Appreciate the quick replies on this. As for the decrease in top speed, I'm not too fussed, as currently know the bike can get around 82mph+, but I solely sit at 70 just to try keep the bike from being worn. As for hills there are relatively none on the a13, so that shouldn't be an issue. Thanks guys I will contact my mechanic and see which he would recommend. As for chain and sprockets brands, can you recommend a good safe brand? Just done the silly option of budget on eBay. But the thing is stretching very quickly.