test results - the great tire search of 2008
 

Well, the tires are on and the first test drives are done.

Original thread.

The old tires (Kelly Charger 225/60/15) have been replaced with Hankook Dynapro A/S 235/75/15.

The Kelly's were 8.5 inches wide, 26 inch diameter, 795 revs per mile.
Hankooks are 7.5 inches wide 28 inch diameter, 760 revs per mile.

The Kelly's weren't far enough from the stock tires to throw the speedo off by more than 1 mph. The Hankooks are nearly the correct diameter for the vehicle.

Measuring the ratio with the tires on:
Kelly Charger: 3.65:1
Hankook: 3.52:1
With the stock tire: 3.55:1

The Hankook Dynapro A/S was rated 3rd best by Consumer Reports with above average (lower than average) rolling resistance. The ride noise was also rated to be above average. This is true. There is very little road noise produced by the Hankooks.

Facts and figures. This test is with a full tank of gasoline, no additives, stock tire pressures. This is on level surface, asphalt.

Kelly:
30 mph - 31 mpg
40 mph - 27 mpg
50 mph - 26-27 mpg
55 mph - 25-26 mpg
My test hill: neutral roll at 45 mph; 61 mpg peak (roll on at 45 mph, neutral at landmark)

Hankook:
30 mph - 37 mpg
40 mph - 35 mpg
50 mph - 27-29 mpg
55 mph - 26-27 mpg
My test hill: neutral roll at 45 mph; 82 mpg peak (roll on at 45 mph, neutral at landmark)

Those numbers are very surprising. I did not expect the difference to be so large!

Was your scangage recalibrated for the new diameter? I'm also suprised at such a large difference. If it's true, WOW!

I have to correct some of the data and add in an additional data set:

The Kelly's were 8.86 inches wide, 25.63 inch diameter, 786.90 revs per mile.
Hankooks are 6.8 inches wide, 28.9 inch diameter, 719 revs per mile.
Stock tires: 8.46 wide, 27.70 inch diameter, 728.17 revs per mile.

What I noticed right off the bat is that the increase is more apparent at lower speeds. What I need to do is get it on the highway and drive for a while at my normal speed. I suspect the numbers are skewed somehow. Maybe I had a tailwind pushing my truck's big fat butt down the road. Or I had gas, which made me lighter. Another point is that I was actually thinking when we changed the tires (an odd event). The wheels weigh 23.7 pounds each. The new tires weigh 30 pounds each, 53.7 pounds. The Chargers, even though they were smaller weighted 32.5 pounds, 56.2 pounds.

So this morning I'm going to pump the tires up to my more normal 38 lbs of air and throw in the Acetone and have at it. My local test loop is from Saline to Milan, Michigan, 13.3 miles. From the entrance to U.S. 23 to Ida (south of Milan) is dead flat. This is the same route I used to do my top end runs in my Stealth, not that there's anything wrong with that.

I also mounted the airtabs yesterday.

https://www.northernmichigansolar.com/airtab1.jpg

https://www.northernmichigansolar.com/airtab2.jpg

https://www.northernmichigansolar.com/airtab3.jpg

Mounting the airtabs in the middle of the tire experiment is bad. :(

Have you measured the tires yourself? Tire sizing can differ between manufacturers; they don't all measure the same way and they aren't all equally accurate.

Yeah, I realize that. But I'm not terribly concerned with that. What I'm looking for is what the entire aero package will do. The first set of data from the tires themselves, especially the downhill coast which is almost impossible to screw up because I've done it so many times (5x week / 9 years) seems pretty clear. Besides, I've given myself a hard deadline for the second part of the gas mileage episode which means I ain't got a lot of time.