MAX Update No. 69: Two Tired to Test

| 3/6/2011 12:41:23 AM


Goodyear sent MAX a quartet of aptly named Goodyear Assurance Fuel Max tires, but it's been a bit of work to get them on because the Corrode Warrior (the rusted out 27 year old Toyota Corolla station wagon that served as MAX's parts donor) had 13” wheels, and nobody but nobody makes a low rolling resistance tire that small. The 14” Goodyears were the smallest I could find in that category (although that was last year, and as gasoline hurtles toward $4 a gallon, the tire companies are thinking things over) and finding wheels took some hunting. A fellow Locost builder bailed me out with a set of vintage 14” Toyota Snowflakes, a common alloy wheel on zootier Toyotas of the day, and they fit MAX just fine.

A number of MAX supporters have donated goods and materials to this project, and it's sure been a help to me, but out of sportsmanship I count them at their retail value when figuring these donations into MAX's budget. It's easy for me to put a dollar amount on the tires (P185/65R14, a google search showed me sources from $81.32 to $98) but it's a bit harder on the wheels. However, my friend salvaged them from a pile of aluminum scrap that was going to be melted down for some amateur foundry experiments and they're far from mint condition (the one in the photo is the nicest of the lot); I'm going to call them $40.

The big question is, will I be able to measure a significant fuel economy improvement. Goodyear says they're good for a 4% improvement on conventional cars, and it's not easy to measure improvements that subtle, but that doesn't mean a 4% improvement is more trouble than it's worth—for the estimated 65,000 mile life of the tires, a 4% improvement saves 2600 miles worth of's easy math for a car that gets 26 mpg (2600 miles saved is 100 gallons saved) and at today's gas prices that's more than the cost of the tires.

But for MAX, which currently gets 85 mpg, well, 2600 miles worth of fuel is only 30 gallons. Ah, but there's another factor to consider: MAX, with its light weight and low drag isn't just easy on fuel, it's easy on tires. I'd wager that tires will last twice as long on MAX as they do on conventional cars, and 4% of 130,000 miles is over 5,000 miles worth of fuel savings. And of course, if I can squeeze MAX's mileage up to 96 mpg with some tweaking and tuning, then a 4% improvement will be just then nudge MAX needs to hit our 100 mpg target, which will be worth a bunch in bragging rights.  I'm quite interested in doing comparison tests, and the only way to do them well is with two sets of wheels and tires, so I'm just as glad that the new tires didn't fit the old wheels.

Photo by Jack McCornack 

4/5/2011 7:23:21 AM

Don't forget to recalibrate your odometer/speedometer. Changing tire diameter will change that, and thus mess up your mileage calculations...

Abbey Bend
3/18/2011 11:39:16 AM

Something to consider doing with the new tires, is to get them nitrogen filled. When nitrogen filled tires maintain the same air pressure over a much longer period of time, helping to keep the fuel savings up. Most of this particular tire would be nitrogen filled by the installer, if they are doing a quality job.

Russell McLean
3/10/2011 9:12:29 AM

I've been lurking here since I saw the article in MEN. Thanks for designing vehicles for shallow pockets. The new tires look taller (larger diameter). I suspect that they will give you a small overdrive effect, since there will be less engine revolutions per mile driven. MAX is light weight, the reduction in engine speed should help. Unfortunately, I have no clue on how to practically separate efficiency gains from improved tires and and efficiency gains from reduced engine speeds. Russ

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