My son's 1991 E30 has 195/65R14 tyres on the stock steel rims. These tyres are quite hard to come by, and he is thinking of using 175/70R14 instead. Apparently, BMW supplied cars with both these options. What this car originally came with is not known. I estimate that the difference in the overall diameter of the two tyres is 0.9%.
Three questions:
- Are the two tyre sizes interchangeable on the same rims? Will everything work correctly, like the speedo? How about the ride?
- Would this count as a modification that his insurers need to be notified about?
- How do we find out what the car was originally supplied with, and just as importantly will the insurance company be able to find out if there is ever a claim?