Update: I actually don't even have the car anymore. But I did immediately change this tire at the time.
It's my rear right tire. It has a significant bulge in the sidewall.
Here are two pictures of the bulge (original URL):
Do I need to replace it before I ever drive on it again? Should I put on the spare to go buy the new tire? Or is it fine to even go a little bit on the highway for a few days before I replace it?
Or is it fine to even go a little bit on the highway for a few days before I replace it?
No. Please don't drive on that tire.
You are seeing a large scale deformation in a portion of the tire that's not designed for point stresses like that. There's pretty clearly a thin layer of rubber standing between the marginally acceptable and explosively decompressive states.
And, just so we're clear, please don't drive for a couple of days on the temporary spare, either. It's not rated for that kind of workload.
Personally I wouldn't drive on that tire - if it delaminates while you're driving you're risking a blowout. You get bulges like that if the rubber basically separates from the various reinforcement plys in the tire and as the air in the tire heats up from driving, it'll slowly expand. All it takes then is something that pokes/cuts the bulge to turn your car into a three wheeler.
I'd slap on the spare tire and take this one down to your local tire place of least distrust. In the trunk, not on the car...
In some jurisdictions (including my own), driving with a tyre looking like that is illegal. There is a question about it on the driving test, and all such academic questions on the test are about things you must do, lest you be found to be in charge of a dangerous vehicle.
For your safety and others . Please change the tire. I had the same size bump on my run flats . Tires with less than 1k .
Don't risk the lives of others to save a few bucks. It will cost you more down the road ... No pun intended.
Your Tire has suffered internal failure of the layers that make up your tire. Replace immediately. Can you drive it to your Tire store? Yes. But maintain low speed and avoid potholes.
