Had a fiddle done some sums and been for a drive with my garmin fitted. Using the garmin and the digital speedo on the dash, my speedo reads spot on with the garmin over a variety of speeds.

Below are the before and after settings. The 255x55x19 is an error as they were originally 50's!

Click image to enlarge

Click image to enlarge

stan wrote:

not sure what you mean Stu...there's a part in the iidtool cff that lets you put in your wheel size and because i have recently changed from 20" to 21" i imputed 21"...
nit sure if this change makes a difference but it hasn't given me any warning lights on the dash..

interesting  ... - .- -.




Y. O. L. O.
.

Only problem is how to calculate the rolling radius.

IE allowing for the tyre deformation due to the weight of the FFRR.

I found this link: http://paws.kettering.edu/~amazzei/tire_calculator.html

The figure I got is 12mm less than I'd worked out for the static radius.

This fits the 8 - 12mm difference (between static and rolling radius) I'd seen when looking at the sizes in the IID tool's settings for Rolling Radius ABS mm.

And driving past some of the roadside thingies which show your speed suggests my speedo is working right. What do I put here then?

Stu, I don't think the 50s. are standard on a 19" rim. 55s are . 2007 Vogue TDV8 in Zermatt Silver with Charcoal

GAC23....

Does this help?

http://www.mkivsupra.net/vbb/showthread.ph...re-Profile Current: TDV8 (3.6) RRS HSE



Past: TDV8(4.4) Vogue
Discovery 3 Commercial
TDV8(3.6) Vogue
TD6 Vogue
D2 V8 ES
D1 V8 ES
RR Vogue Classic

Thanks, Stu.

But that figure assumes the tyre is perfectly round.

Which, of course, with a FFRR sitting on it won't be true

The link I used - shown above - allows for this squashing. What do I put here then?

I’d just use trial and error and a GPS

Adjust the iID setting until it’s showing the right speed