Emergency Temporary Spare Tire - What size do you have

[X5 Meister]

I was wondering what size emergency temporary spare tire came as standard with the X5's? (Not the regular size tire/wheel combo) Was it 17", 18", or 19" (and what tire size)?

[Blue Mountain Raider]

hi curious, if lets say ur rims are 20 inch but your spare in the trunck is 18 inch then u got a flat tire what do u do? put on the 18 inch along with the other three 20 inch? doesnt sound good to me lol.

[X5 Meister]

Call for a tow truck. Not really addressing my question though.

[X5Jones]

Excessive difference in tire width can affect handling characteristics, especially on a front axle, but all you need to do is take it easy to get home safely.

The main hazard comes from different tire outside diameters (OD) where the wheel speed will be higher(undersized tire) or lower(oversize tire) depending on the size of the spare tire you have fitted!

This can damage the differentials (diff wind up) in some vehicles and make the car pull to one side (just like when you have a flat tire and it is spinning faster than the other side), especially when cornering.

If you have OEM wheels and tires and an OEM spare they should all be the same OD. The easiest thing to do is to take a flexible measuring device and wrap it around the tread of your road tire and spare tire and measure the length of the circumferences, if they match you are good top go provided you stick to the manufacturers usage recommendations- i.e, don't go hammering into a tight left hand corner with a 155mm temp spare on the left front axle or you will be in trouble!.

Of course, the circumference may differ up to 1/2" when a tire is not pressed hard on the ground so just because your spare is 3/8" larger that your current road tires I wouldn't be too concerned.

Personally I think they are a $hit idea, but if you have no choice, just use common sense and obey the laws of physics.