New tire, safe to run with my nearly worn out tires?

you can. but tpms cannot be programmed to the 5th tire. tpms is a separate issue from the mechanical mounting/usage of any wheel/tire.

every vehicle equipped with tpms from the factory is supposed to maintain the system. i tend to find tire shops that "forget" to install the sensors and go with standard rubber valve stems. far cheaper, easier to replace, and should be part of a normal vehicle walk-around routine anyways.

 

no sensor on the spare and wont work with the system, you would have to swap them out every time you rotate your tires

 

Please help me with this. Can a brand new sensor be installed into the replacement aluminum wheel? And having done so, when it's put onto the ground, can it be programmed with the other three? With all the interesting conversations here, I am genuinely confused.

 

the sensor must be for an alum wheel, the steel wheel sensor is different, and the tpsm system can only watch 4 sensors, so if you have 5 you have to get a programmer tool (i think) to add a new sensor and kick one out, and i think??? if one of the 4 sensors is idle you would get a dash warning light on all the time

 

if one goes bad and you have to add a new one the reset button on the dash might add it (if someone did this could chime in)

 

If a small difference in tire diameter is going to cause the transmission to grenade on AWD cars then I would think the shoulders of our highways would be littered with Grand Ma's and Outbacks because pops did not check the air pressure in all four tires before she when to Walmart.
A small difference in diameter is not going to immediately grenade drive gear. Inch difference for sure will cause damage if run for long term, but 1/6th, 3/32, gonna be fine.

 

my brz, which is rear wheel drive, with a mechanical limited slip diff, is well documented to have wheel speed sensor issues with people replacing only 2 tires at a time, even if the old pair of tires is at half tread. some even have had documented issues with running same-condition and size tires, but different traction compounds in the front and rear...

but all of it has to do with liability and longevity. subaru's use a viscous coupling for the center awd diff, which can withstand small variances in rotational speed, but extended variances sheers the fluid, creating a larger heat load beyond the design specifications of the component or fluid. this isn't going to matter to grandma going a block to church and the grocery store. but has been known to cause issues over the course of 200-300 mile one-way trips...

but the owners manual in most vehicles specifically states to never run different sized tires on the drive axle, because it creates additional heat load on the differential components beyond the original design specification.