All the donuts you could want!

[OfficeLinebacker]

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!

[IndyIan]

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

[OfficeLinebacker]

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.

[Red]

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

[johnmyster]

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...

[achang1]

aw i thought he meant donuts like jelly filled.

[tasdrouille]

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?

[metromizer]

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.

[OfficeLinebacker]

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.

[OfficeLinebacker]

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!

[OfficeLinebacker]

Originally Posted by tasdrouille

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.

Given that they're designed to be used safely below 50 MPH, and support more weight than the stock tires (being smaller, that corner of the car is lower, thus more weight) and can be used on the driven and/or steering wheels, I don't think the thing is going to blow out unexpectedly.

If you're conscientious about checking it and keeping the pressures up and the speeds down, it's not just going to spontaneously explode on you one day.

As I tread further out on my limb, I'd be wiling to bet that the compounds used are softer, thus giving more grip in relation to width, but therefore wear much faster, so I bet the thing would go bald before it went splat, and you can visually check for that.

[Red]

Originally Posted by johnmyster

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...

A 'stang?

On my Insight, the spare is part of the rear crumple zone......

[johnmyster]

Factory supercharged T-Bird. Not ecomodded. 91 octane or better please. 3600 pound or so. Thing would move. 360 ft.lbs of torque at 2600 rpm, plus a real back seat and trunk.

[achang1]

why dont you just get "narrowest" rims/tires with your bolt pattern?

[Red]

Insight wheels are 4x100m and they are a 14" rim. You probably aren't going to find something lighter or narrower

[Will]

Honestly I think it would be a very bad idea to put donuts on a car and use them as normal tires. I am sure with enough research you can come up with a better option. It's just too much risk. If you lost control and hit someone how would you feel? That is a very big thing to think about, and a bigger thing to live with.

[OfficeLinebacker]

Originally Posted by Will

Honestly I think it would be a very bad idea to put donuts on a car and use them as normal tires. I am sure with enough research you can come up with a better option. It's just too much risk. If you lost control and hit someone how would you feel? That is a very big thing to think about, and a bigger thing to live with.

Is not 'economy' part of the name of this board? What other options are going to be at least as efficient and economical as $50 out the door? I think that driving with the throttle stuck in a certain position, turning off the engine while driving, and various other behaviors discussed on this board are at least as risky.

Note this is all opinion.

I think that with an equal amount of vigilance, it can be as safe as driving around with the engine off sometimes or with tires inflated to 70 PSI.

That all said, I am not a practitioner of said practice, just the person with the most potential to do so.

Heck, maybe I'll slap them on, do a few runs, and find out that there's no mileage improvement. Or that the car feels way too unstable.

I always find the handling limits of my car with no one else around whenever I make significant mods, so that won't be an issue.

I'm a risk-taker, but I don't believe in risking the safety/resources of others for my own benefit. I'll accept totaling my car and injuring myself in the name of discovery, but not even putting a dent in another's car, much less injuring another person.

[SmartTrucker]

I must say you are completely comfortable with yourself if you're willing to drive around with a full set of donuts on .

I'm waiting to hear your results though and do hope you keep the speed down and just use it for in town driving. That's where you should see the biggest gain in my opinion anyway is through lesser rr. Not sure how much of an aero improvement they are.

[OfficeLinebacker]

Oh I must have not explained myself well, it's only two donuts and an FWD car so they'd go on the back axle.

I also agree that the lower weight would help most with stopping and starting.

Thanks for the non-flame, yes I am comfortable w/myself, at times too much--I go around covered in grease and old clothing, and sometimes forget myself.

I'm much more interested in results than looks, though I admit at times looking good is crucial to results. However this is why I am probably switching my business from IT consulting to being a mechanic. Mechanics are expected to be dingy and operate out of dirty industrial parks, which is where I feel most at home. Managing expectations I suppose.

[OfficeLinebacker]

Originally Posted by achang1

aw i thought he meant donuts like jelly filled.

No those would be doughnuts, which could also refer to burnouts with the wheel at lock.