I posted this question a week ago and didn't receive any responses so I thought I would try again. Any input is appreciated. Thanks, Jeff -----Original Message----- From: Jeffrey Schwaia [mailto:jeff@tssgi.com] Sent: Friday, December 13, 2002 11:34 AM To: vanagon@GERRY.VANAGON.COM Subject: RPMs The previous thread about engine RPMs and top speed got me thinking, and I was hoping that some of you gear heads out there could confirm or correct my calculations. Here's what I've come up with: GIVEN.... PI = 3.14159 MILE = 5280' SPEED = ((((RPM /(Gear * Final Drive)) * (2 * PI * Tire Radius)) / 12 ) * 60) / MILE Using this formula with the gear ratios (4th gear = 0.85, Final Drive = 4.83) and tire radius (~12") in my 4 speed Vanagon I come up with: ~71 mph @ 4,000 RPM. This sounds dead on for my van. It also gives me: ~18mph for 1st gear @ 4,000 RPM ~34mph for 2nd gear @ 4,000 RPM ~56mph for 3rd gear @ 4,000 RPM All these speeds sound about right. Am I missing something? I'm looking to build a freeway flyer by mixing gear ratios from different trannys, so this formula could be of great help... if it's correct. Cheers, Jeff |
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