You're asking about tire diameter. "275s" refers to tire width. Without the aspect ratio (275/40, for example), you can't know what the diameter is. Taking the example as a starting point, a 275/40-20 happens to be virtually the same diameter as the standard 245/45-20. That's why they're a popular upgrade for the rear end. Apparently though, they won't suit your purpose of increasing the diameter. Sorry I can't help you on the maximum diameter that will fit, but it will depend somewhat on the width that you chose...