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Ultimate Autocross

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murcielagoGTR

Ready to race!
Location
New Bern NC
Car(s)
91 GTI
Wheels

Picking the Right Wheels for You

Man has long argued as to what was the most important discovery in the technological history of the world. Was it fire? The integrated circuit? Clear cola? Or perhaps the humble wheel?

The wheel is the least pretentious of the simple machines, and probably the one that has gotten us the furthest. Wheels have progressed from basic tools to status symbols these days, but their function is just as basic--and just as important.
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Wheels

While all cars use wheels, their design and construction can vary greatly, from inexpensive stamped steel to high-tech forged alloy examples. Most people base their wheel selection on looks and price, but the process of picking the right wheels for your car should go much deeper.

For the most part, wheels are made of either steel or aluminum alloy. Steel wheels are cheap and easy to produce, which explains why many passenger cars come with them as original equipment. They may look a little plain, but a set of inexpensive hubcaps can quickly change that.

Aluminum alloy wheels, sometimes referred to as just "alloy" or even "mag" wheels, have some serious advantages over basic steel ones. For starters, aluminum alloy wheels, by nature, better dissipate heat and provide more rigidity under high-load cornering maneuvers.

Alloy wheels are usually lighter than steel wheels, which reduces unsprung weight (all weight that is not supported by the suspension). Any reduction in wheel weight reduces the amount of inertial weight at the rotational axis. The less weight there is spinning around, the easier it is for the engine to turn the wheel and the easier it is for the suspension to control wheel and tire movements.

Even small weight reductions of two to three pounds can make a significant difference. As an example, imagine spinning a two-pound weight on a string over your head. Now imagine the same thing with a 10-pound weight. The 10-pound weight will require much more effort to spin, and will be harder to control. The same principle holds true for road wheels and unsprung weight.

Another benefit of reduced wheel weight is that steering response will improve as there is a lighter load on the steering rack. And lighter wheels reduce the rotating mass of the vehicle, providing quicker acceleration and shorter stopping distances.

If you look at the wheels used in our plus-sizing tire test, the 14x6-inch original-equipment steel wheels weigh more than the significantly larger 16x7-inch TRMotorsports Typhoon alloy wheels.

While it may not make your car faster through your favorite series of corners, alloy wheels also tend to look pretty cool.
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Construction Techniques

Nowadays, there are basically three ways in which alloy automotive wheels are constructed. The three types of alloy wheels can be referred to simply by their common names: cast, billet and forged. Let's take a look at these manufacturing processes, and how they make the end product better or worse.
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Cast

Casting is a relatively inexpensive way to produce a high-quality, fairly strong alloy wheel; many aftermarket alloy wheels designed for street use are made this way.

In common gravity casting, the wheel maker begins with a prototype "plug" that is used as the positive to produce the mold. This plug is usually made by machining a piece of material (often plastic or other phenolic material) on CNC machining equipment to produce a highly precise model.

The "negative" is then made from the positive by pressing casting sand around it. The sand is actually a composite slurry that, when compressed under high pressure, becomes quite hard. Think of what happens when you walk down the beach: Your foot compacts the sand and makes a very accurate, very stable negative impression. It's the same principle, just with high-tech sand.

Next, molten aluminum alloy is poured into the sand mold and allowed to cool. When the sand is broken away, you're left with a wheel that only needs minor finishing (like drilling and possibly trimming of some excess metal) to be considering complete.

Negative pressure casting is a similar process, but instead of pouring the molten material into the mold, the molten alloy is drawn up into the mold using a high-pressure vacuum. This eliminates much of the trapped gas found in the gravity casting process, producing a stronger wheel that is much less porous than a gravity-cast one.
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Billet

Billet wheels are machined from a solid chunk, or "billet," of material. First, a telephone pole-sized piece of aluminum alloy is produced (or bought from a vendor). Since this piece of stock is generally extruded, the grain runs through the stock, much like the fibers within a single strand of wire. The stock aluminum is then sliced up into sections which are machined down into either complete wheels or just wheel centers.

Since they retain the grain structure of the extruded stock material, billet wheels are extremely strong. This grain structure, which is not present in a cast wheel, gives the final product a backbone--makes the wheel even stronger without adding weight.

Of course, billet wheels are also extremely expensive to produce because much of the original material is wasted. A lot of time is also spent machining the original stock down to a finished wheel, which only adds to the cost of the final product.

Actually, most "billet" wheels are actually billet centers bolted into stamped or spun rim halves. Entire wheels forged from a single billet are so rare as to be almost nonexistent, and are usually seen only on show cars. Billet centers on multi-piece wheels, however, are common.
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Forged

Unlike casting or machining (billet), forging uses intense heat and pressure to transform a slug of alloy material into the final shape of a wheel. Under this heat and pressure, the original grain structure of the stock material is forced from the center of the wheel towards the outer edge. This grain structure is even stronger than the one found in a billet wheel because it runs along the spokes and serves to further strengthen the forged wheel's spokes, while the grain in a billet wheel simply runs through the spokes. Thanks to this process, a forged wheel can be up to 300 percent stronger than a cast wheel. Additionally, since forged aluminum is stronger than cast aluminum, less material is needed to produce the wheel, resulting in a lighter product.

When shopping for a forged wheel, you may want to ask how close to net the forging is--the closer the forging is to the final product, generally the stronger the wheel.

Because of the basic limitations inherent in forging, most forged wheels are two- or three-piece units. In two-piece construction, a center is forged and then welded or bolted into a spun or stamped outer rim. In a three-piece wheel, the center is bolted to an inner and an outer rim half. Three-piece wheels have the advantage of being easily customizable for a variety of widths and offsets. Crash damage in the form of bent rim outers can also be repaired.
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What Should You Choose?

Honestly, most any type of wheel (except wire) is strong enough for most types of racing. A good quality, pressure cast wheel, if made with the right material (T-6 aluminum), is plenty strong enough for a road racing car, and certainly for an autocross car.

The payoff in forged wheels comes in weight and durability. These racing wheels certainly cost more, but are generally stronger and lighter than an equally-sized cast wheel. Plus, their multi-piece construction allows for custom offsets and the opportunity to be repaired as needed.

And while we're on the subject of repairs, we should mention wheel failure. Few things can be more catastrophic than a wheel coming apart on a race car. Wheels used for racing can be checked for cracks using inexpensive dye-penetrant kits available from racing suppliers or aircraft tool supply outlets. This treatment should be done seasonally at a minimum, and certainly after any incident that you feel could have damaged a wheel. Multi-piece wheels should also have their fasteners checked and re-torqued periodically.

All right, back to picking what's best for you. Let your type of racing and vehicle be the judge. If you have a heavy GT1 Camaro, cast wheels are probably out of the question. Likewise, if you race a Miata, you may not see the gain that you had hoped for with expensive forged wheels. A quality wheel, properly maintained, will provide you with years of competent service on your race car. What's that worth?

When you're talking wheels, some generalizations between the different types can be made:
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murcielagoGTR

Ready to race!
Location
New Bern NC
Car(s)
91 GTI
Steel wheels

pro
· cheap to build
· strong enough for most consumers

con
· some flex
· heavy
· not terribly attractive
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One-piece cast alloy wheels

pro
· much lighter than steel wheels
· stronger than steel wheels
· dissipate heat from brakes
· good looks
· very wide selection of styles

con
· not as light or strong as forged wheels
· no custom fitments
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Two- and three-piece forged and billet wheels
pro
· very light
· very strong
· almost unlimited fitments
· can be repaired

con

· can be more expensive than one-piece wheels
· usually need to be custom ordered
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Glossary:

bead seat: The area on the inside of the rim where the tire rests and seals.

centerline: The exact center of the rim width.

diameter: The measured distance across the bead seat where the tire mounts--not the overall diameter of the wheel itself.

hub centricity: The wheel hub is used as a common center for aligning the lug bolt holes on the center of the wheel to the axle or brake rotors. This ensures a vibration-free fit.

mounting pad: The flat surface at the rear of the hub that mounts against the hub of the vehicle.

offset: The lateral distance measured from the face of the wheel, where the wheel mounts, to the hub to the exact centerline of the wheel.

rear spacing:
The distance between the mounting pad of the wheel and the innermost part of the rim, or inner edge of the flange.

rim diameter: The height measurement from beat seat to bead seat (not flange to flange).

rim flange: The outermost edge of the rim to wheel wheel weights are attached.

rim width:
The width measurement from bead seat to bead seat (not wheel flange to wheel flange).

safety bead: The raised area circling the rim slightly inward from the bead seat. The safety bead is required on all street wheels to prevent the tire from slipping off in case of deflation.
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murcielagoGTR

Ready to race!
Location
New Bern NC
Car(s)
91 GTI
Faster in stock class

Even in Stock Class, There Are Ways to Get an Edge on the Competition

The SCCA's Solo II Stock and Club Racing Showroom Stock classes are designed so folks in off-the-showroom floor cars can compete in racing with a reasonable amount of success-no trick engines and no full-race suspensions, just stock production cars. That's the theory, anyway. In reality, the SCCA rules leave open a few areas where a smart gal or fella can pick up a few horsepower. And in a sport timed to the thousandth of a second, every horsepower counts.
We've had quite a few opportunities to sample a variety of Stock-class-legal modifications over the past few years as part of our testing on the chassis dynamometer facilities of Performance Dyno in Edgewater, Fla. Just about all manner of cars and parts have passed through our "Dyno Days," and we have found that the dyno gives us real-world numbers that quickly separate fact from hype.
We know our readers are always eager to find out what works and what doesn't, so we've decided to open the archives and give you the results of some of this testing. The power figures quoted here were extracted from tests performed on a Dynojet Chassis dynamometer. The figures are for horsepower at the drive wheels, which, due to parasitic losses, is typically 15 to 20 percent less than flywheel horsepower numbers.

Ignition Wires
Ignition wires are free in Solo's Stock class: the rules state they may be replaced with pieces of any origin. From the data we've collected, it's a worthwhile modification.
Replacing the brand-new stock wires on our BMW 318ti project car with a set from Magnecor gave us around two additional horsepower at the drive wheels, while our Neon got a three-horse bump when we replaced the stock wires with some hot ones. Installing a set of performance wires on our Honda CRX project car didn't unleash any more power, but the new horsepower curve was both smoother and no longer fell away at the top end.
In testing with a variety of cars at our Dyno Day events, we've found that nearly every vehicle benefited from having the stock wires replaced with quality aftermarket pieces from companies like Magnecor or Ignition Equipment. We found consistent power jumps in the two- to three-percent range; that's pretty significant. Plus, performance spark plug wires don't cost that much. Figure $50 to $150 depending on the application.

Lubricants
This is another area that surprised us. We have seen gains similar to those we saw with wire changes-three to four percent-in a variety of cars, merely by switching to synthetic oil. The lower friction properties of synthetics really seems to be of some benefit, especially in "today's high revving engines."
While you can expect the numbers to vary a bit from run to run on the chassis dyno (usually less than one horsepower), when you see a consistent two-horsepower jump, you know you have something.
In our BMW 318ti-a car that we had a great deal of trouble extracting more power from-replacing the stock engine oil, tranny fluid and rear end lube with Red Line synthetic products did very little to increase the maximum power output, but it did get us more than five additional horsepower at 4200 rpm-right in the meat of the powerband.
As further proof that less friction is a good thing, we've also realized power gains by using friction-fighting additives. Although we couldn't believe it at first, we did pick up measurable gains-sometimes as much as two or three percent-with a product called Oil Extreme. Although we have no reliable long-term data on these products, for many people, a few easy horsepower are worth the risk.
Oil additives cost around 10 to 15 bucks per application, while converting an entire car to synthetics should cost around $100.

Alternate Air Filters
Stock class rules allow for the substitution of air filters if the replacement is a direct, no-modifications-necessary replacement part. The only dyno testing we've ever done on a direct replacement filter was on our BMW 528i-not the kind of car you usually see in stock classes, but it is a 2.8-liter fuel injected inline six, so the results should be valid.
Replacing the stock air filter in our BMW with a K&N unit gained us nearly four horsepower (almost three percent). This isn't a huge gain, but it is impressive for a two-minute modification. And since K&N filters are washable, and don't need to be replaced, this is a cost-effective modification as well. Depending on what you drive, a K&N replacement filter should set you back between $30 and $100.

Exhaust
Stock class rules allow the exhaust to be replaced from the catalytic converter rearward, though the exhaust must exit near the stock location. Many competitors are now choosing to run straight pipes, taking the as-little-back-pressure-as-possible approach.
We tested three exhaust configurations on a D Stock twin-cam Neon: stock, straight pipe, and a Borla high-performance muffler. We found that both the Borla setup and the straight pipe produced nearly identical gains-about three horsepower at the wheels. However, the dyno graph on the muffled run was much smoother, not to mention the car sounded infinitely better.
On our BMW 318ti, however, the high-performance exhaust failed to produce much of a result. This was unusual since the car seems to have responded well to the synthetic oil and plug wires. We came to the conclusion that the stock exhaust was pretty good to begin with, plus the car's OBD-II computer control system really wasn't letting the car produce much more power.
Aftermarket exhaust systems and high-performance mufflers can range in price anywhere from around $100 to more than $1000. Generally, the more popular the car, the less expensive the system.

Spark Plugs
We also did quite a bit of testing with spark plugs on a different twin-cam Neon. At the end of one frustrating day, we learned that, on a Neon anyway, spark plugs don't make a bit of difference.
We ran the car first with the NGK plugs that had been installed since we took delivery of the Neon several years ago. We then tested the car with a variety of supposedly "better" plugs-hotter, colder, split electrode, pointy electrode. (No matter what your poison, good plugs cost less than a couple of bucks each.) In this case, all of them produced roughly the same power: within one horsepower, plus or minus.
Unfortunately, this was two horsepower shy of where we started with the skanky factory plugs. The skanky factory plugs were quickly reinstalled. Our dyno shop swears by NGK plugs.

Injectors
Blueprinted or factory-fresh fuel injectors can make a difference, says the dyno. In testing of these units on both a Neon and a Toyota MR2, we picked up a repeatable two- to three-percent more power over the existing injectors. The Neon injectors had seen around 60,000 miles, and the Toyota parts had covered more than 100,000 miles.
While new injectors can be quite costly, companies such as Marren Motorsports, RC Engineering and Performance Diesels can blueprint injectors, returning them to factory-spec performance for as little as $25 apiece.

Tricks
During our dyno testing we've even tested a couple of "tricks" along the way. One popular staging line ploy is to ice down the fuel rail on a fuel-injected car. In the old days (and today), drag racers were fond of "cool cans" which would cool the gasoline before it entered the engine, thus making the fuel more dense. But that was more applicable in the days of carburetors, when engines were at the mercy of prevailing atmospheric conditions.
Today's cars are harder to fool. We found that icing the fuel rail on a twin-cam Neon cooled the fuel to a point where the car thought the engine was still cold. The computer richened the mixture to a level that actually caused the car to lose significant power (on the order of three to four horsepower). These cars were designed to run with a very specific air/fuel ratio for maximum performance. It seems that artificially altering that ratio does more harm than good.
We've also tried the popular "blown alternator fuse" trick on a Toyota MR2. Supposedly, by removing the alternator fuse or replacing it with a blown one, the disabled alternator would "free up" some horsepower that would normally be lost to parasitic drag. Maybe this would work if you drove a three-cylinder Geo Metro with a 400-amp alternator, but it didn't seem to affect our Toyota either way. (If you don't believe us and have to try this trick yourself, make sure you have a good battery, okay?)

Caveat Emptor

Remember, these recipes are merely the result of our own observations, and results may vary slightly from car to car. However, all of the gains we did quote were obtained during same-day, similar-condition testing. Every piece may not work on every car, either-like the performance exhaust system, which worked on a Neon but barely affected the BMW 318.
Note also that the figures quoted were power gains for individual pieces only, not pieces used in combination. While a set of wires may get you three horsepower over a stock engine, and an exhaust will get you four, there's no guarantee that the pieces used in combination will get seven.
There is easy power out there, though. Based on our experience and testing, we figure that most stock-class cars can gain eight to 10 horsepower over stock with the use of class-legal modifications. And we haven't met anyone yet who didn't want more power.
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murcielagoGTR

Ready to race!
Location
New Bern NC
Car(s)
91 GTI
Thanks to GRM and all other sources for the above information. All information is copyrighted under law and cannot be duplicated for resale.
 
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