Speedometer query
Discussion
Having just had an origin b2 fitted I was a little peturbed at just how far off the speedo was when compared with the GPS reading. A comparison with another Griff and a Chimera showed they were off by almost exactly the same amount.
As far as I can work out my speedo is over reading by about 14% continuously - which explains why previously sticking to the speed limit had felt a bit slow. Has anyone else had a similar experience (over reading speedo that is - not the speed limit bit)?
<edited to say "I'm a dope" - title should be speedometer query, not tachometer>
<edited again to say thankyou to whoever changed the topic title>
>>> Edited by jimbro1000 on Sunday 22 February 20:18
>>> Edited by jimbro1000 on Monday 23 February 07:52
As far as I can work out my speedo is over reading by about 14% continuously - which explains why previously sticking to the speed limit had felt a bit slow. Has anyone else had a similar experience (over reading speedo that is - not the speed limit bit)?
<edited to say "I'm a dope" - title should be speedometer query, not tachometer>
<edited again to say thankyou to whoever changed the topic title>
>>> Edited by jimbro1000 on Sunday 22 February 20:18
>>> Edited by jimbro1000 on Monday 23 February 07:52
I don't think people buy TVRs for accurate speedos! Having had 3 TVRs in 7 years, MHO is that the speedos have been bang on, but of course TVRs are all different. I can only suggest that you use the other traffic to give you a clue... if the bloke in front doesn't get flashed, neither will you!
Easy fix? yeah - get bigger tyres! The correct fix is to get the speedo recalibrated but that requires a specialist to do the job for you.
I'm not too worried about the inaccuracy either - I was perfectly happy before I fitted the b2 and it doesn't affect my enjoyment of the car. It was the fact that another griff and a chimera (both 500s) had exactly the same level of inaccuracy. It almost seems deliberate...
I'm not too worried about the inaccuracy either - I was perfectly happy before I fitted the b2 and it doesn't affect my enjoyment of the car. It was the fact that another griff and a chimera (both 500s) had exactly the same level of inaccuracy. It almost seems deliberate...
Legally, speedos are not allowed to read under, for obvious reasons. They are, however allowed to read up to 10% over (I think, perhaps someone else can confirm this?)
Most speedos will read over, to give a degree of safety - you only have to look at car tests in AutoCar, for instance where I think they chart speedo accuracy to see that most are over.
Having said that, I had an S2 years ago, and I got knicked driving in the rain at a steady indicated 80, and it turned out that's exactly what I was doing. Thankfully have not had any similar experiences in the Griff yet, so can't comment on that one.
Most speedos will read over, to give a degree of safety - you only have to look at car tests in AutoCar, for instance where I think they chart speedo accuracy to see that most are over.
Having said that, I had an S2 years ago, and I got knicked driving in the rain at a steady indicated 80, and it turned out that's exactly what I was doing. Thankfully have not had any similar experiences in the Griff yet, so can't comment on that one.
My griff reads slightly high since speedo transducer got sticky and was replaced - they are individually calibrated once fitted. The gearing and final drive in 4th gear gives you exactly 20mph/1000 rpm, ie 80mph = 4000 revs. Mine reads about 88mph. No problem, I know that it's reading 10% over.
grm
grm
jimbro1000 said:
So if I relabel the speedo so that it says I'm doing 200+mph at 3000rpm in 5th will it improve the accuracy?
The trick is in getting the label in the right place. You need a friend with a Mundaneo to drive at an agreed speed (say, 70) in front of you. You match his speed and see where your speedo lies. Let us say it says '79'. Then, ideally having stopped, you get a Post-It note, cut a triangle off the sticky bit and write '70' on it with a suitable writing implement such as a ball-point pen. Place the marked paper triangle in such a position on the speedo glass such that it now redefines '79' as '70'.
An illustrated guide to the above procedure, complete with step-by-step DVD and handy tips on paper-cutting, is available in my new book, 'Speedo Calibration for the Blue Peter Generation', available from all good bookshops for either £9.99 or 10,000 milk-bottle tops...
simpo two said:
The trick is in getting the label in the right place. You need a friend with a Mundaneo to drive at an agreed speed (say, 70) in front of you. You match his speed and see where your speedo lies. Let us say it says '79'. Then, ideally having stopped, you get a Post-It note, cut a triangle off the sticky bit and write '70' on it with a suitable writing implement such as a ball-point pen. Place the marked paper triangle in such a position on the speedo glass such that it now redefines '79' as '70'.
But that's what I've got a GPS system for! Isn't this where I came in?
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