Oversized and shimmed or a 25.4 with a bit of a gap?
Neither of the above. Some people have successfully used a 26.0 road stem without modification, but the more robust [stems|users] have enough [metal|mettle] about them to tolerate reaming the bar bore to 26.4, and this is likely to be safer than overstressing the clamp by bending it round the bigger bar.
Neither of the above. Some people have successfully used a 26.0 road stem without modification, but the more robust [stems|users] have enough [metal|mettle] about them to tolerate reaming the bar bore to 26.4, and this is likely to be safer than overstressing the clamp by bending it round the bigger bar.