Fitted some twin spoke alloys on my 3.0l z4 on tuesday, which came off a z4m so the backs hang out slightly, not a problem I thought. But I have found that when I am driving around and using the satnav the satnav is no longer reading correctly and is 20 yards short on junctions. I understand that there is a slight issue with speed at over reading by 3.5% so i guess this is the same with distance also. Has anyone else come across this issue and found a way of resolving it? (intravee etc?
M WHEELS FITTED BUT HAVING A FEW PROBLEMS.
- Thread starter jamiecarpenter
- Start date
CornishRob
Senior member
Surely the sat Nav is GPS, so shoudlnt be affected by the wheel rotations?
Have you retrofitted the Sat Nav? Has the problem only occured since the wheels?
Were you in a built up area at the time? Just wandering if the GPS was multipathing?
Have you retrofitted the Sat Nav? Has the problem only occured since the wheels?
Were you in a built up area at the time? Just wandering if the GPS was multipathing?
Not sure this will be of much help, I had a built in sat nav on my previous car (VW) and it not only relied on the GPS but also the ABS sensor (for the wheel rotation) and so the wheel diameter, because of this there was a setting where you had to set for your wheel diameter and adjust should this change. I assume there might be something similar for the sat nav in BMWs?
CornishRob
Senior member
If thats the case, then the GPS may not be working correctly?
Get it in an open space and see if the GPS positions the car correctly. If it doesnt, you may have a GPS issue, which is meaning its using the wheel sensors as in the posts above, which now wont be calibrated properly.
Get it in an open space and see if the GPS positions the car correctly. If it doesnt, you may have a GPS issue, which is meaning its using the wheel sensors as in the posts above, which now wont be calibrated properly.
You can recalibrate the GPS settings from within a secret menu, however I only know how to do it on the professional sat nav as in mine. You hold the menu button for 10 seconds after you have entered the general settings menu.
Once in there, you will find an option for recalibrating the GPS which essentially involves you driving slowly towards a known junction, in a known direction, then hitting the set.
I'll try and look out the video that explains it when I'm not on iPhone
Once in there, you will find an option for recalibrating the GPS which essentially involves you driving slowly towards a known junction, in a known direction, then hitting the set.
I'll try and look out the video that explains it when I'm not on iPhone
agree with above, there is no way it is using the wheels. Rolling radius changes when tread depth drops and what about when the wheels spin. My nav used to have the odd hiccup where it would show me driving in the houses rather than on the road, it usually resolved itself in a matter of minutes though. My guess would be its either always done it and as you've changed the wheels your playing safe and looking for problems or it was just having one of those days.Steve220 said:
Tapatalking on my iPhone.......
A GPS position has nothing to do with anything on the car. Aftermarket GPS devices that you fix to the windscreen can be ported between vehicles. The signal is sent from the device into the air where a satellite essentially bounces it back to the device, a minimum of three satellites are need to correctly give a position.
On a factory fitted sat nav there may be an external ariel fitted to the car to boost the signal, but it wouldn't be affected by the choice of wheels.
Coincidence I think.
On a factory fitted sat nav there may be an external ariel fitted to the car to boost the signal, but it wouldn't be affected by the choice of wheels.
Coincidence I think.
billygilly
Active member
It's GPS.. You could run monster truck wheels on a push bike and it will make no difference
When the car doesnt pick up a GPS signal is will run off the speedo... this is one of few advantages of using the dated built in nav.
I have driven under long tunnels and the nav still moves the position of the car, with no GPS signal + fitted a built in Nav to my old Toyota.. and i had to splice into the speed sensor loom.
I have driven under long tunnels and the nav still moves the position of the car, with no GPS signal + fitted a built in Nav to my old Toyota.. and i had to splice into the speed sensor loom.
peddy said:
Correct, also many built-in systems also have gyroscopes in them to detect direction changes of the vehicle and the Sat Nav uses these additional inputs to calculate the position when GPS is lost. In large built up areas with high rise buildings GPS outages can be a real problem and so these systems compensate for this until the GPS signal is re-aquired.
You have the logic of this back to front guys as to which (GPS or sensors) is the primary signal. Don't mix the Z4 GPS up with standalone Tom Tom type units which simply use GPS signal.
The Zed uses wheel sensors to calculate rotation (variances gives direction) and ABS on rear left wheel to calculate speed. Reverse light switch is used to determine forward or backward travel. The system also uses a 'gyro value', which I'm not sure if it's a gyro unit or some derived value.
The GPS is used at initiallisation and re-initialisation (ie to calculate the start position). It's also checked to then correct any errors in wheel rotation by matching against lattitute and longitude readings plus GMT time).
This method can easliy explain OP's issue of it becoming inaccurate by 20 yards leading to a junction.It's also why the system is far superior to others (of its era) in towns, trees, tunnels, etc.
Tyre issues are where I'd put my money and once that's checked/rectified I'd be looking at the GPS signal.
The Zed uses wheel sensors to calculate rotation (variances gives direction) and ABS on rear left wheel to calculate speed. Reverse light switch is used to determine forward or backward travel. The system also uses a 'gyro value', which I'm not sure if it's a gyro unit or some derived value.
The GPS is used at initiallisation and re-initialisation (ie to calculate the start position). It's also checked to then correct any errors in wheel rotation by matching against lattitute and longitude readings plus GMT time).
This method can easliy explain OP's issue of it becoming inaccurate by 20 yards leading to a junction.It's also why the system is far superior to others (of its era) in towns, trees, tunnels, etc.
Tyre issues are where I'd put my money and once that's checked/rectified I'd be looking at the GPS signal.
That's incredible Phil!! Ranski did tell me that if you didn't know about something on the Zed then it's not worth bothering about 
Think Phil is probably right. looked into the tyres sizes. The wheels I took off F225/45/ZR18 R255/40/ZR18 the ones I've put on F225/40ZR18
R255/35/ZR18. Certainly found the ride is smoother being deeper. Also had a thought that if it is the tyres throwing off the gps will it throw out the odometer also?
R255/35/ZR18. Certainly found the ride is smoother being deeper. Also had a thought that if it is the tyres throwing off the gps will it throw out the odometer also?
jamiecarpenter said:
Quick check on a tyre calculator gives you a -3.48% difference in diameter. (Speedo reads 60 will be doing 58)
Doesn't sound much but after just 500m you'd be almost out by your 20m error.
