When selecting and installing a different size wheel, customers and service providers must consider three criteria.
Plus sizing. To maintain the correct speedometer and odometer settings while changing the size of the wheels, the total diameter of the tire and wheel assembly must stay the same.
For example, when you mount and balance wheels that are an inch bigger than the old ones, the new tires must have a profile that is an inch smaller than the old ones so that the diameter of the tire and wheel as a whole stays the same.
In this case, the way it is done is called “plus-one sizing.”
Putting on wheels one inch shorter than the originals works the same way. This is called “Minus-One sizing.”
2. The right size of the wheel. The width of the wheel must be right for the size of the tire it will carry.
3. Wheel offset. Choosing and installing new wheels correctly requires careful attention to wheel offset. When replacing wheels, the offset can also be one of the most difficult things to get right. It can be very hard for customers to understand, and it can be very hard for service professionals to explain.
But it’s important to get it right, because if the offset is wrong, the replacement wheels, tires, and suspension parts could be badly damaged, and the driver could be in danger of a blowout.
This article goes over the basics of wheel offset, how to measure it, what are the disadvantages of too much positive offset or too much negative offset.
If you want to measure rims for yourself, I don’t blame you. It’s important for a driver to know everything about their vehicle, so I am glad you’re doing your research.
Getting accurate measurements is easy with the help of a Wheel Offset Chart. Let’s take a step back and talk about the basics first. Here’s a quick introduction to offsets.
What is Wheel Offset?
The offset of a set of wheels refers to the distance between the wheel centerline and the hub mounting surface.
Backspacing is the distance between the back of the wheel and the surface where it is mounted. To keep your car’s performance and handling at its best, you need to get the offset and backspacing of its wheels right.
Too much positive or negative offset can cause problems, the most common of which are bad handling and more stress on the wheel bearings and suspension system. If your new wheels are wider than your old ones, you need to take the backspacing and offset into account. It’s important to make sure that the new offset is within 5 mm of the old offset.
How to calculate the wheel’s offset?
Let’s use the following example to try to figure it out.
- Set the wheel on the flat surface
- Measure the wheel’s width (distance between the surface it touches to the upper point)
- Divide the width in half to find the middle line (for example, if the width is 10 inches, the center of the wheel is – 5 inches)
- Measure the backspacing, which is the distance from the face of the hub to the top of the wheel, for example, 6 inches.
- The wheel offset is the difference between the backspacing and the center of the wheel (6 inches minus 5 inches = 1 inch)
- In this case, the hub would be closer to the middle of the wheel, so the offset is 1 inch in the positive direction.
You also need to think about how close the brakes are to the wheel. It is especially important for cars with Brembos or big brake kits.
A negative offset creates an inset or deep-dish look: -20 is deeper than -10. The wheel will also stick out of the truck. Remember that some states require the fender flares to be as wide as the wheel and tire.
Negative Offset Cons
Problems with wheels that have a lot of negative offset
When you get new wheels, it’s a big problem if they have too much negative wheel offset. The problems can cause damage to your car quickly. Wheels with a lot of negative offset might cause a variety of issues.
When a car has a negative offset, the wheels may always be in a place where they rub against the fenders. This is because the wheels stick out wider than they should. So, if you turn the wheels so that they lock, they will get close to the fenders and rub against them.
Wear and tear on the axle, bearings, and driveline
A negative wheel offset can give you more leverage while driving, but it can also cause your car parts to wear out faster. This is because the axle, bearings, and driveline are overstressed, especially when carrying heavy loads.
Less backspace problem
Offset and backspacing go hand in hand. A negative wheel offset makes a vehicle’s backspace smaller,
In this case, the car’s steering, suspension, and braking systems will not work as well because there is less room in the back.
When the offset is neutral, the wheel face is in the middle of the rim.
The wheel will have less lip and be closer to the front of the car if the number is higher. With a 20mm offset, the wheel face is farther away from the center of the car than with a 1mm offset.
Cons of too much positive offset
Even though there seem to be a lot of pros and cons to negative offset wheels, you should also be aware of the cons of positive offset wheels before you decide to do this. Some problems with wheels with positive offset are:
Brake and clearance problems
Clearance problems happen when a car’s brake calipers are very close to the wheel’s edge. For example, a measurement of 0.3mm might be thought to be good enough.
However, if you brake hard to a corner, the rim may flex. Due to the lack of clearance, this will automatically damage the brakes.
Tire Tear problem
One of the typical causes of tire tearing when moving in a vehicle is excessive rubbing. On the other hand, this wouldn’t be hard if the wheels didn’t constantly touch the brakes, suspension, and other parts. Of course, it also has to do with the problem of not enough clearance.
Upper control arm rubbing
Before installing new wheels, you have to make sure they have enough room to move. For example, every front wheel must be involved in turning corners and moving the car sideways.
Also, when you drive over bumps, the car’s wheels will eventually move up and down. Positive wheel offset makes it hard to do these things because the wheels rub against the upper control arm.