Tire glide.

All else being equal, taller. But, all else is rarely equal.

 

I'll jump in with an answer that is not related to the question.

I just installed Miclien Energy Saver A/T tires. Standard size. I am delighted with how much quieter they are than the OEM, and they "seem" to glide effortlessly. Yesterday was my first trip in the rain, and there was no perceived issue there. I have not had them long enough to cite a fuel savings number, but I suspect it will be somewhat improved from the OEM ..... which were pretty darn good.

 

Yes as to tire width. The narrower the tire, generally the less rolling resistance, so the longer the glide. However, since the Prius needs to be optimized for safety, don't replace the standard width tires with narrower ones if you are still going to drive the car in traffic.

As to the diameter, taller tires will glide farther because they will not be so easily perturbed by imperfections in the pavement, and in some cases to a fly wheel effect. However, taller tires tend to require more power to accelerate and turn, so they generally get worse mpg than smaller diameter tires.

I think a better inquiry would be in to the best tires for mpg for the model of car you currently have. Do you have 15 or 17" wheels?

 

I would think the narrowest tire would give you the most mph as there would be less surface friction with the ground. The problem would be the ride would be much harsher as the tire's lower surface area would transmit the shocks of an uneven surface, (think potholes, etc.) to the car's body. Also, handling in corners and traction would be adversly affected.

Everything's a compromise.

 

my MPG went up 3-4MPG.

With respect to grip and rain they grip well, as long as you do not try to put 44PSI in them. They also have soft sidewalls so there will added body roll.

 

Both wide and narrow tires put the same amount of rubber on the road. The wider tire will have a shorter patch, while the narrow tire will have a longer patch.

Wide patches are best for cornering loads, longer patches accelerate and brake with less slip.

 

I have always thought that contact patch should be independent of aspect ratio of the tire. It should be weight of the car / tire pressure (with perhaps a finagle factor in there somewhere). 3042 pounds / 42 pounds per square inch = 72 square inches of contact patch (18in^2 per tire). Yes?

 

A stickier tire on the 8" wheel could have produced a similar effect. Tire compound/design will trump width in most cases until you are putting down high HP/TQ numbers.

 

Keep in mind that your tire size choice will effect your speedometer such that if there are more or less tire revolutions per mile that your MPG indicated may be different than actual due to speedometer error. The GenII speedometer generally reads 2mph too fast and the GenIII is between 1-2mph too fast. Now is the computer MPG computed from the speedometer or an internal not viewable speed monitoring system? I ask because the Scangauge II reads correct mph (verified with GPS) while the speedometer reads too fast.

Anyway, keep in mind that the wider tire also increase coefficient drag due to larger frontal area. A wide tire has to push through a wider area of air compared to a narrow tire.

Regardless, I'd make sure you get a LRR rated tire otherwise the above are moot points.

 

I'm not sure what you mean by comparing LRR tires to regular tires. You can always click the link in my signature to check out your options for LRR tires then compare them to other tires at TireRack.com or Discount Tire.

 

We have Michelin Energy Saver tires on our Prius, size 195x65x15. All four tires inflated to max sidewall pressure of 44 PSI of Nitrogen from Costco were we bought the tires.

We have about 38,000 miles on them and yes, we gained 2-3 mpg real world increase over the stock Yokohama Avid tires that came from the factory. Looks like we will get at least 15,000 to 20,000 miles on them before they have to be replaced. The extra gain in MPG offsets the initial price.

These tires are quiet and glide forever. In my opinion they are well worth the price and I believe they are the most fuel efficient tires in the world. If they are not which tire is.......

alfon