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How to Determine the Right Wheel Offset

Old 10-30-2010, 08:36 AM
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Default How to Determine the Right Wheel Offset

After struggling for a number of weeks, searching thread after thread trying to work out if a specific width & offset would be suitable, I finally worked out a method allowed me to understand the fitment tweaks.

The process might be helpful for someone in the future!? If this makes any sense ...

a) read the quick basics of ET ..

b) go to your car & check the wheel width & offset and write it down

c) lie on the ground and take a look up in the guards with a torch and understand the potential clash issues. i only needed to understand the rear wheel fitment and could get a good look by looking up from each side of each rear wheel. potential clash items to note on the rear ...
- oil hose pipe on RH side
- suspension arm on the front side of the rear tyres
- inner body area on the top of the LH side
- edge of fender

d) reach in & measure the clearance in those areas by moulding a piece of Blue-Tak until it just squeezes between the gaps. write down the clearance measurements

e) jump in front of your computer and go here

f) enter your current wheel width and offset into the calculator and your proposed wheel. for example ..
8" ET52 - my original wheel
9" ET43 - my proposed wheel
Result - inner clearance 3mm less, outer clearance extends 23mm
Whilst that is useful, if you use the same size tyre eg 255, they are not quite the measurements that you need (unless perhaps you have that stretched tyre look ie the wide tyre on a narrow rim).
Therefore - using the same size tyre, the centre of the tyre moves outwards by = 23-8 = 18mm

So in theory, as an example, you could use the same size tyre, but a wider wheel, the calculator would tell you you have less clearance inside and extends outwards, but the centre of the tyre may not change in position and there could be zero difference in the fitment. And all clearances could remain the same. With a look of your current wheel/tyre example fitment, you can get a good feel.

I was also considering a 10" ET40, so I put the 9 ET43 and 10ET40 into the calculator
Result - inner clearance 10mm less, outer clearance extends 16mm
Therefore the centre of my 255 tyre shifts outwards by = 16 - 10 = 6mm

8 ET52 - fitted
9 ET 43 - centre of tyre moves 18mm outwards compared to original
10 ET40 - centre of tyre moves 6mm outwards compared to 9ET43

g) Using those numbers and tape measure, go back to the car and your previous clearance measurements and you can get a good feel about what is really happening!
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Old 11-19-2010, 05:20 PM
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