Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
Slightly larger tyres, Speedo reading higher or lower?
Just trying to get my head around moving onto slightly larger tyres than standard.
So if the rolling circumference is that bit bigger, how does that show up on the speedo, don't know where it picks up its info from.
At the minute, I have a Snooper with GPS and when that shows say 50mph, the speedo shows 53mph so a bit of a contingency if the GPS is spot on and that's on 255/50's
With larger tyres say 255/55's, will the speedo show an even higher speed than the GPS or be closer to it? thus less safety factor for cameras etc. if closer to it.
Thanks.2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
1st Feb 2019 9:30 am
J@mes
Member Since: 10 Nov 2008
Location: Bomber County
Posts: 4547
If you Google tyre size calculator you can punch all the numbers in and it will tell you all you need to know 2014 D4 XS
2005 D3 SE - Gone
1st Feb 2019 9:48 am
Gazellio
Member Since: 08 Jan 2011
Location: Chilterns
Posts: 4130
I run 255/55 R20 so slightly oversize but using an accurate speedometer I now have 100% accurate car reading. The Factory tyre size give a reading slightly under actual speed.
Click image to enlarge
1st Feb 2019 9:52 am
al cope
Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10352
^^ what he said - speedo will now be closer to acurate
AlVolvo XC90 B5 Plus Dark
Gone - MY18 D5 HSE - Corris on 22's with Black Pack
Now gone - MY16 D4 SE Tech, Loire Blue, Almond Leather, Privacy, plus some other goodies.
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1st Feb 2019 10:24 am
Ceekay
Member Since: 17 May 2009
Location: Bury
Posts: 2089
So when i go into the CCF there are settings for all different tyre sizes. Does this not actually alter the speedo to match the size as long as the size is listed of course?D4 HSE Lux MY16 Club Waitomo
D3 HSE MY06 missing her still…
1st Feb 2019 10:44 am
Griffmaster
Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
CCF?2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
1st Feb 2019 10:50 am
Griffmaster
Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
So if I am understanding correctly, the car has the original tyre data programmed in to it somewhere and that info x the rotational speed gives the speedo reading.
Then if larger diameter tyres are fitted, that data remains the same and although the car is actually going that bit faster the speedo still shows as it did for the programmed original sized tyres.2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
The Car Configuration File (CCF) Function enables certain vehicle settings to be adjusted.
Quote:
By Gap Team|January 12th, 2017
How to adjust the speedometer when fitting bigger tires (tyres)
For Discovery 3 2004-2009 and Range Rover Sport 2005-2009
Menu–Car Config–Instrument Pack–Tyre Radius
For 2010+ vehicles
Only one of the following settings will work and it depends on the car itself:-
Menu–Car Config–Instrument Pack–
This setting, Tyre Size MSB – IPC
Or this one, Tyre Rolling Radius (mm) – ABS
NJSSAm I Gammon or Woke ? - I neither know nor care.
2016 Discovery 4 Landmark
2011 Mercedes Benz SL350 (R230)
1973 MG B GT V8 - 3.9L John Eales engine, 5 speed R380 gearbox, since 1975.
1959 MGA roadster - 1.9L Peter Burgess Engine - 5 speed gearbox
Past LRs - Multiple FFRs, Discos & a Series I - some petrol, some diesel,
none Electric or H2 fuel cell - yet.
There are 10 types of people in this world: Those who understand binary, and those who don’t.
2nd Feb 2019 8:41 am
Griffmaster
Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
Got into secret menu but could not see anything relating to tyre radii/circumferences etc.2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
3rd Feb 2019 11:34 pm
JonM
Member Since: 24 May 2012
Location: North Yorkshire
Posts: 1247
You need an IID tool or similar to edit the CCF but if you're only making a small change in tyre size, I wouldn't bother.MY2022 D5 HSE D300 - with extra nice bits added
MY2019 D5 HSE 3.0 SDV6 - sold to a dealer for a crazy price! - So good I bought another!
MY2012 D4 HSE 3.0 SDV6 - retired to a new home
4th Feb 2019 12:02 am
Oswiperus D3 Decade
Member Since: 02 Apr 2010
Location: Chelmsford, Essex
Posts: 1599
Agree with the others, my D4 used to over read unlike my D3 which is pretty accurate, I now run 255/55/20 on D4 and speedo is spot on.Stu
2016 D4 Landmark current
2022 Defender D300 SE Gone
D4 2014 XS Commercial - Gone
D4 2016 hse lux montalcino red - Gone
D3 2005 se java black - current
D3 2005 base manual - gone
D2 1999 TD5 E white - current
4th Feb 2019 8:18 am
Griffmaster
Member Since: 24 Jun 2006
Location: Different Planet
Posts: 206
It's 255/55/20's then. 2015 D4 HSE in Corris Grey
All below gone but still with happy memories
2010 D4 XS in Stornaway Grey
2006 D3 S in Zermatt Silver
2001 Td5 Oslo Blue
1993 300Tdi Arken Grey
4th Feb 2019 9:57 am
Yambeta
Member Since: 01 Dec 2019
Location: Cornwall
Posts: 2
Has fitting the 55 profile in tyre caused a loss in acceleration and given any issues with auto gearbox or error codes at all? From my understanding its similar to changing a sprocket on a motorcycle and basically makes it harder to accelerate And puts more load on engine.
1st Dec 2019 8:00 am
MorganD379
Member Since: 29 Sep 2016
Location: SA62 3PP
Posts: 425
I have had RR alloys with these tyres without issue on my D3 since April... Lifted the car slightly so watch the multi stories.
1st Dec 2019 8:18 am
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8225
255/55/?, 255/55/19 are standard size.It can when others can't,
It will when others won't,
It goes where others don't.
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