Donut tires
 

I saw a video on youtube and the guy swapped out his normal wheel/tire combo and put donuts on the rear and netted 5mpg or so.

This brings a question to mind...

How much smaller are the donuts vs the normal tires?

Currently looking for a skinny wheel/tire combo for the rear, but am also looking at building a skirt setup.

What are your thoughts on 205 LRR's all around vs 205 fronts and 155 rears?

The main reason for the gain is
1. Higher air pressure

The distant 2nd is the actual size and aero.

My EV has donut spares on all 4 wheels, they are rated for 6x the total weight of my car.

However those donuts are exactly the right size for my car and the car was designed for bias tires.

So for the rear of your car just keeping lots of air in the tires will do almost exactly what donut spares do, if you downsize remember that your car has to be light enough on the backside for the tire or you won't really gain anything and might loose. I would actually weigh the back half and see what they are at if you want to test skinny small tires on the back and make sure you aren't getting too far into the weight rating on little tires.

Another concern is the fact that most small tires do not come LRR. But if you air them up it won't matter much. Just watch your weight ratings.

Cheers
Ryan

What gain? I'm totally not buying it.

I have been running the tires at 44psi, or sidewall max. The car came with Kumho KH25's in 205/65/16 and actually seem to be a pretty good all around tire. Much better in the rain than I thought they would be.
http://www.youtube.com/watch?v=b2K4j037TyY
Check out the video.

Found several tires that are rated well on pressure and weight but the funny thing is most of them for 15 and 16 inch from 205 down to 155 have similar tread widths. I know this does not mean that the actual contact patch is the same, but there is ONE tire that looks good, the Bridgestone Ecopia EP-02. 30% reduction in contact patch, a 2lb weight savings, thinner tread depth and a higher weight rating. Plus the round looking nature from the tread surface to rim looks like a semi boat tail. Another plus from what I hear is that the sidewall is slightly taller, which would rake to car slightly.

I don't know, just thinking out loud about a few other things I could do to help economy.
I get better combined miles than I do straight hwy and I think it is down to how much I e-on-c in town. Need to do that more on the hwy.

Getting a few mods together to try after my Ultragauge gets here.

The donuts have a smaller surface area, they could have a smaller rolling resistance.

Well, since no one know what kind of car you drive.....
because you don't have it listed in your avitar....like 90% of us do

and you don't tell us in your current post what kind of car you drive.....

And you are referring to some guy on youtube.......

as opposed to referring to ...oh any one of 10 different threads on tires sizes right here.....

yeah, you really are talking to yourself.

But the good news is you really have a nut lose behind the wheel if you would consider driving on a dounut tire permanently.

so it really doesn't matter what your car is.
Oh and the disclaimer: Don't come sue this forum when you lose total control of your vehicle, even though you were only going slow. I'm as serious as a heart attack.

Never considered driving on donuts permanently, just considering going skinnier on the rear tires, but only if it can be done safely.

My temporary spare is only 135 wide.

Don't use temporary spares permanently, they're not designed for it.

They'll easily take more than the 50mph / 50 miles labels on them, but they result in serious problems regarding handling and braking.
Especially in the wet, they quickly get skittish .

I don't really buy the gain in the video either, obviously if your odometer is messed up by the tires you can see all sorts of amazing gains.

Donut spares on my C-car yielded a max range of 50 miles, of coarse I was running 72v but it was a relatively impressive number I'm told. I could coast on flat smooth pavement upwards of 2 miles.

Is the potential gain really worth messing up your speedo and driving on hard rubber tires though?

The only way the donut spares will gain you is if the tires are WAY overrated for the weight you put on them, if your paticular car is even 1/3 of the weight rating of the donut spares expect
NO GAIN and very poor wear and life.

I agree with most of that, but like any tire they can last a long time if they are used at a light enough weight. On my C-car some of the donut spares lasted over 10 years, although admittedly I could never break 55mph on flat ground. The donuts are rated at the speed and mileage at their weight limit, many are rated at over 2000lbs EACH, obviously if you run MUCH MUCH less weight than that they can be driven faster (they usually need balancing though) (the rating is based on max weight and speed that causes overheating and failure)

I found them to be VERY sturdy built tires, even fully deflated they looked like they had air in them and even with severe weather checking they lasted and lasted until I finally got a slow leak in 1st one than another. Between me and the previous owners we had over 8k on the tires, some have over 10k now. Which is fairly impressive for a tempory spare that I can buy for $5 with a rim at the junkyard. Most are 3 ply all around like old balloon tires solid nylon core from sidewall to the tread, all one material, very strong, very stiff, very bumpy.

Cheers
Ryan

I've gone back in time and went through my records.
At best my temporary spare was used for some 1600 km - 1000 miles - yet it's almost worn down to the limit.
(That was one additional reason to throw it out of the car.)
But it was used at the load it is intended for - underneath a 3300 lbs car at around 63 mph tops.

I wouldn't think of using 2 of them on my car, far less the four that some brave soul tested :turtle:


Using them at far lower weights will likely help improve their lifespan, but how many miles did you do in those 10 years ?

Standards for Donut Spares
 

A couple of thoughts:

Donut spares are designed to go 50 miles at 50 mph. That does 2 things:

If you are familiar with the fatigue of materials, the number of cycles to failure can be described by the S-N curve for that material. All structural materials - including rubber - have similar S-N curves in that the more cycles that material has to endure, the stronger the part has to be. Put a different way, if a tire is designed to go 50 miles, it can be built to a lower strength level than a tire built to go 50,000 miles.

Ref: http://en.wikipedia.org/wiki/Fatigue_(material)

Also, the higher the speed capability, the higher the strength of the tire has to be. 50 mph tires are built weaker than 112 mph tires.

The net effect is that the government standards for Donut spares is quite a bit lower than for normal tires. There are no wear requirements. There are no traction requirements.

Donut spares are also manufactured to lower quality standards, since everyone in manufacturing knows what their intended purpose is.

Overall, using Donut spares for purposes other than what they were intended for involves some risks that normal tires do not have.

Yer just asking fer the attention of the police...cause we all know they like donuts! :D







*this was meant as a joke...please don't take it seriously or the joke police will be all over you, too! ;)

Who Me...???http://i536.photobucket.com/albums/f...esCA1QK1W9.jpg


:D


>

I've seen a couple people at the track running them on the front of their cars (trapping 100+.) Really dumb

you got a good life insurance policy? if so does your underwriter know you are doing stuff this dumb?

donuts=temporary

just enough to get you to a place for your real tire to get fixed...

nothing more.

please don't try this

Another reason that donut spares are not recommended for long-term use is because if you put a donut on a drive wheel and use it for long periods of time, you'll prematurely wear out your differential.

the guy in the video put the donuts on the back, not affecting the odometer at all, as long as the donuts are on the non drive wheels and you dont have abs or a car with stability control or traction control you will be fine

wow...you really said......
 

Would you mind setting up your credentials first??????
Oh, and your big fat bank account number.

But thank goodness the odometer is ok.....man that was the BIG worry. And thanks for reassuring him that he 'will be fine'!!!!!!!!!

Did you even read the previous posts?

maybe just read what capriRacer said.....he's kinda a tire expert....

I am just STUNNED at the stupidity of the statement 'you will be fine'!

Tyre manufacturers like Michelin, advise their customers to put the best tyres on the rear of a car.

The reasoning being that people will more easily adapt to understeer than cope with massive oversteer once the rear tyres lose it.

We've had the good tires on front/back debate and even though I know full well the insurance/tire companies recommend the good ones on the back, I prefer the good ones on the front because where I live I need traction for starting, stopping, and steering first and foremost, and having had several vehicles with rear weight bias, I'm equipped to handle any oversteer that *may or may not* occur. The thing about some official recommendations is that they have to work for the lowest common denominator- a Cover Your *** sorta thing.

^ I agree. Regardless of FWD/4WD/AWD/RWD, the good tires belong on the front. I'd much rather deal with some oversteer than not be able to stop or turn. Understeer sucks bigtime.

you obviously missed the whole point of my post
it was purely to state that the odometer wouldn't be affected, i mentioned nothing about this being safe or recommended i saw some false information here and decided to share my 2 cents, if you do not like my comments don't read them or simply ask me if you are confused as to what i was talking about im aware some people can be vague when talking on the internet and others can take what was said the wrong way

and please keep your stupidity name calling to yourself

mpg increase gain with donuts in the back comes from friction=traction loss. I'm riding on 165's on all 4 corners and have 0 problems, would I got skinnier? - may be. rear wheels is the place to start since on fwd car most of the weight should be on the front.

Implying a large difference... Reality, however, shows that the weight bias is normally ~60/40 on almost all cars, afaik.

ok, I'll post your entire comment.

Plural Donuts implies that having more than just the spare.
intentionally having more than one.
you'll be fine.

Who cares if the speedo is off when used as intended.....TEMPORARY.
Who cares about the abs etc if it is TEMPORARY.
You refer to the video, where the use IS NOT TEMPORARY.:eek:

You, (impling someone other than the man in the video) will be fine doing the same thing.
That'is saying that it's ok to dupicate 2 rear donuts on a permanent basis.

Sorry, I don't read minds.......I read words.

Gotta stand by what I said.:thumbup:

for clarity, 165 is NOT a TEMPORARY DONUT TIRE. correct?