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Robbo60

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Locally we have a couple of those "watch your speed" signs that shows your speed as you go past and there are also a couple when you travel across Dartmoor as well. Since I pass them all quite frequently I have spotted the discrepancy between the speed on the signs compared to the speed on my speedo. Because I am a sad git I decided to do the same test using the sat nav, keeping my speed as steady as I could I got my partner (yes they thought it was sad as well) to watch the speed on the sign while I checked the speedo and the sat nav. The speedo was almost 10% too low (depends on speed, more inaccurate the faster you go) and the sat nav was either the same speed as the sign showed or +/- 1 MPH of the sign. This was the same across 4 different speed signs, 1 set for 20mph, 1 for 30mph and 2 for 40mph. So while it is far from scientific I thought it was a pretty good way to test.
I have found, using the same method, and comparing to sat nav that the speedos in the last few cars I have owned have all been 3mph out, not a %age. I was also told at a speed awareness course that you will never be fined if exceeding the speed limit by less than 10%. A Traffic officer told me (a few years ago) that Home Office guidelines were 10% + 2mph, but only guidelines. Another thing I learned on a SA course was the old fashioned square Matrix speed limit signs in the central reservation on a motorway are only advisory as they don't have the red circle around then. The newer overhead ones do.
 

Robbo60

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What you have said is very similar to what I have heard in the past from a variety of sources.

When my Speedo reads 70 (it's a dial type so hard to be exact) my Sat Nav is usually saying 63-64, to get the Sat Nav to read 70 the speedo has to be close to touching 80. Considering I normally drive on the motorway at around 65 (speedo) my "real" speed is probably only just 60.
60 on a motorway? Do you sit in the middle lane as well??
 

Lons

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Some tyres have as much as 25 or 30 mm of usable tread so the percentage of the diameter is significant.

What do you mean by that? A standard car tyre even winter tyres or all season as I have on mine have a maximum of around 8mm depth of tread from new and are changed at around 2 - 3 mm so differences are insignificant, the only tyres I can imagine with 30mm depth would be HGV, agricultural or special use. Perhaps I've misunderstood what you've written?

Road sign recognition software in cars is a double edged sword, mine pings up every sign and blocks out the digital readout for probably 10 seconds so can be quite distracting though I still keep it enabled. No sympathy for anyone speeding especially in built up areas or with cameras sited in these spots but sadly as previously mentioned there are numerous examples where fixed and mobile cameras are positioned where safety factors are not a prime justification.

It's a fact that there are many drivers brake when they reach the camera, often sharply and often when they are already below the limit, it's also pretty clear that human nature causes a majority of drivers to look at their speedo as they pass, just to be sure they are OK and there is a cheap, simple way to make the latter safer by fitting every car with a head up display, the technology is there it costs hardly anything but the manufacturers want £500 to spec it. I fitted an aftermarket HUD to my motorhome because the position and colour of the dials make it very hard to read, it's plugged into the OBD port but is dual function and can work just as well by satelite, it's compact and I can read a digital speed and other info in my eyeline in a safe place bottom corner of the screen, no need to look down, pings at set speed if you want. The cost to buy this unit was a huge £21 and fitting took me 15 minutes most of which was tucking a thin wire out of the way.

It's the same with reversing cameras, they're a safety feature that should be on every car and you can buy a whole kit including screen for well under £20, I've fitted 2 for family members and it's pretty simple.
 
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Glitch

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A tyre is never a true circle. If it was there would be little or no grip.
The weight of the vehicle compresses it.
Weight inside the vehicle and tyre pressure make a difference too.
I think that's why speedometers can read quite a bit higher than true speed but are not allowed to read under. It has to compensate for the variables
 

Rorschach

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60 on a motorway? Do you sit in the middle lane as well??

Like I said, approx 65 on the speedo but in reality it is probably closer to 60. My car is underpowered and fuel efficiency drops off very quickly if I try and exceed 65 (speedo). At this speed I find I am quite easily over taking slower moving traffic on the inside lane such as Lorries. Of course I move into the inside lane when safe and sensible to do so. I do spend a fair amount of time in the middle lane as you would expect to do if overtaking traffic on the inside lane but it will depend on the volume of traffic at the time. I follow the highway code of course but I do think this whole middle lane hogging things does get a bit overblown, usually by drivers that are regularly and consistently speeding on the motorway. If a car is in the middle lane when there is a decent volume of traffic in the inside lane that they are overtaking, I don't have a problem with them sitting there when there is a 3rd lane available for other traffic to overtake them. Constantly weaving in and out of the inside lane into small gaps between lorries just to pull out again seconds later seems far more dangerous in my mind.
 

paulrbarnard

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What do you mean by that? A standard car tyre even winter tyres or all season as I have on mine have a maximum of around 8mm depth of tread from new and are changed at around 2 - 3 mm so differences are insignificant, the only tyres I can imagine with 30mm depth would be HGV, agricultural or special use. Perhaps I've misunderstood what you've written?

Road sign recognition software in cars is a double edged sword, mine pings up every sign and blocks out the digital readout for probably 10 seconds so can be quite distracting though I still keep it enabled. No sympathy for anyone speeding especially in built up areas or with cameras sited in these spots but sadly as previously mentioned there are numerous examples where fixed and mobile cameras are positioned where safety factors are not a prime justification.

It's a fact that there are many drivers brake when they reach the camera, often sharply and often when they are already below the limit, it's also pretty clear that human nature causes a majority of drivers to look at their speedo as they pass, just to be sure they are OK and there is a cheap, simple way to make the latter safer by fitting every car with a head up display, the technology is there it costs hardly anything but the manufacturers want £500 to spec it. I fitted an aftermarket HUD to my motorhome because the position and colour of the dials make it very hard to read, it's plugged into the OBD port but is dual function and can work just as well by satelite, it's compact and I can read a digital speed and other info in my eyeline in a safe place bottom corner of the screen, no need to look down, pings at set speed if you want. The cost to buy this unit was a huge £21 and fitting took me 15 minutes most of which was tucking a thin wire out of the way.

It's the same with reversing cameras, they're a safety feature that should be on every car and you can buy a whole kit including screen for well under £20, I've fitted 2 for family members and it's pretty simple.
Take a look at BF Goodrich Mud Terrains, which I have in my car. They have close to 30mm.
 

paulrbarnard

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Specialist tyre really though Paul certainly must be a very small % of tyres in normal day use.
The only type of tire that has been on my landrover for the last 15 years, so depends on your perspective really. For me they are perfect normal daily drivers.
 

Lons

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The only type of tire that has been on my landrover for the last 15 years, so depends on your perspective really. For me they are perfect normal daily drivers.
Yebbut they are off road mud tyres Paul I bet your wife's XC40 has normal tyre treads of not more than 8mm.
Horses for courses and must suit what you do or you wouldn't put them on but definitely not for my AWD SUV and I'd be more than a little surprised if MB recommended them. :ROFLMAO: I run Vredestein all seasons on 20" rims which suit my car perfectly, give decent grip and good life.
 

Fergie 307

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I see we've digressed a little from parking to speeding, Of course parking can be dangerous but not so much as speeding. I know that speed doesn't cause accidents, I don't even see it as a contributing factor, but it certainly can increase the severity of injury/damage to those involved, so a prudent speed is advisable.

Twenty mile speed limit at a school is I suppose justifiable because of the unpredictability of children/youth.

But I find some 30 or 40 limits just seem to be there to make a trap for the vans.

Eighty or a 100 years ago the stopping distance for a motor vehicle was probably three times what it is now, streets were half as wide or less and the lights and wipers were abysmal . But with all the advances we have made the limit is still 30.

I often wonder why 30 was picked.
You haven't been paying attention to all the advertising around this. In a collision at 30 the majority of pedestrians will survive. At 40 most will die, simple really.
 

Fergie 307

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What cost? The technology already exists in most cars already. The savings made by introducing them would be massive though, no prosecution and admin costs, no speed camera costs and the wages of the people who maintain them. And, if speed really does kill as some people are adamant it does, how do you quantify the costs of lives saved? We seem happy to spend millions on that at the moment.

Speed cameras made sense 2 or 3 decades ago maybe, but if your goal is to reduce speeding and save lives then there are better ways to do it.
I'd be quite happy with a limiter on my car, in fact I would gladly pay to have one fitted. I never (intentionally) break the speed limit so it would only be a good thing for me.
Absolutely. Most cars now have say nav, so know the speed limit in any given location, and have cruise control, so have the ability to control the vehicles speed. All that would be required is a bit of software to integrate the two, the cost per vehicle would be pennies.
 

Rorschach

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You haven't been paying attention to all the advertising around this. In a collision at 30 the majority of pedestrians will survive. At 40 most will die, simple really.

That isn't why we have a 30mph limit though, the number was just picked as being suitable, statistics about deaths came later and would have likely picked 20mph if injures and deaths were the prime factor.
 

artie

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I reckon it won't matter soon as the car will be driverless and only take us where we are allowed to go at a prudent speed
 

Blackswanwood

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I reckon it won't matter soon as the car will be driverless and only take us where we are allowed to go at a prudent speed
I agree. It's a big question for insurance companies as to what it will mean for them as the liability won't sit with the driver in an accident and instead will be with the manufacturer.
 

Rorschach

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I agree. It's a big question for insurance companies as to what it will mean for them as the liability won't sit with the driver in an accident and instead will be with the manufacturer.

It's a temporary issue and will be resolved as driverless cars become more common and accidents become virtually non-existent. If you have 20 million driverless cars on the road and you only get 1 fatal accident every year then each "car" need only contribute £1 extra per year and there would be a £20 million pot to cover that accident.

Insurance is minor issue amongst that many that driverless cars will bring up.
 

Blackswanwood

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It's a temporary issue and will be resolved as driverless cars become more common and accidents become virtually non-existent. If you have 20 million driverless cars on the road and you only get 1 fatal accident every year then each "car" need only contribute £1 extra per year and there would be a £20 million pot to cover that accident.

Insurance is minor issue amongst that many that driverless cars will bring up.
Thanks - I'll tell them to stop worrying :LOL: I agree with your general point but it's actually a lot more complicated than it seems at first.

I'm not sure I can see any real negative issues relating to driverless cars ... apart from having been lucky enough to sit in one being tested it's a most disconcerting experience.
 

Rorschach

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Thanks - I'll tell them to stop worrying :LOL: I agree with your general point but it's actually a lot more complicated than it seems at first.

I'm not sure I can see any real negative issues relating to driverless cars ... apart from having been lucky enough to sit in one being tested it's a most disconcerting experience.

Lol, it is a legitimate worry for now, and will be trouble during the transfer period but it won't be a long term problem and certainly won't stop the progression to driverless, but if not handled well it could slow things down.

I don't foresee many negative issues and in general I am very much pro-driverless cars. But I like to think I am a realist and I am sure there will be troubles and probably a very messy crossover. Like so many problems in society I think the biggest problem will be caused by one of the most simple societal problems, poverty and inequality.
 
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