2003 A4 3.0 Speed limiting in ECU

You must have been tempted.....

snipped-for-privacy@anywhere.org wrote: At 135MPH I felt my

On Mon, 11 Apr 2005 15:13:18 -0400, Jules wrote: Now that I know Y rated tires are good till 149MPH, maybe I'll go back.

At an indicated 135mph, I'd expect you to be doing less than 130mph. Does that climate control hack that shows you the speed in KM work on a 2003 A4? It might be worth seeing what that says. Of course, looking down at the climate control screen whilst doing 130mph might not be the smartest course of action!

andyt

wrote

Actually, Y-rated tires are good up to 186 mph.

Cheers,

Pete

It was tough enough looking at the speedometer. I assumed that the ECU would be using the same number as the speedometer, does this mean I have to run the test again? ;)

I'm so jealous; I can't think of anyplace near where I live where I could let my A4 loose like that without fear of cops giving me a major traffic violation ticket.

135MPH in traffic would be impressive. In Paris they drive 140mph in their tunnels, from personal experience.

cp

There's error in the speedo so what you observed is not entirely out of place. I'm sure the ECU is using an electronic measurement of speed from some sensor that's no doubt more accurate than the speedometer.

Why would it? Which additional sensor would there be? And even more, what sense would that make?

Regards

Wolfgang

yep they would, and sometimes under the influence of drink and drugs.........ask Mr Alfyed

Indeed, prob. < 120mph. If you can, borrow a GPS unit which will give you a more accurate "actual" speed. My GPS unit tells me that when I'm doing 70mph, it's actually 65. The differential gets greater the faster you go (compared to say 30 mph).

Funnily enough, I tried the very same thing tonight. It's tricky to say for sure because I had to keep glancing at two things (as well as the road of course.. if I had cruise it might have helped), but I eventually decided that 70mph on the dash was 66mph on the GPS.

andyt

Join a sports car club that has an accurate speed radar (preferably K or Ka band). Take your car to a safe venue (track or closed airfield) and let her rip. Have someone paint you with the radar. Have another brave soul in the car with you to take a reading at the trap. Just be aware that at that speed you need lots of room to stop (145 mph is 213 feet/sec).

Dave (been there, done that with an RS6)

I always use a Garmin GPS and have found the Audi speedometer to read so close to the GPS at all speeds up to 85 mph that I can not tell if there is any difference at all. This was in three T44s and one 98.5 A4.

The GPS is supposedly accurate to 0.1 mph and updated each second.

Tony

Audis and VWs are designed to show a higher than actual speed on the speedo. The ECU knows the real speed (to within the accuracy permitted by variations in tire size due to wear, etc.) and there's a trick you can do with the Climatronic to get it to show the true speed. (On the Passat, it's fan-down, temp-down, and Econ all at the same time, then use temp-up to reach option 16 - don't know if it's the same on an A4.) I recently did this on my Passat and found that the difference was about 3-4 MPH at 50.

-- Mike Smith

It makes legal cover-your-ass sense, at least in the US.

-- Mike Smith

Well, I'm not doubting that it makes sense to have a speedo which is showing a little more than the actual speed. It's the law here as well.

But I'm wondering where the ECU/Air Conditioning display should get different info from.

IMO it's just the same information shown on another display.

Regards

Wolfgang

Interesting, I'll try that as well.

Regards

Wolfgang

The speedo shows a little less than the actual speed.

Both the speedo and the Air Con display get the speed from the same place (usually the ABS Sensor) but the speedo is calibrated to show a little less.

Richard