Zumo User Forums

Hi.
A new XT user, had a 550 from 06 until it's death last month .

Still bonding with the XT.
Did a 205 mile run in the rain on Saturday , Cardiff to Devil's Bridge and home.
Whilst some "fruity" speeds were achieved, on looking at the Active Log , after transferring to Basecamp, it seems my top speed was 175 mph !!
Incredible, and utterly incorrect.
I also appear to have accelerated from 70 to 149 mph in 1 second , also impressive , but nonsense.

An isue with the XT?

More likely simply a rogue GPS fix.

You will probably find that there are values adjacent to the "insane" speeds that are near zero. Average out three or four adjacent intervals and you will find the speed is very close to your actual speed.

Enter a tunnel at 10mph below the speed limit, and then speed up to the speed limit once once in the dark.
Then watch your speed that the satnav says that you are doing as you emerge into daylight. Cork out of a bottle.

This also happens (but less noticeably) in steep valleys, in built up areas, on tree lined routes, with lots of large trucks in the vicinity.
You cannot trust the satnav speed unles you have a clear view of the sky, are travelling a constant speed and the speed display isn't fluctuating.

The displayed speed isn't as dramatic as the emerging from a tunnel scenario - it normally calculates your speed over the last few seconds (5 secs is a value that seems to be how long it takes for the satnav to catch up when you accelerate of brake hard, but I don't know if that is correct).

I think the problems with the speeds in the tracklog of the XT have to do with the software of the tracklog, if you look in the overview of the XT you can see the real max. speed that has been driven and not the extremely high speed that you encounter in the tracklogs. I have never had this problem with the Zumo 660, where you can see the actual speeds in the track logs. I have here 2 examples of the XT and the 660 on the same road route and that clearly shows what is not going well in the XT. Also an example of the XT when entering a ferry.

My XT Rarely does it.

My Xumo 590 and 660 both did it on occasion, My Garmin 60cx did it as well as did my both my Garmin eMaps.

It's just a fact of life when the GPS receiver receives an erroneous signal. On the surface software filters out the bad readings (you don't see your speed display jumping to 900 mph when just looking at the speed reading) but the log shows them.

I suspect it will get worse shortly as lots of talk about solar interference increasing.

..Tom