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Old 23rd April 2018, 23:05   #1
Mercury RV
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Default Speedo Over reading

Back again with another question for you all. I noticed when I collected this new car (well new to me) that the speedo is wildly inaccurate, I know it must be as I tested it against two different devices. At a true 70mph it shows around 79mph and again the same error at slower speeds, are all of the speedos the same? Is there any way of correcting this? I will be changing the standard fit 15" alloy wheels for a set of 16" Forked alloys, not that this will make that much difference I am sure. Any advice about good quality tyres for the new wheels would also be useful please, Avon, Pirelli, Hankook. I am getting old so I am looking for a good ride above all else, well and value for money, just not cheap rubbish tyres though, a bit like some tyres one of our customers purchased, Double Coin tyres, I know how they got their name, its because the coins are 50p pieces!!
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Old 23rd April 2018, 23:38   #2
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There are some great tyres that supposedly help reduce fuel consumption as well as give a better ride - Pirelli Michelin and Goodyear do them, but others may too. I used to have Avons on my old Jag years ago and was very impressed with them back then.
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Old 24th April 2018, 07:51   #3
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Re speedo- "They all do that sir" I checked mine against the sat nav readout and it was up around 5 mph. look on the bright side, it may save you a speeding fine
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Old 24th April 2018, 08:01   #4
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Its the same with mine. If you enable the digital speedo on the IPK this gives you a much more accurate reading (when compared to GPS data). At least it does on my car.
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Old 24th April 2018, 08:07   #5
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JonMs beat me to it!
Quote:
Originally Posted by Mercury RV View Post
Is there any way of correcting this?
Most, if not all, speedometers over-read Simon by varying degrees. I believe that the reason for this is that manufacturers could be legally liable if it under-reads so they err on the side of caution.

The simplest solution is to find somebody with a T4 and ask for the digital speedo to be displayed in the message centre. This will appear as the last option as you press the button in the end of the LH stalk. The digital version will please your desire for accuracy I am sure.

Just bear in mind though that if the car is subsequently connected to a T4 and the operator isn’t made aware of what has been done, the facility could be removed.

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Old 24th April 2018, 12:11   #6
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All Speedo's read higher than usual. Id expect about 3 mph at around 30 mph and about 6 or 7 at 70 reading more out the faster you go. Digital speedo enable isn't a standard T4 operation so check with the T4 user first that they can do it
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Old 24th April 2018, 12:20   #7
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i think the link to phil-T4's speedo activator is still here somewhere... for the sake of a £10 obdII lead you can use a laptop to change it yourself...
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Old 24th April 2018, 12:24   #8
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They almost all do it. My V8 is only 3% over, and my V6's between 5% and a whopping 11% for my Tourer. All judged on standard sized tyres, Michelins for the V6's and Uniroyal for the V8. All properly inflated and compared with the GPS figures over a range of speeds. Legally it can be 10% + 6 kph 'optimistic' in the EU I understand, never pessimistic.
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Old 26th April 2018, 00:36   #9
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Thanks chaps, it is just that I have never had one that is THAT over optomistic, unfortunatley I do not have the message centre on mine I do not think as it is a Connissuer not the C SE model, poverty perhaps, but it is a BX reg and first registered in good old Longbridge/Birmingham, so perhaps sold as a demo or something as it was made in or around July 2002 but not registered until mid 2003, or did they just not sell that well then. Heres hoping changing the wheels for a refurb'ed set of Forked Spoke with Diamond Cut spokes and rim edge and Gunmetal Grey Metallic insets with the 16" tyres will assist? I am looking at Toyo 215/60 x 16 tyres as I want a smooth ride and silent not sporting, am I wrong? any suggestions as always welcome to a newcomer please. Great forum by the way, everyone seems sensible unlike the ones for my own industry, American Motorhomes where they seem to enjoy being back stabbers and just insult people, well done all!!

Last edited by Mercury RV; 26th April 2018 at 00:38.. Reason: Speeling error
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Old 26th April 2018, 21:50   #10
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Quote:
Originally Posted by Mercury RV View Post
Thanks chaps, it is just that I have never had one that is THAT over optomistic, unfortunatley I do not have the message centre on mine I do not think as it is a Connissuer not the C SE model, poverty perhaps, but it is a BX reg and first registered in good old Longbridge/Birmingham, so perhaps sold as a demo or something as it was made in or around July 2002 but not registered until mid 2003, or did they just not sell that well then. Heres hoping changing the wheels for a refurb'ed set of Forked Spoke with Diamond Cut spokes and rim edge and Gunmetal Grey Metallic insets with the 16" tyres will assist? I am looking at Toyo 215/60 x 16 tyres as I want a smooth ride and silent not sporting, am I wrong? any suggestions as always welcome to a newcomer please. Great forum by the way, everyone seems sensible unlike the ones for my own industry, American Motorhomes where they seem to enjoy being back stabbers and just insult people, well done all!!
What size tires are on it now? Your choice of 215/60x16 are ~26.2" diameter. If your current tires are 195/60x15, then they are a full 2" smaller diameter at 24.2". That translates into 66 more revolutions per mile for the smaller tire and that will make a big difference to speedometer accuracy. You may find your speedometer is right on with your new tires. Even if the current tires are 195/65x15, they are still ~1.2" smaller diameter and do 39 revolutions per mile more than the new ones will.

Cheers,
Glenn
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