Has anyone thought of using 4 'donut' tires?

[BumblingB]

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?

[GasSavers_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

[GasSavers_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.

[GasSavers_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.

[GasSavers_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.