How bad do you let your tires get before you replace them?
Performance drop?
hydroplane issues?
Down to wear bars?
Cords showing or almost bald?
I usually let them get pretty bad like to the wear bars or beyond.
Probably illegally so... not by choice, a destroyed economy and too much debt can force you into decisions not wise. I've had multiple blown tires. I never let the wife drive on tires like this.
The oldest pair I used was original 33 year old tires on a 33 year old pickup. The truck was nice/barn find kinda, and I couldn't afford to replace the honestly VERY nice deep tread right away. I limited speed to 55mph and watched like a hawk. They werent weatherchecked, it was mostly garaged most of it's life. I got probably 8-10,000 miles out of the tires that way afraid to drive faster but what I learned about raw age was that the tires become very brittle and tiny cracks turn into larger cracks. It's like chocolate you put in the freezer. I hit certain bad bumps and one deer corpse and it instantly put permanent cracks all thru the sidewall, I had to change the tires shortly after that. They probably would have lasted longer if I hadn't hit anything.
I've driven on multiple sets of 10+ year old tires and they all do this by around that point which is why the tire store stuff about 10 years being the safety limit is probably not far off. Some 12 year old tires, I accidentally got the valve stem stuck trying to air one up and it let the air out too much instead - the sidewall instantly cracked the rubber into a crumble pattern and the tire never aired back up again.
Weather checking is a real killer. I've had again, NICE tread, dang near new old stock but vehicle left outside 12 years. Thought I could safely drive on it for awhile. BIG difference in how quickly a tire degrades if you drive 70-75mph vs 55mph. I'd do it around town with no fear. I got maybe 6000 miles with no apparent wear or worsening of anything at the first 55mph then felt overconfident and sped up to 70-75mph. The right front one started separating and thumping more after 300 miles and I had to limp the car home at 40mph to find fully exposed steel cords an inch across by the time I pulled into the tire store at home.
Old tires have noticibly worse traction on wet. However if you have deep tread on snow they still work surprisingly well, that or mud. So if you can control when and where you drive they can be useable if you have to. Driving at 30mph around town on old or weather checked tires i'm not worried about sudden blowouts really. Driving with super low tread i'm only worried about braking in the wet or ice.
Don't live like this if you can help it. : P It's dangerous, and not just to you. Some of us are in bad, bad situations of everything falling apart trying to make it through one more week - thats when you do stupid crap like this and can only try to do it as intelligently as possible to reduce risk. Limping a car just to work at 30mph on old or weather checked tires tho usually isn't life or death, they still stop. No remaining tread in wet or ice is a different matter.
Right at this moment i've got 2/32's or a hair less on my rears, cuz it's been at that for too long to believe it still is, one front 3/32 mismatched to another newer front maybe 9/32. All my spares from a second set are weatherchecked. I wont drive it on ice. I'm JUST trying to limp thru a little longer around town until I see if I can get my other car fixed, which has new tires but has sat for 3 years due to something needing fixing. If I can't i'm going to have to put a new set on it now that snow has come but then I miss other bills once I do that.