Calculating offset when changing wheel width

[Bubba's Dragon]

I tried using numerous wheel offset programs to try to figure out how much off from FSM:

WHEEL - SRT8 (from fnkychicken)

SPECIFICATIONS
Wheel Size: 20 in. X 9 in.
Wheel Bolt Pattern (Circle) Size: 115 mm (4.53 in.)
Wheel Offset: 25.5 mm
Wheel Mounting Stud Size: M14 x 1.5 mmset you need from changing

So now lets say you drop to a 22x 8.5 front wheel in the front and 22x10 inch wheel in the back?

Does anyone have a good link to where you can plug in old wheel size and offset, then click new width and bamm get the appropriate offset?

Can't do it on this web sight: http://www.1010tires.com/WheelOffsetCalculator.asp
Nope:
http://marksink.com/tire_wheel_offset/offset.html

but this is a good info sight: http://marksink.com/tire_wheel_offset/tires.html but still not what I need

maybe some one can answer or post the math that you use to figure it out please.

[Bubba's Dragon]

Damn no help.... wish we could make a nice database with wheel information on it.... what fits what dosn't...
Anyways. I found this setting for so cheap It just seems that 25's are way to small for my crappy road conditions...

22x8.5, 5x115mm, et 15mm Chrome finish: 2 pcs for front.
22x10, 5x115mm, et 20mm Chrome finish: 2 pcs for rears.

Front tires: Pirelli 265/35/22
Rear tires: Pirelli 295/25/22

Why not go through forums vendor, not that many like to ship internationally its a pain in the but for only a few bucks profit.
I hope they fit and I might have to get new tires in the back... = (

[jg]

I guess i'm "old skool", but my method of using a pencil, scale(metric and standard), and a sheet of paper works pretty well.

I would tell you where your new 8.5" wheel would live relative to the face of the original 20x9" 25.5mm offset SRT8 wheel, but you didn't give us the offset.

[Bubba's Dragon]

Old front wheel:
20 in. X 9 in. 25.5 mm offset

New Front Wheel:
22x8.5, et 15mm (offset)


Old Back Wheels:
20 in. X 9 in. 25.5 mm offset


New Back Wheels:
22x10, et 20mm (offset)

Thanks ^^

[jg]

This is really pretty simple. Start w/ the 9" wide wheel- subtract 1/4" (6.35mm) from the outside face of the wheel (half of the 1/2" width change). Then add back the 10.5mm difference in offset since it's a lower offset. In conclusion, the face of the 8.5" 15mm offset wheel will live 4.15mm further out than the SRT8 wheel would. The back of the wheel would move out the same 6.35mm for the width change, plus the 10.5 for the offset. The inside/back face of wheel will move out 16.85mm.

The rear wheel can be calculated the same way. I'll let you handle that.

EDIT: Nevermind... The 10" rear face would live 18.2mm out from the SRT wheel face and the back of the wheel would move in/deeper 7.2mm.

[Bubba's Dragon]

it seems that the wheels will not just bolt right up.... what the frick... the company is multi million dollar company and cant get wheels perfect.... who wants to pay tons of money for wheels and have to get spacers... hmmmm.

[jg]

Is the centerbore of the wheels big enough? Do the wheels clear the brakes?