Front Brake Vibe???

Hey guys, have a 2001 r1 with standard rotors and pads. bike has done 13,000 klm's and is in good condition. at 90klm/h under heavy or light braking there is a bad shudder through the bike. nothing under 90, nothing over. no pulse at low speed. front wheel bearing is good and so are headstock bearings. wondering if this has happened to anyone else and if it is a rotor problem or something else. i am an automotive technician and am familiar with vehicle disc vibe, but want another opinion before i invest in new rotors. and no the bike has never had a front disc lock......thanks:)

couple things to check. remove top triple clamp and check the steering head bearing and make sure they are tight. prolly needs to be done with miles on bike anyway. It could be brake pad..check them and make sure they arent wore in any funny way. rotor could be warped.. it doesnt take much. if you have to lift front of bike and put dial caliper(get one cheap at harbor freight) and check run out on rotors. you might check manual to see what limit is. but spinning wheel with dial caliper on it will tell you how many .001's it moves back and forth. find good used set or order new one is warped. but first check steering stem nut and bearings. Also check tire pressure and tire wear. could be balance problem in wheel..but i wouldnt guess it would just under breaking..but i have seen weirder things.

Thanks M8, will have a look over my Xmas break. i'll let u know how i go.