SL-C Manual: Wheels and Tires
The SL-C uses the popular Chevrolet Corvette bolt pattern of 5 bolts or studs on a 4.75” (120.7mm) circle, commonly expressed as 5X4.75. The SL-C is shipped with a default wheel package that is the same size as those on the Corvette C6 Z06. You can specify alternate wheels at order time -- check the order form details for availability and prices.
Be aware that most BMW wheels have a very similar bolt circle (120 mm instead of 120.7), but they are different, and should not be used without a careful understanding of the subtle differences that must be managed when using these wheels. If you are considering the use of BMW wheels, also first verify the offset which may be quite different from the correct offset for the SL-C.
Some people have fitted BMW wheels to Corvette hubs with appropriate adapters. Use of these wheels without the correct adapters is not recommended for the SL-C because tightening the wheel nuts will tend to bend the studs which will eventually loosen the stud and cause stud breakage. In addition, the hub-centric dimensions do not match.
Ensure you read the important safety page from Forgestar which cab be found here. This information is applicable to all wheels.
Wheel and Tire Size
Using the stock Corvette C6 Z06 wheels or wheel sizes, as is standard in the kit package, ensures long-term tire availability since there are many of those cars on the road. Click here for wheel and tire size information.
If you use other than the standard wheels, it is likely that you will find that the wheel studs need to be longer, especially in the rear. ARP makes a set of longer studs that can be used to replace the stock ones that come installed in the GM hubs. The longest stud they supply for our cars is part number 100-7708 and is available from Summit and others as shown below:
Recently, Moroso has come out with a metric stud part number 46245 in our sizes with a bull-nose already machined. As of early 2012, they are hard to obtain, but are listed in Jegs and Summit.
GMPP also sells a bull-nosed stud for our cars, part number 22551491, although curiously it is labeled as an Oldsmobile Rocket (!) part. This is a GM Racing part, has an overall length of 3 5/16, has a ½” bull nose for fast easy threading, and is readily available. See the picture to the right. These are arguably the best studs for most cars that need longer ones.
If you decide to swap out studs, the old studs should be pressed out and the new ones pressed in. You’ll want to remove the hubs to do this, as getting sufficient purchase from a press is almost impossible when they are mounted on the car.
Resist the urge to just pound out the old studs with a hammer with hubs mounted to the car. This works to get the studs out, but almost always causes damaged wheel bearings, which is much more expensive than buying an inexpensive press or borrowing one from a buddy with a shop. Remove the hubs to replace the wheel studs. You don't need to take the hubs apart to change studs- just remove the hub and press the studs out and replace.
Some builders have reported success installing the studs by putting a wheel nut on them and running them in with an impact gun, but the preferred method is to press them in with a vise or a press. The primary risk of not using a press is that the studs may come in crooked and make it impossible to mount or properly seat wheels. It is also possible that not using a press will result in damaged bearings.
If you cut the studs to length, or machine a bull nose on them, you will likely remove the plating that protects the stud from rust. Plan to re-coat the studs, select the correct length studs, or just let longer studs extend past the wheel nuts as is often seen in race cars.
Many aftermarket wheels are designed for proprietary nuts. You should verify that the wheels you are considering for your car can be mounted using regular tools and equipment. For example, the Forgestar series of wheels which are standard equipment for the SL-C have openings that will fit a 17mm socket, but not a 19 mm socket, the standard size for the default wheel nuts. Thus, users of these wheels need to find a nut solution that permits thinner sockets to be used in order to install and remove the wheel nuts.
One solution is the Muteki SR48 Black Open End Lug Nuts 12x1.5. These come with a thin socket to fit in the tight wheel stud openings that some aftermarket wheels have. They are available at Amazon and many other web sites.
The topic of open or closed nuts is also important to understand. 'Open' nuts are those that are open on both ends. This allows them to install on long studs of any length. Closed nuts, on the other hand, have a closed outer end, and so can be installed only on a very narrow range of stud lengths before bottoming out, or not having enough threads to engage. Before you order your wheels, be sure you verify the relationship between the openings on the wheels, the length of the wheel studs, and the kind of nuts you will be using – they all have to work together as a system. Generally, it's better to use open nuts as you can always visually see if there are enough threads engaged on the stud.
Unless you cut or machine the studs to length on your car, you will most likely want to use open nuts.
It is your responsibility to select the correct nut for your application. Just because the nuts came with your wheels does not mean they are correct for your application – you must validate that the nuts do not bottom on the stud when fully tightened, and have adequate grip length so that the proper number of threads are engaged at all times.
Nuts can be made of steel, aluminum or titanium. Some people have reported good experiences with aluminum nuts, as are often found on eBay, and they have been standard on Porsche cars for a long time. Lately, titanium nuts have begun to appear. They are more expensive than the aluminum nuts, but offer still lighter weight for their strength. Halltech makes titanium nuts for the C6 Corvette that are relatively inexpensive for the material ($300/set), and being open-ended can fit many wheels and stud combinations. Since they use a 16mm socket, they also fit in small wheel nut openings as is common on aftermarket wheels.
The Titanium wheel nuts weigh about .66 lbs. for a set (of 20), compared to a little over 2 lbs. for a set of the regular chrome acorn nuts in steel. Aluminum nuts are somewhere in the middle, depending on the size and style. The Muteki SR48 nuts weigh about 2 oz. each, or about 2.5 lbs. for a set.
You’ll have the wheels off and on many times during the build. Hand-tight is fine when just rolling the car around, but tighten them to the correct torque (see your wheel manufacturers specs or use the table in the front of the manual) when checking for clearance, as between the rotor and ball joints.
Finally, be sure that the taper on the wheels you select is compatible with the wheel nuts you use. Some wheels use a ball taper, some use a flat angle taper of varying angles. Be sure the taper on the wheel nuts matches the taper machined in the wheels you have.