What’s the model and year? I’ve never actually seen an owners manual say a spare tire should only be used for 50 miles. That’s typically an urban legend caused by people confuse 50mph tires with distance.
I’ve typically seen that limitation on the donut spare itself, e.g. don’t drive faster than 50 MPH or farther than 50 miles, something like that.
But, YMMV.
I guess I’ll have to issue 2 retractions. In the owner’s manual (2017 Impreza), it does say to only mount the spare on the back which fortunately was where the flat was. It also only says to not exceed 50 mph and doesn’t not mention a limit other than to get a normal tire on ASAP. I must have got the 50 miles from the internet and conflated the two.
I think that means before getting a new tire and putting the donut back- which then- after having it checked- can be driven on again and again.
I did some digging after I posted and it’s more than an urban legend, it’s all over, from AAA to literally every auto repair chain, dealership, and car mag I could find. I’ve still never seen it in an owner’s manual, or seen any tire engineer attest to it’s veracity.
IMHO, replacing space saver spares “ASAP” is the correct advice. Other than being round, they’re absolutely garbage at being tires. Would you drive 50 miles on a bald tire with the cords showing? I treat donuts the same way. Again, IMHO, telling people they can drive 50 or 70 miles on a donut is just giving them permission to take an unnecessary risk for a few days.
Especially if you cut corners.
Which damages the transmission how?
So if you get a nail in one of your tires (requiring replacement), you have to replace all 4?
The mismatched load of the spare from the other three tires overheats the transmission fluid. The cars transmission is designed to operate with all four tires carrying a similar load. So when the manufacturer specifies not using a donut spare for more than 50 miles it is stating that you are running out of spec.
So in that since it is a CYA move on their part, but their other option is to give you no spare tire at all and leave you with just a repair kit. Putting a full sized spare in a vehicle is almost never done anymore unless its a large SUV or truck.
I’m pretty sure this has nothing to do with load, and everything to do with diameter.
The last time I had a flat on my AWD CX-5 I was doubly out of luck. First, the nail was too close to the sidewall so it couldn’t be safely repaired. Secondly, the other tires were just a tiny bit too worn to match the new one so I had to get 4 new tires. If the nail had been just a little further into the tread it would have cost me $10 to fix the flat. Instead I ended up spending a lot more on a new set.
The wheel speed sensors will constantly be thinking that one wheel is losing traction since it’s spinning faster, and it will overheat the differentials trying to resolve the situation.
(eta: agreeing with you)
I was got a flat tire near Monroe, MI, when I was driving to Columbus for an event I was working at. I put on the small spare and continued driving. It’s about 160 miles from Monroe to Columbus. I went slower than I usually would, but I drove faster than 50 most of the way. Once I got into Columbus and told the event organizer what happened, I was able to go get a real tire at the closest tire shop. Nothing apparently bad happened from misusing the spare. That doesn’t mean it was necessarily a good idea to do what I did, but I had to get to Columbus when I was expected or the trip was pointless.
My car did suffer from some sort of transmission problem eventually, but it was many years afterwards and wasn’t a complete breakdown of the transmission and was only intermittently weird. I got rid of it soon after it developed the weirdness so I never figured out what was wrong.
Well, yeah, unless the other 3 are relatively new. Your particular comment was a kind “are you serious” moment for me too after I bought my car and started reading about the all 4 thing. Even if you go to a non dealer tire place, you get the “all 4 need to be replaced” thing. (I know this because a family member had some worn tires on his Subaru and was strongly encouraged to have all 4)
Maybe this deserves its own thread, because I dont know the answer and I also haven’t had to replace tires yet. But I didn’t want to F%#K my car up,so planned on having to do all 4 at a future date. Maybe it IS a swindle. Or, if not a swindle, the potential damage is not more than the cost of replacing all 4 tires anytime you hit a pothole or a nail.
The trick is to use four temporary tires.
I think a lot of the caution is that if you use a donut to replace a bad tire you really should get an actual, full-size real tire replacement as soon as possible.
There are extreme situations where you might damn the consequences and just keep driving - escaping an active warzone or Godzilla? Drive on the freakin’ rims if you have to, right? - but outside those extremely rare events as soon as you put the donut on you should be going directly to someplace you can either get your old tire fixed or just get a new tire. Not drive around on it for a week.
Could a donut last more than 50 miles? Sure. It’s possible. But it could also crap out on you in 20, especially if conditions are rough. Given where 90% of people live there’s absolutely no reason not to use a donut to limp as quickly as possible to where you can get an actual fix.
I view “the doughnut” as an emergency device designed to get me home or to a tire shop. The obvious fact is that once you are using it, you no longer have an emergency reserve tire. A more compelling fact is that it is not built up to the same specs as your full usage tires, so the sooner you get it back in the trunk, the better.
So, if you are supposed to replace the donut after 50 mile of use, do you replace just the tire, or is the metal rim no good as well? Can you even purchase the tire only?
Neither the spare tire or its rim go bad. It’s the fact that running the donut spare is out of spec of what the car was designed to handle and cause the transmission to overheat. Whether by diameter size difference or tire width difference (or both), it causes an unbalanced load. You can in fact buy donut spares rather easily at junk yards all day.
I’d still like to see a cite that explains the issue in engineering detail. All the ones I’ve seen just kind of hand wave the description as we have been doing.
I always read the warning as “don’t drive more than 50 miles non-stop” rather than “don’t drive more than 50 miles total.” I thought it was a warning not to drive too long or the spare would overheat.