On Sun, 29 Dec 2013 23:24:21 +0000 (UTC), DerbyDad03
wrote:

I rented a car this weekend. The tire pressure indicator came on. At my
next stop I checked the tires and it turned out to be that the left front
tire was low. I filled it up and decided to check the spare to make sure it
was full of air just in case I needed it. When I opened the trunk, I
initially thought that the spare was a full size spare, because it sure
wasn't a donut.

After closer inspection I noticed that the tires on the car were
Bridgestones, 205/55-16, while the spare was a Pirelli 195/65-15. Under the
numbers it had the words "Standard load" OK, so it's not quite a full size
spare when compared to the tires on the car, but at least it's a real tire.
Then I noticed that the rim had the familiar "donut labels" on it. Limited
Use, Do Not Exceed 50 MPH, etc.

So what's the deal? Why would a full size tire, even if it was slightly
smaller than the original tires, have the Limited Use, reduced speed labels
on it? Granted, the smaller tire might make the handling a little weird.
Could that be the reason they label the spare as "limited use", etc?

How do you know it's a "real tire"? Sure, it may be 'standard load'
but does it really have the same amount of "carcass", tread plies,
sidewall plies, same amount of tread depth, same tread compound, etc.
It's pretty close in size but about 0.1" different in diameter. And
at what inflation pressure did it have "standard load"? Same pressure
as the other tires or did it need to be pumped up to 60psi like the
donut spares needed to be?

My guess is it's not a "real tire" but was specifically built as a
temporary, limited duty, spare with all that implies.