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[barclay03]

cool - yea, 17's, and afaik have 215/40 on them... but why would i need to change them?  :-/ lol

[Danny]

omega 17s sit on 235/45/17s, your speedo will read incorrectly, you're allowed a maximum of 2.5% out either way, but the difference with 215s is -6.14% from originally having omega standard 17s, but if you had omega standard 16s on 225/55/16 then the percentage difference is -7.66%

at -7.66% your speedo will read 64mph when you're actually doing 70
and at -6.14% your speedo will read 66mph instead of 70

[barclay03]

ah... thought you meant for some reason other than that. yea, i know the speedo will be out, tyres would be gettin changed in a few months or so anyway

out of curiousity, who says theres to be a maximum % in regards to the speedo? just wondering as ive had cars pass and MOT without the speedo even working, and on average id say the mega is about 5mph less at 70 on the standard tyres (goin by a few GPS systems ive used at the time)

[Danny]

not too sure about the MOT issue, i just know its a legal requirement to be correctly calibrated in relation to the size of the tyres

[hotel21]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

[barclay03]

lol jus curious, ive heard it mentioned before but never as a requirement to be a certain %  

[Andy B]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

How are you going to check it though? Cars are usually stopped at the side of the road when plod check 'em. My Astra passed its MOT earlier this year with a non working (at all) speedo - it's fixed now!  

[hotel21]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

How are you going to check it though? Cars are usually stopped at the side of the road when plod check 'em. My Astra passed its MOT earlier this year with a non working (at all) speedo - it's fixed now!  

Rolling road at a DOT/VOSA testing station??  Take it for a drive, compare against a hand held speed reader of some persuasion?

Limited only by your own imagination......  

[Danny]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

How are you going to check it though? Cars are usually stopped at the side of the road when plod check 'em. My Astra passed its MOT earlier this year with a non working (at all) speedo - it's fixed now!  

i think usually you're caught out by travelling too slow or too fast for the speed limit while swearing black's white you were doing 30 (or whatever it might be), but if you're about 130 years old like the guy in a pug 306 this morning then there's usually other reasons for ignorant speeds! and also there are (believe it or not) cars floatin about on the road with wheels noticably too small!

for example you dont put 15" alloys with low profile tyres on a Vectra, but someone has!!

[Entwood]

Question raised in the House of Lords

Lord Allen of Abbeydale  asked Her Majesty's Government:

      Whether, in the light of the increasing importance of speed limits, they have any plans to make it easier for the private motorist to have his speedometer tested for accuracy.[HL839]

Lord Whitty: The Road Vehicles (Construction and Use) Regulations 1986, as amended, allows the use of speedometers that meet the requirements of EC Community Directive 75/443(97/39) or ECE Regulation 39. Both the EC Directive and the ECE Regulation lay down accuracy requirements to be applied at the time of vehicle approval for speedometers. These requirements are that the indicated speed must not be more than 10 per cent of the true speed plus 4 km/h. In production, however, a slightly different tolerance of 5 per cent plus 10 km/h is applied. The requirements are also that the indicated speed must never be less than the true speed.

A vehicle meeting these requirements would not be able to travel at a greater speed than that shown on the speedometer and a driver could not, therefore, inadvertently exceed speed restrictions. Her Majesty's Government have no plans to introduce instrument tests.

I highlight the relevant part as this is an easier read than either of the references given !!!

[hotel21]

.... I think usually you're caught out by travelling too slow or too fast for the speed limit while swearing black's white you were doing 30 (or whatever it might be), but if you're about 130 years old like the guy in a pug 306 this morning then there's usually other reasons for ignorant speeds! and also there are (believe it or not) cars floatin about on the road with wheels noticably too small!

for example you dont put 15" alloys with low profile tyres on a Vectra, but someone has!!

 

That and verbal skitters thats talks the driver into a corner that begs for a speedo check, just to shoot down a potential defence plea in months to come....

Been there, done that, not always proud of the fact......

You want a T shirt?  

[Entwood]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

How are you going to check it though? Cars are usually stopped at the side of the road when plod check 'em. My Astra passed its MOT earlier this year with a non working (at all) speedo - it's fixed now!  

As the rules are made under the Construction & Use regs all Mr Plod needs is access to a database with a list of the manufacturers approved wheel and tyre sizes .. and that is just a radio call away ..  

[hotel21]

.....out of curiousity, who says theres to be a maximum % in regards to the speedo? ....

Judge Dredd is da man....  'Cos he is Da Law!!!





ps - plod says the same.....  

How are you going to check it though? Cars are usually stopped at the side of the road when plod check 'em. My Astra passed its MOT earlier this year with a non working (at all) speedo - it's fixed now!  

As the rules are made under the Construction & Use regs all Mr Plod needs is access to a database with a list of the manufacturers approved wheel and tyre sizes .. and that is just a radio call away ..  

True.

But does not take into account those that replace speedo heads and/or gearing with others available in the makers range that alters the speed actually displayed within the car (less so now with digital displays/inputs) but principle remains the same.  Hence the taking it for a drive approach, to see what the needle actually points to....    

[Andy B]

.....True.

But does not take into account those that replace speedo heads and/or gearing with others available in the makers range that alters the speed actually displayed within the car (less so now with digital displays/inputs) but principle remains the same.  Hence the taking it for a drive approach, to see what the needle actually points to....    

I had a Senator that didn't read speed correctly, wheel sizes were correct but I suspect that the gearinging was wrong from the gearbox to the speedo electrickery gizmo. When it read 30 I could have got out & ran around the car and got back in again! (nearly ) Indicated 37 was a true-ish 30 mph.
My point about 'how would you know at th raod side ' was really to ask ... "why would you supsect that the speedo was a mile out" unless of course the accused   swore blind he was 'doing 30 pmh ocifer.'

[hotel21]

See Wilf Lloyds post.  That explains the reasons why suspicions could easily be raised....