Speedometer Accuracy

Oh, boy. Here we go. People get funny on this topic.

How accurate do you think your speedometer is?

Having had two bikes now, and no speeding tickets on them, I think motorcycle speedometers are accurate enough.

I compared my Suzuki C50 to my Nokia cell phone GPS and a speed trailer. They were all within 3 mph of each other. *edit* The C50 was analog. A dial measured in 5 mph increments. So, yeah, saying that was within 3 mph of digital is subjective.

There's a speed trailer down the street from me now. The Honda NCX is dead on with it up to 30 mph. That's the speed limit on this street.

Without comparing one instrument to another, which has its own perils, when I'm on a street with X speed limit, and my speedometer says I'm doing X miles an hour, and the traffic around seems to being doing about X miles an hour, I seem to be keeping pace with it. When I drive past the police checking for speeders, I don't get pulled over. It all points to being accurate enough.

My old Ducati SS was right at 8%, which is kind of standard for Ducati. My Triumph Sprint ST is horrible, about 13% off. Speedo reads about 80 when GPS indicates 70.

GPS indicates various speedometers I have measured have been anywhere from 0 to 8 mph off at 70 mph. Recent BMW's have been very close to accurate. The worst was a DR650. European brands seem to be closer to accurate than Japanese in my limited experience.

I would say most bikes are between 5 and ten percent off.

My TWs all seemed to change whenever I changed the tires. New JDM front tire was dead on, worn NA tire was dead on. Track Master about -11% when new, -3% when worm slap out.

Naw, no big deal. I check speedo readings against known accurate meters. If I ride past 10 roadside radars and 9 say the same thing, I'm paying attention to the 9 and adjusting speed accordingly.

My vfr is 5mph high up the whole speedometer.

Honda puts in a 7% error so in the 60-70mph range the speedo reads 5 mph fast. the odometer (on the new digital models) is dead accurate.

my ZRX11 is about 5% off but so is the odometer.

I have a speedoDRD (micro speedometer corrector doohickey) on my crf250l to adjust for sprocket change and the speedometer is GPS accurate.

My Wee speedo is about 10% on the high side.

From my admittedly scant knowledge, here gore:

I recall reading that DOT regs do not allow the speedometer to be pessimistic (read lower than actual speed). Therefore, manufacturers make them 5% or so optimistic (read a bit higher than actual).

Odometers are required to be accurate, and most are.

Remember, the factory calibrates these with OEM tires. If you change tire sizes or wheel diameters recalibration is needed.

Chuck500 said:

From my admittedly scant knowledge, here gore:

I recall reading that DOT regs do not allow the speedometer to be pessimistic (read lower than actual speed). Therefore, manufacturers make them 5% or so optimistic (read a bit higher than actual).

Odometers are required to be accurate, and most are.

Remember, the factory calibrates these with OEM tires. If you change tire sizes or wheel diameters recalibration is needed.

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yea, my car speedo compared to GPS is 1mph fast at 30mph, switches to 2mph fast at 50mph and holds that 2mph error on well past speed limit.

tires and tire wear oddly don't appear to have any real effect on speedometer when compared to GPS speed.
then who knows, maybe GPS devices have a degree of error built in as well.

Tire wear does have an effect, but since car tires really don't have much tread to begin with there will be little noticeable effect until they are pretty much worn out. However, between new and worn, the Track Master is about 3mph difference on a TW. New drives when I bought this truck put 65 on the speedo at 67 on the GPS. 225,000 miles later, drives are about 25%, and 65 on the speedo is 63.5 on the same GPS. Seems the more aggressive the tread, the greater the difference between new and worn.

My XR650R speedo reads 1 MPH slower at 50. ..... really

10% on the DRZ

3% on the BMW

JMZ said:

My XR650R speedo reads 1 MPH slower at 50. ..... really

Click to expand...

If your front wheel was actually rolling on the ground and not spinning free in the air while doing a wheelie it wouldn't be so accurate.

_

Both of my cages are spot on with local construction zone speed radar signs. My '96 ZX1100E and '93 Nighthawk are spot on at up to about 45, but as the speed increases so does the error rate. At 80 they're right at 8%.

As above I read awhile back that the manufactures deliberately add in this error rate for "safety" reasons. However by law the odometer must be within something like 0.2% accurate.