Has anyone thought of using 4 'donut' tires?

[Peakster]

Just came back from a fill and my tank turned out lousy (41.22 mpg). I'd say the donuts for the front wheels are busted. I'll keep them on for a while (I love the acceleration; the Geo can reach 5000rpm in 5th gear with no problem. I also really like the long glides when coasting), but I will eventually put my old winter tires back on. Maybe installing them in the rear would work out better.

[skewbe]

Sorry they arent working, but nice to know that they glide well though. I suppose if you could gear up, you could overcome the smaller diameter and enjoy longer glides, but they are still 3000 mile tires.

How are they at high speed cornering?

[Peakster]

Originally Posted by skewbe

Sorry they arent working, but nice to know that they glide well though. I suppose if you could gear up, you could overcome the smaller diameter and enjoy longer glides, but they are still 3000 mile tires.

How are they at high speed cornering?

I thought about getting 2 more donut tires from a larger vehicle so the Geo's wheel diameter would be the same (or larger), but the 3000 mile life makes it not worth it. I haven't tried high speed cornering with the tires yet because it's still icy outside (Although I once had the Scangauge reading well over 90mph on flat road with them ) .

[red91sit]

Originally Posted by Peakster

I thought about getting 2 more donut tires from a larger vehicle so the Geo's wheel diameter would be the same (or larger), but the 3000 mile life makes it not worth it. I haven't tried high speed cornering with the tires yet because it's still icy outside (Although I once had the Scangauge reading well over 90mph on flat road with them ) .

Perhpaps its the more agressive driving that is hurting the fuel econ.?

[Peakster]

I just put on my 'real' tires back on today and drove the speed limit (62mph) on the highway. After cruising for a while, I reset the SG and was shocked to see that I was only getting 35.6mpg average for that speed. It's just too cold and ugly out (12*F and 20mph winds) to make any assessment. Only A-B-A testing will show for sure.

By the way, there was some noticeable wear on the donut tires when I took them off. The odometer showed 249,053.1 kms when I put the bigger tires back on, so I'll be sure to make the conversions for my next fill, due to the different tire sizes.

[larryg]

Actually, the contact patch is more dependent on PSI than tire size (unless you get really big) next time you look at your tires, notice that they are not perfectly round, they are a little flat where they touch the ground. this is due to the tire being deformed where it touches the ground by the weight of the car. What holds up the weight of the car? the air in the tires, (let it out and see what happens if you don't believe me) The tires deform until the size of the contact patch in square inches X the psi in the tires = the weight of the car.
In fact, you can weigh the car by using 2 sheets of paper, A ruler and a tire gauge. Just put the two pieces of paper under the tire in the front and rear until you cant slide it in any more, then measure the distance between them, do it side to side and measure. the first number X the second number = area of contact patch, multiply by pressure in the tire for the weight on that tire. do all four tires, you get the weight of the car. So, big tires, little tires, contact patch the same, unless you change the air pressure or the weight of the car.

[Peakster]

Originally Posted by larryg

Actually, the contact patch is more dependent on PSI than tire size (unless you get really big)
...So, big tires, little tires, contact patch the same, unless you change the air pressure or the weight of the car.

The donuts were inflated to the sidewall number which is 60 psi, so they were higher than my "normal" tires that are 44 psi. Also, wouldn't the amount of surface area of the tire touching the ground take into play too (ie. less width to the donut tire)?

[larryg]

You're right the increase in pressure in this case gives you about 1/3 less tire contact area with the road.

[hobbs1808]

This has got to be the dumbest thread I have ever seen, there is a reason donut tires tell you not to go over a certain speed, its because they are cheaply made tires made for short distances. Gas mileage is not going to matter to you when your in the hopital for going off the road because your donut tire exploded on the highway and caused injuries to your self and others. Next somebody will be saying to try them in the snow because their skinny and they might work like ice skates

[theholycow]

This thread is also five and a half years old.