Quote:
Originally Posted by eyesoreracing
Speaking of low RRC tires, we're planning to use Bridgestone B381s in either 185/65-14 or 185/70-14 (trying to determine what will fit). If anybody has any better suggestions, speak now, or talk **** about how stupid we are later, your call...
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You might check the Consumer Reports tire ratings since they also rate rolling resistance. Since I don't have to deal with much snow and ice in Alabama, I went with Sumitomo T4s and they worked out just fine. Best of all, they were $50/ea. from TireRack.
I jumped my tire diameter up from 175/65-14 to 175/70-14 and saved an extra 5% in the tire revolutions per mile. I have to 'adjust' trip and MPG due to the lower revs but the BSFC data suggests you might use every bit to increase in the final engine to wheel rpm ratio you can get. ... just a thought.
One option would be to get a second pair of wheels to put experimental tires on. This would let you try a pair of 'racing bicycle' style tires on the drive wheels (aka., largest diameter, smallest width, highest pressure) for your mileage run. In my testing, I found the larger diameter 175/70-14 were more stable, probably from the gyroscopic effect, and reduced Prius wander.
Of course there is the 'clown car' approach, four donuts, or compact spares. The smaller diameter would result in more revolutions per mile for a higher indicated MPH and MPG. The car would indicate say 70 mph but be actually closer to 60 mph. <GRINS>
We see this in the Prius community when folks complain about a loss of mileage after putting on new tires. The 'folk lore' is the tires have to 'broken-in' when in fact they just have to wear down the tread, reducing the diameter, again.
The other nice thing about the Sumitomo T4s, they have a sidewall maximum pressure of 51 psi. But I'm out for MPG performance in urban commuting and most Alabama roads are in fair shape, not a lot of patches or pot holes.
Have you considered doing a 4-wheel alignment? More for keeping tread on the tires, the literature indicates suggests it has an impact on rolling resistance. Given the high miles on the 'donor car,' I suspect the wheel geometry may have suffered a little 'road rash wear.'
Bob Wilson