245/40/18 Rubbing fender wall check my math

[DTW986]

02, 986 non-s, bone stock.

Bought a set of 18x8.5 on 245/40/18 and 18x9.5 on 275/40/18. The 245's rub just a bit at full stop on the inner fender wall. Need about another .25" of clearance. (had a hinting suspension this would be the case).

THE KICKER IS:
The current tires are just about toast, so new ones will be bought (known beforehand and price accounted for). A search on the forum showed that members claimed success on 245/18(assuming different suspension??), 235/18, and 225/18.

225's would return the wheel to just about the 25.1" diameter the oem 17's have (good!) BUT are the lowest size for the 18x8.5 and bring the side walls to 3.5"

235's are a 'recommended' size for the 18x8.5 increase the side wall to 3.7" but also the diameter to 25.4". Just .3" less than 245's (which rub apparently).

The question! I think a can get away with 235/40/18 but am I flying too close to the sun? What say you?

Here is a picture in bad lighting and a frustrated hand.

[BrantyB]

To give any educated guidance - what is the wheel offset?

[DTW986]

Originally Posted by BrantyB

To give any educated guidance - what is the wheel offset?

PO didn't know. I measured and came up with roughly 50 ET

[Racer Boy]

The offset should be stamped on the wheel.

[Kdnatchez]

These are the offsets from my factory cayman rims. They are stamped on back of rim

[DTW986]

M 40 = ET?

I saw this before but that didn't seem right. These are wheel dynamics

[DTW986]

The only other markings

[WillH]

I am running 235s 49 offset with 12mm spacers here and they rub the front of the wheel well when the wheels are cranked over. I remember someone saying that there is a way to adjust the wheel well liner but I haven’t looked into it yet as it’s not bothering me enough to. Leaving it for when it’s put up for winter.

Also thought 245s rub the strut spring perch.