Can someone explain what the ET and offset means?

[Leemitch-91]

school boy question, but.....

i understand its to do with the fitting of the wheels but unsure what it actually means, and how i know what wheels would fit my car?

cheers

 

[Chip-mk1]

Its the distance from the centreline of the wheel to the mounting face.

So the higher the ET, the further towards the outside of the wheel the mating face is, and hence the further in the wheel will sit.

So running a lower ET will work like spacers to push the wheel further out.

In terms of what fits a clio, around 30mm will sit nicely, but the standard wheels are higher than that. Does depend on the size and width of the wheel though, a wider wheel will require a higher ET not to sit too far out.

 

[Leemitch-91]

Its the distance from the centreline of the wheel to the mounting face.

So the higher the ET, the further towards the outside of the wheel the mating face is, and hence the further in the wheel will sit.

So running a lower ET will work like spacers to push the wheel further out.

In terms of what fits a clio, around 30mm will sit nicely, but the standard wheels are higher than that. Does depend on the size and width of the wheel though, a wider wheel will require a higher ET not to sit too far out.

so a low ET, the outside of the rim will sit further out than the middle of the wheel?

 

[Chip-mk1]

so a low ET, the outside of the rim will sit further out than the middle of the wheel?

An ET of zero means that the mounting face of the wheel where it sits against the disk is in the centre of the wheel width.

higher ET means moves the wheel in, lower ET moves the wheel out.

So for the centreline of the wheel to be further out than the mounting face it would need to be an negative ET, like on an old mini cooper S reverse rim for example.
You will NEVER see a negative offset on a mk2 unless its got some massive bodykit on it though, as that would sit the wheel out even further than mine sit on 30mm spacers.

 

[Cup_Phil]

Got that the wrong way round chip - positive offset means moving the wheel out

ET38 is 5mm narrower track than ET43

 

[Chip-mk1]

Got that the wrong way round chip - positive offset means moving the wheel out

ET38 is 5mm narrower track than ET43

No I didnt get it wrong, your understanding of that diagram is what is wrong mate.

And so is your belief that ET38 is 5mm narrower track than ET43, its 10mm wider track.
(hence when you fit lower offset cup turinis to a non cup it gets wider track not narrower)


Just look a bit closer at the picture you posted, as you can see on the negative offset there is loads of wheel dish sticking out from the mounting face, ie EXACTLY as I said it should be.

 

[matt91]

i've never had a complete understanding of this but reading through this clears it up a bit, the lower the number the wider the track?

 

[Chip-mk1]

i've never had a complete understanding of this but reading through this clears it up a bit, the lower the number the wider the track?

Yes, that is exactly correct, a lower number means the wheel sits further out and hence widens the track.
Bigger number means that the mounting face of the wheel moves towards the outside of the wheel and hence when it bolts to the car more of the wheel is inboard of it.

Like when I fitted 49mm vauxhall wheels to my girlfriends mk1 clio instead of her previous 38mm ones, the use of adaptors I made to do it moved the wheel outwards and hence pushed it back out again to stop the wheels sitting in.

So fitting a spacer reduces the offset, which means it pushes the wheel out.


Well unless you are cup_phil of course, in which case you add spacers to reduce your offset by moving the effective mounting face inboard to the wheel, but that for him will make the wheels sit further in apparently instead, FLOL.

 

[Feates172]

Yes.

Example

e.t 38.5

e.t 18.5

 

[Leemitch-91]

Got that the wrong way round chip - positive offset means moving the wheel out

ET38 is 5mm narrower track than ET43

this diagram is a great help,

cheers!

 

[Leemitch-91]

whilst on the topic, what does 7J or 6.5J mean too?

 

[matt91]

whilst on the topic, what does 7J or 6.5J mean too?

​width of the rim i think

 

[loggyboy]

Yes, the J is the rim width. (in inches)

 

[bozothenutter]

Yes, the J is the rim width. (in inches)

in inches (for completeness)

 

[Cup_Phil]

No I didnt get it wrong, your understanding of that diagram is what is wrong mate.

And so is your belief that ET38 is 5mm narrower track than ET43, its 10mm wider track.
(hence when you fit lower offset cup turinis to a non cup it gets wider track not narrower)


Just look a bit closer at the picture you posted, as you can see on the negative offset there is loads of wheel dish sticking out from the mounting face, ie EXACTLY as I said it should be.

Argghh yes sorry. Quitting coffee FYI is a REALLY bad idea

 

[Chip-mk1]

Argghh yes sorry. Quitting coffee FYI is a REALLY bad idea

I'd have thought at the stage you were thinking I have replied wrongly it should have set alarm bells ringing

 

[Chip-mk1]

in inches (for completeness)

If we are going for completeness, it doesnt have to be a J type of rim either, thats just one of many options describing the shape of the rim and in particular the bead profile where it meets the tyre.

In the context of a clio though, you are unlikely to come across anything else.

 

[bozothenutter]

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

damn there is a lot to know about wheels!

 

[Chip-mk1]

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

damn there is a lot to know about wheels!

Thats quite a good page, but TBH, much like the "doesnt have to be a J profile" thing that I mentioned here, most of it is no real use in the context of clios, all that really matters is width, diameter, pcd, offset, and centre bore really.
(and spoke clearance for brakes if upgrading but there arent numbers for that as such)

 

[bozothenutter]

found it because I started thinking...."i don't know what the J stands for"....lol

my dat had a car with TRX wheels once....oh joy!

 

[Carlos Fandango]

And a wheels width is measured where the tyre sits not its overall width (which will be about 1" more).