Speedo Accuracy ( Or lack thereof)

[Seanii Plunkett]

Hi all,
I get the feeling my 2010 Roadster's speedo is somewhat optimistic.
Sitting on 3 grand on the tacho on mine is an indicated 125 or so kmh. At that speed I'm only travelling marginally faster than most cars on the freeway.
My old Garmin Nüv gps continually reads about 5 to 8 kmh slower than the speedo indicates.
Is that about right?

 

[Pig9r]

Yes, you're correct. I think 6% was the number that corrected it on the dyno.

 

[motolink]

Before I put the Taller Bridgestone on the rear my speedo was reading higher than the actual speed by about 6kph. Can't recall the RPM.

 

[Steel]

The taller Bridgestone on the rear will correct it. At 100 on the spedometer my GPS shows 99 mph. That's pretty close.

 

[Seanii Plunkett]

Taller tyres are not an option for me as I run a sidecar and therefore a car tyre on the rear for better traction and a wider contact patch. So what does the ground speed sensor do then..?

 

[Claviger]

Just adjust it in TuneECU The joys of free amazing software!

Set -5% and it should be dead on. I have my ECU set at -5%, the POD-300 Powercommander does its own speed calculation, and tested 2 days ago using a speed gun road sign, all were 1 mph different, 34(POD-300),35(Radar sign),36(ECU), so close enough

 

[barbagris]

Just adjust it in TuneECU The joys of free amazing software!

Although this screws up the odometer reading!
Fit a GPS speedo - They're no longer stupidly expensive. On the whole MOST speedos on any Euro homologated vehicle will read fast to the tune of about 5%

 

[Blackthou]

Is the odometer reading not dependent on or related to mph?

 

[Boog]

My R3T shows 85 mph on the speedo and 80 mph on the GPS, pretty consistent throughout our bikes it seems.

 

[idk]

Is the odometer reading not dependent on or related to mph?

From the factory the odometer will be correct and the speedometer will read about 6-7% optimistic. If you correct the speedometer then the odometer will be 6-7% pessimistic. I suspect they come that way so that you can't take the manufacturer to court for a speeding ticket by claiming that the speedometer reads low, and because the mileage has to be correct for other legal reasons.