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Old 07-28-2008, 10:16 PM   #11 (permalink)
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I agree that low rpm gives best FE for cruising. What I want to point out is, the manufacturer won't build the gear box optimized for cruising for another good reason.

In fact, the question of the topic is wrong. It should be "what is the ideal gear setting to cruise?" Different models cruise at different rpm with top gear and same speed. I want to cruise at 65mph with 2000rpm. However, my car doesn't allow me. @65mph, the top gear is 3250rpm. We want that but doesn't mean we can have it. What we can choose is what gear we are using at the given speed.

Cruising = constant speed =minimum power needed. And, highest gear = lowest rpm = minimum power. So, we should choose highest gear to cruise!!

Of course, we won't cruise at 10mph. Maybe 25mph or 30mph for minimum speed? If the top gear runs, that is ok. Just be careful when you break (easy to kill the engine) or go up hill. When power is needed, shift to lower gear and go, don't stay in top gear in low speed. That won't save any gas. (faster reaching the speed you want, faster starting cruising, faster start to save gas.)

The above case is for flat road. If cruising uphill, depends on the power of the engine, how steep of the hill, and the speed of cruising. Sometimes can't cruise on top gear, then, choose the next highest one.

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Old 07-28-2008, 10:25 PM   #12 (permalink)
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I agree. If only our cars would allow us to choose that ideal speed and rpm combination. Too bad.
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Old 07-29-2008, 06:16 PM   #13 (permalink)
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The manual will give the best "good enough for everyone" answer. Lower than what they recommend will usually give better performance.
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Old 05-16-2009, 12:58 PM   #14 (permalink)
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Would it be nice to substitute the top gear with one that allows the cruising speed (would never be really 'high', for any ecomodder worth his coroplast) to be achieved at 1k RPM? one would briskly accelerate to the target speed, and then moves into this special 'cruise gear'. Of course it is assumed that the steady state power requirement for this cruise is available from the engine at 1k rpm, with < 80% throttle.

Would this be better than P&G'ing all the way through?
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Old 05-16-2009, 03:58 PM   #15 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
I agree. If only our cars would allow us to choose that ideal speed and rpm combination. Too bad.
Yah, oh wait, this is a modder site!! Get out your wrenches!
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Old 05-16-2009, 05:11 PM   #16 (permalink)
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Seems to me it depends more on piston speed than rpm.

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