You will be fine, Ive used 27 X 1/14 and 27 1X 1/18 on my wheels marked 27 X 1 1/4. psi for the 1/4 was 90 and the psi for the 1/8 was 105 and im yet to have a problem with either of them. Same Araya rims also, no hooked side wall or anything, and I commute 250 miles a week. So you will be fine. good luck.