QLD Rns510

[Roguediver]

Does anybody know how to display vehicle speed on the RNS510. You can get it on over the counter GPS units surley it is available on the 510.

If anybody has any ideas would love to hear from you.

Andrew

[The_Hawk]

If you look really closely, just behind the steering wheel are these guages that can show you various information including the vehicle speed, currents revs as well as total distance travelled...

All kidding aside, nope, not something the RNS510 can display.

[Roguediver]

If you look really closely, just behind the steering wheel are these guages that can show you various information including the vehicle speed, currents revs as well as total distance travelled...

All kidding aside, nope, not something the RNS510 can display.

Pity because I know from my retail GPS that the speedo is generally 6 + kph slow compared to the GPS

[FJ Steve]

Pity because I know from my retail GPS that the speedo is generally 6 + kph slow compared to the GPS

So....if you know this info already, your point is? Bit like spending 5 minutes plugging in the address for your local BP. Almost defeats the purpose eh?

[The_Hawk]

I know my speedo is out by ~6km/h at 100km/h too.

Depending on what car you have and what level of multifunction display you have there is something very interesting for you...

What is very interesting is that while the speedo is out the odometer AND the trip computer are not. To test this, set your cruise control to 106km/h then bring up the average speed... then reset the trip computer and wait a second for it to bring up a number and BAM! It's 100km/h. Seems the computer does indeed know the correct speed, just refuses to actually display it.

What is very interesting is that your speedo (and odometer) are essentially a function of RPMs driven through the wheels. So if the wheel is spinning at xxx RPM then the car is moving at yyy km/h. Now the LARGER the wheel/tyre the less RPM's needed for a given speed and vice versa. So as a tyre wears it gets smaller so while the car thinks the wheels are spinning at the same rate you are actually travelling a shorter distance so your speedo reading becomes out by more and more (over) as your tyres wear.

...
...

But for the fun facts. Lets take the Golf's standard wheel and tyre options and their calculated circumference:

195/65R15 - 1993.3mm
205/55R16 - 1985.2mm
225/45R17 - 1992.7mm
225/40R18 - 2001.8mm
235/35R19 - 2032.9mm

The 19" wheel/tyre combo is slightly larger so requires less RPM to reach 100km/h. Now since ADR requires that you NEVER read under the actual speed you would have to calibrate to the largest wheel. If VWA were to set the speed 100% correct to the largest option then everything else would read under... except that the WORST error would then be 97.7km/h with the smallest option which is the 205/55R16.

Again assuming that a new tyre only provides a 10mm wear by the time your tyre is worn it's out by even more... BUT that error from new to old is only ~3% nowhere near what is actually displayed.

For reference new and worn speeds assuming the speedo was 100% correct with the largest combo:
NEW - 10mm Wear
195/65R15 - 98.1 - 95.0
205/55R16 - 97.7 - 94.6
225/45R17 - 98.0 - 94.9
225/40R18 - 98.5 - 95.4
235/35R19 - 100.0 - 96.9

So in the WORST case a 205/55R16 is now reading over by 5.4km/h

Rambling asides I think it's a EU thing that makes them read the way they do. It's very sad that you can't fix the computer make it show correctly...

[kamold]

Geez Hawk, spare time much?

We just have to accept that speedos are designed to show you approximate speed. You haven't even touched on parallax error

Even if you go into the setup menu and look at the speed reported along with lat/long/altitude you will be told the speed that reported to the CAN ie same as on the speedo.

A stand alone GPS will report the approximate calculated speed on flat ground so that needs to be taken with a grain of salt also. ie it will report a lower calculated speed than your ground speed if travelling down a hill.

In the end, just drive sensibly. What more can you do?