andyborris
Posted a lot
Freedom is just another word for nothing left to lose.
Posts: 2,218
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I understand offset and inset, but how do I calculate ET?
I ask because the wheels I'm hoping to fit will need PCD adaptors which are 15mm+ wide and I'm tight on rubbin' space.
What's the formula? Offset+Spacer = ET? Or something else and please keep it simple, failed my maths exams when I was young and I haven't learnt much since!
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RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
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I'm pretty sure ET is offset, it's just a denomination that's generally used to show the offset. I think it's initials for something in German. So it just shows the distance from the wheels centre-line to the mounting face, adding a 15mm spacer/adapter will reduce the offset/ET by 15mm.
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Last Edit: Nov 1, 2012 20:38:19 GMT by RobinJI
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It's whatever the German for 'insertion depth' is I think. Edit- Google tells me that is 'einsteckteife', which tallies up with ET
Offset minus width of spacer is your new offset (or ET, if you prefer), because the spacer brings the mounting face 15mm closer to the centre of the wheel That's badly worded and doesn't take into account negative ET.
..because the spacer brings the mounting face further back.
Eg. You have a wheel which is ET38, and a 15mm spacer, your effective ET would be 23.
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Last Edit: Nov 1, 2012 20:48:56 GMT by ben711200
...proper medallion man chest wig motoring. |
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ET is the distance from the centre line of the wheel to the mounting face, measured in mm If the ET is positive its offset if its a negative its inset The lower the number the further out from the hub the outside of the rim gets (more so when you get into negative  So as said above its ET minus thickness of the spacer gives new ET |
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andyborris
Posted a lot
Freedom is just another word for nothing left to lose.
Posts: 2,218
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So the new wheels must have an extra 15mm offset to compensate for the 15mm spacer to fit in the same place in the wheel arch?
I.E. Present ET 20mm, so if the new wheels have a 5 mm ET + 15mm spacer = effective ET 20mm?
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Nope, adding any kind of spacers means you subtract the spacer width from the wheel ET. In your example above, if you have a wheel with ET5, adding a spacer/adaptor will give you ET-10
To look at it the other way, if you're looking to replicate your current wheels offset of ET20 then any new wheel will need to be ET35 when using a 15mm spacer.
I hope that makes sense?
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MiataMark
Club Retro Rides Member
Posts: 2,971
Club RR Member Number: 29
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Inset, Offset and ET?MiataMark
@garra
Club Retro Rides Member 29
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and in pictures, if I've got it right  apologies for shonky powerpoint usage... |
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1990 Mazda MX-52012 BMW 118i (170bhp) - white appliance 2011 Land Rover Freelander 2 TD4 2003 Land Rover Discovery II TD52007 Alfa Romeo 159 Sportwagon JTDm
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So the new wheels must have an extra 15mm offset to compensate for the 15mm spacer to fit in the same place in the wheel arch? I.E. Present ET 20mm, so if the new wheels have a 5 mm ET + 15mm spacer = effective ET 20mm? If your present ET is 20 fitting spacers to the current wheels push them out and would give you an effective ET of 5 which would be rubbing on the arch. So you need wheels with a bigger ET to start with so when you subtract the spacer thickness you end up with an ET of 20. So add the spacer thickness to your current ET to give you the ET you require on the new wheels. What you have now is ET20 - nospacer = effective ET20 Fitting the spacer to your current wheels ET20 - spacer15 = effective ET5 So your new wheels need to be ET?? - spacer15 = effective ET20 So if you flip that statement around using algebra (see all those maths lesons did have a reason) effective ET20 + spacer 15 = ET?? Which gives you needing wheels with ET 35 so your spacers reduce it to an effective ET20 so the rim will be in the same place NOTE: ALL this is assuming your new rims will be the same width as your current ones. If they're not thats another load of calculations  |
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ChasR
RR Helper
motivation
Posts: 10,297
Club RR Member Number: 170
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Inset, Offset and ET?ChasR
@chasr
Club Retro Rides Member 170
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Andy, what condition are your current Stag alloys in? I have some wheels in an offset that you may desire  . |
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andyborris
Posted a lot
Freedom is just another word for nothing left to lose.
Posts: 2,218
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Pretty c**p, which why I'm asking about ET and now I'm intrigued as to what you may have?
Got to warn you though, will be waiting till the car is running well, before spending on wheels.
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I was dreading.reading.this thread as I also hate working out the et, then the phrase "insertion depth" was used and twas suddenly very interested;) , unfortunately it didn't turn out to be what I hoped but the thread IS one of the only et threads that has been written for the layman, cheers guys.  |
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Toyota mk3 supra. retro goodness.
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