Wouldn't this be relative to the accuracy of the VSS? In other words - whether or not the car was actually traveling at 170mph - the limiter in the car would believe the 170mph as fed from the VSS. Thereby confirming that the 155mph limiter is actually set at 170mph, whether or not it was the true speed.

Are you saying that the accuracy of the VSS is true and the error is induced solely by the needle reading (inherent to the gauge itself)?

 

The limiter (if it exists and if it works) would be calibrated on engine speed and wheel rotation. Speedometers are calibrated deliberately to over read to avoid litigation on speeding cases. You can check easily using a RaceLogic box or even a Garmin nav system. The speedo says 80 and the gps based system will tell you 76. and the margin increases the higher the speed.

Of all the countries in the world (except Switzerland) removing the speed limiter in the US makes absolutely no sense at all. There's no practical value nor is there any marketing value. Even if YOU can drive at 155 safely, most North Americans are so dumb at driving over 55 that you're essentially asking to commit suicide at that speed. They never look in their mirrors, type txt messages, sit in the left lane grazing on burgers and fries, while doing their nails, and answering the phone. If you want to try 155 or more with that going on around you, you're welcome!

 

True (kinda) - but it is usually derived from the final output shaft rotational speed ... which is the source of the VSS (Vehicle Speed Sensor) signal, and that signal would feed BOTH the ECU (Engine Management) and the Speedometer. It would also be the same signal that any data logging device would read (if it is logging the ECU signals). So, since all devices have the same input signal with reference to speed (the VSS signal) - the only margin for error would lie within the gauge itself. If the VSS is sending the speed to be 155mph, but the speedometer is showing 170mph, then I would agree that the 155mph limiter is set.

However, this is very doubtful. More than likely the error is within the VSS itself - it is sending the speed to be 170mph when in fact the radar speed (or GPS) verified speed is really 157mph or whatever. In that case the limiter would be set to 170mph (kicks in when VSS = 170mph).

 

Hmm my speedo says 72 and gps says 75 or would that be

 

Most cops with radar detectors will "gift" you 5-10mph over the speed limit due to detector calibration error. If your speedo is out of that range you should get the dealer to check it. You might find yourself getting tickets when you don't deserve them.

 

There was more to go from 170 but then again at 4200 ft above sea level and running out of road as well. I think gearing wise the car can do 180 tops thats 6th gear at full 6500 rpm. The hp is there the gearing is the limiting factor.

 

FYI there is no speedo calibration factor or error calibration. All Stalker DS2's used on police vehicles now a days are dead-on-***** accurate. By policy they have to be tested before shift and after shift to ensure calibration. Also after every citation issued for speed it must me tested. The 5 to 10 miles is a leeway given by the officer.

 

Well, here is what Jaguar has to say about it.........

 

Hi, just to share, my stock XFR (5.0) does not seem to be limited.

I had a recent run up a highway, and hit 265+kmh (165mph) before being impeeded by a vehicle.

Seems like the car can probably go beyond the 270kmh maximum reading on my speedo, as it was still pulling strongly despite a very slight incline. If I had to predict, the max speed would probably be about 290-300kmh on a flat road, but will need a GPS reading to confirm that. Dynamic mode was enabled, but wasn't in sports mode on the autoshifter.

Fyi, the car was still very stable. It is such a lovely car to drive!

I have the video of the speedo hitting the speed, but was advised not to post it publicly... (don't worry, the wife was recording it... )

 

That's interesting, I've always been told the 155 MPH limiting was worldwide. When I get the chance I'll pose that question.

Beyond that, all I can say is LUCKY YOU!!!

Cheers,

 

I can also confirm that 155 limit doesn't exist on my XFR 2010. The needle on the clock gets all the way round to the max if you have enough road...err...track

 

On all Jaguar vehicles there is a speed limit set in the CCF file for a standard XF this is set to 249 KPH as I haven't got an XFR I could not tell you what the limit is set to but it can easily be changed using the correct software.

 

Had a 2010 XF Supercharged before, never had an opportunity to test top speed. Traded it in a few months ago for a 2012 XFR. I have confirmed it will go 161 even though limiter is supposed to be set at 155. It was pulling very hard at 161 too. Speed pack raises it to 174 to my knowledge. A friend of mine who races jags in Canada says XFR they will do 201-202 with no restrictor. It's all about the tires and aero when you go over 186.

 

yes mine had it..I remember the first I felt it while at it along with couple buddies of mine.. m3 and 911 4s just took off as my gas pedal felt empty around 260km..

 

The reason for the 121 MPH speed limiter in the US is because the US cars come with HR rated tires, which means they're safe up to 130MPH. I guess they limited the car to 121 to have a margin of safety in case you're going down hill with a tail wind and you hit 130 despite the limiter.