I had the original spare on my 240D. Got a set of 195/70R14s for it as they were an exact match in diameter. They don't rub at all, so I'm happy with the size.

I asked the shop manager at the Walmart tire and lube center I used to work at, and he told me we would usually put 185/70s or 195/70s on W123s.

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission - engine spun a rod bearing, sold to pick your part

1979 300SD, ~90k original miles, all stock