Quote:
Originally Posted by RidingOnRailz
We've hashed and rehashed issues relating to the pressures to run in the road tires, now what about the one in the trunk!
Most care tire information and loading placards on a vehicle equipped with a spare 'donut' specify keeping that tire at its maximum inflation pressure, typically 60psi.
I have faithfully maintained this pressure in the spares in both mine and my wife's car. Some knowns:
It is known that the donut in my wife's 2004 Toyota Corolla is the orginal, because she bought the car practically new - it was either a lease or trade from that model year, and she got an incredible deal buying it that way, less than 6 months old, around 10,000 miles on it. This knowledge will come into play momentarily.
Not known: The age/vintage of the donut in my 2010 Honda Accord. I bought this car in 2020, unlike the Toyota which was 6 or so months old. So I do not know if this is the original donut back there. But since the car itself is 6 years newer than the Corolla, it is possible that mine might be the original spare, or it might have been replaced at some point between 2011 and 2020. The tread depth appears to be quite even, with little scuffing aside from my trunk-to-driveway movement to fill it.
Back to the Corolla. 17-18 year old car, presumably with a spare donut of that vintage, which I have personally had to mount for my stranded wife some years ago.
Just the other day, I topped it off. Now my procedure for spare donuts is to use my automatic inflator set to 62-64psi. Why? Because both screwing the inflator chuck onto, and unscrewing it from, the spare's valve, releases far more air per second than doing so on a lower pressure standard road tire.
Just gauging the spare donut releases about 1psi! So it checked out at 52psi last week. Connecting the inflator probably let out another 2-3. At an inflator indication of 63psi I decided to turn the inflator off and remove it from the tire valve. Then I noticed something odd: one whole side of the donut was swolen, and there were gaps in the rubber on that side, in the transition zone from sidewall to tread!
I gauged the tire: 60.4psi with my high pressure Jaco digital. That gauge reads about 1psi high in general, so good enough. But I know this temp tire should no longer serve as a spare lawn ornament, let alone service a car.
Soooooooh, my question is:
Is it gospel to keep temp donuts at the maximum cold psi as indicated both on the donut and the vehicle's tire/load placard? Or should I just set my automatic inflator to 60psi exactly, and lose a litte air upon unscrewing it from the tire valve? And, was I doing a disservice to this tire by overinflating 3psi or so to compensate for what would seep out upon removing the inflator chuck?
As I said previously, if I didn't overinflate just a couple psi, and inflated exactly to 60, I'd always end up wth a 57-58psi pressured donut, owing to how quickly air escapes from its valve when pressed. Personally I think the safety margin on spare donuts is too thin, keeping their max pressure as the cold inflation pressure.
Do any of you maintain, IE: 55 in your spare donut, if you still have one?
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First, the date of manufacture is on tires - even donut spares! It's encoded in the TIN (Tire Identification Number) commonly called the DOT number. The DOT code is a 9 to 13 digit code that is located near the letters "DOT". More detail here:
http://barrystiretech.com/dotcoding.html
Short version: The date code is the last 4 digits in a week/week/year/year format. So a 3115 is the 31st week of 2015.
An 18 year old tire coming apart is due to the age, not the inflation pressure. Over time, the rubber loses adhesion to the steel belt. That's why tire manufacturers recommend replacing tires after 10 years - and sooner in some instances.
So check your 12 year old Accord spare for the manufacture date. I'll bet its original to the car.
And just an FYI. the burst pressure of a tire is many times the max pressure. Even that 60 psi donut spare will not burst until over 150 psi - except when it gets damaged or is very old!
So what to do about that failed spare? Tire Rack does sell donut spares. If they don't have the size, you can try something close or get a regular wheel and normal tire.