[dd74]

I've read my car's top speed is 126, which may or may not be true with 60 series tires, but for argument, let's say that is the top speed with this height tires. (I'm not certain of the tire height on stock 1974 911s were).

If I change to 50 series (with the decrease in height), the top speed will be less. But how much less?

This is taking into consideration whatever the percentage of "less tire" there is with 50 series as opposed to 60 series.

Hope someone can help.

Thanks.