I've read posts about a vehicle's "sweet spot" with the OP usually citing a given MPH speed such as 55, 60, etc. I suppose that is the speed that gives, in the opinion of the poster, both optimum power and gas mileage. My question is: how is that "sweet spot" determined? Of course, I can determing the speeed at which best MPG is achieved but do not know how to associate that bit of information with determining best power range. My MH is an '05 gas Itasca. Thanks for any input... Larry
My coach shifts into 6th gear at 62 mph. So, 65 is my sweet spot as I can set the cruise and stay in 6 th gear for the best fuel milage and distance covering.
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Driving it is the best way, and it may vary for your conditions and driving style.
Years ago there was a big debate as our '00 Dutch Star gasser was happiest at 70-72 MPH. If I slowed down my MPG went down. Why? Because we normally were traveling in the hills of the east. Too slow and it was constently downshifting and struggling to maintain speed. Keep it up into it's torque band and it would cruise along happily, only dropping a gear when needed, then getting back into overdriver quicker.
Our current rig doesn't care. Hills, flats, whatever - the torque curve is so broad it just keeps rolling along. So on that one slowing down would give us better MPG.
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The usual "sweet spot" is the minimum speed at which you can maintain your rig in top gear. This because wind resistance goes up exponentially with speed, the Big Hill beginning at about 55, and the vehicle efficiency is best in top gear.
But this is also influenced by windy conditions, slope, engine power curve, and other things. So, for example, if you are headed into a steady 20 mph wind, you might get better mileage (and at the same time save your auto tranny having to up- and down-shift frequently) by slowing down enough to run steadily in next-to-top gear.
For my rig, 60 mph and 5th gear is best, but in the headwind case, that becomes 50 mph and 4th gear.
I drive a diesel, and both those speeds/conditions put the engine at the peak of it's torque curve. Since gas engines typically have torque peaking well above engine speeds at which you'd like to cruise, I'd just stick with the speed you determine gives you the best gas mileage. If there is a headwind, slow down, but if a tailwind, do NOT speed up.
We had our truck dyno'ed after installing all of it's electronic and mechanical mods. Where the TQ & HP curve meet, that's the sweet spot and where I try to keep the speed & RPM's when towing. Works out it's about 59 MPH in 6th gear.
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My "sweet spot" is between 62-65mph. I installed a tach and vacuum gauge. I looked for the highest vacuum and lowest rpm while driving down the road in OD. Mine was around 10 inches vacuum at 2500rpm and a speed of 62-65mph depending on wind direction. This also gave me an average of 9-9.5 mpg.
Not to bad for a 95 Winne 31ft, 7.4l(454) with a 4L80E transmission.
Bunch of variables when considering power train configurations, coach weight, towing, and the biggest the driver. I'm comfortable going down the road at about 63 MPH with puts the engine at about 2500 RPM. I hug the right hand lane and let traffic pass me. Fuel usage seems to peak, per my ScanGuage at around 8 MPG at that RPM also.
I don't get the sharp stick poking me in the back of the head by my passenger at that speed which goes back to my comfort level.
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