Originally Posted by Brian Carlton

215-70-15's are a huge tire for a W123.

I ran 215-70-14's on it for awhile and they looked quite big. This is two sizes larger than stock. Now, you are also going up one size on the wheel diameter. This raises the height of the tire significantly.

You are hitting the fenders because the offset might be too low. However, with this huge setup, you may not be able to increase the offset much because the wheel will hit the tierods.

You can check to see how much clearance you currently have to the tierod. I'll bet it's less than 3/8". This would be difficult to safely reduce my much.

Check the existing wheels for the offset, as Sixto explained above. There will be the letters "ET" followed by a number such as "25". The offset of those wheels is 25 mm.

Are the tires hitting the inside of the fenderwells at the top, or is the fenderwell lip digging into the sidewall?