Speedo Wrong by 7mph - Page 20

Dorset Bob · 2nd June 2014, 22:26

Okay Guys, fair enough.

I was rather pleased to enable the digital speed readout in my car.

As, I then had three different instruments giving three different readings

, I was just intrigued about which one was closest to the truth.

SD1too · 19th June 2014, 08:09

I have now had the message centre digital speed display activated in my car and had an opportunity yesterday to compare readings over a 300 mile trip.

Up until now I had believed that my analogue speedometer over-read by 10% based on a comparison with a 'Road Angel' device. I now find that, at 70 mph, my speedometer's error is more like 5% when compared with the car's digital display. But more surprising was that, at slow speeds such as 15 and 20 mph, it appeared to agree with the message centre figures exactly.

These are initial impressions so I will continue to monitor it as carefully as I can, but it seems that the error on my speedometer dial is not linear as I first thought.

Simon

klarzy · 19th June 2014, 08:55

Quote:

Originally Posted by SD1too

I have now had the message centre digital speed display activated in my car and had an opportunity yesterday to compare readings over a 300 mile trip.

Up until now I had believed that my analogue speedometer over-read by 10% based on a comparison with a 'Road Angel' device. I now find that, at 70 mph, my speedometer's error is more like 5% when compared with the car's digital display. But more surprising was that, at slow speeds such as 15 and 20 mph, it appeared to agree with the message centre figures exactly.

These are initial impressions so I will continue to monitor it as carefully as I can, but it seems that the error on my speedometer dial is not linear as I first thought.

Simon

As 5% of 15-20 MPH is 0.75 - 1 MPH and taking the parallax phenomonon into account as well you would be doing pretty good to spot the offset accurately.

if 70 or above is 5% (i.e. 70 = 73.5 80=84) then i would accept this as ok.
Don't forget as the speed gets lower the offset gets smaller when dealing with percentages.

Dorset Bob · 30th June 2014, 11:15

Quote:

Originally Posted by SD1too

I have now had the message centre digital speed display activated in my car and had an opportunity yesterday to compare readings over a 300 mile trip.

Up until now I had believed that my analogue speedometer over-read by 10% based on a comparison with a 'Road Angel' device. I now find that, at 70 mph, my speedometer's error is more like 5% when compared with the car's digital display. But more surprising was that, at slow speeds such as 15 and 20 mph, it appeared to agree with the message centre figures exactly.

These are initial impressions so I will continue to monitor it as carefully as I can, but it seems that the error on my speedometer dial is not linear as I first thought.

Simon

With the help of a photographic assistant, these are the speeds recorded, on my car, at 20,30,40,50,60 and 70mph on the digital readout:

kaiser · 30th June 2014, 11:22

Well, that looks close to 10% over read on the analogue speedo.

It would be nice to know what the actual speed would be at the same time.

Union Wheels · 30th June 2014, 19:39

Hi All,
I have just had the digital MPH enabled on my retro-fitted message centre curtsey of Big Russ, and the speed, compared with the speedo, is about the same as Dorset Bobs.

I was just wondering if anybody had investigated the possibility of have the engine temperature showing in the message centre like the digital MPH does.

I realize that it may require changes to a string of data with the BMW interface as the digital MPH did, and may be a lot of trial and error to get there, but it would save having to go through 1 to 19 and then to 7 with the trip button if it could be done.

Cheers, Pete.

Avulon · 30th June 2014, 20:13

Quote:

Originally Posted by Dorset Bob

With the help of a photographic assistant, these are the speeds recorded, on my car, at 20,30,40,50,60 and 70mph on the digital readout:

It's interesting when you look closely that the reading appears very close to 10% over on the needle from 20 mph to 50 mph. But look closely at 60 and its definitely not as much as 10% and it's even less when you look at 70 it only appears to read around 74mph on the needle not 77 as you might expect. So obviously the overread % isn't constant.

kaiser · 1st July 2014, 06:35

As I said originally it is normally about 5 to 7 % over read at normal road speeds. compared to true measured speed.

I know that because I use it to set my cruise control to the fastest safe speed in order not to get tickets, so I can do an indicated 138 km/h and just be on the safe side in a 120 zone.

2nd June 2014, 22:26	#191
Dorset Bob Senior Citizen Rover 75 2.5 Connoisseur SE,Chrysler 300C,124 Spider, Daytona 955i,Honda XL250 & Royal Enfield 650GT Join Date: Feb 2008 Location: The Kingdom of Wessex Posts: 6,976 Thanks: 2,391 Thanked 2,685 Times in 1,686 Posts	Okay Guys, fair enough. I was rather pleased to enable the digital speed readout in my car. As, I then had three different instruments giving three different readings , I was just intrigued about which one was closest to the truth. __________________ Let the good times roll............

19th June 2014, 08:09	#192
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,511 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Update I have now had the message centre digital speed display activated in my car and had an opportunity yesterday to compare readings over a 300 mile trip. Up until now I had believed that my analogue speedometer over-read by 10% based on a comparison with a 'Road Angel' device. I now find that, at 70 mph, my speedometer's error is more like 5% when compared with the car's digital display. But more surprising was that, at slow speeds such as 15 and 20 mph, it appeared to agree with the message centre figures exactly. These are initial impressions so I will continue to monitor it as carefully as I can, but it seems that the error on my speedometer dial is not linear as I first thought. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

30th June 2014, 19:39	#196
Union Wheels Loves to post Honda Accord Tourer i dtec Join Date: Jul 2011 Location: Wakefield Posts: 331 Thanks: 56 Thanked 90 Times in 75 Posts	Hi All, I have just had the digital MPH enabled on my retro-fitted message centre curtsey of Big Russ, and the speed, compared with the speedo, is about the same as Dorset Bobs. I was just wondering if anybody had investigated the possibility of have the engine temperature showing in the message centre like the digital MPH does. I realize that it may require changes to a string of data with the BMW interface as the digital MPH did, and may be a lot of trial and error to get there, but it would save having to go through 1 to 19 and then to 7 with the trip button if it could be done. Cheers, Pete. __________________ [SIGPIC][/SIGPIC] How to Retrofit Diesel Cruise Control + Loom http://www.the75andztclub.co.uk/foru...87&postcount=1 How to Modify a 3 Speed Fan for CDT & V6 into a 2 Speed with a Resistor. http://www.the75andztclub.co.uk/foru...d.php?t=209920 CDT now gone to new owner, but still on forum

30th June 2014, 11:22	#195
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	Well, that looks close to 10% over read on the analogue speedo. It would be nice to know what the actual speed would be at the same time.

1st July 2014, 06:35	#198
kaiser This is my second home 75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007 Location: Johannesburg ZA Posts: 6,200 Thanks: 1 Thanked 859 Times in 613 Posts	As I said originally it is normally about 5 to 7 % over read at normal road speeds. compared to true measured speed. I know that because I use it to set my cruise control to the fastest safe speed in order not to get tickets, so I can do an indicated 138 km/h and just be on the safe side in a 120 zone.