Re: 5 tire rotation
Its recommended so that you have even tire wear on all 5 tires. Think of it this way. If you have all 4 tire rotated regularly (every 5 to 6k miles) they will all wear at even rates. If you have a full size matching spare then when those 4 tires on the vehicle are say 50% or 5 to 6/32nds of tread remaining the spare will still be nearly brand new with 100% to 12+ 32nds remaining.
Some people dont care about that but on AWD and 4x4 vehicles its not recommended to have any one tire be more then 4/32nds tread more or less then any other tread. This is because the diameter of all 4 tires should never be more then 4/32nds different overall diameter. With AWD and 4x4 vehicles especially those with any kind of sophisticated four wheel drive system or traction control the vehicle needs to use the tire diameter to determine slippage and traction control use. if one or more tires have a different diameter large enough then it can cause the vehicle to get different readings from those tires and potentially damage the 4x4 system.
It would end up thinking 1 or more tires are slipping when they are not. it can also cause the physical 4x4 components to potentially be damaged because its trying to spin 2 tires on one axle with one tire being smaller then the other and wanting to spin more then the larger tire on the axle.
Will any of this really happen for that few miles you may need to drive when you use your spare and the other tires are worn down? Most likely not. but it is a possibility that it can happen while on pavement. this would be especially bad on any vehicle with a locking differential or Quadra Drive system.
This is why most reputable tire shops will not install 2 new tires on an AWD suv or truck and 2 used tires if there is more then 4/32nds tread depth difference.
-Kyle '05 Dark Khaki (PJT) WK Limited 4.7L V8, '08 Overland Front End, Custom Exhaust, 245/70/17 GY Silent Armors, Bilstein 4600s, K40 Calibre DL Radar Detector/Laser Diffuser, CB.
Wife's Jeep: '06 Jeep Liberty KJ 4x4 2.8L CRD Diesel