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[Martin_1962]

My speedo over reads and I don't like it.

What is the point in an incorret speedo?

Can it be fixed with Tech 2?

[FRE07962128]

My speedo over reads and I don't like it.

What is the point in an incorret speedo?

Can it be fixed with Tech 2?

I have always understood that unless a speedo is constantly re-calibrated as the police do, a completely accurate speedo is not possible due to tyre wear. :-? :-?

Can a speedo be permantly corrected now?

[Marks DTM Calib]

No it cant.

How much does it over read by, its normaly about 3mph across the full speed range.

[TheBoy]

My speedo over reads and I don't like it.

What is the point in an incorret speedo?

Can it be fixed with Tech 2?

All speedos are designed to overread slightly.

No, Tech2 can't do anything.

[trebor]

according to my sat nav, my speedo over-reads by 2mph all the way upto  90

[tunnie]

its a GOOD thing.

Speedo says i am doing 85... i pass plod, i am doing 82. Tad safter.

I would rather it over read.

[Gooders]

My Speedo reads around 3 m.p.h faster as well. Can be the diff between a ticket or not.

[serek]

my 5 mph more then show tom tom

[TheBoy]

my 5 mph more then show tom tom

Dont believe TomTom, it ain't that accurate

[Martin_1962]

I just it infuriating that they can get within 1 mph but will not do it, tyre wear would not effect by more than that.

Purposely over reading - so why bother fitting them!

You can see the difference using average speed.

Pity it is not easily fixable.

I think I will hunt for a friendy Policeman and find out where my 30mph / 60 mph really are.

[Kevin Wood]

It's the law at type approval that's to blame. Any measuring device has an error which is normally distributed either side of the true reading.

However, car speedos are required by the powers that be NOT to read under the true speed under any circumstances so a car manufacturer is no longer aiming to make an accurate speedo. They have to decide what the largest possible error from a speedo will be, and they have adjust their aiming point so that "worst case speedo" still won't read lower than the true speed. Result? Everyone's speedo reads fast.

Once set up, electronic speedos are susprisingly accurate. My kit car reads about 1 or 2 MPH fast at 60MPH. This was tested on a rolling road at SVA and also compared with a GPS on a number of occasions in the 8 years since I built it and it hasn't moved despite having been through a couple of sets of tyres.

Of course if you put a set of carlos fandangos on it will change the speedo calibration.

Kevin

[TheBoy]

I just it infuriating that they can get within 1 mph but will not do it, tyre wear would not effect by more than that.

Purposely over reading - so why bother fitting them!

You can see the difference using average speed.

Pity it is not easily fixable.

I think I will hunt for a friendy Policeman and find out where my 30mph / 60 mph really are.

They are made cheaply to a tolerance, and to ensure that tolerance is never causing to read under, its normally set to around 2mph fast.

[Martin_1962]

When I take over the world

Law 1

All speedos to 1% accuracy

*********** politicians!

[Marks DTM Calib]

When I take over the world

Law 1

All speedos to 1% accuracy

*********** politicians!

Which I supect is not a viable option

Consider that a 225/55/16 tyre has a circumference of 2054mm with a tread depth of 8mm......at 2mm tread depth the circumference is now 2016mm......Thats a 1.85% change just through tyre wear!

Then add in component tolerances etc......and you actually find that the Current speedo setup is pretty dam good!

[TheBoy]

When I take over the world

Law 1

All speedos to 1% accuracy

*********** politicians!

New tyre - 9mm tread
Old tyre - 1.6mm tread

Before you get into inflation, I reckon you're near 1% tolerance just on tyre...