All the donuts you could want!
 

I went to a used tire place yesterday and asked if they had any donuts. The owner let my son and I to "donut alley." It's basically a big truck and a trailer full of donuts. We dug through the stuff for about an hour and came up with about six 14" donuts with 4-bolt 100mm pattern. Two of them were exact matches so we bought them for $25/ea. The asking price was $35/ea but the owner was cool.

So anyway if you look around, you can find these deals!

I assume you are going to put the donuts on your car? I all for abusing the safety margins of tire design but I think you may attract some unwanted attention from the police. Also I would do some wet road stopping tests.

I have found that trailer tires have no where near the winter traction of even crappy all season tires and maybe donuts are the same?

I am interested in seeing the difference in rolling resistence though, I would assume donuts are better but by how much?
Ian

The rolling resistance is probably marginally better, but the aero affects are where it's at.

Trust me, the cops around here don't care.

Are you looking to reuse the rim or the whole doughnut? While they do have a lower RR and contact patch, they still weren't designed for long term use or high speed. Not to rain on your parade or anything

Once I had a car where the (alloy) spare rim was considered disposeable. Sports car, Ford wanted to save weight. The rim was so light, it wasn't designed to outlive the spare. A limited mileage tire AND rim...

aw i thought he meant donuts like jelly filled.:mad:

I would like to focus solely on the safety aspect of running small spare tires in the back. More precisely on the probabillity of a sudden and unexpected blowout from what would be normal use for regular tires. I don't care about traction, I don't care about wear, I don't care about sudden failure from hitting a pot hole, I can compensate through the way I drive to account for that. All I care about is a which point will it unexpectedly fail if I drive on the highway at 50 mph. Assuming the spares are relatively new, say less than 4 years, or even brand new.

How are those tires constructed? Are they significantly structurally different than regular tires?

Space saver spares, if that's what you're talking about, have a very limited mileage lifetime.

I don't think you'd be happy using them as everyday tires, even if they were free.

I haven't put the donuts on the car so no danger there. The trailer we dug through has several tires only in it. The owner of the place said sometimes they replace the actual tire on the donut (presumably quite rarely). I didn't look closely but the tires appeared of normal The vast majority of the donuts were new or like-new. Owner cited trade in for full sized spare as primary reason to dispose of donut.

I think that the main issue is heat dissipation. There's not much rubber to absorb the heat, that's the limiting factor when it comes to speed ratings, is heat dissipation and resistance.

That, and the width of the tread is like half the stock width. The thing is smaller so it turns faster at any given speed so you can assume the tread life, is less than half. Add in that it's not designed to last and make your own assumptions.

That all said, we all know of cars we've seen where the people have driven around on the spare for weeks with no ill effects other than to their reputation. Also, I am sure different brands of rubber and different manuf. of rims make a big difference. The ones I picked out are Firestones, which have a reputation for great tread life.

I also admit that I wonder just how bad the car would oversteer with the donuts on the rear. Given that the car pushes like a dump truck in stock trim, and has a rear sway bar about the diameter of a #2 pencil, it'd be fun to drift with it. Of course that's completely counter to what we're trying to accomplish here, but I am a contrarian among contrarians. Don't flame me!