The Dirt (Episode 3): Understanding Wheel Offset & Backspacing & Spacers

So this is a topic that often has people scratching their head. Read along and hopefully we will achieve an "Ahh Haa" Moment.

The terms Offset and Backspacing will surely come up if you decide to get new wheels for your Renegade. This may apply as well if you are just getting new tires, trying to decide if you need a spacer or any combination of these.

So what are these dirty words?

Offset: is the measured distance between the hub mounting surface and the wheels center line.



BackSpacing: is the measured distance from the hub mounting surface to the back edge of the wheel.



Ok but what does this all mean?

In relation to the Renegade, nearly all wheels will be measured in Offset, often references as ET40 for example. This means the wheel has a 40mm positive offset, Or a distance of 40mm from the wheel's centerline to the mounting surface. As this number increases the wheel moves further in towards the car, as this number gets closer to zero or negative the further it will move away from the car sticking out of the wheel well more. Here is an infographic showing these offsets in relations to a zero offest the green lines would be the zero offest wheel edges and the orange is the hub mounting surface.



Well what happens if I use a spacer?

If you use a spacer you are effectively reducing the positive offset number from the example wheel with a ET40 or a positive offset of 40mm. A 1 inch spacer (pink in drawing) would be subtracted from the positive 40mm offset reducing the effective offset to an ET15 or 15mm of positive offset. This can see seen in the infographic below.



FAQs:

Q: How come the wheels available for the renegade all have a positive offset of 38-40mm?
A: The Renegade falls into the class of FWD wheels. Most FWD cars use a positive offset wheel.

Q: Why would I need to change the offset?
A: With the distance between the hub and strut tower being fixed, you may need to reduce the positive offset to increase clearance if you decide to run larger tires or larger/wider wheels.

Q: How much will my spacer reduce Offset?
A: 0.75" Spacer Reduces Offset 19mm
1.00" Spacer Reduces Offset 25mm
1.25" Spacer Reduces Offset 32mm

Q: So what types of cars use what offsets?
A: Many FWD cars use a Positive Offset
Many 4x4 Trucks and Full size SUVs use Small Positive to Zero Offset.
Most Aftermarket 4x4 style wheels are Zero Offset.
Some RWD and Race Cars use a Negative Offset.

Q: Are there any issues with reducing the positive offset?
A: Yes, the lower the positive number gets the more and more likely you are to have issues with the tire rubbing on the inner fender well in the rear of the front wheel opening.

Q: I want my wheels to "Stick Out Farther" what do I need?
A: You would need a Lower effective positive offset then you currently have. But see the questions above!