(I'm posting this in the fuel economy section instead of the tire section because this is all about figuring out which tire is better for MPG.)
Within the past year or so, I happened to score both a set of nearly new Dunlop Enasaves on alloys AND a set of nearly new Bridgestone Potenza RE92's on steelies.
Both are 165/65R14 size.
For those who may not know, the RE92 was the factory tire on the 2000-2006 Honda Insight hybrid, which still holds the crown as the most efficient gasoline hybrid sold. That tire is widely regarded in the Insight community as the best tire for MPG. (The Insight has very low aerodynamic drag, so reducing rolling resistance is key, because it makes up a higher proportion of total drag than the average car.)
I had a 2000 Insight for a couple of years. That's my car, above -- 1.0L engine, 5-speed. It was an absolutely amazing machine. Honda let its engineers go farther in pursuit of efficiency than any other production car except for the smaller, super streamlined VW XL-1 diesel hybrid. I could regularly get 100+ MPG tanks in mine, in summer weather. Eco-modified, of course.
Long story short: in my simple coastdown test, both tires rolled almost identical distances.
Testing details:
-- Ambient temperature: 24 C / 75 F
-- Tire pressure: 55 PSI / 3.8 bar
-- Tread depth: Enasave = 5.6 mm / 0.22", RE92 = 5.1 mm / 0.20"
-- Each set of tires got 4 coastdown runs, plus one last run after switching back to the first set.
-- The testing area is 2 blocks from where the car was parked overnight, so tire temperature should have been extremely close for both sets (but not measured).
-- The car was positioned at the same point on a slight hill, then allowed to roll out to a level section, where the distance was marked on the pavement.
-- To minimize the potential of brake drag affecting the results, the car was stopped/positioned using only the handbrake rather than the hydraulic (foot) brakes.
Results:
-- The average coastdown distance was around 34.7 m / 112 ft.
-- The end points for all 9 runs were clustered within the last 122 cm / 48 inches!
-- 34.6 m / 113.6 ft ... Ensave average coastdown distance
-- 34.7 m / 113.7 ft ... RE92 average coastdown distance
Conclusion?
How much faith would you put in this test? Enough to say that both tires appear to have similar rolling resistance? It sure seems that way to me.
I'd be interested to hear from our resident tire engineer on the test method.
If it's a valid & accurate test, then Insight owners should be happy to know the Enasave appears to be a viable alternative to the RE92 in terms of preserving MPG performance. (There are always fears in the Insight community that the RE92 is going to be discontinued soon. Although I it was still available as of a year or 2 ago as far as I know.)
I'm not sure which tire costs more, but that might be a consideration too.