Corvette D6C Forgeline Wheels - New Shoes

Forgeline And Yokohama Give D6C A New Look And Some Much Needed Grip

Chris Endres Oct 1, 2008 0 Comment(s)
Vemp_0810_01_z D6c_new_shoes Front_view 2/20

It's no secret that the right set of wheels can make a car's look. Though you've undoubtedly heard it before, it bears repeating: No other element of your vehicle has quite so much impact on its look as the wheel-and-tire package.

But there's more to choosing wheels and tires than just picking out the prettiest rims and the widest rubber that'll fit 'em. Performance is an even better reason to upgrade your rolling stock. Straight-line and cornering traction, transient response, and braking are all heavily influenced by your selection. If you want to maximize your Corvette's performance, you can ill afford to overlook these components.

There are countless reasons enthusiasts change the wheels on their cars. Sometimes it's for performance reasons, such as reducing weight or allowing the fitment of larger brakes. Sometimes the change is purely cosmetic, to keep one's ride from looking just like everyone else's.

For this round of mods on D6C, I installed a set of Forgeline SO3P wheels and Yokohama ADVAN Sport tires. My goals were to reduce unsprung weight, increase traction via a larger contact patch and a softer tire compound, gain clearance for a future big-brake kit, and freshen the car's appearance. I'm happy to report that all four objectives were easily achieved.

Vemp_0810_20_z D6c_new_shoes Rear_view 3/20

Ordinary no more, the car's look and performance have been completely transformed by the Forgeline and Yokohama wheel-and-tire package.

Weight Reduction
From a performance standpoint, changing to a lightweight set of wheels is a terrific investment. A car's weight directly impacts its ability to accelerate, decelerate, and turn. The lighter the car, the easier it is to get it to do these things.

Because the wheels represent rotating weight, removing one pound in this area is roughly the equivalent to removing eight pounds of static weight elsewhere in the car. When you multiply this by four (wheels), you quickly arrive at a very substantial weight savings. Less weight benefits you each time you change speed or direction.

Brake Clearance
Another oft-cited reason for changing wheels is to gain clearance for larger brakes. While the stock C6 binders are actually very good, they are a bit overmatched for prolonged high-speed use, such as at track days. Hard-core lap dogs often upgrade to larger calipers and rotors in an effort to sidestep issues with brake fade.

While you might think that simply moving to a larger wheel will get you the caliper clearance you need, such is not the case. Often, it is the back side of the wheel that interferes with the caliper. Wheels designed for use with large brakes often have their spoke profiles designed to bow out slightly closer to the rim, where they pass the caliper. Aftermarket wheels can also improve brake cooling by allowing more air to pass through.

Unlike the previous two generations, the C6 was blessed with good-looking wheels upon the platform's introduction. While C4 and C5 owners had to endure some downright homely hoops for the first few years of production, C6 owners had a lean, handsome casting right from the get-go. Does that mean they're perfect? Not by a long shot. And I'm going to show you how much better aftermarket wheels and tires can be.

As you may recall from the outset of this project nearly two years ago, D6C was completely stock when I purchased it. Stock, that is, except for a set of aftermarket chrome C6 replica wheels. While not bad looking, they were far from unique. Though one to usually buck trends, I do like the look of larger wheels and tires (within the bounds of good taste, of course). Therefore, I decided to increase both the wheel diameter and width by one inch beyond stock.

As you probably know, the C6 wears 18x8.5 front and 19x10 rear wheels. I selected a 19x9.5 / 20x11 set to give the car a slightly more aggressive presence. This allowed an increase in tire size as well. The stock rubber measures 245/40ZR18 up front and 285/35ZR19 in the rear. The extra inch of wheel width allowed me to move up to a set of stickier 275/30ZR19 / 305/25ZR20 Yokohama rubber. More on these in a bit.

There are many reputable wheel companies producing wheels for the C6. But for every reputable company, there are a dozen marketing companies selling low-quality rims made god-knows-where. As with all other components you purchase for your car, it's caveat emptor when it comes to wheels.

So, how do you separate the good stuff from the crap? There are several features you should know about. First and foremost is the type of construction.

Cast vs. Forged
Alloy wheels are generally made in one of two methods: casting or forging. Almost all low- and midrange alloy wheels, including those originally installed on the C6, are produced by a manufacturing method known as casting. Casting involves flowing molten aluminum alloy into a mold, which then forms the wheel. There are actually several types of casting, each with its own advantages. The most common types are gravity casting and low-pressure casting.

Vemp_0810_08_z D6c_new_shoes Front_wheels 10/20

C6s are equipped with 18x8.5 front wheels (right). The new Forgelines add an inch to both diameter and width, giving the car an even more aggressive look.

Gravity casting is the simplest form of casting aluminum. Molten aluminum is simply poured into the mold and allowed to cool. This method is the cheapest way of casting aluminum and results in economical wheels that look OK but may not be as strong as those produced by more sophisticated means. The reason is that there are often small voids or air pockets in the casting. To overcome this limitation, the wheel must be made with thicker walls to compensate for the porosity, resulting in wheels that are heavier than those produced in higher-end processes.

In low-pressure casting, pressure is applied to the molten aluminum to improve its density. This allows a slightly thinner casting with more uniform density than gravity-cast wheels, resulting in less weight and an only slightly higher price tag. Most original-equipment wheels are produced in this way. There's also a variation that uses higher pressures to further enhance the benefits of this method. This is less common, as it increases costs.

Forging is the most advanced method of manufacturing wheels and also the most expensive. A forged wheel starts as solid billet aluminum that is forced between dies at very high pressure. In the case of the Forgelines we're featuring here, a 6,000-ton hydraulic press is utilized. As Forgeline's Scott Main explains, "Forging aligns the grain structure, improving the strength-to-weight ratio with consistent results. Forging also allows the use of 6061 material, which can be heat treated to be 40 percent stronger than cast aluminum."

Vemp_0810_09_z D6c_new_shoes Rear_wheels 11/20

The stock rear wheels are a fairly beefy 19x10, but the Forgelines are enormous at 20x11.

As you might imagine, this creates an extremely dense structure with unsurpassed strength. Because of this, the wheel can be made thinner and lighter. Once the wheel center is forged into its general shape, it is CNC-machined to create the design style. Forging is clearly the best way to build a high-performance wheel, assuming cost is no object. It is on forged wheels that we will concentrate here.

Forged wheels are available in one-piece and multipiece varieties. Multipiece wheels are an excellent choice for several reasons. Three-piece wheels offer more flexibility in specifying offset (also known as backspacing) than a one- or two-piece wheel. This is because the center of the wheel can be adjusted to different thicknesses and then mixed and matched with different inner and outer rim halves to make virtually any combination desired. This also offers more flexibility in repair should the wheel become damaged. Rather than replacing an entire wheel, you can simply disassemble it and replace the damaged component.

This also benefits you if your fitment changes. For instance, say you decide to add a pair of Z06 quarter-panels to the rear of your C6. Rather than replace both rear wheels, your existing wheels can be rebuilt with different rim shells to achieve your desired fit. That's way better (and less costly) than replacing two perfectly good wheels.

As mentioned, I selected Forgeline wheels for the Daytona 600 project. Forgeline is a no-nonsense manufacturer (not a marketing brand) with a 15-year history in racing. Forgeline wheels are commonly seen in American Le Mans Series, Grand Am, and SCCA Pro Racing competition. This racing experience translates into a wheel that performs perfectly under all driving situations. Forgeline's wheels are also among the most beautifully designed in the industry. You could say this company understands both show and go.

Vemp_0810_14_z D6c_new_shoes Added_stability 12/20

Broad tread blocks on the shoulder of the ADVAN Sports add stability in heavy cornering and resist chunking under extreme conditions.

Clearly, Forgeline designs its wheels for strength and performance, as well as light weight. The forged wheel centers have all unnecessary aluminum machined away to minimize rotating weight without sacrificing strength. The rims are formed from 6061-T6 aluminum, further lightening and strengthening them.

These traits are ensured through the simulation of a load using computer stress analysis. The completed design is then tested to ensure that it exceeds SAE standards. The finished products are then evaluated again using real-life racing variables to determine the test criteria.

As for style, Forgeline offers a diverse palette. I selected the classic, clean design of the five-spoke SO3P in a fully polished finish. There is a wide variety of finish options available, including powdercoating, paint, and even chrome. And you can mix and match finishes between the center and rim shells to achieve precisely the look you desire.

Other options include centersections profiled for big brakes, and even lightweight titanium and jet-nut fasteners to reduce weight at the most critical point: the wheel's perimeter. This option can take approximately one pound off the weight of each wheel.

It's no secret that tires are among the most important components on your car. The simple fact is, no matter how much power you have or how capable your suspension is, the car will not perform with subpar rubber.

Vemp_0810_13_z D6c_new_shoes 300_rating 13/20

Besides size, rubber compound heavily influences a tire's ability to stick to the road. Here, you can see the stock rubber wears a treadwear rating of 300. The higher the number, the harder and longer lasting the tire.

Having used Yokohama tires on past projects, I knew the company's products were among the best money can buy. So, I was anxious to try the new line of ADVAN Sports. These are Yokohama's top-of-the-line performance tires, and they're brimming with innovative design and technology.

Delivering both exceptional cornering and superior straight-line traction while also providing a comfortable ride is no small feat. Yet, Yokohama's engineers were able to achieve all of this in one handsome package that might just be the ultimate enthusiast Corvette tire.

Tread And Rubber Compound
The first thing most people notice about tires is the tread pattern. Yokohama developed a unique asymmetric tread for the ADVAN Sport that features five main ribs and a massive outside shoulder to maximize handling while keeping road noise and ride comfort acceptable. The four resulting circumferential grooves are wide to allow water to flow through the contact patch and minimize the chances of hydroplan-ing. The ribs are further cut with round or arc-shaped grooves to control stress to the block and further enhance wet-weather performance.

The ADVAN Sport's tread is formed from what Yokohama claims is the industry's first nanotechnology tread compound. The company bonds its proprietary polymer with silica and carbon at a molecular level to increase the rubber's flexibility and durability, enlarging the contact patch by 10 percent. This makes the tire less sensitive to both high-and low-temperature extremes. Yokohama stresses, though, that this tire is not ideal for use in near-freezing temperatures or in snow. Of course, you shouldn't be driving your Corvette in the slop anyway.

Internal Construction
The tire's internals are perhaps its most important attribute, yet almost no attention is paid to them because they are mostly invisible. It is the construction of the sidewalls and tread plies that give a tire its personality and, to a large degree, determine its performance.

Vemp_0810_15_z D6c_new_shoes Side_view 17/20

Here's the "before" shot. D6C looks like pretty much every other C6 you've seen.

The ADVAN Sport carries a Z speed rating, making it suitable for use at over 186 mph. Though your car may never approach these speeds, a tire's speed rating is an important indicator of its quality. Tires constructed with subpar materials and design will not achieve this high-speed rating. The Sport is constructed with two wide steel belts reinforced by spirally wound nylon cap plies. It also benefits from three layers at the shoulder for unparalleled strength. This contributes to improved high-speed stability and crisp handling by resisting lateral deflection.

Besides their relatively hard rubber compound, the other major gripe most enthusiasts have with the stock runflats is their lack of feedback. When pushing the tires hard, they often let go with little warning. This seems to be true of all tires of this type, not just the OEM Goodyears. Most blame this characteristic on the exceedingly stiff sidewalls required for the tire to perform its duty with no air pressure.

For this reason, I followed most other enthusiasts' lead and forewent the runflat-type tires for D6C. Yes, I am aware there's no spare tire on the C6, so I've simply elected to do what everyone else does: Carry a cell phone and a can of Fix-a-Flat. Hey, it was good enough for the C5 Z06!

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The big Forgelines make the stock brakes look fairly puny. This will be rectified in a future installment.

Fit And Performance
As you can see in the photos, this wheel-and-tire package fits the C6 perfectly. There's no rubbing during hard cornering and no scrubbing of the inner fenderwells even in the tightest parking-lot maneuvers. Equally important, the wheels and tires do not protrude past the fender lines when viewed from front or rear of the car. In fact, they fill the wheelwells perfectly.

Immediately upon bolting on the Forgeline/Yokohama package, I noticed a tremendous difference in D6C's performance. Steering response sharpened considerably, as did ultimate cornering traction. The ADVAN Sports provide clear feedback as you approach their traction limits, allowing the driver to push right to the edge without stepping over.

Vemp_0810_17_z D6c_new_shoes Quality_lugs 19/20

Invest in some quality lug nuts to fasten your wheels. McGard makes a wide variety of lugs for nearly every vehicle on the road. The chrome is top-notch and will not chip or peel.

The wheel package's light weight also was evident immediately. The car seemed to better cope with rough pavement that would previously have pushed its spring-and-shock combination to the limit, resulting in a jarring ride. While the same stretch of road was not magically transformed into a magic carpet ride, it was noticeably more comfortable.

Aesthetically, the Forgeline SO3P's are without rival. Their simple, bold design and unbelievable shine have been enough to elicit comments from complete strangers at the fuel pump and stoplight alike. If you want to set yourself apart from the crowd visually and performance-wise, these could be the wheels for you.

As I mentioned at the beginning of this article, one of my goals was increased straight-line traction. So do they stick? Um, yeah. Maybe a little too well. Can you say broken parts? Carnage to follow next month ...

Vemp_0810_16_z D6c_new_shoes Jewel_finish 20/20

A precautionary layer of masking tape on your socket or lug wrench will spare the jewel-like finish of the Forgelines.

Chrome reproduction C6 wheels
Front 18x8.5: 27 pounds
Rear 19x10: 30 pounds

Forgeline S03P polished wheels
Front 19x9.5: 24 pounds [22]*
Rear 20x11: 25 pounds [23]*

Goodyear Eagle F1 Supercar EMT tires (OEM Z51)
Front 245/40ZR18: 28 pounds
Rear 285/35ZR19: 33 pounds

Yokohama ADVAN Sport tires
Front 275/30ZR19: 27 pounds [23]*
Rear 305/25ZR20: 31 pounds [31]*

*For you conservative types, stock replacement sizes are available. The weights for these are shown in brackets.


Yokohama Tire Corporation
Fullerton, CA 92831
Forgeline Motorsports
Dayton, OH 45439


How To
A D6C gets a weight reduction and improven handling as it gets a new set of wheels.
Chris Endres Oct 1, 2008


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