That excuse worked for me once. I have an old Honda FT 500 Ascot and the speedo and tach are stripped out so they just bounce all over the gauge. I got pulled over once for "allegedly" doing 75 mph in a 40 mph zone. The cop asked me "what the hell my problem was" and I told him flat out, my gauges are not accurate. He asked me then, "How the hell do I have the nerve to ride the bike like that?" I told him that its only a piece of sh*t 500c.c. single cylinder with five gears. I know that full throttle in 5th gear will only get me up to about 80 mph and when he pulled me over I was not at full throttle I had just shifted into 5th so I couldn't have been going more than about 55 mph. His response was, "You expect me to believe that bullsh*t story?" My answer, "Yes I do since my father who is a policeman himself paced me in his car to verify my speed at whatever throttle and gear I'm in. Here is his PBA card and courtesy badge."
The look on a cop's face when he hears and sees that is worth the price of admission I have to say. He gave me the "turn around and go home now very slowly. I'll be calling ahead to warn the other cops on the road about you." My answer, "Ok no problem since your precinct border is three blocks that way." He stuffed my license and regi into my broken gauge cluster and stomped off to his car then proceeded to follow me three blocks to where his precinct ended. Needless to say I didn't see another police car for the next thirty minutes it took me to get home . . .
. . . full throttle in fifth gear.