Optimistic Speedo

[kmoney_imp]

Summer is here and all the "your speed" signs are on the highway. Noticed on longer ride today that these things seem to all clock my speed at about 10 km/hr under what the bike speedo indicates (usually 111 on an indicated 120). All my older bikes (80's) were like this, but figured the digital speedo (assuming it takes it from one of the abs rings) would be better. Don't really care, but wondered if anyone noticed the same.

[flynrider]

Summer is here and all the "your speed" signs are on the highway. Noticed on longer ride today that these things seem to all clock my speed at about 10 km/hr under what the bike speedo indicates (usually 111 on an indicated 120). All my older bikes (80's) were like this, but figured the digital speedo (assuming it takes it from one of the abs rings) would be better. Don't really care, but wondered if anyone noticed the same.

My old bikes with gear driven mechanical speedos tended to read higher than actual speed (tested with GPS). After I got my CB11 I strapped on the GPS and found that the speedo was within a few mph of the GPS all the way up to 95 mph.

If you've mounted a larger or smaller diameter rear tire, that could throw off the speedo's accuracy. Now that I mentioned that, I realize that I haven't done a GPS check with my 160/60 rear tire. It's about .16" smaller in diameter than the stock 140/70 rear tire.

[Randy B]

Summer is here and all the "your speed" signs are on the highway. Noticed on longer ride today that these things seem to all clock my speed at about 10 km/hr under what the bike speedo indicates (usually 111 on an indicated 120). All my older bikes (80's) were like this, but figured the digital speedo (assuming it takes it from one of the abs rings) would be better. Don't really care, but wondered if anyone noticed the same.

Keep in mind that those don't have to be calibrated for court so there is a distinct possibility that they could be off.

[CIP57_imp]

German manufactures tend to be the optimistic. My daughter Jetta was off as much as 5 mph. Trips to my house in NC is 640mi door to door. Traveling with her car would be 670mi. I brought the car to the dealer and they recalculated the odometer.

[Cormanus]

My CB is under. At an indicated 110 kph it is actually about 104 kph.

[Motogeezer1949_imp]

Whenever I've checked against those digital "your speed" signs, it's been pretty close. 1 or 2 off. Don't know about higher speeds though.

[Django]

When I have my Garmin Zumo 660 mounted, I can compare speedo to GPS speed.

Until approx. 80 kph, my speedo is about 2-3 km above gps. Then the gap starts to increase.
From about 110 kph it's constantly 10 km above gps, up to the limiter. My CB runs into the limiter at speedo 190 kph, gps shows 179 kph.

I thought, this offset is on purpose. Speedos may show more but never less than real speed.