I am this very minute finalising the offsets for my new rims.
I have measured so many bloody times and still question my sizing calculations. I would suggest you measure your own car and confirm it on a sizing chart such as
www.rims-n-tires.com I have asked your question many times and it only takes some one to tell you what they believe to be true but is not 100% and you have a set of rims which don't fit!!
Is your Starion a widebody? Do you have std suspension? Have you changed the ride height? All these variables change spacings.
Do you realise for instance that a 10" width rim is not 254mm wide but actually 278mm - the extra 24mm is the 12mm lip on the rim circumfrence each side.
I have a lowered ride height with coil overs. I am going to fit 18' x 10' rims to the rear. I have a std 8" widebody rim on it to compare sizing and I believe that to fill the guard I need an exta 30mm of dish which would place an extra 20mm on the inside of the rim (totalling the exta 50mm - 2" in rim width) this calulates out to be a 18"x10" rim with a negative 15mm offset.
According to my measurements this would place the outside lip of the rim about 6mm inside the outside face of the guard (tyre might contact guard lip but on compression of suspension it should actually move away from the guard.
The fronts are 18"x9" with a positive 13mm offset. This would not work on std suspension. I believe that this would place the outside rim lip 30mm closer to the guard and bring the inside rim lip 20mm closer to the strut. Both the front and rear calculations are based on std rim offsets and actual physical measurements.
I am concerned with my front internal clearance with a 9" rim and should play it safe with an 8.5" width. The other concern I have is that most people have suggested a 0mm offset for a 10" rear but this I believe would place the outside rim lip some 15mm inside the guard face.
What have you and others calculated?
