Speedometer Error

OK, it's a bike.

From a published road test on a 250cc Ducati in 1965:

Indicated speed True speed

30 mph 29.9 mph

50 mph 51.6 mph

70 mph 69.5 mph

110 mph approx 72 mph

135 mph approx 80 mph

!!

JA

Hi, and some of the plonkers don't seem to understand what average speed cameras are, as I've seen many slow down to 50 when they approach one of the cameras and then put their foot down once they have passed it.

Regards Nick.

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... Including some who commission them: The set on the Cat & Fiddle road being a notorious case in point.

MichaelG.

Hi John, according to the 2015 Official Highway Code, goods vehicles not exceeding 7.5 T max laden weight with exception to all 30 MPH areas the limits are; single carriage 50, duel 60, motorway 70 or 60 when pulling a trailer. Goods exceeding 7.5 T max l w; single 50, duel 60, motorway 60, in England and Wales and single 40, duel 50, motorway 60, in Scotland.

Oh and if they are all fitted with limiters there are a lot of them that don't work, as I've seen them pulling away from me when I've been doing 70. I have also heard from a reputable source that their is officially no allowance for over speeding during overtaking, i.e. if you can't keep within the speed limit while overtaking, you should not overtake.

Regards Nick.

Edited By Nicholas Farr on 16/08/2015 19:32:19

Hi Neil, my little Corsa reads about 1 1/2 MPH over true speed according to my Sat-Nav and my Astra is around 2 1/2 MPH over true speed. The worst car I had was my last Cavalier which was reading 10 MPH over true speed, always wondered why I never triggered a speed camera when I accidently passed them at what I thought was 78-80. My younger brother had a Cavalier which was reading about 5 MPH under true speed and for a long time didn't know it until one of his workmates was following him once.

I've always been surprised that the accuracy of the speedometer isn't included in the MOT.

Tyre wear has no significant effect on the reading of the speedometer, I once had both of my driving ones right on the legal limit and before I had them changed I noted the difference between my Sat-Nav and speedometer on a few different occasions and roads and the difference was always the same, when I had new tyres put on both wheels at the same time, I checked the speedometer with my Sat-Nav again on different occasions and different roads and the difference between the two was exactly the same as with the worn tyres.

Regards Nick.

Edited By Nicholas Farr on 16/08/2015 19:22:37

I'm talking about artics Nick or Prime Movers - the posh name in the trade. The ones that have a trailer behind them and usually have 2 to 4 axles on the truck. I think the max single axle loading is now 7.5 tonnes. I'm not sure about the speed the limiters are set at now but it was 56 mph / 90kph. The trucks are often fundamentally capable of going faster than that. I have heard comments about the limit being 50mph 80kph in the past but don't think that is correct.

I did find a link that goes through this area. There are probably others

**LINK**

As I haven't noticed any change in artic speeds while driving around I'd guess what it states on that is still correct. One of the things I used to ensure when towing a caravan was that I was at or above this speed. Anybody who has towed one will know why. As an aside I spent rather a long time working on tractor and trailer ABS on this class of vehicle also ADR's. The company was briefly interested in getting into limiters when the forthcoming legislation was announced. That is why they went into ABS as well.

John

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Hi John, **LINK** HGV speed limit changes (blog)

Regards Nick.

my ceed gt shows 30 when the sat nav shows 27, but my mgb gt look 3 mph slow from my viewing angle whilst my wife says it reads spot on.

Yes I did see that and also read the comments below. Just to add to the confusion have a read of the speed limiter section of this

**LINK**

It's a .gov.uk pdf

I still suspect if anyone could makes sense of it all artics = 56mph. Actually I think that is agreed EU wide.

Personally I am more bugged by the overtake must be <= 10sec, if true. Since the limiters were fitted they generally can't overtake in that short a time on any road where they could because the limiters are set so precisely and generally take a lot longer that that which in turn holds every one else up particularly on motorways.

John

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Interesting comment:

"downhill descent and uphill ascent"

Guaranteed to appeal to bikers, that....

Neil

John,

Fair enough. My local stretch of the M6 doesn't have them other than occasionally for road works.

But, as a caravanner, I am limited to 50mph on single carriageways or 60mph on dual cariageways/motorways and thus can't avoid getting mixed up with HGV's which now have the same speed limits in England.

Judging by the portable speed display signs I've seen around, my car does indeed read high at 30mph - perhaps 2 or 3 mph. By that I mean that my speedo shows 32 or 33 when the roadside device shows 29 or 30. I assume that this applies through out the range which means that as long as I do not exceed the posted limit as shown by my speedo, then I should be ok. To be honest, if I'm travelling at the posted limit as shown by my car, then I don't care what other drivers are doing - if they want to overtake, then good luck to them - it's their licence, not mine.

What really does annoy me though, is, eg on the A75 in Scotland where the HGV limit is 40mph, mine is 50mph, and I'm being tailgated by a HGV.

Regards,

Peter G. Shaw

Re HGV's, until he retired a friend worked for a quarry company as their mechanic and they bought several eight wheeler tipper wagons for delivery work and they were governed which the drivers didn't like but they soon learned that if they used the hand throttle in the cab used to operate the tipper when unloading it in turn would overide the governor thus allowing them to increase the road speed using the throttle

Martin P

> Personally I am more bugged by the overtake must be <= 10sec, if true. Since the limiters were fitted they generally can't overtake in that short a time on any road where they could because the limiters are set so precisely and generally take a lot longer that that which in turn holds every one else up particularly on motorways.

Eddie Stobart drivers are told to slow down if a plonker with a limiter set to 56.1 mph tries to overtake them. Not entirely sure they all do though

Neil

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...and it comes from the very people who are "trying to get the message across"

For a slightly more detailed description of their ineptitude, have a look at this from 2011.

MichaelG.

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P.S. ... Yes, it's a dangerous stretch of road; and yes, there are a few too many wannabe TT Racers playing on it: But making it a one-way-street might have been more cost-effective than the cameras

I reckon you could probably live with ± ten thou on the body of the speedometer with maybe another ± ten thou on the hole it fits into.

I can assure you that HGV's can travel rather faster than any posted speed limit in the UK, 90mph on an A class road approaching a bend! give or take 5mph.

A few years ago I was going east across the Nullarbor. I saw a couple of trucks approaching in my RV mirror, I was doing about 107 in a 110 zone, contacted them on the radio and told them the road ahead was clear for about 5 km. They passed me, the second truck was about 1 metre behind the first, slipstreaming. I speeded up and tucked in behind, about 15 metres back and when I checked the speedo, it was showing 155 ! I followed them for about 50km until the road started to get a few curves. Incidentally, the world's second longest stretch of straight road, 146.6 km / 90 miles. The only variation is about +/- 10 metres in height. Driving at night you have to dip headlights about 20 km before you pass as the truck drivers, being so much higher are dazzled by your high beams even though you cannot see theirs. I may go east again in February to see my cousin in Melbourne.

I think there may be some confusion here caused by the use of the term HGV. There is one class where the trailer can't exceed the weight of the vehicle towing it that is an HGV. The classes are explained well on gov sites that go through the various driving licence codes. These don't seem to cover the case where the trailer weight does exceed the weight of the vehicle towing it. These are the ones that I suspect will still be limited to 56mph but MAY be changing to 60. What is effectively happening is that limiters are slowly being applied to lower weight range vehicles against a lot of resistance from people who use them.

Anyway I'm about to drive around 200 miles and as I worked on them always notice ARTIC's. I'll be interested to see if any are travelling at over 56mph.

John

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The a77 road to Stranraer had average speed cameras for a couple of years when I used it a lot, the speed being 50. Setting my cruise control at 55 and overtaking the 40-50mph muppets at 60 to get them behind me never elicited a response from the clergy

They are really only after the idiots, judges don't like their courts being cluttered with frivolous 2mph nonsense that serves no practical purpose for society

They are (confusingly) called LGVs now.

HGV Class 1 /LGV C+E is for trailers heavier than the tractor i.e. 'proper artics'.

Speed limit for them is 60 on dual carriageway or motorway BUT new ones must be fitted with a 56mph limiter.

Amazing how many people don't realise that non-car derived vans are limited to 60 on dual carriageways - a fair few points doled out that way.

Neil