Wheel ET confusion!
Discussion
I think it's pretty well known that the OZ Slots were produced in ET 25 and 29.
Picked up a set recently and sure enough, three are 29's with what I take to be a manufacturing date of '87 whilst the fourth has a date of '91 (Original owner badly kerbed or buckled one?) and ET25.
A quick Google search will soon bring up a photo of how to measure.................
What the measurement is is irrelevant but 29 - 25 = 4 so why when I measure them do I only get 1mm difference?
I guess the good news is, with TVR's close tollerences (
) that 1 little millimetre is neither here nor there!
Picked up a set recently and sure enough, three are 29's with what I take to be a manufacturing date of '87 whilst the fourth has a date of '91 (Original owner badly kerbed or buckled one?) and ET25.
A quick Google search will soon bring up a photo of how to measure.................
What the measurement is is irrelevant but 29 - 25 = 4 so why when I measure them do I only get 1mm difference?
I guess the good news is, with TVR's close tollerences (
) that 1 little millimetre is neither here nor there! GreenV8S said:
The ET measurement should be taken from the centerline of the rim. You're comparing measurements from one side. Have you confirmed the overall widths of the two rims you're comparing are the same?
Yes, put on a flat surface (kitchen worktop) the rims are exactly same width.to measure the ET I would need to work from the centre line, but surely this measurement should show up a 4mm difference?
Seems to me that your measurements and logic are correct and the wheels don't differ as much as expected.
One of the pictures shows strange colour variations which could suggest the surface is not flat. Can you confirm you're measuring from the highest point of the mounting face i.e. the part that will be in contact with the hub?
As a sanity check, if you measure the depth from the top edge of the rim to the mounting face and subtract half the rim width, that ought to equal the inset - rim width measure from the parallel on top of the rim, down to the surface it sits on.
One of the pictures shows strange colour variations which could suggest the surface is not flat. Can you confirm you're measuring from the highest point of the mounting face i.e. the part that will be in contact with the hub?
As a sanity check, if you measure the depth from the top edge of the rim to the mounting face and subtract half the rim width, that ought to equal the inset - rim width measure from the parallel on top of the rim, down to the surface it sits on.
GreenV8S said:
One of the pictures shows strange colour variations which could suggest the surface is not flat. Can you confirm you're measuring from the highest point of the mounting face i.e. the part that will be in contact with the hub?
It is just discoloration from the hub,the surface is flat although for my measurements I did avoid the rusty brown areas GreenV8S said:
As a sanity check, if you measure the depth from the top edge of the rim to the mounting face
Measuring from front to here gives same measurement on both wheels..... 
And finally measuring the depth of the bolt holes (i.e. between the two faces I've measured from) I get 1mm thicker on the 25ET, so everything "adds up"
DamianS3 said:
Is it possible its been machined down to 25 ish to make it fit at some point?
I don't think so, by coincidence some one was asking on FB about ET on these Oz "slot mags" yesterday while I was starting this post, I asked him if he could check his and his measurements agree with mine! Edited by phillpot on Tuesday 4th September 15:33
phillpot said:
Measuring from front to here gives same measurement.....
Can't quite figure out what that picture is showing. Are you saying the actual inset is over 40mm? Small changes in inset don't make a huge difference to the feel and handling. Ideally it'd be identical from side to side, but fwiw as long as everything physically clears I wouldn't lose sleep over a 4mm discrepancy and I'd ignore a 1mm discrepancy.
GreenV8S said:
Can't quite figure out what that picture is showing. Are you saying the actual inset is over 40mm?
It's just showing where I measured from, rim to the flat face the four mounting holes are drilled through (ignore any measurements you can read)GreenV8S said:
I'd ignore a 1mm discrepancy.
phillpot said:
It's just showing where I measured from, rim to the flat face the four mounting holes are drilled through (ignore any measurements you can read)
The inset is measured from the face that mounts on the hub, as I'm sure you know. Looks as if that picture shows you measuring to the front face of the wheels, which doesn't tell us anything about the inset. ETA But I think your point is that the two wheels have the same dimensions on the front face, and only 1mm difference on the thickness, so it's consistent with them being the same part with just a 1mm difference in the machining of the mounting face. I think you already concluded you're good to go, and I agree with you.
Edited by GreenV8S on Tuesday 4th September 00:47
RobXjcoupe said:
Are the depth of the securing but clearance holes the same depth in all 4 wheels in the hub?
phillpot said:
And finally measuring the depth of the bolt holes (i.e. between the two faces I've measured from) I get 1mm thicker on the 25ET
RobXjcoupe said:
Also the offset is measured from the inside of the wheel tyre bead and not from the wheel outer edges. The outer edges may have been re-faced which can effect your offset measurements.
Wheels are identical widths, I'm happy nothing has been re-faced or machined. All measurements were for comparison and not to actually calculate the ET , measuring from the outer edge is much easier phillpot said:
RobXjcoupe said:
Are the depth of the securing but clearance holes the same depth in all 4 wheels in the hub?
phillpot said:
And finally measuring the depth of the bolt holes (i.e. between the two faces I've measured from) I get 1mm thicker on the 25ET
RobXjcoupe said:
Also the offset is measured from the inside of the wheel tyre bead and not from the wheel outer edges. The outer edges may have been re-faced which can effect your offset measurements.
Wheels are identical widths, I'm happy nothing has been re-faced or machined. All measurements were for comparison and not to actually calculate the ET , measuring from the outer edge is much easier 
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