2012 Aurion speedo out

[Sean K]

Hey guys... i own a 2012 aurion sx6 and i have been driving a around for just over 2 years with my aftermarket rims and tires (245/45/18)

I decided to put my old stocks rims and tires back on (215/55/17) and my speedo is now out by 3km/h. I sit on 80 im doing 77 and at 100 im doing the same 3 km down,

does any one know why?

[Steven]

So you don't lose your license. Nearly every speedo is out from factory, and shows you going faster than you are.

Works better for the Manufacturer as you can't blame them if you get caught speeding, and you appear to get better economy even if it's only slight.

You're aftermarket rims/tires were larger overall than the factory, so they might have made up the difference to having your speedo read 100% true.

[trentmeyer23]

What Steve has said above is correct. Most manufacturers will do this.

[LordBug]

The placebo effect is great. And it's even better when you know it's placebo effect, but the knowledge doesn't stop it!
I find it pretty satisfying setting the cruise control a few klicks above the limit number, though I know I'm bang on the limit, looking at the needle being that bit over just feels satisfying.
The downside is when you're stuck behind a slow driver, and you know that they're even slower than they think they are.

[Sean K]

LordBug yeah i have had that so many times

thanks everyone!

[nswnotill]

I use the speed readout from the aftermarket GPS that is in my Aurion, to accurately set the cruise control at 99 -100 kph on the open road. It is interesting to note that many drivers are travelling at around 5 kph below the limit, and I am sure they are not aware of it.

[trentmeyer23]

It is interesting to note that many drivers are travelling at around 5 kph below the limit, and I am sure they are not aware of it.

Most wouldn't have a clue, unless they have some form of GPS speed display.

[Full-Throttle]

I have an UltraGauge in my Aurion which gets connected to the OBD-II port under the dashboard (reads the data directly from the ECU) and when my speedometer shows 110kph in reality I'm only doing 100kph, so the ECU knows exactly what speed you're doing but they program the cluster to read slower. So at any speeds over 70kph I ignore the speedometer and just watch the UltraGauge instead.

[V6_fan]

Er, hang on, what you said doesn't make sense to me.....

Unless your box has GPS capability it CANNOT know the exact speed of the vehicle. The ECU typically gets its speed info from a sensor in the gearbox, or a sensor on a wheel, which are both dependent on the rolling circumference of the tyres. Different makes of tyres with the same specs have different rolling circumference, so it's impossible to know for sure, so ECU value will have a margin of error too.

This doesn't make the numbers given above invalid - it could well be that the speedo display is set 10% higher than the ECU, but that doesn't mean the ECU readout is automatically valid....

Edited September 9, 2015 by V6_fan

[Full-Throttle]

The speed is read though the ABS sensors on each hub, which goes to the ABS computer, then to the ECU and then to the cluster......The UltraGauge is connected to the OBD-II port which reads the information received by the ECU. My wheels are factory optional TRD's with the same equivalent tyre size to the factory 17's, and the speed on my GPS is the same as what's shown on my UltraGauge, hence why I ignore what my cluster is telling me after 70kph.....

[Sean K]

thanks guys!!!