thanks for your responses- I think the terminology is a little confusing- every time I mention clipless pedals to a non-cyclist I have to explain what they are "you know clipless pedals-the one with clips on" hmm very logical. Anyway I will persevere for a while and try adjusting the tension on the binding. If that does not work I might look out for some different pedals like M520 on ebay and put the M646's on my MTB