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Old 05-27-2011, 05:35 PM   #28 (permalink)
SentraSE-R's Avatar
Join Date: Jun 2009
Location: Bay Area, California
Posts: 1,485

Mean Green Toaster Machine - '06 Scion xB
Team Toyota
90 day: 48.92 mpg (US)
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Time to resurrect this thread. I just bought two used 195/65-15s for $20 each. When I get them mounted next week, I'll be able to test my stock 35 lb. 185/60-15s, my current 47 lb. 205/50-17s, and a lighter 37 lb. 195/65-15 combination. The latter two tire/wheel combos are 5.31% and 4.97% taller than stock, respectively, and have -5.605% and -5.224% rolling circumference differences from stock.

While my mpg has not suffered with the 17" tires, I think that's because my first three tanks with them were on a long road trip. The taller & heavier tires do best under highway conditions where their greater inertia isn't detrimental, and their taller height/taller gearing is beneficial. Also, my AB testing was done under constant speed conditions where the heavier tires' inertia ramp-up isn't measurable.

Using the new tires today under a competition low speed P&G regimen, I was unable to approach the 94.5 mpg I got with the stock tires. In fact, I could only get 70 mpg. I suspect that's because the big, heavy tires need more fuel to come up to speed.

Next week, I plan to do ABCA testing under cruise control and different P&G conditions. I think that testing will be very interesting and educational for me, and probably for all of us.

Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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