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Tomtom install mit photos

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I noticed that my Tomtom is reading about 5-10 mph slower than my speedometer. The difference increases with increasing speed. I'm reading that gps is MORE accurate than a vehicle's speedometer, so I guess I very well could be going 5-10 mph slower than previously thought. Anyone have any experience like this? Is there a way to calibrate the speedometer? Gs-911 or app? I should probably confirm with a radar trap.
 
Generally, speedometers are calibrated to read 2 to 5 percent faster than actaul vehicle speed.
35mph reading is actually about 33 mph, 70 mph reading is approx, 67mph.
This for legal reasons. A sprrdo that is calibrated from the factory to read 70 when your actual speed is 75 could have legal implications for the Manufacturer.
GPS and Police radar guns measure actual distance traveled divided by time equals speed.
Vehicles usually measure speed by wheel rotation, either at the wheel or the output shat of the transmission.
This can vary with tire size, inflation or changing the final drive ratio.
Now, which do you trust the most, the speedo or the GPS.

A man with one watch knows what time it is.
A man with two is never sure.
 
Black Dog said:
Generally, speedometers are calibrated to read 2 to 5 percent faster than actaul vehicle speed.
35mph reading is actually about 33 mph, 70 mph reading is approx, 67mph.
This for legal reasons. A sprrdo that is calibrated from the factory to read 70 when your actual speed is 75 could have legal implications for the Manufacturer.
GPS and Police radar guns measure actual distance traveled divided by time equals speed.
Vehicles usually measure speed by wheel rotation, either at the wheel or the output shat of the transmission.
This can vary with tire size, inflation or changing the final drive ratio.
Now, which do you trust the most, the speedo or the GPS.

A man with one watch knows what time it is.
A man with two is never sure.
Click to expand...
Very insightful, Black Dog, thank you. So my question should be, does anyone know how to turn off the Tomtom speedometer?

/my dad wears his Rolex on one wrist to keep it wound, and a quartz Swiss Army watch on the other because it keeps better time
//I says, why don't you get the Rolex serviced?
///he says, no need, I have the Swiss Army watch.
 
Black Dog said:
Generally, speedometers are calibrated to read 2 to 5 percent faster than actaul vehicle speed.
35mph reading is actually about 33 mph, 70 mph reading is approx, 67mph.
This for legal reasons. A sprrdo that is calibrated from the factory to read 70 when your actual speed is 75 could have legal implications for the Manufacturer.
GPS and Police radar guns measure actual distance traveled divided by time equals speed.
Vehicles usually measure speed by wheel rotation, either at the wheel or the output shat of the transmission.
This can vary with tire size, inflation or changing the final drive ratio.
Now, which do you trust the most, the speedo or the GPS.

A man with one watch knows what time it is.
A man with two is never sure.
Click to expand...
That is correct but also 'in theory'. In reality, speedometers are often much more than 5% out of sync. I prefer instruments to be accurate - otherwise, we should call them guess-truments (-:

I use the SpeedoHealer on several of my rides; SpeedoHealer v4 (SH) - HealTech Electronics Ltd. (healtech-electronics.com). Unfortunately not yet available for the R18 per se.

But several of their other goodies are; Product Advisor - HealTech Electronics Ltd. (healtech-electronics.com), including their Quick Shifter; Quick Shifter easy (iQSE) - HealTech Electronics Ltd. (healtech-electronics.com). I use them on my Victories. If installed correctly, it will accommodate both up and downshifts, except it will not blip the throttle when downshifting, mind. In anticipation of why anyone would consider fitting a Quick Shifter on a Victory or R18 cruiser - to soften their pretty hard gear changes. HealTech's Quick Shifter only monitors pressure on the gear lever, not the clutch switch as well, so it still momentarily cuts out ignition whilst changing gears. I found this to improve gear-change 'clunking' on my Victories dramatically.

I prefer to have the GPS speed indication visible specifically to vet my ride's speedometer.
 
As a former cop, I can tell you that police radar AND laser measure speed using the doppler effect. Not by measuring distance traveled over time. But that IS how a GPS device measures speed. BOTH are extremely accurate and therefore are perfect comparisons to a speedometer's reading.

I have never verified this but I have been told that the American guvmint requires that all vehicle manufacturers who sell their products in America MUST either produce ACCURATE speedometers OR, if not accurate, they must read higher than actual speed. It makes sense because a speedo that shows less than actual speed is virtually unheard of (provided no non-stock changes have been made to effect speedo results).

Doppler effect - Wikipedia

en.wikipedia.org en.wikipedia.org
 
Yesterday going to Two Wheels of Suches in North GA for Wooly's R 18 only demonstration rides. (most bikes had NJ tags on them, and were trucked in for the rides), my Zumo 660 GPS indicated 71 MPH while the Speedomiter read 75 MPH a difference of 4 MPH. Checked it on the way back and it was the same reading on both.
 
Submariner said:
Yesterday going to Two Wheels of Suches in North GA for Wooly's R 18 only demonstration rides. (most bikes had NJ tags on them, and were trucked in for the rides), my Zumo 660 GPS indicated 71 MPH while the Speedomiter read 75 MPH a difference of 4 MPH. Checked it on the way back and it was the same reading on both.
Click to expand...
Sounds correct and operating as designed., have you checked you cars speedo against the gps speed
 
I've got a Miata, a Grand Cherokee, a Roadmaster and the R18 and all read higher than actual speed. The Roadmaster is closest to accurate at just 2 MPH above actual.
 
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