RPM, Speed and gear ratios...

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Jan 14, 2007 | 08:01 AM

boxerfan

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RPM, Speed and gear ratios...

OK everyone, here is the result of a little digging and calculator exercise.

The equation is:

kph = RPM * 60 [min/hr] * pi * Tire Diameter[m] * 1/Ratio(final drive) * 1/Ratio(gear) * 1/1000[m/km]

The rolling tire circumfrence is given at 1.9m in the manual.

It looks like I have an 0.838 5th gear with the 4.11 final drive. At 3000 rpm I'm guzzling gas going 99.27kph. At 120kph I'm revving at 3626rpm.

If I can change the 5th gear to a 0.73 cluster I'll see 114kph at 3000rpm and 120kph at 3159rpm. If I can find a 0.6 5th gear cluster I'll see 138.64kph at 3000 rpm. That's 46kph/1000rpm instead of a meager 33kph/1000rpm.

HTH

Jan 14, 2007 | 08:57 AM

dwengi

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Re: RPM, Speed and gear ratios...

Or swap in a 6 speed with a .684 6th gear ratio and 4.11 final drive?

Jan 14, 2007 | 12:49 PM

boxerfan

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Re: RPM, Speed and gear ratios...

Yea... but I don't like rowing everytime I drive... :-). More importantly... money is an issue. The meanie has an 016 so swapping 4th 5th gear clusters while the tranny is down for an engine rear main seal seems prudent.

Jan 14, 2007 | 07:25 PM

dwengi

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Re: RPM, Speed and gear ratios...

Yeah 6 speed definitely not required with a torquey motor. I routinely skip gears in my A6. My Scout has a 4 spped and I start out in 2nd and I'm in 4th by about 35MPH.