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orange4boy · 09-26-2010, 04:39 PM

Drag from wheels is one of the biggest single drag sources in a car. Widening tires with all other things the same will almost certainly increase your drag. There is one reference in Hucho which shows a .29 to .30 change going from 175-70-15 to 185-65-15.

Lowering a car may or may not increase drag. It depends on the car. Most wind tunnel tests show a reduction in drag with increasing road clearance. Belly pan it and you may offset the increase.

RR seems to be much more compound related than section and width related. The differences in compounds in the tires you choose will have a much greater effect on RR than differences in section.

The rotational mass issue is really trivial AFAIK. It may make a slight difference in acceleration but almost none in FE. Your engine's efficiency in converting heat to kinetic energy will have a much greater effect on FE that how quickly you can convert that energy into velocity. The extra weight will have a small effect on RR but that would be almost unmeasurable. If you are drag racing (or stopping quickly) then it will make a difference.

My two bits.

09-26-2010, 04:39 PM	#15 (permalink)
orange4boy Master EcoModder Join Date: Aug 2008 Location: The Wet Coast, Kanuckistan. Posts: 1,275 The Golden Egg - '93 Toyota Previa DX 90 day: 31.91 mpg (US) Chewie - '03 Toyota Prius 90 day: 57 mpg (US) The Spaceship - '00 Honda Insight Thanks: 100 Thanked 306 Times in 178 Posts	Drag from wheels is one of the biggest single drag sources in a car. Widening tires with all other things the same will almost certainly increase your drag. There is one reference in Hucho which shows a .29 to .30 change going from 175-70-15 to 185-65-15. Lowering a car may or may not increase drag. It depends on the car. Most wind tunnel tests show a reduction in drag with increasing road clearance. Belly pan it and you may offset the increase. RR seems to be much more compound related than section and width related. The differences in compounds in the tires you choose will have a much greater effect on RR than differences in section. The rotational mass issue is really trivial AFAIK. It may make a slight difference in acceleration but almost none in FE. Your engine's efficiency in converting heat to kinetic energy will have a much greater effect on FE that how quickly you can convert that energy into velocity. The extra weight will have a small effect on RR but that would be almost unmeasurable. If you are drag racing (or stopping quickly) then it will make a difference. My two bits. __________________ Vortex generators are old tech. My new and improved vortex alternators are unstoppable. "It’s easy to explain how rockets work but explaining the aerodynamics of a wing takes a rocket scientist.