Fitting tri bars safely

Hi there people
I've just bought some tri bars for a new bike set up.
http://www.ebay.co.uk/itm/180898450615? ... 1439.l2649
They have detachable clamps which are tigthen by hex keys.
I've used some off cuts of inner tube so that they are a snug fit on the handle bars but if I apply any large amount of pressure they to tend to move downwards despite the allen bolts being particularly tight. I really would n't want that to happen if I was flying down some hill or other. Is there anything I've done wrong or can anyone advise a better way to secure them safely?
Many thanks
Nick
I've just bought some tri bars for a new bike set up.
http://www.ebay.co.uk/itm/180898450615? ... 1439.l2649
They have detachable clamps which are tigthen by hex keys.
I've used some off cuts of inner tube so that they are a snug fit on the handle bars but if I apply any large amount of pressure they to tend to move downwards despite the allen bolts being particularly tight. I really would n't want that to happen if I was flying down some hill or other. Is there anything I've done wrong or can anyone advise a better way to secure them safely?
Many thanks
Nick
0
Posts
Many thanks again
Nick
Thanks