Sunshine and Showers

Sunshine and Showers

max temp: 14°C

min temp: 10°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

Police were called after a car left the former A12 road at the bottom of Copdock Hill on Saturday morning.

A 75-year-old man from Stowmarket who was brought back to life after suffering a heart attack believes if he had collapsed anywhere else he may not be alive today.

A community leader has made an impassioned plea for a precious area of countryside where 560 homes could be built to be saved from the developers’ bulldozers.

Daryl Goodrich to talk about his life in film making at University of Suffolk

Please get in touch and please come home is the message to missing RAF Honington serviceman Corrie McKeague from his uncle, a week after he was last seen.

From the minute The Dreamboys stepped on stage, I knew it was going to be a great show.

Health workers have been caught stealing controlled drugs from some of the region’s hospitals, it can be revealed.

Aspiring rock-gods and up-and-coming shredders have pitted their axe-wielding skills to the test in a competition to find Ipswich’s top air guitar hero.

Five men have been jailed for a total of 112 years for conspiring to murder a man in Bury St Edmunds who was left for dead after being shot with a sawn-off shotgun.

Now 10 games into the season and Ipswich Town sit 13th in the table. Is that going to be the club’s level for the rest of the season?

Most read

Most commented

HOT JOBS

Show Job Lists

Topic pages

Streetlife

Newsletter Sign Up

MyDate24 MyPhotos24