i am the happy owner of a rrs which came with 22" wheels i decided that they were too harsh a ride so found someone selling a set of 20" wheels and tyres which i bought and fitted and also found a breakers selling a fith alloy which is the spare , whilst driving down the motorway my wife informed me that we were speeding i looked at the speedo it showed 70 the tomtom satnav showed 77 ... took a trip to my local garage who pluged in his diagnostic computer my tyre profiles are 225 55 20 and he couldn't adjust the ecu to compensate he said that i could change the tyres to 225 50 20 and that would correct things and my cruise control which upto now would not work will be ok

anyone have any ideas if this is correct ??

I hope that is a typing error as the should be 255 not 225, standard tyre sizes I believe were 275/40 x 20" and 255/50 x 19" not sure a 255/55 was ever fitted only as a 19" durable spare, as you haven't mentioned it but I am assuming you have a RRS1.

Cheers
Col

As Col says ^ but some have fitted 275/45r20 to make it a even more comfortable ride,the 255/50r20s were fitted to the FFRR which yours could have come off.As for the cruise control it should work with any size tyre so yours could be faulty. Andy.
21 Ford Ranger
Gone but not forgotten
Focus RS Red Edition
2015 RRS AB Fuji.
2014 RRS SC Santorini
2016 VW Amarok
2014 RRS AB Fuji
2012 RRS Red Edition Fuji
2015 Nissan Navara
2012 RRS SE Santorini
2008 RRS White
2007 RRS Santorino

Yeah, I ran 275/45 x 20" for a long time. then compromised as I don't like 22's fitted a set of early SVR 21" rims with funnily enough 275/45 x 21" tyres filled the arches nicely, higher wall to protect rims a little better, slightly better ride and absolutely no cruise control, speedo reading, transmission or suspension issues in four years..

Cheers
Col

Was it your local garage or specikist. I think most I've tools will tell you the information in the ECU but not all will allow you to change the CCF. ( Car config file) 2012 SDV6 HSE (technically its hers)
2000 D2 TD5 - definitely mine
2005 D3 V8
Metalian Camper trailer for adventures

I played about changing the Tyre/Wheel size in the CCF files with a Gap diag. tool and it never appeared to make a blind bit of difference to any of the original default parameters, so reset it to original setting for 275/40 x 20 and left it at that.

Cheers
Col

sorry yes was typo should be 255 55 20 have been on google and inputted tyre sizes and it gives me the error in speed between 255 55 20 and 175 45 20 . its a local independant garage that i have been to but he has diagnostic equipment that allow him to adjust parameters to dealer level . Am running a 07 3.6ltr v8 diesel

175/45r20 must be a terrible ride,the original size for the TDV8 was 275/40r20’s. Andy.
21 Ford Ranger
Gone but not forgotten
Focus RS Red Edition
2015 RRS AB Fuji.
2014 RRS SC Santorini
2016 VW Amarok
2014 RRS AB Fuji
2012 RRS Red Edition Fuji
2015 Nissan Navara
2012 RRS SE Santorini
2008 RRS White
2007 RRS Santorino

Surely you mean 275 not 175. A 175 tyre wouldn't even inflate on any land rover wheel 2012 SDV6 HSE (technically its hers)
2000 D2 TD5 - definitely mine
2005 D3 V8
Metalian Camper trailer for adventures

I was on factory fitted 275/40/20. At gps of 70mph the speedo needle would be on 67mph and the digital cruise control would read 74mph.
I asked one guy at the indi I use a month ago that if the speedo was chucked out even more or got just a bit better could they adjust on Idd tool, he said yes, couple weeks ago asked the other mechanic and he said impossible to change on idd tool (hoped that would be wrong from what I’ve read on here).
Had the tyres done, slightly better ride but fill arch nicely.
Checked on gps at 70mph and needle bang on 70mph but cruise/digital reads 72mph but well happy.
Anyone know why rr send out sports with varying wheel sizes but don’t set them with speedo.

It is definitely possible to change the tyre sizes on the iid tool, but I have the beta version, so it may not be available yet on the standard firmware.
I have 255/55/20's on mine (one of the standard size's on the newer shape sport). I don't have an issue at all. MY12 RRS HSE
Gone 4.2 supercharged RRS
Gone 90
Gone s2000

Just realised I didn’t post that I went up to 275/45/20

shepp wrote:

I have 255/55/20's on mine (one of the standard size's on the newer shape sport). I don't have an issue at all.

Kevin Pryor wrote:

I was on factory fitted 275/40/20.
I asked one guy at the indi I use a month ago that if the speedo was chucked out even more or got just a bit better could they adjust on Idd tool, he said yes, couple weeks ago asked the other mechanic and he said impossible to change on idd tool (hoped that would be wrong from what I’ve read on here).

Checked on gps at 70mph and needle bang on 70mph but cruise/digital reads 72mph but well happy.
Anyone know why rr send out sports with varying wheel sizes but don’t set them with speedo.

These are a partial view of a print out of the actual CCF files for my own RRS1, not really sure quite sure the percentage value equates, but there are only two different wheel/ tyre size listed for the vehicle 275/40 x 20 and 255/50 x 19 which were the only factory fitted wheel/size's on a UK spec car. I fail to see how changing the CCF files to accommodate a different size wheel/tyre can actualy change anything for a size that is not even a factory option for that particular vehicle as the software etc. would not be there in the first place unless of course changing the size adds the additional software reguired. As I said I changed mine to various combinations listed in the Gap diag. and it didn't make a blind bit of difference to the speedo reading or anything else.

Perhaps a e-mail to Patrick at Gap asking the question whether it actualy changes anything or not would get a definitive answer, as they are the guy's design and build that particular tool and have always found their customer service second to none.









Cheers
Col

I was on factory fitted 275/40/20. At gps of 70mph the speedo needle would be on 67mph and the digital cruise control would read 74mph.
I asked one guy at the indi I use a month ago that if the speedo was chucked out even more or got just a bit better could they adjust on Idd tool, he said yes, couple weeks ago asked the other mechanic and he said impossible to change on idd tool (hoped that would be wrong from what I’ve read on here).
Had the tyres done, slightly better ride but fill arch nicely.
Checked on gps at 70mph and needle bang on 70mph but cruise/digital reads 72mph but well happy.
Anyone know why rr send out sports with varying wheel sizes but don’t set them with speedo.

So couple weeks after changing up to the 275/45/20 which has given me a more accurate speedo.
I have noticed that my digital read out of average mile per gallon has lowered by approx 2/3 mpg.
Any thoughts whether this tyre size change would have this effect because of tyre dimension.