Partly Cloudy

Partly Cloudy

max temp: 7°C

min temp: 2°C

Search

Can you trust your car’s speedometer?

10:08 13 March 2016

Trust your cars speedometer and it will keep you within the law

Trust your cars speedometer and it will keep you within the law

PA

Is your car’s speedometer telling the truth? None of us wants to end up with a speeding ticket when we think we’ve been travelling at the legal permissible speed, so it’s important that the speed you see is accurate.

The simple answer is yes, you can trust your car’s speed reading. While some much older cars that are now very much classics might have speedos that tell fibs, any car built from the 1980s onwards will have a speedo that is reasonably accurate. Even allowing for wear, tear and age, a speedo is not going to start telling you are driving at the legal limit when, in fact, you are going faster.

Don’t panic

Cars made in modern times are built with speedometers that deliberately over-read by a small amount. This is usually not obvious at lower speeds in town or even on 40mph stretches of road. Head on to faster roads, such as a 60mph limit or the motorway and you may notice some discrepancy between the reading on your car’s speedo and that on a satellite navigation system or an app on you smartphone.

Don’t panic about this. For one thing, if the speed on the sat-nav or phone is lower than the one on the car’s dash, you are safely within legal limits. Sat-navs and phones use GPS tracking to calculate speed based on time and distance – great for military aircraft and ships but not so good for cars on normal roads as it doesn’t account for undulations and curves in the road.

The main reason car speedos over-read is because car companies do not want to face legal action for a driver going too quickly. This could be legal action from a driver who feels a false reading caused them to be prosecuted for speeding or it could be a criminal prosecution if someone was hurt as a result of excessive speed.

Margins

So, all cars’ speedo’s over-read, but this has to be within a 10% 
margin as it could be just as dangerous for a car to be travelling too slowly on a road and cause 
hold-ups and frustration for other drivers. The speedo must never under-read, so if it says 60mph 
it cannot be any more than that speed.

A worry for some drivers is the speedo might become incorrect as the tyres wear down. However, as the tyres wear, the speedo is only likely to over-read very slightly more, not less, so it won’t risk you speeding when you think you are within the law.

What can catch you out is if you change to a set of larger wheels and tyres. If the rolling circumference of the new tyres is larger than the original ones, the speedo can begin to under-read and put you at risk of speeding without knowing it. Check with your tyre supplier because you may have to get your car’s speedo recalibrated to allow for this. Otherwise, trust your car’s speedometer and it will keep you within the law.

0 comments

Welcome , please leave your message below.

Optional - JPG files only
Optional - MP3 files only
Optional - 3GP, AVI, MOV, MPG or WMV files
Comments

Please log in to leave a comment and share your views with other Ipswich Star visitors.

We enable people to post comments with the aim of encouraging open debate.

Only people who register and sign up to our terms and conditions can post comments. These terms and conditions explain our house rules and legal guidelines.

Comments are not edited by Ipswich Star staff prior to publication but may be automatically filtered.

If you have a complaint about a comment please contact us by clicking on the Report This Comment button next to the comment.

Not a member yet?

Register to create your own unique Ipswich Star account for free.

Signing up is free, quick and easy and offers you the chance to add comments, personalise the site with local information picked just for you, and more.

Sign up now

Students gained exclusive insights into the growing creative media industry at an event at the University of Suffolk.

A consultation exercise over possible huge rent rises for beach hut owners at Felixstowe has generated more than 700 responses.

The death of a well known Stowmarket couple has left a community in shock, as police are understood to be investigating the incident as a potential murder and suicide.

Churchgoers are devastated by the theft of a memorial donated to a Suffolk village by two war heroes in memory of a British martyr.

Liberal Democrat peers will attempt to force the government to set out its strategy on local funding and economic growth post-Brexit.

The search is on to find the UK’s best up-and-coming stylist as ‘Create the Look’ returns for 2017.

A Suffolk police officer facing a misconduct hearing for allegedly drink driving last year has said a previously undiagnosed medical condition could have affected the breathalyser test.

The Environment Agency is expecting high tide levels in the region tonight and in the early hours of tomorrow and has warned: “Flooding is possible – be prepared.”

Suffolk Constabulary has received a pay-out after being billed double the amount it should have been for use of the police helicopter.

One of the most famous landscapes immortalised by artist John Constable has been returned to its former glory thanks to a £180,000 project to remove overhead power lines.

Most read

HOT JOBS

Show Job Lists

Topic pages

Newsletter Sign Up

Sign up to receive our regular email newsletter
MyDate24 MyPhotos24