Wheel offset - why does it matter?

[garethj]

For example, if the car I'm about to buy is rwd and it's got wheels from a fwd on it, is the offset likely to be different and how will it matter?

Is it just because the track will perhaps be narrower, affecting its stability? Or is there likely to be any other issue?

Getting hold of the original wheels looks to be difficult, and most others with the right PCD seem to be fwd too.

Ta

[Ranger 6]

Clues to car and offset numbers would help - basically if you get it wrong the wheels will either stick out or foul the suspension.

[garethj]

Ranger 6 said:

Clues to car and offset numbers would help - basically if you get it wrong the wheels will either stick out or foul the suspension.

Good point, well presented. But I'm not sure I know the answers....

The car is a Ginetta G26 which is Cortina Mk4 based, but Ginetta specified wider wheels, the size and offset I don't know. The car is currently on Mondeo steel wheels and I think the bigger diameter helps fill the arches better.

Cortina PCD is 4x108 which is mostly Audis, Peugeots and the Volvo 850. I don't really want wide wheels (195 tyres is ample I think) but you're right, fouling the suspension is a potential issue.

Any use?

[Ranger 6]

Ultimately without the actual offset numbers you'll have difficulty knowing what will happen unless you trial fit.

So you need OEM spec offset and the offset of the wheels you want to fit. To measure the offset of the wheels you have try using the guidance here which could help;

http://www.carbibles.com/tyre_bible_pg4.html

[Sam_68]

garethj said:

Or is there likely to be any other issue?

Potential problems include:

• Fouling or wheel arches
• Overloading of wheel bearings
• Serious changes to the kingpin offset(the distance between the centre of the tyre contact patch and where an imaginary line projected from the axis the wheel pivots around when you turn the steering intersects the ground), which can have a really quite noticeable effect on steering feel and feedback.

It would also change the track of the car, which would affect grip and weight transfer when cornering a little but provided the wheels are the same width and offset front and rear (both before and after the change), the front:rear balance will remain pretty much the same, so it shouldn't make too much differnece to grip.

[Mr2Mike]

Sam_68 said:

• Serious changes to the kingpin offset(the distance between the centre of the tyre contact patch and where an imaginary line projected from the axis the wheel pivots around when you turn the steering intersects the ground), which can have a really quite noticeable effect on steering feel and feedback.

AKA Scrub Radius. This is important on heavier cars, sticking wheels with random offset on can ruin the feel of a car and make it more prone to tram-lining, torque steer (in the case of FWD), and instability under braking.

Edited by Mr2Mike on Monday 1st March 18:10