Donut tires

[BHarvey]

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?

[rmay635703]

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

[Frank Lee]

What gain? I'm totally not buying it.

[BHarvey]

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.

[KITT222]

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

[mcrews]

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.

[BHarvey]

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

[euromodder]

Originally Posted by BHarvey

How much smaller are the donuts vs the normal tires?

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 .

[rmay635703]

Originally Posted by Frank Lee

What gain? I'm totally not buying it.

Originally Posted by Ryan May

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.

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.

Originally Posted by euromodder

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 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

[euromodder]

Originally Posted by rmay635703

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

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


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