More accurate speedo
- Thread starter Hunter
- Start date
Shipkiller
Lifer
Correct...
BMW adds a little bias to the speedometer, but not to the odometer.
BMW adds a little bias to the speedometer, but not to the odometer.
GP20 said:On the other hand, your odometer will now read more than the actual mileage.
I understand the speedo being correct as the larger rolling radius make it actually travel faster for a given number of wheel revolutions, so close to actual speed indicated rather than over, but surely if you put a bigger rolling radius wheel tyre combo on then it will have travelled furhter than the odometer says. ie if the rolling radius is 10% biggger then for each mile indicated it will have actually travelled 1.1m so the odometer will under read. Did I miss something after a bottle of vino GP?
cj10jeeper said:GP20 said:On the other hand, your odometer will now read more than the actual mileage.
I understand the speedo being correct as the larger rolling radius make it actually travel faster for a given number of wheel revolutions, so close to actual speed indicated rather than over, but surely if you put a bigger rolling radius wheel tyre combo on then it will have travelled furhter than the odometer says. ie if the rolling radius is 10% biggger then for each mile indicated it will have actually travelled 1.1m so the odometer will under read. Did I miss something after a bottle of vino GP?
You're absolutely correct.
I wasn't thinking right.Shipkiller
Lifer
Neither was I. 
Mine's the same. went from 17's to the 18 z4m wheels and now the speedo reads spot on.
It's a bit of a con really!
Legislation states that the speedo mustn't read 0% under but can read up to 10% over true speed.
So you'll notice that nearly any car you get in the speedo reads 10% faster than what you are actually traving / indicated by gps.
This means you clock up more miles, so you change your car more often and it appears you get better MPG than you actually do which makes the manufacturer look good.
It may not sound alot but for every 1000 miles that's 100 miles extra the car clocks up!
Obviously if you change the wheels so the speedo reeds correctly your going to clock up less miles but your MPG will look less. still acheived an indicated 38 MPG today
It's a bit of a con really!
Legislation states that the speedo mustn't read 0% under but can read up to 10% over true speed.
So you'll notice that nearly any car you get in the speedo reads 10% faster than what you are actually traving / indicated by gps.
This means you clock up more miles, so you change your car more often and it appears you get better MPG than you actually do which makes the manufacturer look good.
It may not sound alot but for every 1000 miles that's 100 miles extra the car clocks up!
Obviously if you change the wheels so the speedo reeds correctly your going to clock up less miles but your MPG will look less. still acheived an indicated 38 MPG today
Shipkiller
Lifer
Actually, on the Zed, the odometer is spot on. This was checked via GPS and on a Measured Mile.
So taken from that, I guess BMW takes into account and does not mess with the odometer...
Everything about your Gauge cluster is electronic. It is very easy for the software programmers to add a 10% bias to the indicated speed but leave the original VSS (Vehicle Speed Sensor) input alone to the odometer indicating true miles driven.
When I went from 16" wheels to 18" wheels, I took into account the rolling circumference so my speedometer read the same... actually, it was off .92%....
So taken from that, I guess BMW takes into account and does not mess with the odometer...
Everything about your Gauge cluster is electronic. It is very easy for the software programmers to add a 10% bias to the indicated speed but leave the original VSS (Vehicle Speed Sensor) input alone to the odometer indicating true miles driven.
When I went from 16" wheels to 18" wheels, I took into account the rolling circumference so my speedometer read the same... actually, it was off .92%....
GP20 - so glad after the vino my thinking was still clear enough 
Shipkilleer I agree with you r comment about the input being digital. Speed can tehrefore be overstated to avoid litigation issues and of course flatters the driver, makes 0-60 for the average guy seem better, etc.
The comment by others re paying more, etc. are just wrong. Even In the old days of a cable driven odometer the mileage was spot on, but speed just an approximate figure.
Shipkilleer I agree with you r comment about the input being digital. Speed can tehrefore be overstated to avoid litigation issues and of course flatters the driver, makes 0-60 for the average guy seem better, etc.
The comment by others re paying more, etc. are just wrong. Even In the old days of a cable driven odometer the mileage was spot on, but speed just an approximate figure.
Medium Dave
Member
GPS speed will only be accurate on a flat surface and when going in a straight line. The GPS speed measures travel across the earth's surface and takes no account of the fact you are climbing or descending. If you are climbing the GPS will only give speed along the flat whereas your actual speed will be higher as you are actually travelling along the hypotenuse of the triangle. It is for this reason you shouldn't rely on the GPS to stop you from setting off a speed camera.
Did that make sense???????
Did that make sense???????
gers said:Hunter said:Yep, course it did...im a nuclear physisist
You changed your job arnie,this week am gony be a brain surgeon.
weekend job, relieves the stress of being a bikini line waxer at the play boy mansion through the week. Most of it is ok, but hugh heffner wants his done too !!!!
-- :lol:Shipkiller
Lifer
Medium Dave said:
Is that with only three or four satellites, or does having more delta time slices increase your accuracy?
-- Medium Dave
Member
I think that is true no matter how many satellites you pick up because car GPS systems are not set up for vertical navigation like aircraft GPS.Shipkiller said:
