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WHEEL OFFSET (ET) 3 years 3 months ago #82543

  • PTmunji
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  • Steve & Moni
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This is a topic that has been raised here about 100,000 times (ok, slight exaggeration), by many people with limited information.
After years of reading about it, half answering questions about it, reading all sorts of ill-informed replies about it, I have decided that it’s time to explain it !!!

Firstly we need to understand the difference between diameter and width.

Imagine a wheel mounted on the car. The diameter is the distance from one edge of the wheel to the edge directly opposite- or from the point of the wheel closest to the road to the point directly vertically above that point. This is expressed as 15”, 16”, 17”, etc.
The width of the wheel is the measurement taken from the outermost edge of the wheel to the innermost edge. This is expressed as 5.5”, 6.0”, 6.5”, 7.0”, etc.

The offset of a wheel is the distance from the hub mounting surface (that is, the inside part of the wheel that seats against the hub) to the middle/centre of the wheel. The wheel offset is measured in millimetres and is expressed as a positive, negative, or zero offset or ET (ET is an abbreviation of a German term that basically means ‘depressed depth’).
So this means that a positive offset (or an ET without a – sign) is when the hub mounting surface is toward the outside of the wheel, and an ET- would mean that the mounting surface is towards the inside of the wheel.
SO, offset is relative to width and not diameter
Most front wheel drive cars (including PT Cruisers) have a +ve offset.
To try to explain this- imagine that the wheel has been pushed from the outside inwards towards the middle of the car. It is thus ‘protecting’ the brakes, etc.- hence ‘depressed depth’.
This all starts to get confusing because ET (offset) is measured in millimetres (whereas everything else is in inches).

So, diameter has nothing to do with offset. As long as any replacement wheels are not smaller in diameter than the smallest original wheels fitted to a particular car there will be no problems with disc calliper clearance, etc. (provided of course that the wheels are designed for cars fitted with disc brakes. If they are for a car with drum front brakes then you could have problems).

Sooooo, as the wheel width increases from the manufacturers standard sizes one needs to look at the ET so that the wheels don’t start rubbing on suspension parts or body panels.

In the case of a Chrysler PT Cruiser-
ALL models have the same hub to hub width, so the ET (offset) has NOTHING to do with the year model (despite what some may have been told by various tyre dealers). The ET required depends on the width of the wheel, and there is a reasonable amount of room to play with.
For example- a 16” x 6” factory rim normally has an ET 40, but they have been fitted with 6" ET 37. If the PT is fitted with 6.5” wide rims the factory offset will be ET43. This means basically that the amount of wheel that is toward the inside (suspension parts) and the outside (body panels) stays relative.
Having said that, my 7" rims are ET40...!!!
To try and make this as simple as possible, the wider the rim generally the smaller the ET (offset) has to be to keep the inner and outer distances relative. And the difference between ET40 and ET42 is only 2mm (not much!) As long as you're not trying to fit 8" rims with ET48 for example, most 'normal' aftermarket rims that fall roughly into the size range will fit.

I hope that this information will be of use to others in the future......

Happy Cruising,

Steve & Moni & her Bat-Cruiser
Last Edit: 3 years 3 months ago by PTmunji.
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The following user(s) said Thank You: White Cruisn, GangsterGiz, i2s2bme

WHEEL OFFSET (ET) 3 years 1 month ago #82838

  • Britinoz
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Last Edit: 3 years 1 month ago by Britinoz.
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