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Jun 14th, 2026
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Joined: Jan 2020
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OP
New to Talk Morgan
Joined: Jan 2020
Posts: 20 |
Having checked my speedo against a portable sat nav reading, I am horrified to see it is way out.
At true 30mph it is showing 39mph and gets progressively worse.
Is this common with Morgans, mine is a 1995 plus 4, and any suggestions as to the possibility of getting it recalibrated or is it a replacement job.
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Joined: Feb 2020
Posts: 586 Likes: 21
Talk Morgan Regular
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Talk Morgan Regular
Joined: Feb 2020
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Curiously, my speedo was regularly 5mph-9mph out (under reading) against sat nav. When I replaced my tyres, all 4, I found it back to parity at low to midrange speeds, and 2-3mph under at motorway speed.
"DOT" 35th Anniversary Edition Plus 8- family owned from new. Rolls Royce Pewter.
06 Saab 93
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New to Talk Morgan
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New to Talk Morgan
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I bought it with full set of new tyres fitted so nothing to compare previously.
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Joined: Jul 2007
Posts: 28,892 Likes: 350
Salty Sea Dog Member of the Inner Circle
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Salty Sea Dog Member of the Inner Circle
Joined: Jul 2007
Posts: 28,892 Likes: 350 |
Graham (G4FUJ)
Sold L44FOR 4/4 Giallo Fly
'11 MINI Countryman Cooper D All4
'90 LR 90 SW
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Joined: Aug 2013
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Formerly known as Aldermog Member of the Inner Circle
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Formerly known as Aldermog Member of the Inner Circle
Joined: Aug 2013
Posts: 15,794 Likes: 15 |
Having checked my speedo against a portable sat nav reading, I am horrified to see it is way out.
At true 30mph it is showing 39mph and gets progressively worse.
Is this common with Morgans, mine is a 1995 plus 4, and any suggestions as to the possibility of getting it recalibrated or is it a replacement job.
At least you are very unlikely to get caught speeding, if you go by the speedo reading! But you might be pulled for causing an obstruction. I suspect someone has fitted tyres with a different profile, so effectively changing the wheel size and altering the speedo drive gearing. You don't mention the model and the wheel/tyre size fitted.
Peter,
66, 2016 Porsche Boxster S
No longer driving Tarka, the 2014 Plus 8...
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Joined: Jul 2013
Posts: 3,732 Likes: 79
Talk Morgan Addict
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Talk Morgan Addict
Joined: Jul 2013
Posts: 3,732 Likes: 79 |
Construction and use regulations allow a speedo tolerance of -0% to +10% so all speedos should overread. To accommodate manufacturing tolerances most are towards the 10% error but 39mph at 30mph is outside the limit.
Red Leader 
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Joined: Jan 2009
Posts: 5,945 Likes: 28
Charter Member
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Charter Member
Joined: Jan 2009
Posts: 5,945 Likes: 28 |
Construction and use regulations allow a speedo tolerance of -0% to +10% so all speedos should overread. To accommodate manufacturing tolerances most are towards the 10% error but 39mph at 30mph is outside the limit. True but since its never checked by officialdom, that doesnt matter. I would be a bit cautious comparing with a satnav because they arent htat accurate on speeds paricularly if unudlations and hills are involved. Their speed calculation is the distance between two calculated points on the geoid and the time difference. That said the satnav wont be 30% out or anything like it. Check wheel and tyre sizes. Check if the speedo has been replaced - does wonders for resale value sometimes!
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Joined: Aug 2010
Posts: 5,464 Likes: 171
Charter Member
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Charter Member
Joined: Aug 2010
Posts: 5,464 Likes: 171 |
If the speedo is digitally calibrated, another possibility is that someone has inadvertently changed the calibration number.
I cannot remember the numbers or the button sequence required to display the number - hopefully someone will be along soon who knows what they are talking about.
Paul
Costock, UK
Plus Four 75th - Furka Rouge - Pip
Disco 5
Teddy - 17h1 Irish Draught cross
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Joined: Feb 2016
Posts: 8,659 Likes: 407
Needs to Get Out More!
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Needs to Get Out More!
Joined: Feb 2016
Posts: 8,659 Likes: 407 |
Construction and use regulations allow a speedo tolerance of -0% to +10% so all speedos should overread. To accommodate manufacturing tolerances most are towards the 10% error but 39mph at 30mph is outside the limit. The law allows more than that Chris, it's up to 110% + 6.25 mph over read in the range 25 to 70 mph. A cars speedo could legallly be indicating 50.25 mph when actually travelling at 40 mph 
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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Joined: Jul 2007
Posts: 27,804 Likes: 749
Member of the Inner Circle
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Member of the Inner Circle
Joined: Jul 2007
Posts: 27,804 Likes: 749 |
Sadly mine under reads by c 10%. MMC say it is legal, hence my GPS speedo. I know the GPS has faults but that combined with rpm & gearing is helpful
JohnV6
2022 CX Plus Four
2025 Renault Scenic Alpine etech "Yvette"
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