Fernando BR wrote: ( i am going to change oil again at 3500 Km and after at each 7000 km )
Lots of oil changes, why so often? Is that what the manual specifies?
Fernando BR wrote:Guido , speedo shows almost same GPS speed with those tires , and very precise with maths
One wheel turn corresponds to (31" x 3.14 x 25.4) mm = 2,472.47 mm/wheel turn or 0.0024725 Km /wheel turn.
You'll be slightly wrong calculating the distance this way. Your tire may be 31", but the radius between center of the hub and ground is not 1/2 * 31", because of tire compression under load, thread depth etc.
If want to calculate this distance per rotation, mark the tire and the ground on a certain position and then move the vehicle forward until the tire mark is a the bottom position again, mark the ground here again. Then measure the distance between the markings on the ground. This is your distance per one tire rotation.
If you do multiple tire rotations, you're fault in measuring and marking will be reduced.