Lower rolling resistance: space saver spare tire donuts @70 psi, or RE92's @ 51 psi?

[MetroMPG]

To help visualize just HOW bad the donuts were compared to the RE92's (which henceforth shall be known as the Tires Of The Gods), a photo with the car at actual starting & stopping points:



I used a big parking lot that's empty on weekends. The starting "hill" isn't huge - maybe a couple of feet elevation change where the entrance/exit goes up to meet the road grade.

But it was enough of a slope that the car rolled ...

• 216.9 feet on the RE92's @ 51 psi (average of 5 runs).

• 155 feet on the donuts @ 70 psi (average of 2 runs).

• just 138.8 feet (!!) on the donuts @ 51 psi (average of 3 runs).

[Old Tele man]

...the numbers don't lie...but, the people cussing & discussing them might (ha,ha)

[Patrick]

Is it possible that the spares are bias-ply instead of radial? That would help to explain their poor performance.

[Frank Lee]

I drove the tempo on 4 donuts once while refinishing the stock wheels. I did have the distinct impression that rr and ride were poor vs stock- unfortunately, did no roll test tho'.

[eph]

Originally Posted by Kodak

I'm going with the Potenzas for a few reasons.

I know that tire pressure increases help rr with diminishing returns, and 51 is already pretty high.

Secondly, I think CapriRacer said that wider can be better for rr: Barry's Tire Tech, rolling resistance part 2

I'm also assuming that the donut spare is built heavy-duty, and that you won't be going fast enough for the improved aero of the skinnier tire to matter much.

But now you got me curious.

nah the artical is B.S sorry to say i run spares in the back all year around and first off, they last up to a year long and i pay 10 bucks each from the wreckers for them so thats 20 bucks per year cost driving can not be beat, Second* i use them in winter and believe it or not they are the best tire ive ever used they cut right threw the snow and ice, they are great in mud also, adn third if you dont believe me just watch this link Video: Can Skinnier Tires Increase Fuel Economy?

no cussing this is the truth right here just watch the vid i run these tires alll year around and no problems and i my self have calculated 4 mpg inrease and able to coste almost twice as long in neutral

yes youn are right watch this vid, this tells the truth