Hi All,

Today, I passed an unmanned radar site. It was the type with a digital readout about 2' X 3' on a little trailer. Anyway, when I went by it said 35 mph , my speedometer said 40. I went back again and it read the same. Has anyone else ever had an occasion to have their speed "clocked", officially or otherwise? Either my speedometer or that radar unit was off by quite a bit. I would not want to mention this to the dealer without some sort of informationabouta problemlike this beyond my own experience.

I checked past posts but did not see anything about this issue.

Any info you can provide would be appreciated.

 

Do you have the stock tires?

 

There's a a maximum 5% error allowed on speedometer readings according to most motor vehicle acts. Different tire and wheel sizes or different differential gearing, can cause speedometer inaccuracy.

Unless it's completely wonky, it is considered normal.

 

That's a reported 13% error.

 

its normal 10%+ 2 mph is what the dealers specs say, if you have GPS satnav it confirms this

 

Yes, I have stock tires,Pirelli P6225x45R17. An "allowance" of 5-10% +/- wouldexplain all this but I can't believe a manufacturer cannot get more precise than this.

If the speed is artificially high, would the total mileage on the odometer be overstated as well and eat into the warranty period faster than it should??

Anyway, thanks for the replies. If the radar unit is there tomorrow, I'll run through at different speeds.

 

Try 130mph and see if the percentage of error still holds true.

 

It's not that they cannot, it's more that they won't. They are trying to compensate somewhat for the diversity of wheel sizes/tires that exists on the market. Either that, or every one and every time you changed wheels/tires, would have to have his speedometer recalibrated.

 

Great! [sm=bling.gif]

 

Maybe you are right but wouldn't it make sense for the manufacturers to have the speedometer correct for the stock tires and have the variations occur ifother sized tiresare used.

As for 130MPH, in my dreams!!! Could a stock A3 achieve that speed?