Smokey001 said:
I am going to ask a stupid question!
The BMAX Titanium has 16 inch wheels but the optional spare wheel is 14 inch. How does that work if you need to actually use the spare?
It is only a stupid question AFTER you are told the answer!
I asked a Traffic Police Officer if it would be illegal to drive with a 14" spare wheel when the other wheels were 16". He said he thought it would be but was not sure. he said he would consult Fords and let me know. He never replied because after got the answer he felt stupid!
The wheel size refers to the size of the rim (alloy). Therefore a wheel can have 14", 15", 16" rims with the same size tyre which keeps the rolling size the same. All that changes is the height of the tyre wall. That is why you see some wheels with a very small tyre wall and others with a large tyre wall. Their rolling wheel size is the same.
If you change the rolling size you must adjust the electronics to take account of the different circumference of the tyre as it rolls along the road. Bigger tyre, less rotations for the same distance, hence speedo is wrong, distance traveled is wrong etc.
If you change the rim diameter and not the tyre diameter, everything stays normal.