Hi folks, after reading some time ago Col’s thread (https://www.rrsport.co.uk/forum/topic56851.html) I thought I’d have a look whilst periodically firing up the IID tool to clear any faults.

I’m running 10 spoke 20 inch wheels on 275/40 tyres. Taking a measurement from the centre to the ground gave me 360mm. Front tyres are inflated to 2.3 bar. Going to the CCF file/instrument pack/tyre radius; it was set at 359mm.

In a month or so I’ll be changing over to my Winters which are the 19in V spoke running 255/55s’. Having previously not known about such parameters, should I go to the effort of changing to radius?

If it is the done thing should we create a list of alloys/tyre sizes and their radius for reference. I’m bored at the mo so I’ll get my coat  2006 2.7 TDV6 HSE in Cairns Blue.

Hi Steve, I tried altering this setting when I put the fatter tyres on. It made no difference to the way the speedo was reading. I'm not sure if it has any effect on the other systems in the car, however. Kev

MY2014 L405 RR Vogue SE 4.4 SDV8 in Corris Grey
MY2010 L320 RRS HSE 3.0 TDV6 in Stornoway Grey

Stevepd wrote:

Hi folks, after reading some time ago Col’s thread (https://www.rrsport.co.uk/forum/topic56851.html) I thought I’d have a look whilst periodically firing up the IID tool to clear any faults.

I’m running 10 spoke 20 inch wheels on 275/40 tyres. Taking a measurement from the centre to the ground gave me 360mm. Front tyres are inflated to 2.3 bar. Going to the CCF file/instrument pack/tyre radius; it was set at 359mm.

In a month or so I’ll be changing over to my Winters which are the 19in V spoke running 255/55s’. Having previously not known about such parameters, should I go to the effort of changing to radius?

If it is the done thing should we create a list of alloys/tyre sizes and their radius for reference. I’m bored at the mo so I’ll get my coat

I wouldn't think 1mm makes aby difference considering tbe the rolling circumference allows for greater +/- tolerance.

Also just simply could be you simply.over measured.

Not questioning your measuring skills..

No Ash3 that’s not my point. Does it need to be done for each wheel size change?

Like Kev says it probably does something in the background...... 2006 2.7 TDV6 HSE in Cairns Blue.

Oh ok...

Personally never done that for tyre changes...I just put on the correct profile size ie 40/45/50 etc for the respective rim sizes and off I go

Changing the CCF settings won't make a blind bit of difference in correcting the speedo reading for the different tyre/wheel size, it may vary the actual mileage covered and fuel consumption on the dash lie-o-meter but the difference will be negligible. I spent some time and fuel out of curiosity experimenting with various CCF wheel/tyre size combinations to see what difference it actualy made if any, to the vehicle systems i.e. Gear Changes, Brakes, ABS etc. and the answer is absolutely nothing that was remotely noticeable. That is however on a MY13 car, but would not really know on pre-facelift 05-09 variants.

Just bolt the wheels on and have done with it.

Cheers
Coli

Thanks all, I won’t now give it a second thought. 2006 2.7 TDV6 HSE in Cairns Blue.

I've been told it makes all difference on my 05 D3 and a little bit of difference on her MY12 l320 btu nothing significant 2012 SDV6 HSE (technically its hers)
2000 D2 TD5 - definitely mine
2005 D3 V8
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