[OneDayDriver]

I have a new (three  months) 2015 badged i30GD4.  The cruise control does not keep close control over speed, as opposed to other CCs I have used in other brand vehicles, even the after market version in my last car (not Hyundai).  For instance, set to 50kph to keep to a tightly policed speed control zone, it easily runs past the 50 mark on a slight down hill slope and does not correct.  Similarly, when climbing, the car does not accelerate.
Is this just a low performing feature on the Hyundai, or should I expect better?
Would replacing the system with an after-market product or should I expect this to be fixed under the warranty?
There  is one other matter I will raise in a separate topic.
Appreciate any comments.

[Dazzler]

Welcome OneDayDriver,

Interesting question.

My wife has a 2014 Tourer 1.6 GDi manual and when I have driven that using cruise it didn't seem too bad on down hill sections, but did tend to lose a bit of speed (maybe 10 kph) on long up hill sections in 6th gear. But with two adults and a boot full of luggage I wasn't surprised.

Just did nearly 1500 kilometres in a 2016 rental i30 (1.8ltr Petrol Auto) . I found it pretty good at staying within about 2 kph of the speed I set, however it was mainly driven on motorways between Kingscliff in NSW and Caloundra on the Sunshine coast. We did venture up as far north as Hervey Bay, but not many hills to speak of.

[pidim]

My GD (2012) is the same. It severely overuns itself on a downhill before it figures that it needs to gear down but can never claw itself back in time. 

Also it accelerates very slow and can feel like eternity when it has to get up to speed. However, I do prefer this method of acceleration which was similar to a Ford Territory I had. I then had a Kluger which had manic acceleration to get to speed and was awful. 

[AlanHo]

The C C controls the throttle and not the brakes in the i30.

Hence all it can do on a downhill section is lift off completely - if this doesn't apply enough retardation the speed will increase. 

My son has a Golf GT Diesel with adaptive cruise which can also apply the brakes, making the C C very accurate in all situations.

[The Gonz]

The Falcons I used to hire on Canberra business used to downshift to add extra retardation on the Queanbeyan downhill stretches. As if Falcons aren't retarded enough already!

[Dazzler]

Newer hybrids use regenerative braking to keep to set speed on down hill sections, which works well. Hopefully the Niro does that for you Alan. My Calais is pretty good at holding speed. I guess that uses the compression of the big 6cyl?

[Thunderbird]

  Mine works great with the auto transmission. Sometimes it will kick down, coming to the crest of a hill (small hills around here) and sneaks a couple of K's over, on the down side, but soon corrects itself.

[dnalor50]

My 2015 i30 SR manual cruise control is very good, except when going over a crest and into a steep descent. I guess smaller motors don't have a lot of engine braking. The cruise control is a lot better, however, than my previous focus LS which accelerated rapidly when going over the slightest crest.

[xiziz]

I think it does a good job, keeps speed uphill(aslong as I'm in the correct gear). Downhill it lifts and lets the car roll, I'd hate if it braked me downhill though. I want full control of the brakes.
It does apply the throttle too early after rolling down a hill instead of waiting until it hits the set speed, like 15kph too early.

Probably slightly differs with manual compared to auto though

[Phil №❶]

There is of course no braking in the auto, but level & uphill , cc works beautifully.