Has anyone thought of using 4 'donut' tires?

[Peakster]

I'm not sure if this has been proposed for an experiment in the past, but I'll ask anyways:

Has anyone tried replacing all 4 of their tires with the skinny "donut" tires that can be inflated to 75psi? Almost all donut tires are designed to last over 5,000km (3,100 miles) yet they are rarely used and can be found in junk yards for a song and dance.

Makes me think of how easy it is to pedal speed bikes with the skinny tires compared to the thick tires of mountain bikes. The thinner tires might improve aerodynamics too?

- Peakster

[rh77]

Originally Posted by Peakster

I'm not sure if this has been proposed for an experiment in the past, but I'll ask anyways:

Has anyone tried replacing all 4 of their tires with the skinny "donut" tires that can be inflated to 75psi? Almost all donut tires are designed to last over 5,000km (3,100 miles) yet they are rarely used and can be found in junk yards for a song and dance.

Makes me think of how easy it is to pedal speed bikes with the skinny tires compared to the thick tires of mountain bikes. The thinner tires might improve aerodynamics too?

- Peakster

That is a good idea, but from my experience with do-nut spares, the recommended distance is to last 50 miles and the speed is limited to 45 mph. I wore one out once because I had to work over a Holiday weekend and the tire stores were closed. The tread was nearly gone over about 125 miles and 55-60 mph.

I have wanted a lighter tire and less of a footprint to propel, but it just seems to be cost-ineffective right now.

RH77

[ketel0ne]

http://www.lucasclassictires.com/

Portawalls would work, you would need wheels though, could be a challenge.

[onegammyleg]

Changing to a significantly narrower tyre than what the car came with when new could encur fines from those blue guys and in some places ANY deviation from standard can get you a defect notice.

[zpiloto]

I think you would need to see how much it would increase the rpms for a given speed and see how that would affect the FE. The increase in RPM might cancel the other benifets.

[kickflipjr]

I think 2 donuts in the rear might help a bit and be safer.

plus it would be easier to make rear wheel skirts

[onegammyleg]

MMM -- donuts

[onegammyleg]

Hi theclencher -¨and one pair of smaller and really skinny tires¨

In many countires missmatched tyres like this would result in a defect notice and/or a fine.
It may be law , but perhaps the cops may not be eager (or observant) to chase it up.

I remember our local chineese resturaunt owner had a brand NEW Benz , and he had some after market (but very high quality) mags and tyres fitted.
Perhaps it was racially motivated , perhaps not , but a cop stopped him and defected his car , giving him 7 days to change back to original equipment or go unregistered.

[psyshack]

Okmulgee, Ok. is the only place in my life where Ive seen 4 donut tires on cars. You see this from the welfare crowd. its there last chance effort to stay ,oble around here. And it dosent last long.

[rh77]

Originally Posted by onegammyleg

Changing to a significantly narrower tyre than what the car came with when new could encur fines from those blue guys and in some places ANY deviation from standard can get you a defect notice.

I've seen cars that look like skateboards, Caprices with 22-inch chrome wheels, racing-only tires on the street, dark tint, etc. It seems like around here either you've committed a crime, look like a drug car, or are speeding to get busted. For state inspections (50-states, 50 different methods, some states no inspection at all) -- just take in the stock wheels (or here get a shop you know will pass you). The Police is generally pretty busy with other stuff.

Originally Posted by theclencher

Geez- I thought our cops were ******!

Police Officers are out there putting their lives on the line, so I see it a bit differently.

RH77

[Wazabi Owner]

About a month and a half ago I had a flat on my Insight and had to put the donut on. Mileage dropped SIGNIFICANTLY just from using one over my stock RE92's. So at least with a vehicle that is already running LRR tires it should drop the mileage . For something else who knows?

[elg]

I?ve done it in mpg purpose !

First test Saab 9000i.
(donut for Saab is 115/70-16, in stock 185/65-15)
Got 4 "donuts" from junkyard and tested to run down a hill. Ran about 5 times (let the car roll free and messured distance). Then I changed back to stock wheels I got in the trunk, just to make sure that the mass of the car should be an other. Ran 5 times again and in total there was a very small hint that the "donuts" were better but I desided that was just faith or something. Much more less than 1%.
BUT I started the downhill-test with the recomended 2.1 bar pressure in stock tire and there was a clear difference when I later filled them to 3.5 bar.
That was for real !
Second test with the Saab was out on the road. No Difference at all.
Third test was highspeed test, about the drag. I let the car slow down in neutral from 150km/h to 100km/h on a flat not windy road. No dif.

This was maybe two years ago but I belive also had them on for a week but no dif.

The Nissan I now driving has also been under the donut test, I?m not finished yet but after 2000km I blow one front tire so it may take a while till I put them on again.

At all testings, Speed and distance were compared to GPS. Donut pressure around 4 bar.

For my personal, narrow tires=less drag and less friction.

// Elg

[Ryland]

the other day I took my spare donut out of the trunk and inflated it, realized it weighed a ton, so I set it on the scale, 21 pounds, compared to 23 pounds of my vx rims and 165/70 tires (weight new) so I'm temped to replace my donut with another vx rim, and a narrow tire, something like a 155/80-13, as it would be narrower and lighter then a wider tire, hell, next time I get tires I might just get 155/80's all around, unless I can find some 145/80-13's like VW diesel rabbits came with.

[jolt-tsp]

Unless you never exceed 30mph, I wouldn't do this. If you need to brake hard, you're putting all the weight up front, spread across two tires that combined are maybe the width of one normal tire. Your 60-0 distances will be far increased. Also, swerving to avoid an accident could very well put you out of control.

[omgwtfbyobbq]

Heh, I made the same claim and got scolded by a physics grad. Ideally, braking ability, with solid tires, only depends on the

normal force and coefficient of friction between the surfaces.
As we start using two surfaces that can't be approximated as solid, like sticky drag racing tires on asphalt, or mountain bike tires on sand, then the area plays a significant part. But for donuts, the biggest risk is wear and inflation. Wear can be monitered, and inflation is just noting the speed rating/max pressure and never exceeding that. Braking will primarily be influenced by the difference in tire compound.

[elg]

Just to make sure no missunderstandings.
Donut I used were with the flat driving suface and made by michelin.

There are one other model, almost like a tire for motorcykle, I tried that one on the car but after inflated 5 bar the surface to the ground was the same almost, depressed by cars weight so I never tested these.

Maybe how ever the pattern of my Donut (The tested version) is very small and narrow one with a lot of friction surface to ground, the legal 155 has wide water canals. I have not messured that, other with my sight.

This is a guess but anyway, donut of 115 compared to a 145 or 155mm tire of low friction type, I don?t belive the difference is that big. In friction matters. Ofcause in aerodynamic even if it?s a small one.
BUT don?t go fast on Donuts and don?t go long, It?s just for temparary use !!! A few km before front tire blowed my 3year son was in the car.

So there is a lot to do for saving money and fuel but this trick is maybe the last one to do.
Here VW sold a model called Lupo 3L, diesel version, that one came with 145mm Michelins and these were special Low-friction. Thats what I?m going for instead of donuts.

// elg

[Peakster]

P.S. Peakster- what are you doing sitting on that hood- you'll crush it!

Also what is that thing in your avatar?

I was extra careful not to crush it, so there was no damage to the car when I took that picture.

As for the avatar, that's my 2005 RezMobile Miser that I made in my 1st year university. I have a webpage set up for the vehicle at http://www.cardomain.com/ride/567996 if you want to see it sometime.

[Ryland]

I was looking around on some tire web sites, and it looks like everyone but the US has narrow tires avalible to them, down to 135/85-13" it's crazy, why are amaricans obsessed with big cars, wide tires, and poor gas mileage?

[red91sit]

another thing to think about, 4 skinny tires at 40psi have the same size contact patch as a regular tire at 40psi, since they're all applying 40psi to the ground, it uses the same amount of area to support the weight of the vehicle.

[jolt-tsp]

Originally Posted by theclencher

It is good practice to be able to quantify your claims- otherwise they are just speculation. Logical, educated guesses- yes, but unproven nonetheless.

While that made you look smart, you are incorrect. It is not a guess. When racing you deal largely with altering your contact patch and dealing with the effects. I'm not going to come on here and argue the fundamentals of traction. I gave my two sense, if you choose to ignore it, that no blood on my hands. If someone would like to bring a logical counter-argument to my attention, I will be more than happy to indulge them with my side of the argument.

[onegammyleg]

Hi Ryland -?why are amaricans obsessed with big cars, wide tires, and poor gas mileage??

Are they ?
,, Or are they just buying what they are allowed to get ? . perhaps the decision has already been made for them and that it is a sellers driven market not a buyers market as people believe.
Remember , the more gas you burn , the more tax money the government gets.
The more taxes they get the happier they are.

I dont think any government wants gas economy cars untill they have worked out how to tax the heebyjeebies out of a new fuel source and then they will push a move toward that and abandon gas.

Either way , we are well and trully .....

[rh77]

Post-War 1950's brought a boom of suburb home building, and the consequent system of roads. The automobile was/is a symbol of independence. Over time, people liked the luxury of big cars, even if they could get one cheap.

LSS, tradition has kept a majority of buyers, from this generation, to buy big cars (large percentage of the population). Without mass transit, younger generations follow the same pattern and tradition still holds. Fact is, most Americans don't care about gas mileage until it hits them hard in the wallet. A survey shows that we're getting "Greener", but is it a phase, and what will it produce?

Luckily, Honda and Toyota changed some minds in the '80s onward to shift the paradigm to smaller, more fuel efficient vehicles. Then the SUV craze started (incorrect perception of safety, convenience, and dominance). Companies had to follow the trend to keep profits up.

It can be argued: but if more people demand smaller cars, do you think we'll get them??? I'm thinking so...

RH77

edited for grammar, punctuation

[Matt Timion]

Originally Posted by onegammyleg

Hi Ryland -?why are amaricans obsessed with big cars, wide tires, and poor gas mileage??

Are they ?
,, Or are they just buying what they are allowed to get ? . perhaps the decision has already been made for them and that it is a sellers driven market not a buyers market as people believe.
Remember , the more gas you burn , the more tax money the government gets.
The more taxes they get the happier they are.

I dont think any government wants gas economy cars untill they have worked out how to tax the heebyjeebies out of a new fuel source and then they will push a move toward that and abandon gas.

Either way , we are well and trully .....

THis hits it on the head, and perhaps we're in need of a new thread as to not hijack this one.

I'm working on an article right now that will be syndicated about how most of Americas problems are due to the auto manufacturers not allowing us to have a better selection. Part of it I'm sure is due to the gov't safety regulations... which is another important article that must be written. Have fatalities gone DOWN as a result of stricter safety laws?

[diamondlarry]

Originally Posted by theclencher

The way I see it, ultimately it's the buyer that has the control, they make the purchase decision and fork over the money and they don't have a gun to their head. But the seller does everything in their power to influence the sale.

Buyers do have options; for example they could have been choosing crx's, sprints, metros, etc. for years and in vast numbers instead of F150s, Explorers, Suburbans, etc.... but they didn't. They could have but they didn't.

They opted to buy into the line the manufacturers were selling them- "safety", convenience, capability, status, all that. Never mind that it's largely a crock.

I noticed that during the 10 year (?) run of U.S. Metro sales, I never saw a single TV ad for them. Not one. Nothing in the newspapers either. I might have seen one in a mag, but it could have been a story about that ad and not the actual ad? HOWEVER, turn on the TV, open a newspaper, or read a mag and you will see a deluge of adverts for suvs and 4x4s.

I think the U.S. national fleet is composed of more gas hogs than necessary. (understatement of the year!) I blame the buyer for choosing to be selfish, gluttonous, and willfully ignorant. I blame the manufacturers for enabling that line of thought.

AMEN! I agree. Honda killed the Insight this year and I don't ever remember seeing an ad on TV, or anywhere for that matter, for the Insight.

[MetroMPG]

Trucks and SUVs make the automakers vastly more profit than sub-compact cars. It's no surprise which they are flogging harder for the sales.

[omgwtfbyobbq]

Originally Posted by jolt-tsp

While that made you look smart, you are incorrect. It is not a guess. When racing you deal largely with altering your contact patch and dealing with the effects. I'm not going to come on here and argue the fundamentals of traction. I gave my two sense, if you choose to ignore it, that no blood on my hands. If someone would like to bring a logical counter-argument to my attention, I will be more than happy to indulge them with my side of the argument.

We're on the complete opposite end of the spectrum. Racing tires have a very soft compound, and leave a lot of themselves on the road so to speak. In terms of economy, everyone here, given the chance, is probably running the hardest tire available at above the sidewall pressure rating, because that's where we can minimize rolling friction.
It's two completely different situations. On one hand, racing requires traction for high speed cornering and braking, so a high wear/sticky tire is an advantage, and because it's sticky, the greater the contact patch, the greater it sticks to the pavement, the greater the traction. Otoh, economy requires the minimization of traction (and speed) in order to maximize how well the cars roll. So in this case we're effectively dealing with two solid surfaces, and the difference in traction between a donut and a LRR tire is very small compared (heck, the donut might have better traction) to the LRR tire and the racing tire.

[jolt-tsp]

Originally Posted by theclencher

"I'm not going to come on here and argue the fundamentals of traction"- uh, isn't that exactly what you're doing?

No, that is what you're doing. I just came in and stated quick facts. The only thing I came back arguing was your assumption that I was making guesses.

What the issue may be, as omgwtfbyobbq pointed out was the opposite ideas of how we want our tires to perform. The a skinny tire with less traction will improve efficiency, there is no question about that. So if you're not at all concerned about safely, than my earlier comments can be disregarded, as I was speaking solely from a safety standpoint. I had read previously on this board where people speak against tailgating a semi for safety reasons, so I made the assumption that this was an issue of some importance for this board.

Your argument that a 5000 lbs Microbus stops on a dime with 100mm tires is not something I would consider a logical argument. So, as I mentioned, I will not argue that.

As far as the article you loosely described (that is also 20 years old) there are ways to use the traction of your other tires when one is dead.

-If the tire is on the inside of the car, it is not supporting hardly any weight during a skidpad test, so you would not expect a dramatic change in performance.
-On the outside rear, the LSD will put the torque to the inside where there is sufficient traction.
-On the outside front (this would be the hardest test to pass) the driver would have to use the torque of the vette (of which it has plenty) to keep the car from understeering.

The last test mentioned should show fair reduction in lateral g's, but should still be a street-able number. However, all that test shows us is that driving on one spare is not significantly more dangerous than driving on the four OE tires (on a RWD car with an LSD).

As I said, I was just offering information, I'm not trying to start an argument.

[onegammyleg]

?with an LSD?

Yeah , man , LSD , ime hearin ya .... KOOOL

[jolt-tsp]

Originally Posted by theclencher

That Bus can throw you right out of your seat on those 4 puny contact patches. That is something I can easily prove (to anyone in the Bus anyway) and it is germane to the subject. That the vehicle can stop and corner well with small contact patches is the issue. Millions of motorists in Kei cars and other dinky-tired vehicles can attest to that.

To say the traction is sufficient for your taste is different from saying that the contact patch makes no difference in stopping power. Getting thrown from your seat is no impressive feat and I would more than expect four spares to at least have that much grip.

I'm not saying your car will slide forever when you hit the brake, I'm just saying that your stopping distance will increase when you decrease the CoF (which occurs when using more narrow tires).

I fully understand if you feel the stopping power to be safe. I was only stating I do not feel compact spare tires will yeild a short enough stopping distance over about 35 mph for my taste.

While you know millions are not having problems stopping with their thin tires, a friend of mine running 165's on a 2200lbs Sentra rear ended a truck primarily due to the tires. He was only travelling 30 mph and following about 2 seconds behind the truck. He's a cautious driver that has some racing experiance, so I have no reason to doubt his reaction time.

[jolt-tsp]

Ya, I would expect a decent set of 175s or 185s slightly overinflated would be the norm for most the cars on this board. I ran 185s on my Civic until I turned it track car.

No 315s for me, 255 is going to be the upper limit on my Civic's new wheels