Thanks for the replies, I Think the speed is constantly out however i can't be 100 percent sure as I've only really check it a couple of times and only up to about fourty. I know it's not a sprocket problem, the rear sprocket is standard and I've done my maths and a front sprocket on it's own can't make that much difference. Apparently my zx9r 98 c1 doesn't have a speedo cable, it's electric something to do with magnets. I have now got a manual and trying to work things out. I now think, either the sensors knackered or may be as you said there's something wrong at dail end. I have call the old owner and he didn't know it was out, I've now got a sat nav so can get a more accurate reading instead of following or being followed. but stil need it sorted. My mate with a c2 said that if it's not a big problem and the same sensor, we can take his and fit it to mine to eliminate or comfirm weather thats the problem. the saga continues