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| UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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BMW on Motorway??
Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway.
I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar.. I dont know if they can be driven on the motorway. How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) |
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BMW on Motorway??
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#3
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BMW on Motorway??
On Wednesday, February 13, 2019 at 12:27:03 PM UTC, wrote:
Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. If she is that stupid she shouldn't be driving on any road. Perhaps she was trying to be sarky, etc. I mean, she must have noticed the other carss around her when driving in her Jag. |
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#4
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BMW on Motorway??
In article ,
wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. Most BMWs probably overtook her on the motorway going so fast she couldn't read the badge. And likely plenty white vans too. How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) Which just means they were vaguely keeping to the speed limit. Given most BMWs and Jags ever made were faster than a 1 litre Metro. But at least the Metro had a speedo which told you you were going fast. ;-) -- *Work like you don't need the money. Love like you've never been hurt. Dave Plowman London SW To e-mail, change noise into sound. |
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#6
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BMW on Motorway??
Actually my neighbour had a Metro and boy could that thing move. The speedo
kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. Brian -- ----- -- This newsgroup posting comes to you directly from... The Sofa of Brian Gaff... Blind user, so no pictures please Note this Signature is meaningless.! "TimW" wrote in message ... On 13/02/2019 12:27, wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said "I don't know anything about BMW's I drive a Jaguar. I don't know if they can be driven on the motorway." How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) Ah yes! Push the throttle down as far as it will go and keep it there. Turn the stereo cassette player up loud enough to hear over the noise and leave that there too. About 90 on the flat, slowing to 70 or less if it's up hill. It was a Renault5 for me, when I could get it started. Back and forth on the M3 and M4. TW |
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#7
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BMW on Motorway??
In article ,
Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. -- *The closest I ever got to a 4.0 in school was my blood alcohol content* Dave Plowman London SW To e-mail, change noise into sound. |
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#8
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BMW on Motorway??
On 13/02/2019 13:59, sm_jamieson wrote:
On Wednesday, February 13, 2019 at 12:27:03 PM UTC, wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. If she is that stupid she shouldn't be driving on any road. Perhaps she was trying to be sarky, etc. I mean, she must have noticed the other carss around her when driving in her Jag. Had a dumb 50+ blonde ( but out of a bottle at that age) in a big Mercedes saloon (350 or 450) in front of me at the lights once. All rear fog lights on, plus rear lights plus brake lights. Couldn't see a damn thing. At the next set of lights she was turning right, I was going straight ahead. I hooted the horn and she looked and we wound down our windows. "You have your fog lights and are dazzling everyone behind you." "No I don't". (I could see the warning light from my car.) "Yes you do, you are dazzling everyone. Turn them off it's not foggy." "No I do not. This is a Mercedes, the lights are just brighter and better than cheap cars like yours." So I can quite believe the overheard conversation. |
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#9
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BMW on Motorway??
On 13/02/2019 16:54, Dave Plowman (News) wrote:
In article , Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. The speedo *mustn't* read low. That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. -- Robin reply-to address is (intended to be) valid |
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#10
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BMW on Motorway??
"Robin" wrote in message
... On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. The speedo *mustn't* read low. That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. I'm surprised it's that much. Is the difference between the external diameter of a new tyre and of a just-legal tyre as much as 2%? I presume manufacturers design the speedo to over-read by at least 2% so it never under-reads even with just-legal tyres. Mine seems to under read by 5 mph across the whole range from 10 - 70, compared with a GPS speedo app. |
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#11
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BMW on Motorway??
On 13/02/2019 17:57, NY wrote:
"Robin" wrote in message ... On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , *** Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. The speedo *mustn't* read low.* That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. I'm surprised it's that much. Is the difference between the external diameter of a new tyre and of a just-legal tyre as much as 2%? yes. More probably - I reckon 3%. I presume manufacturers design the speedo to over-read by at least 2% so it never under-reads even with just-legal tyres. Mine seems to under read by 5 mph across the whole range from 10 - 70, compared with a GPS speedo app. mine is bang on 10% with half worn tyres. ± 3% for tyre wear. -- "The most difficult subjects can be explained to the most slow witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of doubt, what is laid before him." - Leo Tolstoy |
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#12
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BMW on Motorway??
On 13/02/2019 17:57, NY wrote:
"Robin" wrote in message ... On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , *** Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. The speedo *mustn't* read low.* That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. I'm surprised it's that much. Is the difference between the external diameter of a new tyre and of a just-legal tyre as much as 2%? I presume manufacturers design the speedo to over-read by at least 2% so it never under-reads even with just-legal tyres. Mine seems to under read by 5 mph across the whole range from 10 - 70, compared with a GPS speedo app. depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. Or of course misreckoning if others get different answers  -- Robin reply-to address is (intended to be) valid |
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#13
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BMW on Motorway??
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#14
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BMW on Motorway??
On 13/02/2019 14:48, Dave Plowman (News) wrote:
In article , wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. Most BMWs probably overtook her on the motorway going so fast she couldn't read the badge. And likely plenty white vans too. How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) Which just means they were vaguely keeping to the speed limit. Given most BMWs and Jags ever made were faster than a 1 litre Metro. But at least the Metro had a speedo which told you you were going fast. ;-) I sometimes set my cruise control to a true 70MPG (GPS calibrated with sat nav and mobile phone) and there are still very few cars overtaking me. I have also had a couple of phone calls about me undertaking on a 50 MPH dual carriageway on the way to work. I have flown past the other vehicles with my van set at a true 50MPH. This is always where the fixed speed camera is and they slow down to 40 MPH or less. -- Adam |
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#15
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BMW on Motorway??
"ARW" wrote in message
news  I have also had a couple of phone calls about me undertaking on a 50 MPH dual carriageway on the way to work. I have flown past the other vehicles with my van set at a true 50MPH. This is always where the fixed speed camera is and they slow down to 40 MPH or less. I've lost count of the number of times that I've been following other traffic that is all doing under the speed limit, and yet one of them *still* slams the anchors on dangerously hard when they see a police car that might be looking for speeding drivers. Many drivers seem to think that they must brake even if they are nowhere near exceeding the speed limit. Probably the same people that slow down as they approach the back end of a lorry that they are about to overtake, crawl past the lorry at maybe 2 mph faster than it and then accelerate away as soon as they have passed its cab. I prefer to spend as little (rather than as much) time alongside a lorry, in case it happens to pull out without looking - especially if it's an LHD lorry. |
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#16
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BMW on Motorway??
In article , ARW
wrote: On 13/02/2019 14:48, Dave Plowman (News) wrote: In article , wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. Most BMWs probably overtook her on the motorway going so fast she couldn't read the badge. And likely plenty white vans too. How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) Which just means they were vaguely keeping to the speed limit. Given most BMWs and Jags ever made were faster than a 1 litre Metro. But at least the Metro had a speedo which told you you were going fast. ;-) I sometimes set my cruise control to a true 70MPG (GPS calibrated with sat nav and mobile phone) and there are still very few cars overtaking me. not so down south. Mostly BMWs I have also had a couple of phone calls about me undertaking on a 50 MPH dual carriageway on the way to work. I have flown past the other vehicles with my van set at a true 50MPH. This is always where the fixed speed camera is and they slow down to 40 MPH or less. -- Adam -- from KT24 in Surrey, England "I'd rather die of exhaustion than die of boredom" Thomas Carlyle |
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#17
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BMW on Motorway??
Robin has brought this to us :
I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. My does around 50 pulses per revolution of the wheel, there are electronic methods to predict the likely next pulse period and predict when the next pulse will arrive. I have three speed displays available to me - the dial on the dash, which reads a few percent high, digital display which does not interpret the wheel pulses at all, it just displays the value and entirely independently - satnav. The latter two always agree within 1mph at a steady speed. |
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#18
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BMW on Motorway??
NY expressed precisely :
I presume manufacturers design the speedo to over-read by at least 2% so it never under-reads even with just-legal tyres. Yes, they make sure you can never get done for speeding, unless you actually are speeding. Mine seems to under read by 5 mph across the whole range from 10 - 70, compared with a GPS speedo app. How they read, depends on how the calculate the speed - adding a safe percentage or simply adding 3, 4 or 5 to the value. Mine uses plus a percentage and the mph difference increases with increased speed. Last time I checked, it was 73mph when doing a genuine 70mph from memory. |
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#19
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BMW on Motorway??
ARW laid this down on his screen :
I have also had a couple of phone calls about me undertaking on a 50 MPH dual carriageway on the way to work. Phone calls from whom? |
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#20
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BMW on Motorway??
NY explained :
I've lost count of the number of times that I've been following other traffic that is all doing under the speed limit, and yet one of them *still* slams the anchors on dangerously hard when they see a police car that might be looking for speeding drivers. Many drivers seem to think that they must brake even if they are nowhere near exceeding the speed limit. I think that is likely them braking, because they don't even know what the speed limit is and suddenly develop a guilty conscience. |
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#21
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BMW on Motorway??
"sm_jamieson" wrote in message ... On Wednesday, February 13, 2019 at 12:27:03 PM UTC, wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. If she is that stupid she shouldn't be driving on any road. Perhaps she was trying to be sarky, etc. I mean, she must have noticed the other carss around her when driving in her Jag. Not necessarily, many stupid women wouldnt. Some arent even aware of the brand of the car they drive all the time. |
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#22
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BMW on Motorway??
On 13/02/2019 18:12, Robin wrote:
On 13/02/2019 17:57, NY wrote: "Robin" wrote in message depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. Or of course misreckoning if others get different answers What do you drive? A Dinky toy? |
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#23
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BMW on Motorway??
In article ,
Rod Speed wrote: "sm_jamieson" wrote in message ... On Wednesday, February 13, 2019 at 12:27:03 PM UTC, wrote: Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. If she is that stupid she shouldn't be driving on any road. Perhaps she was trying to be sarky, etc. I mean, she must have noticed the other carss around her when driving in her Jag. Not necessarily, many stupid women wouldnt. Some arent even aware of the brand of the car they drive all the time. Some years ago, I was helping with a children's show at our Village Hall. During the interval.meone who lived across the road appearedc and asked if we could geta car moved which was blocking the driveway into his house. So, I announced that Make & Number of car was in the way and aslked for it to be moved. Nothing happened. After the show I stood besdie the vehicle until the driver appeared "Didn't you hear me ask you to move?" "I don't know what I drive." and drove off. -- from KT24 in Surrey, England "I'd rather die of exhaustion than die of boredom" Thomas Carlyle |
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#24
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BMW on Motorway??
In article , Robin
writes On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. The speedo *mustn't* read low. That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. And also For all true speeds of between 25 mph and 70 mph (or the maximum speed if lower), the difference between the indicated speed and the true speed shall not exceed V/10 + 6.25 mph where V = the true speed of the vehicle in mph. Which seems to me a very wide variation. -- bert |
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#25
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BMW on Motorway??
On Wednesday, 13 February 2019 19:46:28 UTC, Andy Bennet wrote:
On 13/02/2019 18:12, Robin wrote: On 13/02/2019 17:57, NY wrote: "Robin" wrote in message depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. Or of course misreckoning if others get different answers What do you drive? A Dinky toy? maybe a Willam Sulky. NT |
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#26
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BMW on Motorway??
On Wednesday, 13 February 2019 12:27:03 UTC, wrote:
Overheard someone talking to someone that was going to supply her a temporary vehicle. She was very concerned that the car should be at least a 2.0 as she intends to dive on the motorway. I assume they offered a beemer, because she said I dont know anything about BMWs I drive a Jaguar. I dont know if they can be driven on the motorway. How the other half lives! I used to take my 1.0 Metros from London to Preston & back on the motorway on a regular basis (leaving Jaguars and BMs eating my lead!) Luxury! I used to do long journeys in a thing with a wooden floor that topped out at 52mph. Eventually. NT |
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#27
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BMW on Motorway??
On 13/02/2019 19:46, Andy Bennet wrote:
On 13/02/2019 18:12, Robin wrote: On 13/02/2019 17:57, NY wrote: "Robin" wrote in message depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. Or of course misreckoning if others get different answers What do you drive? A Dinky toy? Oh bother. Ah, I've found where I dropped it. Here it is: 0 -- Robin reply-to address is (intended to be) valid |
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#28
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BMW on Motorway??
On 13/02/2019 19:28, Harry Bloomfield wrote:
ARW laid this down on his screen : I have also had a couple of phone calls about me undertaking on a 50 MPH dual carriageway on the way to work. Phone calls from whom? Wank drivers doing well under the 50MPH speed limit whilst hogging the RHL when the LHL is empty and then taking the companies phone number off the van signage. -- Adam |
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#29
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BMW on Motorway??
On 13/02/2019 19:11, charles wrote:
In article , ARW I sometimes set my cruise control to a true 70MPG (GPS calibrated with sat nav and mobile phone) and there are still very few cars overtaking me. not so down south. Mostly BMWs A lot down south if you count Watford as South. The standard of driving on the M1 South of Luton is probably some of the worst motorway driving I have seen in the UK. -- Adam |
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#30
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BMW on Motorway??
On 13/02/2019 18:12, Robin wrote:
depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. What about different minor variants of the same basic car? It wouldn't be unusual for them to be fitted with either,say, 16 or 17 inch wheels. Do the manufactures adjust the calibration for different factory fitted wheels or do they rely of range they allowed on the speedo readings? What about the reading within spec with a space-saver wheel on one corner -- mailto : news {at} admac {dot} myzen {dot} co {dot} uk |
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#31
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BMW on Motorway??
After serious thinking ARW wrote :
Wank drivers doing well under the 50MPH speed limit whilst hogging the RHL when the LHL is empty and then taking the companies phone number off the van signage. Change the number to that of the Samaritans. |
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#32
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#33
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BMW on Motorway??
In article ,
Robin wrote: On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. Really? The speedo *mustn't* read low. That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. So you start out with a speedo dead accurate with new tyres. Then the maximum error would be 2%. Not 10% as allowed. Things have moved on since that reg was written. -- *Frustration is trying to find your glasses without your glasses. Dave Plowman London SW To e-mail, change noise into sound. |
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#34
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BMW on Motorway??
alan_m wrote:
On 13/02/2019 18:12, Robin wrote: depends on wheel/tyre of course but I was reckoning on tread going from 8mm to 2mm on a tyre of around 180mm circumference. What about different minor variants of the same basic car?* It wouldn't be unusual for them to be fitted with either,say, 16 or 17 inch wheels. Same external diameter. Do the manufactures adjust the calibration for different factory fitted wheels or do they rely of range they allowed on the speedo readings? What about the reading within spec with a space-saver wheel on one corner |
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#35
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BMW on Motorway??
Dave Plowman (News) wrote:
In article , Robin wrote: On 13/02/2019 16:54, Dave Plowman (News) wrote: In article , Brian Gaff wrote: Actually my neighbour had a Metro and boy could that thing move. The speedo kind of just hit the end and after that it was guesswork. Only problem with it was that it tended to be full of rust even when new. As I said - a very optimistic speedo. Some makers today do just the same. When making one which is within 1% accuracy should be child's play since they are counting pulses. I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. Really? The speedo *mustn't* read low. That's a statutory requirement: "the true speed shall not exceed the indicated speed" in your no-doubt well-thumbed copy of the The Motor Vehicles (Approval) Regulations 2001. Wear on tyres alone can produce a difference of 2 per cent in the circumference. So you start out with a speedo dead accurate with new tyres. Then the maximum error would be 2%. Not 10% as allowed. Things have moved on since that reg was written. They start out never true speed reading,they always read less, except for police speedos in police vehicles. |
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#36
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BMW on Motorway??
Harry Bloomfield wrote:
NY explained : I've lost count of the number of times that I've been following other traffic that is all doing under the speed limit, and yet one of them *still* slams the anchors on dangerously hard when they see a police car that might be looking for speeding drivers. Many drivers seem to think that they must brake even if they are nowhere near exceeding the speed limit. I think that is likely them braking, because they don't even know what the speed limit is and suddenly develop a guilty conscience. You lot are lucky,here in Australia we have just made a law that any flashing police or emergency vehicles at the side of the road means that you have to slow to 40 kmph which means that you have to reduce speed from 110 kmph to 40 kmph suddenly on the highway, it has already caused accidents. |
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#37
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BMW on Motorway??
On 13/02/2019 18:58, NY wrote:
I've lost count of the number of times that I've been following other traffic that is all doing under the speed limit, and yet one of them *still* slams the anchors on dangerously hard when they see a police car that might be looking for speeding drivers. Many drivers seem to think that they must brake even if they are nowhere near exceeding the speed limit. I mentioned ths top a plumber. His tale was interesting. "Most people dont know what the speed limit is, so around town they drive at 20mph to be safe, and out of town they drive at 50mph". -- Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read. Groucho Marx |
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#38
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BMW on Motorway??
On 13/02/2019 19:24, Harry Bloomfield wrote:
NY expressed precisely : I presume manufacturers design the speedo to over-read by at least 2% so it never under-reads even with just-legal tyres. Yes, they make sure you can never get done for speeding, unless you actually are speeding. Mine seems to under read by 5 mph across the whole range from 10 - 70, compared with a GPS speedo app. How they read, depends on how the calculate the speed - adding a safe percentage or simply adding 3, 4 or 5 to the value. Mine uses plus a percentage and the mph difference increases with increased speed. Last time I checked, it was 73mph when doing a genuine 70mph from memory. All depends on the rolling radius of the tyre , which is not only due to the tread depth but mainly the tyre inflation pressure. A fully inflated tyre should give the most accurate reading. Fortunatly the flatter the tyre the more the speedo over reads. I think the fuzz now use a laser velometer fitted under the vehicle which measures the true road speed relative to the vehicle. |
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#39
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BMW on Motorway??
On 13/02/2019 19:19, Harry Bloomfield wrote:
Robin has brought this to us : I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. My does around 50 pulses per revolution of the wheel, there are electronic methods to predict the likely next pulse period and predict when the next pulse will arrive. I have three speed displays available to me - the dial on the dash, which reads a few percent high, digital display which does not interpret the wheel pulses at all, it just displays the value and entirely independently - satnav. The latter two always agree within 1mph at a steady speed. Only trust the satnav speed when on a level road. The speed is calculated by rate of change of position on a flat surface. If you are going up or down a hill it will under read. The derivation of altitude via GPS is not very accurate anyway and is ignored in domestic satnav devices. |
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#40
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BMW on Motorway??
On 14/02/2019 08:34, Andy Bennet wrote:
On 13/02/2019 19:19, Harry Bloomfield wrote: Robin has brought this to us : I find it hard to see how a simple count of pulses can deliver 1 per cent accuracy. My does around 50 pulses per revolution of the wheel, there are electronic methods to predict the likely next pulse period and predict when the next pulse will arrive. I have three speed displays available to me - the dial on the dash, which reads a few percent high, digital display which does not interpret the wheel pulses at all, it just displays the value and entirely independently - satnav. The latter two always agree within 1mph at a steady speed. Only trust the satnav speed when on a level road. The speed is calculated by rate of change of position on a flat surface. If you are going up or down a hill it will under read. The derivation of altitude via GPS is not very accurate anyway and is ignored in domestic satnav devices. A one in ten hill is so steep that most people would slow right down on it. A one in ten hill would underead by 10%. In essence practically negligible on any normal slope of 1 in 100 or so. -- Those who can make you believe absurdities, can make you commit atrocities. Voltaire, Questions sur les Miracles * M. Claparede, Professeur de Théologie * Genève, par un Proposant: Ou Extrait de Diverses Lettres de M. de Voltaire |
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