal.

And remember—as we talk about racing a production street vehicle: it was designed for Pam, not for us.

Pam


Look at all the ways we can adjust the gain in the system for the driver.

Increasing or decreasing the bore/diameter of the brake master cylinder relative to the bore/diameter of the piston(s) in the calipers; changing the rotor effective radius; the friction characteristics of the brake pads, and even the very location and geometries of the brake pedal linkage to the master cylinder.

Brake Pedal: Here we have a simple mechanical advantage provided by a lever. If B is five times as long as A, we have a 5:1 mechanical advantage or gain. Too much and we loose pedal feel and increase pedal travel. Too little and we have too short of pedal travel which makes the system difficult to modulate and we wear out the driver. As you can see, compromise will be the name of the game here.

A sister project with any talk about the brake pedal is its location.

Here we will be correcting any miss-match between pedal heights that makes it difficult to heel-and-toe when racing. So it isn’t just the height of the brake pedal at rest (as shown I this picture) but, more importantly for the racer, the height of the brake pedal under pressure – and how that lines up (or doesn’t) with the accelerator pedal.

Calipers: Construction

We are likely to have cast iron calipers on our stock car, with a few large single pistons and a design intent to go 30,000 miles between brake service intervals. Cheap, reliable, and good enough for the grocery-getter.

The racer will want none of that. He or she will happily shorten the service interval to “after every race” if needs be to bring the performance up to his needs. Using more and smaller pistons spread out over the back of the brake pad can decrease pad taper as it wears and increase the effective pad area. Both good things.

That’s why you see the popularity of 4 and 6-piston calipers. However – keep in mind that every piston in the caliper represents a “hole” and a structural weak spot. Sometimes, four piston calipers that are nice, light and rigid can be better than 6-piston calipers that are either flexing within their structure, or, if not flexing, are reinforced to the point of being heavy. Again, compromise.


Calipers, Location: The distance the caliper is mounted from the center of rotation of the wheel changes the Effective radius.

Effective radius: the benefit received when using a longer wrench to turn a tough bolt. In this case, using a longer wrench to stop the rotor from spinning. The longer the effective radius of the caliper/rotor combination, the more powerful the brakes. Not the same as the radius of the rotor, but the distance from the center of the rotor to the center of the caliper piston.

The diameter of the wheel will impact the effective radius that we are able to build, because unless we are going so far as inboard-mounted brakes, our calipers and rotors will be mounted out on the spindle and nested inside the wheel. So, right away if the stock car is driving on 15” or 16” rims –we are already in trouble. Larger diameter wheels will be needed to expand our effective radius.

Moving the calipers out and increasing our effective radius is a win-win. It allows us to fit larger diameter rotors and that also Increases our swept area and thermal mass (decreasing brake fade). The conversion of our kinetic energy to heat energy is the core of what braking the car is all about, and we benefit from having a larger thermal mass or “heat sink” to rapidly make that conversion.

Rotor Section: Because the brake system converts kinetic energy to heat energy – and we want to brake harder and more often because we are racing…. We should expect to make more heat. The stock, cast one-piece rotors will fail and warp under these conditions. The stock rotor lacks both the necessary thermal mass and section for the demands we will be putting on them. Note the difference in section of these two rotors, both from Porsche. On the left, a stock early Porsche 928. A touring car. On the right, a 996 Turbo. You can see which car was expected to make harder stops more frequently!

Rotor Weight: although increased thermal mass helps decrease brake temps, increased weight means more unsprung weight and higher rotational inertia - both which hurt performance. The answer is a two-piece rotor/hat combination that gives the rotor the thermal mass it needs, but lightens the assembly for less unsprung weight and inertia. You won’t find two-piece brake rotors on your stock grocery-getter! Lessening the unsprung weight on your race car is a Big Deal and pays dividends in lower lap times.


And, as anybody who has raced stock brakes hard has learned, the one-piece rotor transmits the heat generated up into the bearing hub, boiling out the grease, and destroying the front wheel bearings. Two-piece hats and rotors have a loose or “floating” connection between the rotor and the hat because of the differences in expansion characteristics between the cast iron brake rotor and the aluminum or titanium brake rotor hat. But, we pick up another win-win here because we also get a thermal-break or “dam” between the two parts. This slows the transfer of heat from the rotor into the hub, and saves our wheel bearings.

Drilled, Dimpled, or Grooved: A brief word on brake rotor features – drilling, dimpling, or grooving. First the myths: “venting” (as it is called) of the rotor is NOT done to help the brakes shed water for racing in heavy rain, and it is NOT for helping to cool the rotor. It IS for sweeping away spent, glazed brake pad residue so the pad always presents an unglazed, fresh surface to the rotor. And it can, where brake pads that out-gas when heated are used, prevent the lift of the pad off the rotor by the trapped gasses.

In almost all cases, drilled brake rotors still exist today largely as a cosmetic feature. People just won’t let them go. In my opinion the structural weakening of the rotor isn’t worth it, and you end up replacing your rotors because they are cracked long before they are worn out. If you gotta have drilled rotors, locate rotors that were cast with the holes in them, or that have wider directional vanes in the core that are meant to be drilled.

Dimpled and/or grooved rotors are the way to go. They have dimples that do not go all the way through combined with grooves that will sweep the brake pad surface and clean it off for us, but without sacrificing the structural integrity of the rotor.

Fluids: The DOT 3 brake fluid, the stuff that probably came with your car – has the lowest boiling point of all – both wet and dry. “The “Dry” rating from the DOT is the boiling point of new, fresh brake fluid. Zero water content. Anywhere the brake fluid is in contact with air – be that through the vent in the cap of your brake fluid reservoir or around the seals – it is designed to absorb moisture. It is hygroscopic. This is because if it didn’t absorb the moisture, you would eventually get a concentration of water in the brake system that under hard use would boil and gas out. Read: NO BRAKES. The “Wet” rating from the DOT is the brake fluid with more than 3,7% water by volume. That is meant to reflect the brake fluid after it has been in the car one year.

Note that even if a small amount of water is absorbed into the brake fluid, the boiling point can drop to less than half of the original value. This hygroscopic action is why the brake fluid in a race car needs to be flushed out and replaced seasonally.


All the brake fluids that are Glycol Ester-based can be mixed with one another. Not that you’d want to, but at least you don’t have to be crazy-careful of getting rid of the DOT 3 fluid before putting in the DOT 4 or 5.1. Not so the silicone-based DOT 5 fluid. That will not play well with others, and the system has to be carefully purged before it can be put in.

So the stock brake fluid has got to go while we change to a fluid with higher boiling points. Because if the brake fluid boils in your caliper – you will have NO BRAKES and that is a sphincter-factor of about 9 on the race track!

Brake pads – those OEM brake pads that came with the car are entirely unsuited for the task at hand. With the emphasis on dust-free and quiet operation over a long life, they just wont stand up to our temperatures or deliver the coefficient of friction we desire to bring the race car down in a short distance from high speeds. Our emphasis will be on high-friction compounds, and almost nothing else. We will tolerate brake dust, a short life, and squealing when cold just to get the performance we want.

There is a world of choices out there – but the general rule of thumb is “the more aggressive the pad, the shorter the stopping distance”. A sister formula that is talked about less often is “the more

aggressive the pad, the shorter the rotor life”. Depending on how deep you pockets are to be buying new rotors all the time – you may dial your pads back just a notch!

Compliance: the stock system is likely to be outfitted with standard flexible brake lines that have a fair degree of compliance under pressure. They will expand slightly as the pressure in the line increases, and give Pam the grocery getter the nice broad pedal range she desires – also they are cheaper to put into the car. Our racer will want more pedal feel, more immediate response, and the ability to carry more of his leg pressure and hydraulic gain through the system to the caliper without loss. Braided brake lines with little-to-no compliance need to be fitted.

Brake Bias – the stock car was set up to bias the brakes as it was built, with the weight distribution it had in both the X and Y axis. Now that we have changed all that – weight has been removed; heavy objects may have been moved; we may have altered the brakes themselves out-of-stock specification with larger

rotors ( a larger effective radius) and more aggressive pads, so I ask: How could the OEM brake bias possibly be correct? The brake bias can be adjusted front or rear and side to side as well. There are adjustable hydraulic valves that can be fitted into brake lines, and brake bias bars that can be fitted at the pedal for dual-master cylinder setups.

Air Ducts and cooling: Generally speaking, the cooler a brake system operates, the happier it is. This is apart from the initial application on metallic pads and others that require a little latent heat in them to work as intended. But after that – heat becomes the enemy.


We fight it with thermal mass in the rotor, me control it with heat dykes from the rotor to the rotor hat, and we need to cool it with air as fast as possible. Positive air flow is a must. The street vehicle can get away with whatever air gets to the integral rotor cooling vanes and little else. The racer can’t. So any blockages to good air flow to the center of the rotor must be removed, and where they cannot be removed, deliberate air ducting from a high-pressure area such as at the nose of the car right to the rotor inlets (at the center of the rotor) must be added.

Braking Conclusion: The stock brake system – depending on the what your selected vehicle is equipped with now – can be very poorly suited for racing. As the car is modified for racing, the brake system must be modified to follow the weight bias and built up to cope with frequent threshold braking at high speeds.

Suspension and Steering

With the emphasis on comfortable ride characteristics over a broad curb-weight range from one driver all the way to 4 adults plus luggage, shock settings that are so soft all they can prevent is car-sickness, and steering geometries designed to produce under-steer no matter what, (presumably to protect us from ourselves), it’s no wonder that the stock suspension is so far away from what it needs to be for race use.

But rather than throw the baby out with the bath-water, and in the spirit of “run what you brung” let’s see what we can do with what we have.

Center of Gravity: earlier we were lightening the car, and I would think that with the sedans that are the focus of this discussion – you will have lowered your center of gravity (CG) too. As you remove weight located up high, or just relocate it (like a battery box, or an engine) closer to the ground, you lower your center of gravity. This is how that helps...

When we corner, we are going to have centrifugal force (inertia) pressing out from the center of the corner causing lateral weight transfer. This is a given. The higher the center of gravity, the more leverage (the roll moment arm) we give to that centrifugal force to roll us over. Or in the reverse, the lower the center of gravity, the less leverage (a shorter roll moment arm) and effect the centrifugal force will have on the vehicles stability.

What’s wrong with this picture?


Like we said before in the section on lightening, all weight is bad, it all has to go. And weight up high is worse than weight down low where cornering is concerned. In a similar fashion – weight located further from the vertical center axis is bad because it increases our moment of polar inertia.

That’s why we not only move battery boxes down on race cars but also in towards the vertical rotational axis. I know this is all sort of no-brainer basic, but lowering your center of gravity from stock is pretty easy and in may cases costs nothing but time.

Roll Center The roll center is controlled by the suspension geometries found in the vehicle, so we have less control over them unless we are prepared to spend money on all-new a-arms and trailing arms. Caution needs to be expressed here as changes to link and arm lengths also change weight transfer (side to side and for and aft), anti-dive and anti-squat characteristics.

Fortunately, many sedans have fairly low roll centers, especially if equipped with double-wishbone suspensions (like the 928). Strut-based suspensions (Chapmen, McPherson struts, and similar) have a naturally high mounting point for the upper spindle link. This raises their roll centers a bit. However, there are two relatively easy ways to lower our roll center that are well within our reach:

Ride Height – by lowering your car at the springs you can lower your Center of gravity and your Roll Center both. Win-win. I say at the springs because if you lower your car at the wheels – by taking a car with 17” wheels from the factory and installing 14” wheels on it – it is quite possible to raise your roll center.

When have you gone too far? You have lowered your car too far when you are bottoming out or “panning” too often, when the links or tie-rod ends and ball joints are binding, or

when you have taken your suspension out of its best (most effective) range (like when your bump-steer gets worse. More on Bump-steer in the alignment section below). After you lower your vehicle, operate your suspension from full droop to full rise and make sure there are no binding rod ends or joints at the new, lowered ride height. If panning, add bump stops, spring rate, or raise the ride height a bit. If binding links, raise the car a bit to get back into your range, or relocate the suspension attachment points as needed.

Track is the stance the vehicle has on the pavement from side-to-side. A wider track will raise your roll center, but lower your center of gravity. So what’s the point? The point is that increasing your track 1” has the same effect of lowering your

center of gravity 0.5”. Increase your track 2 inches, and its like you lowered your CG 1 inch. This is why it’s worth it!

Besides, do you remember what Carroll Smith said: “Have you ever tried to corner hard on a tricycle? “


Note that wide track has it limits – we found out in Can-Am that a too-wide racer had to literally drive through the esses on the road course, where a racer with a narrower track could effectively shoot them as a straight line. Food for thought.

The compliance of the rubber suspension bushing – the stock vehicle you have decided to race will have a great number of rubber bushings and insulators throughout the suspension. Focused on quiet, vibration-free comfort – they are there to please. They also provide

greater compliance to the manufacturer during assembly so they can lower costs – as long as the part is to be rubber-mounted, the manufacturing tolerances within the part itself can be a little greater.

The bad part for us is that the increase in loads caused by the combination of high speeds and those big wide sticky tires will make a joke out of the Shore ratings on every rubber part. The OEM engineer selected a Shore hardness of X based on his load, and not only do we want less deflection and faster response, but we are going to give that part X+ loads, not X, so it has no chance of holding its designed positions.

The rubber bushings are a triple-threat for us: 1) we can’t be expected to hold our suspension settings with all this float going on, 2) it prevents the vestibular feedback (aka “seat-of-the pants”) that we rely on, 3) and it lengthens all our response times and delays our control actions from being acted upon.

An easy way to look for compliance in the steering linkages alone is this: with the car at rest, on the ground with engine off, lay down on the ground and find the place where you can easily see your steering rack. For my car, it’s by placing my head just behind the Left Front tire. Now have an assistant move the steering wheel back-and-forth two or three inches. Note how many things move before the tires start to move! Hunt them down and eliminate them with prejudice.

Look for rubber bits in your Steering column mounts, the steering rack mounts, the a-arms (upper and lower), the trailing arms, the shock mounts, the sway bar mounts and sway bar drop-links. Replacing the rubber with modern polyurethane pieces is an

excellent intermediate step and may be good enough for you. Some, like steering rack mounts – can go to solid aluminum.

The final solution for the major bushes at the a-arms and trailing arms is the conversion to quality spherical rod ends at every link, but this is not a job you can do on your driveway.


It’s worth noting that some sedan racers who have removed all their compliance at every link and replaced them with spherical rods ends have reported back that the car is harder to drive fast. Ultimately, its faster, but the cars with polyurethane bushings and a little bit of compliance are easier to drive and only a tiny bit slower. Your choice.

Springs: These are obviously soft in the passenger sedan, and even in the street-driven “sports car” the owner still would rather enjoy the ride than have his fillings knocked out.

So there is no question the racer is going to want to install stiffer springs because he will gain some cornering and anti-dive characteristics that he wants.

Some things to look out for where springs are concerned:

Static vs. Progressive Springs Stick with static or normally-wound springs. Avoid the temptation to go to a “progressive” spring. Progressive springs are designed to be “softer” on the interstate and get “stronger” on the off-ramps the further the car heals over. They do. And that’s the problem with them. Cornering well is hard enough without your spring rate changing mid corner! It’s no fun to have corner-entry oversteer as you dive in on soft springs and then change to understeer mid-corner as the spring rate climbs in the front – especially when now you have the steering wheel cranked over to correct the previous understeer! No thanks!

Buy quality springs – cheap springs aren’t worth the time it takes to install them. They may take uneven “set” after being loaded for a while, or worse, arrive with uneven lengths right out of the box. You cannot know what you’re doing to the suspension if the springs are not actually the length or strength that they are supposed to be.

Plan to use progressive bump stops as part of your spring package.

If you don’t use bump stops at all, your carrying a higher spring rate than you need so your suspension never bottoms. The progressive bump stop is a form of spring, and the best ones are very smooth. Not using a bump

stop and allowing your shock to crash into itself at the bottom is a fast way to a) have your spring rate suddenly go to infinity (do you remember what I said about changing spring rates mid-corner?) and b) ruin your shock.

The next spring in the suspension is the swaybar (aka anti-roll bar, anti-sway bar)


Swaybars and their mounts – The sway bar is a torsion spring in most cases, mounted transversely across the car. How many of us reach for a stiffer swaybar for our street vehicle to help it corner flatter? Sure. It’s a common upgrade, and usually pretty fast to make. So fast, in fact, its not uncommon for racers to carry several of them in the trailer so they can set up their car best for certain chicanes at certain tracks.

But remember when you are hooking up the latest beef-stick that the stock sway bar mounts and links were meant for the stock sway bar loads. And we are about to exceed those loads.

Failed mounts all the spot-welded attachment points for the suspension bits require scrutiny. The loads the manufacturer intended for these junctions are about to be exceeded, and a failure of suspension attachment points are is

rarely minor. It’s faster to get through them and strengthen them before they tear out and deform, it will take a lot more of your time to fab up new bits and repair the damage after the mounts have torn out.

They can be strengthened by stitch-welding over the seams, or adding additional material or braces. Reinforce these attachment points, and put them on your regular post-race inspection procedure.

Shocks: Shocks are valved to dampen the oscillations of a particular spring. If you install a stiffer spring, you need a “stronger” shock to match it. That being said, the reverse is also true: if you are still using stock springs and upgrade to much stronger shocks, you could end up over-

shocked. The spring and the shock (aka the dampener) constitute a system, and need to be sized to each other.

So because our stock springs on this project car were too soft, we’re going to put in stiffer ones. The moment we do, our old shock is no longer adequate. Even worse, they aren’t adjustable. They didn’t need to be adjustable in their stock application. All they had to do was control some pretty soft springs and dampen the spring oscillations enough to prevent accidents or nausea of the vehicles occupants.


But we want and need the ability to control the dampening actions under different circumstances. They are: compression, extension

(cornering forces), high-speed compression and high speed extension (bumps and rumble strips).

Back in the 70’s, there were a lot fewer shock options then there are now. You had Koni, Bilstein, and Moog and you were pretty much done. There are a lot of good shock manufacturers now so it’s not difficult anymore to find a pretty good aluminum adjustable shock for almost any car – especially if you have converted your shock mounts to use ½” spherical rod ends.

Terms that they will be using:

Single-adjustable: rebound adjustable only

Double-Adjustable: adjustable on rebound and compression

4-way adjustable: adjustable rebound, compression, high-speed rebound, high-speed compression

You can go a long-long ways with a double-adjustable shock, honing your skills as a driver, before you will get to the point of needing a 4-way adjustable shock. So, in my opinion, you can save some money there at least for the moment.

Be aware of the bar-stool argument about shock designs (A bar-stool argument is one that has no end or answer until the beer runs out). There are mono-tube and twin-tube shock designs, and within that, regular twin-tube and low-pressure twin-tube designs. Which technology is best? Just put the kettle on, Google “twin-tube vs. mono-tube” and good luck. My answer is: a quality after-market adjustable shock will be better for racing than the stock shock you had.

I guess I can give you a little better answer than that…. If your suspension travel is slight, let’s say less than 2.0”, a twin-tube shock reacts and dampens faster under smaller piston movements than a mono-tube design. In my own car, our suspension travel is about 1.5” at max, and that helped me decide to go with a twin-tube shock.

You should seek to mount the shock so it is supported by the car (sprung) and not support it on the suspension arm (unsprung). It was probably mounted big-end-down by the factory. The difference is how it affects sprung and unsprung weight. Anytime you can lower unsprung weight, you should.

Power steering pump- with larger front tires than the manufacturer ever intended, and the frequency that we are cranking the wheel this way and that; expect the power steering fluid temps to get higher than expected. We have even, on some circuits on some days, boiled ours out. Add a power steering fluid cooler if you don’t have one, and look into a performance power steering fluid with a higher boiling point. They work well.


We found at Pikes Peak, where we were turning 190 deg switch-backs, that the driver could apply enough force to the steering wheel to cavitate the fluid with the impeller and momentarily loose all our power steering assist. That’s a nice “wake up call” when staring at either cliffs or rock faces and you just lost all your power steering! The fix was keeping the rpm’s higher in those corners, and the afore-mentioned power steering cooler plus synthetic fluid with a higher boiling point.

ALIGNMENT: the alignment set by the factory for the street driven sedan bears little resemblance to what the racer will want. Where the manufacturer wants the tires to wear evenly, track straight, and behave unagressively – the racer values different attributes: high speed and slow speed cornering, and aggressive response times. Tire wear doesn’t even make the list!

Camber and the Race Car – First, select your tires, and discover what the tire manufacturer wants to see regarding a camber angle for their tire. A lot of guessing can be eliminated by just following this simple act. Not that the tire manufacturer’s camber recommendation is the last word on your car: we must factor in the tread width of the tire, the offset of the wheel, and the suspension itself into our final camber setting; but I am saying that

should we do what we want and ignore the tire manufacturer’s recommendations it will never perform as it should or could.

Many race tires are now made to run best at -2 deg of camber angle. Depending on your stock car – you may not even be able to reach that camber setting with stock parts. Modification of stock parts or aftermarket bits may need to be installed to get enough adjustment.

How are you going to know when your Camber is “there”? When the lap-times say so, and when the tire temps say so. Note I did not say “when the driver is comfortable”. Drivers that are “comfortable” or announce it “corners like its on rails” are under-driving the tires and the car. “The limit” does have some slip in it; the tires do feel a little greasy, and driving at the limit requires the driver provide constant attention. It may not be -2 deg on your racer, the sweet spot may be less than that – but it certainly will be more than the stock setting!

Too much can be a bad thing: enter the fella who bets that if 2 degrees of neg camber is good, 4 degrees is better. Then he wonders why he flat-spots his tires on braking so often! He may also experience hunting down the long straights as the car is running up on its tippy-toes.


Caster – we don’t spend a lot of time on caster settings as road racers… the more caster the more stable the car feels on straights but the more turn-in effort the car will require to fight the caster. Less caster can mean quicker corner turn-ins and it can, on some cars, allow for more Camber adjustment. Try it. And finally, avoid the Caster limits – way too much caster can cause the car to under-steer more, as way to little caster can make the car over-steer more.

Toe – The toe angle is the last one we adjust in an alignment, as ride height, caster and camber will all affect toe. The stock toe setting for your vehicle is most likely slightly negative – or “toe-in” as they don’t want the car hunting on the interstate and this helps. It isn’t likely to be what we want. Along with Camber, the toe settings are the other tools used to combat under-steer and turn our car into a cornering rocket.

Bump Steer - “Bump Steer” is the amount of change in toe (in or out) that occurs as the suspension rises and falls throughout its range. Toe is normally set on a car at rest in the garage, and that’s good enough for stock. But the toe we care most about is the toe on a live system, mid-corner, with the suspension loaded. If, when the suspension swings up because of the weight-transfer of that corner, the toe angle changes from your static setting a great deal, then you will have a harder time figuring out what your toe setting at rest should be. It’s like your going to the track with two toe settings: toe on the straights and toe in corners. Which do you set too? Answer: you want them both to be right. Bad bump steer can also make the car dart this-way-and-that over bumpy sections.

Consider this: a) If you have lowered your car: you probably changed your bump-steer.

b) If you have shortened your swing-arms or A-arms or changed your spindles away from what came with your car: you made changes in bump steer. Check your car’s bump steer or have it checked, the goal is to make the static toe angle and the toe angle mid-corner the same or as near the same as you can.

Depending on the car you have decided to race, you may find an aftermarket solution to help bring bump-steer back into line once you have lowered the vehicle.

Common are either steering rack spacers (left) to move the rack down; or

(right) long tie-rod end adapters to move the tie rods up. .


Ackerman angles - Like bump-steer, this is a change in toe that affects which way the tire is pointing in corners, so it’s important. Unlike bump-steer, it has nothing to do with vertical suspension travel. This one is a product of the suspension geometries themselves. We all know that on a given turn, the inner and outer tires take different radiuses to get around the corner. The factories do not consider slip angles of a racing tire in their calculations, so we also know that – relative our purposes, it’s wrong.

The goal is combating under-steer, and you may find that a little Ackerman toe-out mid-corner allows the inside (unloaded) front tire to help get around the corner faster. The slip-angle of the tire you select will determine how much toe-out it can tolerate before it falls off, so that means that there will be a sweet-spot regards Ackerman angle where the under-steer is most reduced, and that more or less Ackerman will not corner as well. And remember that toe-out is accumulative: so if you are running static toe-out already, the effect of Ackerman adds on to that.

Suspension Conclusion: Here again we see the design parameters of the stock car are and the race car do not run parallel. No surprise really, after all we have different objectives. We know the stock springs, sway bars, and shocks are all too soft. Everything in the suspension has to be considered inadequate and, as in the case of a lowered car and bump-steer, may even be mounted wrong.

This is the end of Session I .

The 2nd Session covers Engine, Exhaust and Drivetrain issues when trying to race a vehicle that was designed for street use.


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Challenges When Racing a Street Vehicle - 928 Motorsports, LLC When Racing a... · Challenges When Taking a Vehicle ... own Carl Fausett of 928 Motorsports, LLC ... drag racing and