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Discussion Starter #1
My wife has a 2019 Q50.

The cruise control will not hold the vehicle's speed when going down hill. If I crest a hill at 100 km/h, it accelerates down the slope with no intervention by the cruise control. All that happens is the cruise speed number flashes.

I live in British Columbia with some steep mountain highways. Every other car I've driven holds the vehicle speed down even the steepest grades when the cruise control is set.

According to my dealer, "they all do that" and there's nothing wrong with the car.

I find it hard to believe the cruise control in a 2019 Infiniti doesn't work as well as the cruise control in the 2012 and newer Fords I drive with work. Is the dealer right?
 

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Most cruise control doesn't apply brakes, it just cuts throttle. A steep enough hill and your car will still accelerate.
 
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As general practice, it's not a wise idea to use cruise control on hilly or curvy roads; especially when steep or winding. Those situations should require your full attention in driving.

The Owner's Manual has that warning, too:
95850




even states it probably will not maintain the speed on hills, especially steep.

95849
 

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Discussion Starter #4
Thanks for the replies. I am quite surprised by this.

I live in British Columbia where mountain roads and steep grades are common. Travel anywhere outside the Vancouver area, even just to Whistler, involves substantial changes of elevation. An 8% grade for 5 km on the 120 km/h Coquihalla Highway is a common route.

I've driven extensively in 2012 and 2015 Ford Explorers as well as 2019 F150, F250 and 2020 F250 for work. With cruise control all the Fords have no difficulty maintaining speed both up and down the steepest grades.

So for a driver in British Columbia if the cruise control doesn't work on hills it's very noticeable and irritating.
 

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Thanks for the replies. I am quite surprised by this.

I live in British Columbia where mountain roads and steep grades are common. Travel anywhere outside the Vancouver area, even just to Whistler, involves substantial changes of elevation. An 8% grade for 5 km on the 120 km/h Coquihalla Highway is a common route.

I've driven extensively in 2012 and 2015 Ford Explorers as well as 2019 F150, F250 and 2020 F250 for work. With cruise control all the Fords have no difficulty maintaining speed both up and down the steepest grades.

So for a driver in British Columbia if the cruise control doesn't work on hills it's very noticeable and irritating.
Explorers (and likely other Fords) have a special "Hill Descent Control" which stops the car from accelerating downhill, but it turns off over 32kmh. Maybe a difference in how engine braking is applied?
 

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Yeah, most trucks/suv's are designed with more potential for towing in mind, and have different torque converter behavior than most cars, and they all have brains that think they know more than you about how much lockup should be applied in a given situation. In all fairness, they're usually right, but that sort of depends on the user. The only way to get engine breaking to be that effective in most modern cars is to have three pedals, as standard transmissions let you decide if the clutch is in, out, or somewhere in between. If you have paddle shifters, tapping it down a gear (or two) on hills can help, but it isn't going to turn your cruise control into an F250. The only way I can think it may work better is to keep it in manual mode so it will hold the gear you pick, giving it more power for climbing and more engine breaking for coasting down the other side... but expect a mpg hit.
 

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My wife's Mercedes will brake to maintain the speed downhill. I'm pretty sure all Mercs do this. I believe it will even downshift a gear or two before applying the brake. At least her '98 did that. That behavior is more the exception than the rule. I personally have never driven any other make that will retard the speed like that. My Q50 hybrid will do it in a limited fashion by using regen.

Big bore diesels as found in OTR semis can be programmed to latch the cruise control to a compression brake if so equipped. This has been true since the '90s. A must if driving in hilly terrain. Nothing like having overheated brakes when you are at 80,000 LB. GVW.
 

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Just down shift manually (4th gear seems to work best in most situations) and engine brake will keep you from accelerating when using cruise control going down hill.
 

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Like they say above, I think your previous vehicles must be geared in a way that gives you more engine drag when your at a no throttle condition. I have never experienced a "dumb" cruise control that brakes or changes the gears to slow a car. There are transmissions that sense downhill acceleration and downshift to compensate (regardless if cruise is on or not). I had a 2007 Armada that worked that way...probably safety cuz its such a heavy clumsy vehicle you could have real issues if too much momentum down a grade.

Switch it to manual mode and hold it in a lower gear for the hilly mountain drives. 4th, 5th or 6th may do the trick depending on your desired speed. I would think you would just need to be at about 2000 RPM or so to do the trick for the braking...trick will be what RPM/gear combo keeps speed up the steep grades as well...might need to be closer to 2500 RPM for that...not sure but let us know back how it works out. As I write this I am not sure I have ever tried cruise in manual mode...hopefully it isn't disabled or anything.
 

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Interesting, next time I am coming down from the mountain canyons here in Utah I will have to give cruise control a try. My wife's '18 Forester also has no problem cruise control down steep hills, we just road tripped to Colorado and I had cruise control on almost the entire time, up and down long freeway hills at like 70+ mph it had no problems.
 

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I just did a 2300 mile road trip. Mostly highway and long rural routes. It seems like the adaptive cruise in our cars give you ( I think ) a 2 mph lea way before the starts applying the brakes going down hills. And it is not gente in any way. It hits them hard. It's actually very annoying, but it does work well.
 

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I just did a 2300 mile road trip. Mostly highway and long rural routes. It seems like the adaptive cruise in our cars give you ( I think ) a 2 mph lea way before the starts applying the brakes going down hills. And it is not gente in any way. It hits them hard. It's actually very annoying, but it does work well.
That leeway is called a "soft" cruise. Supposedly better for economy. Again, big bore diesels since the '90s gave you a choice between the two.
 
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