Member Since: 04 Jan 2012
Location: Benfleet
Posts: 124
255 50x20 CCF VALUES
Hi Can anyone check with iid tool and confirm the values below are correct for 255x50x20 tyres please. There seems to be some variation in the different inputs people have ?
2nd May 2019 10:05 am
al cope
Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10361
never changed the CCF when I have swaped wheel and tyres sizes as always stayed within 2.5% of a standard tyre size (e.g 255/55x19), as a 255/50x20 will have, near enough, the same rolling circumference
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2nd May 2019 12:24 pm
rosspopp1
Member Since: 04 Jan 2012
Location: Benfleet
Posts: 124
Yes I agree , all I would like to now is what other people currently have listed as values in the CCF that run 19 or 20 inch tyres ?
2nd May 2019 12:27 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8244
It appears, and this comes from GAP that none on your list makes little difference but only one or maybe 2 will work depending on the vehicle. I have changed them all one at a time and can confirm on my D4 they have done nothing except for Tyre Rolling Radius ABS, this may be shown as a 3 digit number ie 377 or by scrolling down the actual tyre size ie 255 55 19.
I changed from summer tyres 275 40 21 with a number reading of 377 which where on the car from new, when I fitted the 19s the speedo was 3 mph fast at 30mph, changing the above setting put it right.
This does not mean it will work on your car but worth a try, make one change at a time to the CCF and write it down so you know exactly what you have done It can when others can't,
It will when others won't,
It goes where others don't.
2nd May 2019 2:09 pm
MorganD379
Member Since: 29 Sep 2016
Location: SA62 3PP
Posts: 425
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8244
That confirms exactly what I found It can when others can't,
It will when others won't,
It goes where others don't.
3rd May 2019 7:03 am
rosspopp1
Member Since: 04 Jan 2012
Location: Benfleet
Posts: 124
Thanks all, so what have you all got listed in your ccf log for these parameters ?
3rd May 2019 5:22 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8244
Well I know what I’ve got, as above 255 55 19 with............🙁255 55 19 tyres and speedo is spot on
Figures below are from the notes I made a few weeks back when I changed from 275 40 21 to 255 55 19, after experimenting only the TRR ABS was changed.
Tyre aspect rating=55
Tyre width=255
Wheel diameter=19
Tyre size msb.ipic =31
Tyre rolling radius abs=was 377, now 255 55 19
Rolling circumference =2375
From the figures you give you are running on 235 70 17 tyre but as I’ve said I tried changing the other settings and it made no difference whatsoever on my D4, only TRR abs made any difference and if you scroll down the list of settings periodically it gives actual tyre sizes, Inthink the extra numbers are for fine tuning only.
The fuel offset % was the same as yours. There was a setting for Cruise Control % that I did not make a note of, I would appreciate it if you could tell me yours It can when others can't,
It will when others won't,
It goes where others don't.
3rd May 2019 6:33 pm
MorganD379
Member Since: 29 Sep 2016
Location: SA62 3PP
Posts: 425
Different for me as have a D3...
When it was on the 255/60/18 it was set at 370 (factory) now on 255/55/20 set at 394, tested Speedo with GPS and near enough dead on.
4th May 2019 7:15 am
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8244
With a D3 there is(or was) a setting that could be made in the satnav setup for when a new set of tyres is fitted
Just like telling a D4 you have fitted a new battery.It can when others can't,
It will when others won't,
It goes where others don't.
4th May 2019 7:34 am
logche
Member Since: 30 Jul 2013
Location: Waterlooville
Posts: 56
M3DPO wrote:
Well I know what I’ve got, as above 255 55 19 with............🙁255 55 19 tyres and speedo is spot on
Figures below are from the notes I made a few weeks back when I changed from 275 40 21 to 255 55 19, after experimenting only the TRR ABS was changed.
Tyre aspect rating=55
Tyre width=255
Wheel diameter=19
Tyre size msb.ipic =31
Tyre rolling radius abs=was 377, now 255 55 19
Rolling circumference =2375
From the figures you give you are running on 235 70 17 tyre but as I’ve said I tried changing the other settings and it made no difference whatsoever on my D4, only TRR abs made any difference and if you scroll down the list of settings periodically it gives actual tyre sizes, Inthink the extra numbers are for fine tuning only.
The fuel offset % was the same as yours. There was a setting for Cruise Control % that I did not make a note of, I would appreciate it if you could tell me yours
Hi M3DPO,
where do you see all these values for the tyre?
On my disco 3, with IID I see only Tyre rolling radius. Is it enough to change only that value when going for bigger tyres?
Where is the fuel offset %?Thanks,
Tiho
13th Feb 2021 12:54 pm
M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8244
Sorry can’t help, it was nearly two years ago! - all I can say is I am still running on the same settings, it may have now been updated with later firmware on the Iid tool.It can when others can't,
It will when others won't,
It goes where others don't.
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but only one or maybe 2 will work depending on the vehicle. I have changed them all one at a time and can confirm on my D4 they have done nothing except for Tyre Rolling Radius ABS, this may be shown as a 3 digit number ie 377 or by scrolling down the actual tyre size ie 255 55 19.
and speedo is spot on 
