Space Saver Spare

(14-04-2016 07:07am)Pete Wrote:  The guys above are quoting differences in diameter. I'm not sure where your figure of 7 inches has come from.

This has turned into a bit of a Simon Mayo Homework Question, but I think the consensus is that the differential can deal with the slight change in diameter but you wouldn't want to push it too far (i.e. 50mph max for a short duration)

I calculated rolling circumference based on the quoted tyre sizes and there is a 7 inch difference in the distance travelled by 1 wheel than the other in a single rotation.

(Remember from school Circumference and Diameter are intrinsically linked by PI )

The op's space saver is 135/80 R18 and normal wheel 235/60 R18
Compared to 155/85 R18 from above and (using mine) 245/45 R20

That's a 7 inch rolling difference in the ops space saver to normal Evoque wheels.

Normal Evoque is approx 90 inch circumference and 28.7 inch diameter
Ops space saver is 83.2 inch circumference and 26.5 inch Diameter based on sizes quoted.

In an overall 90 inch circumference that's a 8% rotational differential the diff has to continually deal with.

Either way it'll get him home or to the tyre shop, but Maybe not good to drive John o'groats to Lands end in!

(13-04-2016 02:27pm)Pete Wrote:  It doesn't matter that it's slightly smaller, the suspension will deal with the difference without any problem. Jeff's estimate of 33mm means that the hub centre will be 16.5mm lower.

Evoques have a lot more suspension travel than that.

I think the hubcenter will be 33mm lower, as the difference in the tire wall is 33mm. When you measure the total height of the wheel it is the diameter of the rim + 2 times the tire wall. So with the smaller wheel the centre of the hub will be one wall size lower