I am confused, (been on nights al week )

i would like to change my wheels on the locost <, for lighter and more stylish ones, also to lose the wheels spacers on the back

so if my wheels are 7x13 (they are at present) and i want the mounting flange of the wheel to be 50mm in from the back face of the wheel,

My rear wheels would be quite a big negative offset

what would be the "et"

hope this makes sense, as its doing my head in !!

[Edited on 29/10/10 by steve m]

7inch = 178mm
178/2 = 89 centre line
ET is measured from the centreline
89-50 = 39 and that would be negative

Most wheels have a positive ET, ie ford is about 38, vauxhall is 49.
Meaning you would need 77mm spacer to acheive a 39mm negative ET on standard ford wheel with 38mm (pos) offset.


[Edited on 29/10/10 by loggyboy]

http://www.1010tires.com/WheelOffsetCalculator.asp

Yup but the backspace is measured from the outside of the inner rim and the width is measured from the inside edges of the rim.

In effect this makes the ET about 12mm more. i.e. -52

This www.rimsntires.com/rt_specs.jsp explains it better

[Edited on 29-10-10 by v8kid]

The car wheel bible shows this well.
I have deliberated long and hard on this and look at it this way,
1. if the wheel has an ET of 0 then the centre line of the rim is level with the mounting face.
2. Making the back space longer, pushed the mounting face closer to the outside of the wheel, the difference is +ET, -ET if the back space is less.
3. It becomes more difficult to picture when you increase wheel width and want to keep back space the same.

quote:

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Originally posted by snapper1. if the wheel has an ET of 0 then the centre line of the rim is level with the mounting face.

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What is generally overlooked is that if you fit a 195 70 13 tyre to a 6x13 wheel with an 19mm offset, it will be in exactly the same position as fitting it to a 8x13 wheel with the same 19mm offset.

It is always the tyre that will foul any bodywork than the wheel. You will have to check the scrub radius though.

I do have PLENTY of room under tghe rear arches

i also came up with -52 so that a good start

now to look for some 2 wheels 7x13 -52
and 2 7x13 et38

steve

You don't have to get -52> suppose you can only get -32 if you add a 20mm spacer that makes it -52.

More commonly with a -18 offset you would require a 34mm spacer which is probably as far as you woud want to go.

If you don't like the idea of spacers you could buy 3 piece wheels which you can build to any size you want.

For a 7" rim you would want around a 3" inner rim and a 3.5" outer rim. (the center is approx 0.5". This will vary depending on the offset built into the differnt centers