I've noticed my speedo always indicates fast by about 6% or so. IAW, at a indicated 100kph, true speed is 94kph.

I'm running the correct OEM size tires. 235/50/17.

Anybody else?

 

Try Test Mode (a search will find it) and see if speed's better there.

 

From what I've heard most manufacturers put in a "buffer" on their vehicles, meaning the speedo will show up to 5mph faster than your actual speed. Typically that is why State Troopers give you a 5mph variance. Im not sure if Jag does it, but I will check using my Tom Tom and report back. I put 17"s on my wife's Saab that originally had 15"'s, and much larger tires. Now I am actually going 2MPH faster than what that speedo says according to TomTom, and I think the GPS reading is as accurate as you can get.

 

Bull27,

I drive based on having a 5%error in the speedo reading. Generally, I go 7 mph over the posted limit to account for it.

Mike

 

If you have factory navigation you can go into test mode and display the GPS speed while you’re driving. I found my 2005 STR to be almost completely accurate. It never was off more than 1 mph compared to the GPS!!
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I have the original tires and wheels and my speed difference between the speedometer and my Magellan SATNAV is about 2-3 mph.

 

My TomTom shows a 5 MPH difference on both cars....

 

So it sounds fairly common. My others cars show a much smaller variance- the old plastic fantastic is spot on at all speeds over 30kph and the GF's Honda reads fast by one 1-2%.

I'll try the Test Mode recalibration and see if it helps.

 

Manufacturers have been making their speedos optimistic for years. Commonly 30mph was more like 28mph. Remember when a wheel goes over a 'bump' in the road, it will travel slightly further than if the road were flat, same with a depression. So when you do your checking over a measured mile, you need a reasonably flat road. Years ago I bought an ex-coppers BMW bike; its had a special speedo on it, a Jaeger guaranteed 2% accurate.
Leedsman.
n.b. Don't lose any sleep over it!

 

i have 2000 V8,i was driving with my obd2 connected,odb was reading 60, and speedo was reading 65.I reckon both are fed from the same source.

 

Tried the test mode thing, no change. Will be getting new tires soon, I'm curious to see how much difference that makes in accuracy.

 

No change? It displayed exactly the same speed?

 

Yup, no change. Does the test thing actually recalibrate the gauges, or just do a quick function test- ie supply a voltage to drive them full scale?

 

You didn't read up on it? The details tell you what's available, including the speed. See: https://www.jaguarforums.com/forum/s...ode#post185626

 

Ah- obviously I didn't read far enough and stopped after ETM test 2, gauge sweep. I'll do 18 and 19 next time out in the car.

Thanks.

 

Mine is checked by the local police department maybe once every couple of years, more if I'm not careful..... Usually done with a remote radar read....

Sorry, couldn't resist.....

 

I experimented with the Test Mode today. I can get it into Test Mode. When I tap the trip computer button (the one that I used to set the Trip Mode active)....nothing happens except that the left hand window changes to show the next unit being measured. These are the normal measurements.

What am I doing wrong?

 

Well, some interesting progress. Went for a drive with the panel displaying 'Met Speed' and compared that number to the analog gauge reading and GPS. Probably not the safest thing to do and I should just concentrate on driving instead.

In any case, the ETM number and GPS are very very close, probably within 1-2% but the gauge reading still lags considerably as indicated in my first post.

Is there such a thing as gauge recalibration that can be done by the home mechanic?

 

lags? In your first post you said it was more, didn't you?

 

Yes you're right again. Tripped on my own words and the futility of trying to multi task.

The speedo leads (not lags) by the 6% orignally mentioned.