In his latest advice feature, our Tow Car Editor is talking speed limits when towing a caravan. Take a look.
Towing: speed limits
- Thread starter LizziePope
- Start date
A useful summary article. I notice that since the speed limit for HGV has been raised on two lane roads where the solo limit is 60 mph, or even 50 mph I now seem to get more of them coming up behind me as I guess they are using the 10% tolerance on speedometer accuracy before the police or cameras pounce.
Most people are sensible (most) & know the speed limits , even the people that go down the outside lane doing extra 10 / 15 mph compare to what you are doing . I cringe when I see that happen , only takes the one or two that do this to give the whole caravan hobby a bad name!
otherclive said:
There is no legally allowable tolerance on speed limits.
Most speedometers are set to read a little slow, at least that's my experience of those that I have owned and checked.
Dodger524 said:
I know that there is no legal allowance on speedometers but “guidance “ issued to enforcement agencies has been for up to 10% before taking action. My speedometer reads 65mph when doing 60 mph as recorded by my satnav gps and is virtually spot on at 30 mph.
otherclive said:
In that case be careful when travelling through Northamptonshire as the police here have said that no tolerance will be allowed because they consider speedometers to now be sufficiently accurate not to need it.
Dodger,
I do , I go off the car speedo only , the sat nav is there for guidance and alerts ; ( and speed cameras)
I do , I go off the car speedo only , the sat nav is there for guidance and alerts ; ( and speed cameras)
Likewise with Craig, but Dodger have any speeding convictions been reported in Northants for speeds much less than 10% above the legal speed limits? You really wouldn’t expect any police force to say anything other than what Northampton have said otherwise they would be condoning speeding wouldn’t they. Northants don’t feature in the top ten for tickets issued, excluding auto issues for roadworks offences such as A14 etc.
Basically if you know the speed limit and exceed it then you are taking a risk and cannot complain if you get caught. It is a matter of opinion if a speed limit is appropriate but the limit is the law so stick to it if you value your licence.
Not sure on how accurate car speedometers are but the heads up display on our car does read slightly higher than the dial. They are always going to read slightly high though as this makes the performance look better than it is and the maker never wants to find its customers being caught for speeding when the speedo says they are not.
Some police forces do not allow any tolerance, my sister was caught near Redcar for 31 in a 30 area, and I think North Wales are also less tolerant than others or at least they were.
Not sure on how accurate car speedometers are but the heads up display on our car does read slightly higher than the dial. They are always going to read slightly high though as this makes the performance look better than it is and the maker never wants to find its customers being caught for speeding when the speedo says they are not.
Some police forces do not allow any tolerance, my sister was caught near Redcar for 31 in a 30 area, and I think North Wales are also less tolerant than others or at least they were.
Raywood said:
Don't know about the tolerances but North Wales were hot on speeding particularly on the A470 which had some very bad accidents. They used to use converted trailer horse box with a speed camera installed. But it met the legal requirements for visibility. My son and his biker mates used to refer to the Chief Constable as the "Mad Mullah of the Speeding Taliban". I don't recall that any of them were ever caught for speeding in that area as there was an effective headlight flashing and mobile phone intel squad. Thankfully he's grown out of it and we sleep better at nights.
Well said ray ,
that's me , i drive for my living, I can't afford points on my licence or lose my licence , I tend to stick to the limit or just under , plus I have my sat nav set to three mile an hour above the speed limit just in case and it beeps and then the wife thumps me in the leg for a gentle reminder!!
that's me , i drive for my living, I can't afford points on my licence or lose my licence , I tend to stick to the limit or just under , plus I have my sat nav set to three mile an hour above the speed limit just in case and it beeps and then the wife thumps me in the leg for a gentle reminder!!
otherclive said:
You will find its actually to do with the difference is speedo readings.
As cars are not calibrated, the higher the speed the less accurate it is. Where as the hgv is calibrated and alot more accurate, so when you think your doing 50, you will most prob be at 45 and the hgv doing 50.
I use my sat nav aswell as speedo in my hgv, dont speed but pass loads of cars in the lower speed limit roads
HNB said:
A useful point but it doesn’t explain why in a 50 mph motorway limit for road works I get pushed along or overtaken by hgvs. My 50 mph is based on my satnav read out. Also the government are consulting about raising the motorway roadworks speed limit from 50 mph to 60 mph as trials have shown its less stressful on Car drivers who don’t feel so intimidated by the hgvs running st 56 mph on limiters.
Every so often the subject of speed limits comes up and time and time again the same misconceptions are banded about.
The fact is that the Acts of parliament that control speed limits do not prescribe any allowance for tolerance. If you exceed a set speed limit you could be prosecuted, in theory anything over even 0.1 mile an hour is exceeding the limit and is therefore in theory prosecutable. The practical limiting factor is the uncertainty of detection equipment or operation.
As it stands at the moment there are a number of possible defences that are all based on the possible inaccuracy of the detection systems, and as a consequence if an accused can show the measurement falls within the region of uncertainty, the prosecution may fail. Lost prosecutions cost the Police and CPS money, where as successful prosecutions are paid for by the convict.
As the principal player for initiating speeding prosecutions are the police, if they can reduce the number of failed prosecutions it will save money and resources. The Association of Chief Police Officers, (APCO) have suggested that by adding a tolerance to the speed limit and only prosecuting if that tolerance is exceeded, it significantly reduces the possibility that a prosecution will fail. This has given rise to the myth that there is a tolerance to speed limits.
As technology advances and the certainty of speed detection systems improves, (for example Average speed systems) the APCO advice could change
The essential point is that there is actually no legal basis to the APCO advice, and as such there is no barre to applying a zero tolerance to some sections of road.
In terms of the speedometers fitted to vehicles, The motor manufactures would rightly be to blame if the devices they fit to cars encouraged excess speeds by under reading actual speed. There is a code of practice that manufacturers will ensure speedometers will never under read speed. Due to manufacturing tolerances it is more likely they will indicate a higher speed than actual.
GPS (systems (Sat Nav's) have the capacity to be more accurate than the systems fitted to most motor vehicles. But they are not perfect. For starters they take some time to acquire enough satellites before they can produce a speed reading. The accuracy of the device is dependent on the number of satellites it can detect. It is most likely that when a Sat Nav does show a speed it will be more accurate than most vehicle based systems. As an indication of the potential of GPS based units, Specialised GPS systems are used for monitoring performance vehicles with a high degree of accuracy.
I personally would trust a Sat Nav speed indication over any vehicles speedometer.
The fact is that the Acts of parliament that control speed limits do not prescribe any allowance for tolerance. If you exceed a set speed limit you could be prosecuted, in theory anything over even 0.1 mile an hour is exceeding the limit and is therefore in theory prosecutable. The practical limiting factor is the uncertainty of detection equipment or operation.
As it stands at the moment there are a number of possible defences that are all based on the possible inaccuracy of the detection systems, and as a consequence if an accused can show the measurement falls within the region of uncertainty, the prosecution may fail. Lost prosecutions cost the Police and CPS money, where as successful prosecutions are paid for by the convict.
As the principal player for initiating speeding prosecutions are the police, if they can reduce the number of failed prosecutions it will save money and resources. The Association of Chief Police Officers, (APCO) have suggested that by adding a tolerance to the speed limit and only prosecuting if that tolerance is exceeded, it significantly reduces the possibility that a prosecution will fail. This has given rise to the myth that there is a tolerance to speed limits.
As technology advances and the certainty of speed detection systems improves, (for example Average speed systems) the APCO advice could change
The essential point is that there is actually no legal basis to the APCO advice, and as such there is no barre to applying a zero tolerance to some sections of road.
In terms of the speedometers fitted to vehicles, The motor manufactures would rightly be to blame if the devices they fit to cars encouraged excess speeds by under reading actual speed. There is a code of practice that manufacturers will ensure speedometers will never under read speed. Due to manufacturing tolerances it is more likely they will indicate a higher speed than actual.
GPS (systems (Sat Nav's) have the capacity to be more accurate than the systems fitted to most motor vehicles. But they are not perfect. For starters they take some time to acquire enough satellites before they can produce a speed reading. The accuracy of the device is dependent on the number of satellites it can detect. It is most likely that when a Sat Nav does show a speed it will be more accurate than most vehicle based systems. As an indication of the potential of GPS based units, Specialised GPS systems are used for monitoring performance vehicles with a high degree of accuracy.
I personally would trust a Sat Nav speed indication over any vehicles speedometer.
It must also be remembered that failure to make adequate progress where safe is as dangerous as exceeding the limit :evil:
Yes too true as i dont like MIss daisy either.Dustydog said:
On to a simular point was .upon driving home the other morning i had a spate of cars in the opposite direction flashing there headlight.Presumably indicating there was something ahead.So i slowed to just under the speed limit and ready to brake.Then all of a sundden in had a car come zumming up behind me flashing his lights.so i pulled over thinking there way now something wrong.clearly not.as around the next bend was a 3 police cars with radar.and had pulled over the car that was behind e earlier.
ProfJohnL said:
Prof, I trust you have considered the situation of a car going downhill on a steep road? I don't think many (if any) Sat Nav's compensate for altitude difference when calculating speed. Speed traps on long downhill stretches are quite common
yes we have a van that regularly parks at the bottom of hill.30mph.might i add that i have thought it may save lives by cutting speed but what does it do to our health with wearing out our brakes.never mind the cost of repairing them from over use.VicMallows said:
VicMallows said:
I am aware of that effect but I rarely encounter such steep hills where the error will be significant. I can think of some in places like Bath and Bristol, but even then the 30mph speed limit is in reality too fast.
I have worked out the error of my cars speedo by comparing it to a Sat Nav on the flat, and I use the corrected reading on the cars speedo so that eliminates the sat van incline error.
I also extensively use the cars cruise control which can be incremented in 1mph steps which I find to be very effective, and can maintain a speed far more accurately than I can do manually. - thou it too can run away down steeper hills so I will select lower gears to provide enough engine breaking or use the cars brakes as required.
Nothing to do with exagerating performance, it is a legal requrement, I believe in the vehicle construction laws that a speedo, should never read below actual speed and is allowed a small tolerance above actual speed. For obvious reasons.Raywood said:
ummm small tolerance? i will chuck in wheels and tyres with so many cars coming with a range of wheel sizes and tyres to suit as standard or optional ie 16 17 18 inch wheels this itself can make an added difference .set up can vary by plus or minus 1.5%.in tyre circumference which then has the effect of making the car speedo more inaccurate or more accurate depending which way the difference is applied..DrZhivago said:
I fitted my Pajero with 33 inch tyres compared to the standard 29/30 inch ones. Kept the wheels at 15 inch though. Didn’t do much for acceleration but economy improved. I recalibrated the speedometer using the satnav and then placed small hiviz stickers at critical speed points 30-70 mph.
Hi prof john , its a long time since i've been on this forum .
I'm very familiar with Bristol Bath and Plymouth too . and for once I agree with you ,I've even done with the sat nav, what you did .
Found it disconcerting someone should point out about changes of altitude i.e. Hills, and did we know the effects on GPS !
The only thing ,on a point of interest is , The VW tiguan we have, once the cruise control is set , it will give engine braking and retardation by itself and will quite happily keep it at 30mph or 40mph etc. without my intervention ,makes Bristol easy, going up or down hill . Just the bus lanes to contend with . One oddity , set speed control to thirty and speedo reads a little faster though . best regards Martin .
I'm very familiar with Bristol Bath and Plymouth too . and for once I agree with you ,I've even done with the sat nav, what you did .
Found it disconcerting someone should point out about changes of altitude i.e. Hills, and did we know the effects on GPS !
The only thing ,on a point of interest is , The VW tiguan we have, once the cruise control is set , it will give engine braking and retardation by itself and will quite happily keep it at 30mph or 40mph etc. without my intervention ,makes Bristol easy, going up or down hill . Just the bus lanes to contend with . One oddity , set speed control to thirty and speedo reads a little faster though . best regards Martin .
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