Offset calculation
 

I am trying to figure out where the edge of my tire will be when using different offset and width numbers.

My logic using an arbitrary example:

Current position of tire edge: 0
Current Tire 222/60
Current offset: 25mm

New tire 265/35
New offset: 35

Offset difference 35-25= 10 --> moves tire edge in by 10mm
Tire width difference: 265-225=40 --> moves outer tire edge out by 20mm
Net: 20-10mm = 10mm --> tire edges moves out by 10mm

Am I on the right track here?

vtraudt,
Nothing I can think of. Initially I thought the wheel widths might play into the measurement but once I double checked I realized it would not be a problem. Even if the wheel width differed, it would not affect the tire size or offset so it does not need to be considered.

I think you are right on!

The tires outer edge distance can vary by as much as 5-10mm. Changes in barometric pressure affect the pressure in teh tire, which can affect the overall tire profile. Same, too, with how heavy your car is or isn't loaded. Also how hot or cold the tire is or isn't. How good you are about keeping them properly inflated plays a part, also, too, as well.

10mm = something <1/2-inch

Unless you're rolling completely SLAMMED, I wouldn't worry about it, too much.

Naturally, only a test fit will tell.
Regarding the tire influence: a similarly contributing factor is on what wheel width the (given) tires are mounted. Some crazies out there use superwide wheels (looks god awful, stretching the bottom of the tires so far out); the opposite is possible too (wheels to narrow for tire), and tires look like a sausage (nice protection for curb rash, though).

But it sure can serve as a starting point.
Particularly, if - like me - you are going off the 'beaten path' with tires and wheel sizes, offset, etc.

I will now also use it to 'predict' how far out the tires move out. I have a large (positive) offset wheel to fit with adapters to a lower offset car..

Push out amount = (old (positive) offset - new (positive) offset) + (new tire width - old tire width)/2 + adapter thickness

Example:
(+22mm - +35mm) + (265-225)/2 + 32mm
= -13 + 20 + 32
= push out of 39mm

Example (from 265/60x18 to 265/35-22, 1.25" adapter to adjust bolt pattern)
(+0 - +35) + (265-265)/2 + 32
= -3 (edge of tire 3mm out).

Example(ditto, but 1.5" adapter to adjust bolt pattern)
(0-35) + 0 + 38mm
= +3 (edge of tire moved 3mm out)

The width of the wheel is directly deeling with the offset. A +0 offset is where the area of the wheel that bolts to the hub is sitting directly in the center of the wheel. So if u have a 9" wide wheel with a +0 it will poke out further towards the outside of the car than if u had a 7.5" wide wheel with the same offset.