What width tires will fit on a 1999 Trek Postal? I'm using my old Trek Postal (5200/5400) as my winter beater. I'd like to test some studded tires, such as the Schwalbe Winter700x30 Wire but I'm not sure if the 30's will fit as the largest I've ridden to date is a 25 (or 27?).  

Has anyone ridden a 30 or know how to determine if they'll fit, especially with the aggressive tread and studs.

Thanks,
Matt

Tire for reference: http://www.amazon.com/dp/B00AAZFGVI/ref=wl_it_dp_o_pd_nS_ttl?_encoding=UTF8&amp;colid=313MZ1AZTU1DO&amp;coliid=I19MD4W468VK20
Most likely not.  

Most frames with caliper brakes can at a maximum take a 28 or really narrow and slick 30 (assuming a modern short reach caliper). A nobby tire will almost certainly not fit regardless of size. if there's a lot of clearance currently ( > 1cm), I would take it to your lbs and check with them.