- Wheel Offsets
What does Offset mean?
Offset is the distance between the hub mounting face at the back of the wheel and the wheel's centraline.
Offset is usually stamped or engraved into the wheel and is measured in millimetres of 'ET' [ET is the short form of the German word 'Einpresstiefe' which literally translates as 'insertion depth']
Positive Offset wheels have their mounting face toward the front face of the wheel. Most front wheel drive vehicles have positive ET wheels.
Zero Offset wheels have their mounting face even with the centerline of the wheel and are by definition "ET 0".
Negative Offset wheels have their mounting face toward the rear of the wheel - powerful rear-wheel drive cars often have wheels with negative offset.
- What is PCD?
The Pitch Circle Diameter (PCD) is the diameter of the circle which passes through the centre of all the studs, wheel bolts or wheel rim holes.
The easiest way calculate the PCD is as follows:
1) Measure the distance 'S' between two adjacent studs from the centre of each hole.
2) Calculate from the formula below
**Note: on 4 lug fitments you can measure from the center of one stud to the center of the stud directly opposite.
PCD Calculation Formula
4 Stud PCD = S / 0.7071
5 Stud PCD = S / 0.5278
6 Stud PCD = S / 0.5
- Hub-centric and Centerbore
The 'centerbore' of a wheel is the size of the hole at the back of the wheel which the 'hub' fits into. To help the wheels to seat properly this hole needs to be an exact match to the size of the hub.
Most modern wheels are what's called 'hub-centric' - this means that the hub which protrudes from your car [and mates with the equivalent sized hole at the back of your wheel] is 'load bearing'. All the studs or bolts do therefore is hold the wheel onto the hub!
Some people will say the term 'lug-centric'. They are referring to the use of the lugs to position the wheel on the vehicle in the proper position. If you have' lug-centric' wheels, the state of your studs or bolts is obviously more critical - be sure to replace these from time to time and always 3/4 tighten the wheels off the car to ensure they're centerd. However this is a term that should not really be used with modern day vehicles. Hub centric rings are the correct way to align a wheel properly on the vehicle.
Why are hub-centric rings so important?
As mentioned above these rings keep the wheel aligned on the vehicle hub while your fastening the wheel to vehicle. After the wheel is properly torqued the hub-centric ring does NOTHING! The ring is only used at the time of fastening.
Does the hub-centric ring material matter?
The answer here is NOT REALLY. Again these rings only are needed while fastening the wheel to the vehicle. While some people may think that metal is better because its stronger, there is no need for a strong ring because its not a structural piece. Additionally metal rings tend to corrode and can make it difficult to remove the wheel or the hub-centric ring from the vehicle.
The argument has also been made that plastic rings melt. Well while at some point this may be true, we have witnessed the use of race vehicles using them on track for multiple seasons without ever running into this melting problem.
- Upsizing Your Wheels
Plus-Sizing or Up-Stepping are two terms given to the practice of increasing the diameter of your wheels while simultaneously reducing the profile of your tires to keep the overall rolling diameter the same.
Benefits - Plus-Sizing will improve the handling of your car! - each step will reduce the proportion of flexible tire 'sidewall' to rigid alloy. This will improve response, will help keep the tire tread square to the road and will improve your car's 'feedback'. If done properly speedo and odometer accuracy will be retained and the car's sure to look better (note: properly refers to maintaining the vehicles stock overall rolling diameter).
Disadvantages - In the majority of situations, tire inches are lighter than wheel inches. Plus-sizing can make your overall wheel/tire package heavier. Reducing the profile of your tyres will also reduce your car's damping deflection under compression [the ride quality will get worse]. Other disadvantages can include you needing more expensive tyres, your brakes looking puny.
One more important thing to think about whenever you change the tire or wheel size. Consider your environment and the area your usually drive on. If you drive in areas where the road surface tends to be rough (i.e. non paved roads or pot hole invested streets) you may want to consider leaving a decent amount of tire. The more tire and cushion the less wheel bends you may encounter. Sometimes choosing a wheel is more then just what looks best.
- Tightening Your Wheels
All wheels should be installed using a torque wrench. This ensures that the wheels are not too tight or too loose. Check your vehicle's manual for correct settings. When you install wheels for the first time, you should re-torque the wheels after about 60 to 90 miles. Always refer to Owner's Manual for proper factory specifications that take precedence over the listed recommendations.
Here are some basic starting numbers you can follow: 12mm = 70-80 ft. lbs, 7/16″ = 55-65ft. lbs, 1/2″ = 75-85ft. lbs, 14mm = 85-95ft. lbs, 9/16″ = 95-115ft. lbs, 5/8″ =135-145ft. lbs.
This torque should be applied in the correct pattern for the amount of studs of that particular vehicle.
- Wheel Finish Care
One of the most asked questions is what is the best way to care or clean a wheel. The answer is far less complicated then most would think. The answer is soap and warm water. The use of chemical cleaners often cause damage to the clear coat which is used on the wheels. This can result in pealing, flaking or burn spots. The use of special cleaners and wheels soaps should be viewed very carefully. Any soap, or cleaner that you put on your wheel may contain chemicals or some type of acidity to help remove dirt. This is why we only recommend a "safe" vehicle soap and warm water for wheel cleaning.
The best care for any wheel is to clean them often so that brake dust and other contaminants do not remain on the wheel for too long. Things like Brake dust overtime actually becomes acidic and corrosive itself. Others who experience winter weather driving, should be proactive in cleaning "road salt" off their wheels during the winter also. These chemical that they place on the roads to aid in snow melting and tire traction, "salt", can be a few different chemicals. In either case it should be cleaned off your cars paint and wheels regularly during the winter to maintain a safe and proper finish. The best way to care for a wheel is to think of it like an extension of your vehicles paint. If you wouldn't put it on your paint you shouldn't put it on your wheel.