Really dont understand offsets - Alfa Romeo Forum
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(Post Link) post #1 of 7 Old 20-06-13 Thread Starter
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Really dont understand offsets

Guys i need a little help.

Ive just brought a set of 16" teledials for my 2001 twinny. How much of a difference does the offset make on these. Originally they were going on just to get it through the mot.

Ive never really understood the offset thing? Can anyone shed me a bit of light to whatever pitfalls there may be?? Trying to get the car mot'd tomorrow.....

cheers in advance
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Offset is the position of the centre of the tyre contact patch relative to the wheel mounting face.

The steering geometry is optimised for a specific relationship between the steering axis & tyre contact patch. Incorrect offset changes that relationship & may give problems such as torque steer, braking instability, etc.

That's my understanding of the situation - I stand to be corrected.
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Wheels for a twinny with standard brakes need an offset of 30.5mm. This should be marked somewhere on the wheel. It is the distance between the wheel mounting face and the centre of the rim across its width.
If a wheel had zero offset, the mounting face would be equidistant from each rim edge.
If you use a rim with a 45mm offset (a common Alfa dimension) the wheel sits too far in to the wheel arch. Some people might use spacers to "correct" this. Far better to use the proper wheel.
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You can still use the 16" teledials on your twinny but they will sit slightly towards the centre line of the car - i.e. you will have a narrower track. The rear wheels on a GTV sit 'in the arches' so this will accentuate that look - I prefer the look the other way - where the wheels have a wider track, most do.
Your problem may come with any old style wheel balance weights that are clipped onto the inner edge of the alloys on the rear. These clip the the spring pans on cornering due to the wheels sitting that much closer to the car.

You can of course fit spacers to counteract the wrong offset you have.
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You presumably have wheels off a 156 - in which case they will be 41.5 offset, compared to the 30.5 of the GTV wheel, so you'd need a 10mm spacer to (nearly) correct it, tho I'm not sure if you can get 10mm hubcentric spacers....
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Go for 15mm hubcentric spacers.
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(Post Link) post #7 of 7 Old 24-06-13 Thread Starter
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Guess that explains the knocking noise from the back!! Dam it. Now I just have to weigh up if its worth buying some spacers or saving a little more to replace the front tyres (18's vs the 156 16's currently on the car). I manage to wear out a set of falkens in 6 months. Its an expensive habit!!
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