They may not be suckers - ramblers have one main flush of flowers on stems grown the previous year, so if you've new stems this year, they'll flower next. Trace the ones you're suspicious about back to their point of origin - if the come from above the graft point (the knobbly bit between the base of the stems and the roots) they're not suckers - if the arise from below the graft, they're suckers. Usually, suckers grow very rapidly, are light green and tend to grow straight, often with more leaflets than the original rose.