2017~2022 CX-5 Cruise Control in Mountains

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Mazda CX-5 GT 2017
When driving in the mountains is it ok to let cruise control handle down shifting/braking to keep my speed at the posted 35mph or should I do this manually? On rolling hills around mountains is it more fuel efficient for me to accelerate / decelerate because I can see when a hill is coming and accelerate as appropriate while cruise control has to wait for the speed to decrease before accelerating. Just wondering, been driving in the mountains a lot lately.
 
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CX5 GT
Using the cruise would use your brakes more often, i.e wear them out more. Otherwise if you are used to, try the manual shifting up and down. Sometimes it's much better but requires more engagement from the driver.
 
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Pueblo county CO
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CX-5 Sport 16.5 6M
I think you're right, the cruise control is reactive and can't anticipate, unless it's connected to the GPS somehow.
 
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Occupied Calif.
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2019 CX 5 GT-R
I live in the mountains and wouldn't even think of using the cruise control on any of the highways around here. The Adaptive cruise control works quite well at maintaining distance when cruising on the freeway but if traffic starts to bunch up and start & stop I turn it off.
The best cruise controls on the market are not Full Self Driving systems by any means. You shouldn't expect Mazda's system to work as well as your brain, especially when driving under as dynamically changing conditions as mountain driving.
 

HardRightEdg

US 2020 CX-5 Touring AWD Soul Red
Hills, rain, snow, fog, heavy traffic, curvy roads--cruise off. The warnings in the manual about when not to use cruise should be taken seriously. Whether conventional or MRCC with Stop and Go, it's for expressway driving in light to moderate traffic. And don't expect MRCC to slow down or speed up to allow somebody coming down a ramp to enter the highway--it's a forward facing radar system only.

As for some future GPS application, I wouldn't expect that soon if ever. Commercially available GPS, not the military kind, is accurate only within about 5 meters. Even if more accurate I have a hard time envisioning how that would work.
 
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PaulZooms

16.5 GT Sensing
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Lakewood, CO
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2016.5 CX-5 GT
Hills, rain, snow, fog, heavy traffic, curvy roads--cruise off. The warnings in the manual about when not to use cruise should be taken seriously. Whether conventional or MRCC with Stop and Go, it's for expressway driving in light to moderate traffic. And don't expect MRCC to slow down or speed up to allow somebody coming down a ramp to enter the highway--it's a forward facing radar system only.

As for some future GPS application, I wouldn't expect that soon if ever. Commercially available GPS, not the military kind, is accurate only within about 5 meters. Even if more accurate I have a hard time envisioning how that would work.
Agree on not using MRCC on snow, but hills, rain etc. are fine with adequate vigilance.
 
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There are no issues using the cruise control to do its job, but i don’t think it is the most efficient way. Not only does the cruise control does not plan ahead as the OP says, but it also brakes on the way down to maintain its speed. For efficiency purposes it is better to allow the car to gain momentum. To save your brake on long descent you also want to avoid continuous brake application to prevent the brake from overheating.
 
I just went on a cross Canada road trip recently and used cruise control a lot even on hills. It is not a predictive system but you can be as involved as if driving with your feet and pedals. Such as gives it a bit more gas before going up the hill, you can either dial up the set speed or just step on the gas padel momentarily to override the set speed. While going up the hill

The fuel economy indicator helps me to know how hard the engine is working. In the downhill condition, the fuel consumption will be getting less. Once it starts to reach near zero, you can dial up the set speed a bit more to prevent the upcoming automatic break if permitted.
 
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'16.5 CX-5 AWD
My cc reacts before the car loses 1 mph. That is quicker than I can react and it never adds excess power, that I can detect.

Whatever method that uses the LEAST amount of power wins the mpg competition. Accelerating in anticipation of a grade is not it. Downshifting to gain engine braking does not hurt mpg. Neither does braking unless the car's speed falls below the cruise setpoint, requiring extra power to return to the setpoint. However, braking does give up extra energy that might be gained on a downhill slope.

With concentration, I have been able to beat the cc mpg in some cars by allowing my speed to drop a little going uphill and gain a little going downhill, basically holding constant throttle position (constant power).