[eye30]

On my new i30 I've got CC but I've noticed that if I set it when I'm doing less than mid 50's mph it seems to have a jerking to it. 

I can only describe it as if you are moving at a predetermined speed, say 50, then you take your foot off the gas and the car slows, say 45, then you accelerate back to 50.

Once I'm above mid 50's it maintains a smooth movement.

Anyone else have this jerking movement?

Also, when in CC mode when going down a slope/hill it "pulls" back as if it is applying the brakes to prevent the car exceeding the preset CC limit.

Does anyone else get this?

Are the brakes being applied and if so are the rear brake light on?

[AlanHo]

The CC on my car is quite smooth - but I rarely use it other than on a motorway. About town I prefer to use the speed limiter to prevent me from exceeding the speed limit but give me full control of the car at all speeds below the limit..

I do notice however that on a downhill slope the engine braking feels more jerky than when the CC is off. I put this down to the CC trying to keep the car at a constant speed on the over-run whereas if the CC is off you would tend to let it over speed a little and gently apply the brakes or throttle to maintain a reasonable speed.

[eye30]

I do notice however that on a downhill slope the engine braking feels more jerky than when the CC is off. I put this down to the CC trying to keep the car at a constant speed on the over-run

Given that you have experienced the same as me, are the brakes applied and if so do the brake lights come on?

If the brake light does flash on/off then this will be annoying to those behind

[AlanHo]

I don't know for sure whether the brakes are applied by the CC or not - but I very much doubt it. In my car if I hit the minus button to lower the set speed I feel the throttle back off and the car loses speed gradually as a result of wind and rolling resistance. If the brakes were applied it would lose speed quickly.

I sense that when going downhill with the CC set at say 60 mph - if the car gets to 61 mph the fuel is cut off, if the car then loses speed because the slope changes or wind resistance increases, when it falls below 60 mph the throttle is applied and the car speeds up again and goes just over the set speed. Hence when conditions are such that the car naturally wants to proceed at or about the set speed without need of much power - you get this slight surging as it hunts about the set speed..

Your car being petrol, the effect may be more pronounced because you get more engine braking than I do in the diesel.

[Surferdude]

I'm sure that at least in older cars with CC the brakes were applied by the unit when going down hill. I never thought about whether or not the brake lights came on. Don't know how the modern versions work.

But, isn't there a lower speed limit at which the book says not to activate the CC. I know they say only in 4th or 5th gear.
TBH, I never use it in traffic which is where I would be doing the slower speeds.

To me CC is for the open road and then only when there's not much traffic around.

[Dazzler]

But, isn't there a lower speed limit at which the book says not to activate the CC. I know they say only in 4th or 5th gear.
TBH, I never use it in traffic which is where I would be doing the slower speeds.

To me CC is for the open road and then only when there's not much traffic around.

 

[Surferdude]

^^^^
Having said that I googled the lower speed thing and found a lot of discussion with the recommended lower limit being somewhere between 15 mph and 30 mph.
But it seems many drivers in the UK use them on those long stretches of 30 mph signed roads where you can get several cameras (I found five in about 3 miles once), to keep them from creeping over the limit.
I can understand that having experienced that sort of thing first hand.

[FatBoy]

I have noticed with my CC that there is one speed where the engine seems to surge to maintain the speed (feels like my foot coming on and off the accelerator), unfortunately this happens at 100 km/h indicated (about 98 km/h on the GPS).  The way I get over it is to press either the Accel or Coast button once to get away from that speed and the surging stops.

I doubt very much whether CC will apply the brakes. Surely that would be asking for problems. What if you had such a mechanism and it failed such that the brakes were applied hard in error while in traffic?

Even the ABS doesn't apply brakes, it only releases them in a controlled manner to keep them on the lockup cusp but you have to push the pedal.

Having said that I guess you have all read of the newer developments with automatic braking and collision avoidance systems and what about that automatic parallel park thingy? Pretty soon even the driver will be a passenger.

[eye30]

Even the ABS doesn't apply brakes, it only releases them in a controlled manner to keep them on the lockup cusp but you have to push the pedal.

For ABS to operate you will have applied the brakes and therefore the brake lights will already be on.

[FatBoy]

My understanding is that the brake light is operated from the pedal, not the application of brake. (ie  you have to depress the pedal for the light to come on) Therefore if the brake is applied by the CC, then the light would not go on.

[Dazzler]

My understanding is that the brake light is operated from the pedal, not the application of brake. (ie  you have to depress the pedal for the light to come on) Therefore if the brake is applied by the CC, then the light would not go on.

...and that would be fraught with danger (the brake applied with no visual warning to those behind) So it further supports the no brake theory 

[rustynutz]

Also, when in CC mode when going down a slope/hill it "pulls" back as if it is applying the brakes to prevent the car exceeding the preset CC limit.

Does anyone else get this?

Are the brakes being applied and if so are the rear brake light on?

Should be easy enough to test......

I can see the centre brake light light up when I apply the brakes at night so glancing in your mirror when your cruise is set and going down a hill shouldn't be too hard... 

[Surferdude]

Did a bit of research. Doesn't look like the brakes are applied by CC. But even if they were they would be in short bursts, just enough to keep you at the set speed. So it's not like they'd suddenly throw out the anchors and stop you in the middle of the road.

I don't like CC in hilly terrain either as it tends to apply the power pretty heavily when you hit a rise. A good driver will see the rise coming and gradually increase power BEFORE the hill so that the increase in acceleration meshes with the inertia loss as you start to rise. Much better on fuel economy IMHO.

[rustynutz]

 

[eye30]

Also, when in CC mode when going down a slope/hill it "pulls" back as if it is applying the brakes to prevent the car exceeding the preset CC limit.

Does anyone else get this?

Are the brakes being applied and if so are the rear brake light on?

Should be easy enough to test......

I can see the centre brake light light up when I apply the brakes at night so glancing in your mirror when your cruise is set and going down a hill shouldn't be too hard... 

If you are free tonight come over and you can follow me down the road to see what happens...

[rustynutz]

Pay for my flight there & back and I will....

[Phil №❶]

There's no braking on our car under CC, going down hill it just goes faster & faster, not enough engine braking unfortunately. 

[bumpkin]

I also mainly use the speed limiter when in town or built up areas.  CC mainly for 5th and 6th gear for me, but I have had the CC set at 40 mph in 6th and no felt any surging.  Also no wheel braking takes place when CC set, it is all engine braking and even the i40 holds itself at speed on steep downhill without taking off

[eye30]

The "surging" is noticeable when I'm on the motorway or long stretches of roads were I don't have to stop for lights etc. 

The roads have a few sections which have rise and falls and that was when it was noticeable.

On the "flat" sections it is a smooth ride.

[bumpkin]

I would perhaps be asking about it, on the i40 you feel the engine providing more power on the uphill bits, but it's not a surge, very smooth and kicks in with a drop of just a couple of mph and sorts itself out after "over powering" by again only a couple of mph, certainly nowhere near 5mph.

Even when resuming speed the CC is very controlled, I can be at 65mph and slow to go around a roundabout, back into 6th gear at little above 40mph and then press resume and she smoothly powers up and I haven't even noticed any over speed once back to cruise, the parameters look to be really nicely set.

[eye30]

I would perhaps be asking about it,

Just for peace of mind I will do next time I'm passing the dealers

[bumpkin]

I have just been out in the i40 and thought I would check the CC at 30mph for you, worked fine, sat at 30 with no surging or lack of control, so I would definitely be getting yours checked.

[eye30]

I have just been out in the i40 and thought I would check the CC at 30mph for you, worked fine, sat at 30 with no surging or lack of control, so I would definitely be getting yours checked.

Cheers. 

Before I visit the dealers I'll log results of various speeds/gear selection/road types.

[eye30]

OK been doing a little bit of testing.

I find that when the jerking happens if I drop down a gear it runs smoother.

[bumpkin]

I seem to recall suggesting that on your thread at the HOCGB didn't I?


Thought so

[AlanHo]

I was in slow traffic today so I took my mind off the frustration by checking out the minimum set points for each gear.

The CC will not set at any speed in 1st or 2nd gear

In 3rd gear it will not allow me to set at speeds below 16 mph (26 kph)  - because it is limited by the natural  idling speed of the engine (900 rpm) when loaded - but you can set the cruise at this point if you were daft enough.

In 4th gear the car will not do less than 22 mph (35 kph) - again because it is limited by the natural  idling speed of the engine (900 rpm) when loaded - with or without the cruise set.

Similarly you can set the cruise at the equivalent speed given by engine revs of 900 rpm in 5th and 6th gear - 26 mph (42 kph) and 32 mph (51 kph) respectively.

I should add that whilst my car will move at these low speeds with the CC set - it will only do this smoothly on a dead flat road with no headwind.  It will however work fine if the engine revs are not below about 1800 rpm.

Hence the practical minimum speeds for using cruise on my car - if you need some leeway to accelerate above the set speed are :_
1st and 2nd gears - no can do
3rd gear - 32 mph (51 kph)
4th gear - 44 mph (71 kph)
5th gear - 52 mph (84 kph)
6th gear - 64 mph (102 kph)

[Phil №❶]

Interesting your 6th gear is so high. I regularly engage cc @ 60 kmh / 38 mph in the city to avoid speed cameras. 

[Dazzler]

Thanks Alan 

[bumpkin]

Wow, I am also surprised by your 5th gear, I can do 30 in 5th with the CC set no problem!