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![]() | Home > Wheels & Tyres > I think my speedo is out, help calculating correction please |
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RRSTDV8 Member Since: 13 Aug 2011 Location: Northamptonshire Posts: 5703 ![]() ![]() ![]() |
Go here: https://tiresize.com/comparison/
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Tim in Scotland Member Since: 30 May 2005 Location: Driving along in my automobile Posts: 16082 ![]() ![]() |
How do you know that the Leaf’s speedo was correct? Remember that up to 10% error is permitted so the Leaf’s could have been over reading by 10% and yours under-reading.............. you would be more accurate to compare your speedo to the speed reading on a hand held GPS in the windscreen. 2018 Melting Silver Mini Countryman PHEV on order for April delivery, bye bye Land Rover after 21 years and 11 LR products..... all because you won’t give me reassurance that should my SDv6 crankshaft break because of a design fault, not MY fault, but the engine builders fault - it will be replaced for free.
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RRSTDV8 Member Since: 13 Aug 2011 Location: Northamptonshire Posts: 5703 ![]() ![]() ![]() |
I thought that too Tim. I've used GPS-indicated speed on my phone (using CoPilot software) and the Speedo is not far off. Interestingly, its accuracy compared to the GPS varies in a non-linear manner. 2012 SDV6 - it's missing a couple of cylinders
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Stevepd Member Since: 22 May 2017 Location: Warminster Posts: 207 ![]() ![]() ![]() |
OK thanks, I'll break out the TomTom and see what that says. |
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Tim in Scotland Member Since: 30 May 2005 Location: Driving along in my automobile Posts: 16082 ![]() ![]() |
GPS does have problems with windy roads when calculating speeds, best to find somewhere with long straights where you can set the cruise and see what the difference is over several speeds held for a few minutes. I have done this in my Defender using both one of the routing apps on a iPhone and simultaneously using digital OS maps on an iPad in a cradle. They agreed within 0.1mph and my speedo on factory recommended MTR tyres was reading 4mph high at 50mph and 6mph high at 60mph. I am lucky to have a 6 mile long straight and flat A road between home and the local town. 2018 Melting Silver Mini Countryman PHEV on order for April delivery, bye bye Land Rover after 21 years and 11 LR products..... all because you won’t give me reassurance that should my SDv6 crankshaft break because of a design fault, not MY fault, but the engine builders fault - it will be replaced for free.
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flydive Member Since: 17 May 2007 Location: South Posts: 1186 ![]() ![]() ![]() |
One easy way, if a bit expensive, is to drive in front of a speed camera at 100 mph.
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geoffsnook Member Since: 19 Nov 2016 Location: cardiff Posts: 1024 ![]() ![]() ![]() |
mime is the same showing faster at 50 60 70 had a look to reset the tyre size as i am running 275 45 20's but could not fathom out what size it should be as it said 353 but not sure if that is circumference/diameter or something else |
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riverblanche Member Since: 11 Jun 2011 Location: Retford'ish Posts: 508 ![]() ![]() |
Hi Steve,
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Stevepd Member Since: 22 May 2017 Location: Warminster Posts: 207 ![]() ![]() ![]() |
So just a quick question, the 255/55/20 tyres that are fitted (and came with the wheels/car on purchase http://www.hubcaphaven.com/p/21612/aly7225...44848.html), are they the correct size for the vehicle that they would have been fitted to "L494 HSE - RRS2" originally? or has somebody changed the tyre size for a reason......
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Stevepd Member Since: 22 May 2017 Location: Warminster Posts: 207 ![]() ![]() ![]() |
And just a quick look at the website that RRSTDV8 posted:
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aljo Member Since: 13 Jun 2006 Location: West Sussex Posts: 3216 ![]() ![]() ![]() |
you can adjust the cars ccf to allow for bigger wheel circumference with iid bt tool |
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riverblanche Member Since: 11 Jun 2011 Location: Retford'ish Posts: 508 ![]() ![]() |
Hi,
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Nottsman Member Since: 29 Jan 2013 Location: Nottingham Posts: 29 ![]() ![]() |
The increase from 275 40 20 to 275 45 20 on my 2012 RRS (increase of 3.8% in rolling radius) made the speedo exact as well. 12MY RRS 3.0 SDV6 HSE Lux Sumatra / Black + contrast/ Grand Black
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