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Discussion Starter #1
Has anyone tried putting four of the compact "donut" spares on and seeing what MPG you get?

If the size was common, I'd think you could find the inexpensively at junkyards and at tire stores that get them from people who swap them for "real" spares, but if matching the insight size is hard it could be an expensive proposition since you'd have to replace them quite often!

Charlie
 

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Discussion Starter #3
Yup, limited distance is why I was interested in finding an inexpensive supply of discarded ones. And limited speed is not problem for us hypermilers!

Charlie
 

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It has been explored in a different thread, and the mpg went down, as the tire height is smaller requiring higher rpm for same speed, AND they are not LRR tires... don't have time to find the link, but rest assurd it doesn't work.
 

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Discussion Starter #6
Very interesting. Thanks. Let me know if you happen across that old thread--I'd love to read it.

Charlie
 

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I believe Rick Reese tried it. He is over in Afghanistan now, or he probably would have replied. He, also was surprised at the results, but I'm sure it has to do with the rolling resistance, sidewall construction and compound of the tires.
robert
 

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I'm less concerned about the two rear tires as the front tires.

Have not researched it, but there might be permanent tires of that size somewhere....
 

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There are probably permanent tires that size, but I would be concerned about the footprint of the tire for braking, especially under a panic condition. Wet weather might be another concern with contact area. Check the weight of the rim and tire and compare them to the stock ones, because every time you accelerate, any difference in rotational inertia, if more, will take more energy. That also includes maintaining speed going up hills and accelerating down them. That's the main reason I got rid of the Sumitomos that were on my car when I got it. Sure the Bridgestones are a little rougher and a little noisier, but 90% of my driving is interstate and pretty hilly, and I doubt I can improve my mileage much and maintain the same safety measure.
robert
 

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I had a flat and had to drive on a spare for a few hours. The spare definitely kills your milage. I went from the mid-60s to low 50s in a fairly short time.
 

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I agree that the spare tire is not the way to go, but the stock 165 width tires are only narrow by today's "fat tires are cool" standards. Cars typically came with 135 or 155 width tires in the 1970s. For example, the MGB had 155 width tires, and weighed about 2300 pounds. The Lotus Elan had 145 width tires and weighed about 1800 pounds--the same as the Insight.

I hope that the surge of interest in hybrids will cause tire manufacturers to offer improved low rolling resistance tires that fit our cars. Reduced tire drag is probably the single biggest improvement possible on the existing cars.
 

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....excellent point, Dougie. You are right, earlier cars did have narrower tires and I dislike this whole trend toward fat, low profile shoes. In all of my vehicles (expect my Insights) I have always replaced the stock tires with a notch or two narrower.

Many of the old tires and sizes are available (at a high cost) from Coker Tire. They purchased many of Michelins old molds. For example, I bought a set of 185 SR 15 Michelin XZX for my 1973 Porsche 914.

Nowdays, technology has brought the ability to make even better tires for efficiency, with new HARD rubber compounds and good tread patterns. Hopefully there will be more demand for skinnier dimensions as well....
 

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Discussion Starter #13
I'm not sure though that narrower tires necessarily mean lower rolling resistance. For a given pressure, a wider tire actually has to deform less to support the weight of the vehicle, and that deformation is what causes rolling resistance. The flip side, or course, is that there is more rubber there deforming, but I think the net result may be that within reason, wider tires win.

Before someone uses the narrow tires on road racing bicycles as an example to prove that narrower tires have lower rolling resistance, I should hasten to point out that tests of bike tire rolling resistance actually show that all else equal, wider tires have lower rolling resistance. (It's rare for all else to be equal, since wider tires often have deeper, higher rolling resistance treads, and are rated for lower pressure, but some tires do come in different widths and are otherwise identical.) The reason that narrower tires are used on road racing bikes are that they have slightly lower weight and slightly lower wind resistance. (And because of people who think they have lower rolling resistance even though they don't.)

Charlie
 

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tires

Tire "contact" patch area is the key.

If they could design a tire like the tires used in motorcycle racing (tri shape) you would have very little contact area. Wouldn't work going around corners though.

WIllie
 

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In route home from Afghanistan. Anyway I did try both the spare tires (two on rear wheels) and four 145/80 Goodyear tires I bought on ebay (made in Brazil). Neither came close to the mpg of the bridgestones. Actually I thought the small tires had pretty good handling but they were not LRR. There is a government study somewhere posted that has the LRR numbers of various tires. The bridgestones are by far the best. (LRR I believe just means that it is 30% better than a normal radial). As a result there are a lot of range in the LRR name. I never bought them but thought about getting the Goodyear tires made for the prototype EV1. They guy wanted 400 for 10 year old unused tires with the project managers signature. I was tempted as they were the same size and had a even lower rolling resistance. I didn't buy them however as 10 years sitting probably effected their Rolling resistance. Have fun, RIck
 

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Rick Reece said:
In route home from Afghanistan. Anyway I did try both the spare tires (two on rear wheels) and four 145/80 Goodyear tires I bought on ebay (made in Brazil). Neither came close to the mpg of the bridgestones.
Afghanistan is a wild place. Thank-you for your service. Looks like it is hard to top the potenzas for mpg. My 2000 Insight is still rolling along on the original tires so when the time comes to replace them (soon) I plan to go with the bridgestones.

Thanks again. Regards for a good trip home.
 
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