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Let's see if we can sort this out. I'll put this up so that it can be shot down / amended etc. It appears that 750mm on 18" wheels is a standard measurement from bottom of rim to bottom of wing, at the front. I understand that the rears are 10mm less than the fronts. It should then follow:
STANDARD HEIGHT MEASUREMENTS
FRONT
18" 750mm ± 2 mm (or 741mm ± 2 mm? see below)
19" 763mm ± 2 mm (or 753mm ± 2 mm? see below)
20" 775mm ± 2 mm (or 767mm ± 2 mm? see below)
REAR
18" 740mm ± 2 mm (or 731mm ± 2 mm? see below)
19" 753mm ± 2 mm (or 743mm ± 2 mm? see below)
20" 765mm ± 2 mm (or 757mm ± 2 mm? see below)
Height from bottom of wing to the ground should be the same for all wheel sizes, given you have the correct tyres on to maintain the correct rolling circumference, though this is more difficult to measure accurately due to tyre wall strength, air pressure, temperature, tyre type and make.
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From the service manual:
Nominal height from hub centre to wheel arch (not liner):
Front 493 ± 2 mm (19.4 in ± 0.08 in)
Rear 483 ± 2 mm (19.0 in ± 0.08 in).
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So need some measurements in of 18",19",20" rim to rim (because an 18" rim is not 18" across on the rim, etc)
Just measured my 20" wheels and they are 548mm rim to rim (21.5"), so half that is 274mm. Add this to 493mm gives 767mm, which is a bit different to 775mm above ?
Measured 18" wheels now and these are 496mm (19.5"), so half that is 248 add 493mm gives 741mm
Seems wheel rims are 1.5" wider than stated size so 19" wheels should measure 520 (20.5") half is 260 add 493 gives 753mm .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember 
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962
Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999
Last edited by Joe90 on 26th Jun 2012 7:07pm. Edited 2 times in total
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26th Jun 2012 8:29am
