Ok, here is what I got:

1 mph equals 88 fpm

160 mph equals 14,080 fpm
31" tire equals 8.1 feet circumference
14,080 divided by 8.1 equals 1736 rpm
7,000 rpm : 1736 rpm equals .248
1 divided by .248 equals 4.032

SO , 4:1

Calculated, 7,000 rpm times .25 yields 1750 rpm.
1750 rpm times 8.1' equals 14175 fpm divided by 88fpm yields 161 mph.