Merry Christmas all!
I figured I'd throw this up here because everyone seems to be asking wether specific wheels will fit or not when it really isn't that hard to figure this out on your own with a little basic math, wheel knowledge and of course a specific reference which in this case is a measurement from the hub face to the air bellows (all of the measurements I'm using are with the bags at 30psi as this represents the bellows at their narrowest point. Also remember that due to the shape of the bellows different diameter wheels, 18" 19" etc. may have different clearances so all measurements will be based on the more common 18" wheel)
so to get started first off you need know how to know how to reverse engineer the measurements from a specific wheel/offset combination. To do so is easier than you might think. To start off, you will need the true width of the wheel in question, which is not actually the width as you know it. Advertised widths and true widths are not the same. The advertised width is measured from inside lip to inside lip and the true with is of course from outside to outside. Most of the time, actually about 99.9 percent of the time with most common wheels this outside measurement is approximately 1 inch wider than advertised width. So using my wheels as an example, on the box it says they're 9.75 inches wide. But based on our knowledge of true width we know that they're actually 10.75 inches wide. Or if you have an 8 inch wheel then you know that the true width is 9 inches etc.
So with that out of the way we now need to figure out our offset measurements but in order to do so we need to convert our inches to mm as it is in mm that all offset measurements are made. So our example is 10.75 inches. I just have to Google 10.75 inches to mm and I get a result straight away: 273.05mm, we can drop the .05 as its too small a number to make much of a difference. next, we divide my 2. This gives us 135.5mm.
So now a little on offset. It's rediculously simple. Offset is simply the exact location of the hub-face portion of the wheel relative to the centre of the rim. So the measurements you see are how many millimeters the hub-face is from the exact centre of the wheel. The - and + signs simply tell us wether that measurement is towards the inside or outside of the wheel. So +20, for example means that the hub-face is 20mm from the center of the wheel and the fact that it's positive means that this measurement is taken from the center OUT rather than in.
So now that we know what offset is, all we have to do is apply the theory to our example wheel and we can successfully reverse engineer it's measurements. We've already measured and converted our wheel and halved the conversion, so all thats left to do is apply the offset to work out our measurement from the hub-face to the furthest inside point on the wheel. Because our wheel is +20 we simply add 20mm to our measuement. So 135.5 + 20 + 155.5. Success! We now know that the actual distance from the hub to the furthest extremities of the rim is 155.5mm. I also know that from the outside of this particular wheel to the air bellows (at 30psi) is 15mm. So not only have we reverse engineered the measurements of my wheels but we have also found our all important reference! Based on these measurements we now know that on any car the distance from the face of the hub back to the air bellows (for an 18" wheel and once again at 30psi) is 170.5mm (155.5mm + 15mm)
So based on that figure (170.5mm) you can now apply those basic principals to any wheel size/offset combo and determine whether they would fit!
So another example for clarification:
Lets use th above mentioned 18X9.5 +45...
First, add an inch:
9.5" + 1 " = 10.5"
Next, convert to mm:
10.5 inches to mm = 266.7 (round off to 267)
Now divide by 2:
267 / 2 = 133.5
Now add the offset (if the offset were negative we would subtract)
133.5 + 45 = 178.5
Lastly compare to our reference:
Our measurement of 178.5 is larger than our reference of 170.5. So it seems that unfortunately this wheel is too large by approximately 8mm
(sorry lol)
(just remember that all of these measurements are focused purely on the wheel without tires. Meaty tires can affect your measurements so make sure to include any tyre overhang ect to your measurements)
And thats it! apply the same theory as above to any wheel to get an approximate idea of whether they will fit or not. Happy Holidays!
