The next time a cop asks you...
The next time a cop asks you how fast you were going, just say: “I don’t know, actually.”
Looks can be deceiving, kinda like that $5 buffet in Vegas. Although not quite as shady as the endless grease pit scenario, just because your speedo has popped 165 MPH doesn’t necessarily mean you were actually traveling at that incredible speed. In fact, it’s commonplace for a motorcycle speedometer to be five or ten percent off from the factory, and when you gear it without correcting the error (with something like a SpeedoHealer) you’re in for a world of hurt with readings as far off as 30 percent or higher.
While we’ve heard of speedometers reading low, in general most tend to read higher than your actual speed. Some self-proclaimed experts have suggested that manufacturers do this to help prevent people from speeding, since mindlessly looking at your speedo might fool you into thinking that you’re over the limit, thus preventing you from actually speeding…or something like that.
With the rumor that most speedometers are substantially inaccurate bouncing inside our helmets we hit the road to see how a handful of modern bikes stack up.
The test
Since actually testing speedometer error at 165 MPH isn’t exactly practical on the street we opted to use our trusty Racelogic PBOX. This GPS-based timing equipment is accurate to the T and allowed us to pinpoint just how far off our speedos were. As for the speeds, everything was tested at 70 MPH for safety and accuracy’s sake. However, as speeds increase the percentage of error should remain the same, but the actual amount will increase substantially since five percent of 140 is a lot larger than five percent of 70. You get the point.
2011 Yamaha R1 (stock gearing, stock tires)
Indicated Speed: 70 MPH
Actual Speed: 66 MPH
Error: 6%
2006 Kawasaki ZX-10R (stock gearing, stock tires)
Indicated Speed: 70 MPH
Actual Speed: 67 MPH
Error: 4.5%
2008 Honda CBR600RR (-1/+1 gearing, stock tires)
Indicated Speed: 70 MPH
Actual Speed: 51 MPH
Error: 27%
2002 Buell Firebolt (stock gearing, stock tires)
Indicated Speed: 70 MPH
Actual Speed: 68 MPH
Error: 3%
Myth: Confirmed
Of the four bikes tested, not a single one accurately displayed speed. However, the Buell was close enough that the 3500-mile tires could have worn enough to account for the error. Aspects like tire size/wear and gearing variations from stock can affect the indicated speed–in some instances the speedometer is inaccurate even from the factory.
In the case of our CBR600RR with -1/+1 gearing, it was a whopping 27 percent optimistic, which not only means the speedo isn’t remotely accurate, but the odometer is also accruing erroneous miles. Since it’s always reading high, the odometer will display a falsely inflated number, thus making it seem that the bike has more miles than it really does. This is a bad thing for resale and why it’s important to correct speedometer error with aftermarket speedo components. Unless the speedometer has been verified with an accurate device, the figures most of us have witnessed probably aren’t as impressive as we’d like to think.