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MadisonMPG · 03-26-2010, 01:32 PM

All of the components that the engine drives via belt are slowed down. They spin slower, so they don't produce as much friction/parasitic loss. How many RPMs they slow down vary on the size of the pulley. 99.99% an underdrive won't "pay for itself".

03-26-2010, 01:32 PM	#5 (permalink)
MadisonMPG Master EcoModder Join Date: Nov 2008 Location: Madison AL Posts: 1,123 The Geo - '93 Geo Metro Team Metro 90 day: 45.16 mpg (US) Thanks: 30 Thanked 40 Times in 37 Posts	All of the components that the engine drives via belt are slowed down. They spin slower, so they don't produce as much friction/parasitic loss. How many RPMs they slow down vary on the size of the pulley. 99.99% an underdrive won't "pay for itself".