Replace the old space saver spare?

This discussion about replacing or cycling in full sized spare tires makes me think about when do you replace the space saver spare tires. 

My Miata is a 99, the Ralliart wagon is an 04, and the civic is an 08. All of those tires are far older than anything I would want to drive on. Our Mazda five is a 2013, so it's reaching the ten year point at which I normally would not use a tire. All of these are original tires. I don't think any of them have been used on the car, none have visible cracks, and they all hold air well enough to need filling no more than twice a year (and that's not because it's flat, just dropped from 60 to about 45 pounds. 

I mean, I guess it outlasted the car, but I wouldn't recommend it.

Though the spare tires are older than you'd might drive on a traditional road-going tire, I think the fact that spare tires live a life in a dark dry place tend to help them last longer than something exposed to the elements.  Sure, that would be different for a exterior mounted Jeep spare tire.  

If that still bothers you, the best answer is likely a JY sourced spare tire from a newer car with same bolt pattern.  I once bought a salvage, theft recovery Chevy Sonic to sell.  It no longer had a spare.  I think the one I sourced from a JY was about $35.  Not bad when you figure that was the price for the rubber and metal combined.  

This is an old bolt reference site that I have bookmarked years ago.  By modern standards the site is old and clunky but it should at least help you figure the current size your car has (which may also be old and clunky) 

Sites like car-part do not have listings for which JY has a spare tire in stock.  The site doesn't promote used tires, but...  If I were looking for one like from a 2019 Miata ND(which I think went back to 4x100) I would probably just seek out on the site a 2019 Miata trunk lid.  If it has the trunk lid still, the spare tire has likely been living in the dark still.  Find a JY with the lid and then call them directly to see if they have a spare tire.  

For Mazda5, a newer Mazda3 will likely fit.  If you find a JY with a new Mazda3 trunk lid listed, and they have a spare it might be wise to drive the Mazda5 to that JY and bring a floor jack to do a test fitment before leaving the parking lot.  Do that test fitment on the front which is where the largest brakes usually are.  

Further thought...  These days, many cars do not come with a spare.  Finding a newer, used one could be harder due to that.  

Even further thought... On the site car-part they don't list tires but they do list wheels.  Choose "wheel (display with image)" and one of those listings will be spare wheel.  It's not like the JY is going to remove the rubber off the metal so find a spare tire (metal) and it will come with the spare tire (rubber.)  As suspected ND Miatas don't have a spare tire listed.  But, for a 2022 Mazda3 (5 bolt) I am finding spares for $50-$100 near me. 

I have a 27 year old space saver in my Jeep. Dry, but not in the sun. I think I'd trust it to drive off the highway slowly to call AAA.

From car-part.  Spare tire off a Mitsu Outlander Sport in Orange City, FL asking $102.  

Sebring, FL for 2022 Mazda3 spare asking $90

Tire rack used to sell spare tires in certain sizes.

If the donut spare is used as it should be used--to get you slowly home or to a place to repair/replace flat tire, then you should be fine, even with one that is old enough to drink.  If you leave it on the vehicle long enough to wear the tread off it and take it to highway speeds, then you'd do better to replace it.

If you wanted to put a new spare tire on your original spare rim does anyone even make them anymore ?
 

In reply to californiamilleghia :

https://www.tirerack.com/tires/types/perfCat.jsp

Go to "other special use"

I might do this soon. I got my 97 mustang in 2002 and it had lost its spare before I got it. I just got one recently off eBay, but it would be good to ditch the *does math* 26 year old tire.  (I feel very old now)

I happen to agree that a spare can be something that is never used.    Maybe not ideal to drive on but certainly OK  to keep in the trunk  far beyond the arbitrary 10 year life .   
         There are too many real problems that have a higher priority  than the age of the spare unused tire in the trunk.  
 

I've a friend that had to use the space saver spare on her Saturn Ion.  Well, she wanted to.  She says it's never been used and when she got it out it was a pile of wire and dust.  Looking online it seems like this is actually common and most likely due to being near the car's battery.  Like as the battery vents gasses in normal use the rubber of the spare gets attacked and kills them fast.

I think if the spare is passing visual inspection and you follow the speed and loading restrictions of these things, they're fine if they're old, but they're quite expensive to replace and I'd go used to get a new-to-me one.  Or figure out what cheap real tire fits on the spare's wheel. 

The spare on my 97 Saturn was coming apart despite never being out of the trunk.  It was over 15 years old at the time and the battery was not near by.  Just got a good one at the JY for $20. Never did use it...

Take it out, inflate it, check it carefully and probably replace it anyway.

My kid had a 2002 Civic and needed to use the new looking and presumably original spare about 2 years ago. He got home, but when I went out the next morning it was flat. When I inflated it, it immediately showed several BIG sidewall bulges. No good. I was quite surprised and would have previously agreed with the reasoning above that storing the tire in a dark place keeps it nicer longer.

A replacement dedicated mounted spare was more expensive than a regular-sized tire and wheel, so I went with the full-sized option, which didn't quite fit on the spare tire well, but was 100% functional and cheaper.  So now I'm inclined to replace all my spare tires after ten years or so.