WHEEL OFFSET ON ELAN +2 STEEL WHEELS ?
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Post by: 45bvtc » Mon Aug 15, 2011 12:56 pm
Hello L,
Just found your question and hope I can positively assist.
Offset (ET) is the distance in mm from the running centre-line of rim (C) to the wheel mounting face (M): see diagram.
Note: modern wheels are usually stamped with their offset using the German prefix "ET", meaning "Einpresstiefe" or, literally, "press depth".
You can determine the 'ET' dimension of your own wheels by first measuring:
(1) The distance from the inside edge of the rim to the wheel mounting surface, and then
(2) the overall width of the rim.
You'll then need to subtract half of overall width dimension (2) from the inside edge of the rim to the wheel mounting surface dimension (1) to get to the 'ET'.
For example: assume (1) to be 135mm (my own records show this to be the dimension of the 'original' 5.1/2 J alloy wheel as fitted to my 1974 +2S 130/5) and (2) to be 160mm (again from my own records).
The difference: 135mm - 80mm (half of the 160mm) = 55mm (and 55 is the 'ET')
Note a): Before someone says I'm wrong, again, the principles of the above are as I used in the preparation of Type Approval documentation for motor vehicle testing at MIRA (Leicestershire).
Note b): Just checked this on some modern Audi 18-inch alloys in my garage and the calculations are spot-on (or spot-bollock even, to use an early Lotus term) for those wheels.
Note c): There were two wheels fitted to the Elan +2, early (without chrome plating) and late (with chrome plating) both having a different 'ET'. I had both using the later wheel for summer tyres and the early wheel for winter tyres (oh those glory days?).
No apologies for the length of my explanation (you know who you are) but hopefully all will be able to understand.
Just found your question and hope I can positively assist.
Offset (ET) is the distance in mm from the running centre-line of rim (C) to the wheel mounting face (M): see diagram.
Note: modern wheels are usually stamped with their offset using the German prefix "ET", meaning "Einpresstiefe" or, literally, "press depth".
You can determine the 'ET' dimension of your own wheels by first measuring:
(1) The distance from the inside edge of the rim to the wheel mounting surface, and then
(2) the overall width of the rim.
You'll then need to subtract half of overall width dimension (2) from the inside edge of the rim to the wheel mounting surface dimension (1) to get to the 'ET'.
For example: assume (1) to be 135mm (my own records show this to be the dimension of the 'original' 5.1/2 J alloy wheel as fitted to my 1974 +2S 130/5) and (2) to be 160mm (again from my own records).
The difference: 135mm - 80mm (half of the 160mm) = 55mm (and 55 is the 'ET')
Note a): Before someone says I'm wrong, again, the principles of the above are as I used in the preparation of Type Approval documentation for motor vehicle testing at MIRA (Leicestershire).
Note b): Just checked this on some modern Audi 18-inch alloys in my garage and the calculations are spot-on (or spot-bollock even, to use an early Lotus term) for those wheels.
Note c): There were two wheels fitted to the Elan +2, early (without chrome plating) and late (with chrome plating) both having a different 'ET'. I had both using the later wheel for summer tyres and the early wheel for winter tyres (oh those glory days?).
No apologies for the length of my explanation (you know who you are) but hopefully all will be able to understand.
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