At tire shop. This size (135-80-17) has same diameter as tires on car (245-40-18) Seem some with -25-80-17. But that size is smaller than the /45-40-18 I have. The 245-40-18 tires I got are also same diameter as stock tires 225-45-18. Would not want to drive with a Spare that is smaller by itself but also smaller in diameter. That would not be safe.