Speedometer accuracy

[Ian Vincent]

My speedo measures slightly over 10% high when I calibrate it against a sat nav, so for example 60 MPH on the sat nav is an indicated 68 mph on the speedometer. On a recent trip from Dorset to Devon along the south coast, I checked the odometer against the sat nav and although it was still over reading it was only about 2 to 3 percent out, after 110 miles on the sat nav, the odometer was indicating that I had travelled between 112 and 113 miles.

 

Has anyone else had this kind of variation in the relative accuracies of the Speedo and Odometer and is it something that it's worth getting the Speedometer recalibrated for?

 

Rgds Ian

[Eddie Cairns]

At say 55 years old that is an excellent result for the speedo. I would leave it alone!

[Drewmotty]

My speedo reads spot on but the odometer reads under.

[monty]

I have an electronic speedo which is spot on compared to the speed reading on my satnav but the odometer is not too accurate!

On my other car the speedo needle waves around by around 10mph!

Cheers.

[Lebro]

The two functions (speedo, & odometer) are separate. The odometer works by gearing, based on gearbox speedo output drive ratio (2.5:1 for a TR), diff ratio, & tyre diameter.

The speedo is much less precise, & relies on magnetic pickup. Most read high unless you are very lucky, the main thing is that they should be steady.

 

Bob.

[Guest ntc]

Your Modern will read high just the same.

[peejay4A]

Mine doesn't. Not all that modern though.

[Nigel Triumph]

The speedo in my TR6 read high by about the same ratio as yours, same with the odometer.

 

I had mine rebuilt and recalibrated. Now it over reads by about 3 mph at most speeds, which is just like my modern BMW. If your speedo works, albeit not as accurately as you would like, that's good enough for the MoT. As it over reads, at least you shouldn't inadvertently fall foul of the boys in blue.

 

 

Nigel

[Ben Freer]

I've often wondered if GPS distance is that accurate...........does it take in to account all the ups and downs on the Dorset to Devon coast road when it (the odometer) measures actual distance travelled?

Edited August 27, 2016 by Ben Freer

[john.r.davies]

Ma ufacturerz mustNOT by law, provide a speedo that under reads.

Else it would be too easy to dodge a speedo ng fine.

So they ALWAYS provide o e that under reads ,and not by more than 10%, bylaw.

 

So long after that it is a surprise that there is no more slop in the mileomter mechanism

John

[Lebro]

Manufacturerz must NOT by law, provide a speedo that under reads.

Else it would be too easy to dodge a speeding fine.

So they ALWAYS provide one that over reads ,and not by more than 10%, bylaw.

 

So long after that it is a surprise that there is no more slop in the mileomter mechanism

John

Edited August 27, 2016 by Lebro

[tim hunt]

According to the wife's say nav my speedo is spot on at all speeds up to 70mph. It has been ever since it was recalibrated by Speedograph Richfield in Nottingham over 30 years ago! The odometer over reads by 1.5%. In both cases the accuracy is better than on my nine year old Volvo!

 

Tim

[RogerH]

Hi Ben,

I think the answer to your question is yes. The satellites know what you are doing.

If you go from the flat to up hill at a steady speed; the satnav will still show that speed going up hill.

But from directly above you appear to have slowed down - if you could move vertically then it would look as though you were stationary.

 

Roger

[Lebro]

Just trying to visualise a ream of A4 paper climbing a ladder

 

Bob.

[RogerH]

You silly boy young Bob

 

Ary is not moving

Ery allows you to write about it.

 

Roger (I know my worms)

[monty]

In my previous life as a commercial balloon pilot the GPS we carried was accurate to within a couple of yards so we always knew exactly where we were on a map. When landing you could relay the ordnance survey map reference shown on the GPS & the ground crew would always know exactly where you were to the yard (unless they had got lost!). Before GPS was available it was often guesswork!

[tim hunt]

Bob is in good company Roger. Recently there was confusion in my local Sainsburys until I sorted the manager out.

 

Tim

[Ian Vincent]

Stationary or stationery!.jpg Stationary or stationery!.jpgBob is in good company Roger. Recently there was confusion in my local Sainsburys until I sorted the manager out.

 

Tim

I can't see the problem, it's not moving

 

Rgds Ian