Adaptive Cruise Control (ACC) and after-market towbars.

[RogerL]

Just a heads up that some cars fitted with Adaptive Cruise Control (ACC) and an after-market towbar may suffer repeated issues with the ACC which dealers may not be able to correct. The problem being that the noseweight makes the radar look upwards and registers as a fault.

I've been made aware that several 2018+ VW Touareg owners have had issues with their ACC which dealers haven't been able to recalibrate properly - one owner discovered that Touaregs with a factory-fit towbar have uprated rear springs to counter the extra weight of the noseweight - of course after-market towbar fitment doesn't normally involve changing the rear springs - this owner has now fitted uprated rear springs to their car and cured the problem.

This problem could potentially apply to any make of car fitted with ACC and an after-market towbar - but it doesn't apply to cars with air suspension or self-levelling rear suspension.

 

[Oscarmax]

Our 2023 Suzuki Across has ACC and a aftermarket tower zero problems

 

[Mr Plodd]

Mazda 6 estate, no problems and I use ACC all the time.

 

[Beardy]

Interesting. I wouldn't expect 80kg nose weight to be much different to having 80kg in the boot. There would be some difference due to the extra leverage as the tow bar is further away from the axle than a load in the boot but if the rear axle isn't overloaded I would have thought it would be OK.

 

[RogerL]

Interesting. I wouldn't expect 80kg nose weight to be much different to having 80kg in the boot. There would be some difference due to the extra leverage as the tow bar is further away from the axle than a load in the boot but if the rear axle isn't overloaded I would have thought it would be OK.

As well as the noseweight on the towball, many caravanners have a boot load of equipment when towing and some will have rear seat passengers.

 

[Beardy]

As well as the noseweight on the towball, many caravanners have a boot load of equipment when towing and some will have rear seat passengers.

Very true, but to remain legal they have to stay within axle limits. (It wouldn't surprise me if some people don't).

 

[trevormonty]

As well as the noseweight on the towball, many caravanners have a boot load of equipment when towing and some will have rear seat passengers.

Cars lights and ACC are setup for average expected load not max.

 

[ProfJohnL]

Cars lights and ACC are setup for average expected load not max.

If that correct then its crazy. The systems in place should all be be capable of correct and safe operation with any load that is within the vehicles specifications.

 

[trevormonty]

If that correct then its crazy. The systems in place should all be be capable of correct and safe operation with any load that is within the vehicles specifications.

Load boot up vehicle front points upwards, no getting around that if suspension is to give comfortable ride lightly loaded. If lights are fixed then their will point higher. Its been that way sinces cars were invented. Some newer cars have self adjusting headlights but older cars it was manual if any.

 

[Buckman]

Cars lights and ACC are setup for average expected load not max.

Would not apply if you have self levelling suspension.

 

[xtrailman]

No problem with my Sportage with dealer fitted towbar.

 

[Beardy]

Some newer cars have self adjusting headlights but older cars it was manual if any.

Apparently headlight leveling devices became mandatory in 1993 (I'm struggling to verify this). Most of the cars I've owned have had a small thumb wheel potentiometer on the dashboard somewhere. No doubt my early cars didn't but it's so long ago I can't remember. I do remember a very basic 1999 Hyundai Accent I owned. I thought it odd at the time that it had headlight adjustment but manual side windows (and pretty much manual everything else).

 

[GUMPY]

Cars lights and ACC are setup for average expected load not max.

On my Yeti there are levelers attached to rear suspension so that the lights always point in the same direction irrespective of load.
There is no manual adjustment on the dashboard.
If the levellers fail then the lights have a default position whereby the go to the lowest position possible so as not to dazzle.

 

[Buckman]

Apparently headlight leveling devices became mandatory in 1993 (I'm struggling to verify this). Most of the cars I've owned have had a small thumb wheel potentiometer on the dashboard somewhere. No doubt my early cars didn't but it's so long ago I can't remember. I do remember a very basic 1999 Hyundai Accent I owned. I thought it odd at the time that it had headlight adjustment but manual side windows (and pretty much manual everything else).

We have a 1996 Corolla and it doesn't have the headlight levelling device, but then I have never needed to adjust the headlights.

 

[otherclive]

Apparently headlight leveling devices became mandatory in 1993 (I'm struggling to verify this). Most of the cars I've owned have had a small thumb wheel potentiometer on the dashboard somewhere. No doubt my early cars didn't but it's so long ago I can't remember. I do remember a very basic 1999 Hyundai Accent I owned. I thought it odd at the time that it had headlight adjustment but manual side windows (and pretty much manual everything else).

Same here on a gen 1 &2 Mondeo and 1997 saab9000. I was the auto leveling device as I am with a 2017/Kia Rio.

 

[ProfJohnL]

Load boot up vehicle front points upwards, no getting around that if suspension is to give comfortable ride lightly loaded. If lights are fixed then their will point higher. Its been that way sinces cars were invented. Some newer cars have self adjusting headlights but older cars it was manual if any.

I'm not suggesting rear loading of a vehicle doesn't affect its attitude, but the car manufacture specifies the the limits for loading and they should ensure other features that are part of safety systems will still operate safely with any load that remains within the vehicle specifications.

If you have a safety device that fails to operate correctly whilst the vehicle is within all of its load limits defined in its specifications, then the safety device is not fit for purpose.

The problem is there are so many new fangled driver assistance systems on modern cars, we tend to become blasiae about them and simply accept they will work correctly at all times. If an adaptive cruise control fails to work when a trailer is hitched and there is no manufacturers warning about possible malfunction under specified conditions that would normally be within the vehicles specification , then it or its operating instructions are not fit for purpose.

 

[RogerL]

I'm not suggesting rear loading of a vehicle doesn't affect its attitude, but the car manufacture specifies the the limits for loading and they should ensure other features that are part of safety systems will still operate safely with any load that remains within the vehicle specifications.

If you have a safety device that fails to operate correctly whilst the vehicle is within all of its load limits defined in its specifications, then the safety device is not fit for purpose.

The problem is there are so many new fangled driver assistance systems on modern cars, we tend to become blasiae about them and simply accept they will work correctly at all times. If an adaptive cruise control fails to work when a trailer is hitched and there is no manufacturers warning about possible malfunction under specified conditions that would normally be within the vehicles specification , then it or its operating instructions are not fit for purpose.

In the specific example of a VW Touareg, the system works as intended when a factory-fit towbar is fitted as the package includes uprated rear springs - but it becomes a grey area when third-party towbars are fitted - whose responsibility is it ensure the springs are uprated, the car maker or the towbar maker?

 

[Beardy]

In the specific example of a VW Touareg, the system works as intended when a factory-fit towbar is fitted as the package includes uprated rear springs - but it becomes a grey area when third-party towbars are fitted - whose responsibility is it ensure the springs are uprated, the car maker or the towbar maker?

This goes back to the point I was trying to make earlier. If the load on the rear axle is within the manufacturers specifications the ACC system should work. It shouldn't matter whether that load is XXX kg of concrete slabs in the boot, or the nose weight of a caravan plus Les Dawson and two Roly Poly's on the back seat.
The fact that VW upgrade the rear springs when they fit a towbar suggests that there is something I'm not accounting (quite possible) or their suspension / ACC is not fit for purpose (considering the dieselgate fiasco also quite possible).

 

[otherclive]

In the specific example of a VW Touareg, the system works as intended when a factory-fit towbar is fitted as the package includes uprated rear springs - but it becomes a grey area when third-party towbars are fitted - whose responsibility is it ensure the springs are uprated, the car maker or the towbar maker?

It's the responsibility of the cars owner, but the tow bar company should indicate that uprated or ancillary springs may be required. The owner should then source them from the car maker, to ensure the correct spring rates.

 

[otherclive]

This goes back to the point I was trying to make earlier. If the load on the rear axle is within the manufacturers specifications the ACC system should work. It shouldn't matter whether that load is XXX kg of concrete slabs in the boot, or the nose weight of a caravan plus Les Dawson and two Roly Poly's on the back seat.
The fact that VW upgrade the rear springs when they fit a towbar suggests that there is something I'm not accounting (quite possible) or their suspension / ACC is not fit for purpose (considering the dieselgate fiasco also quite possible).

Could it be that the caravans dynamic load on the hitch is causing problem whereas if the static load were carried with the car as equipment it would not have the same effect.

 

[Buckman]

I have had several tow cars and none required any modification when a tow bar was fitted. Maybe this abnormality is only confined to VW? No wonder insurers ask if tow bars are fitted.

 

[Beardy]

Could it be that the caravans dynamic load on the hitch is causing problem whereas if the static load were carried with the car as equipment it would not have the same effect.

That could well be what i was missing. Although the load in the car also becomes dynamic once the car is moving, the caravan applies its load a few feet further away from the centre of mass of the car so would have a greater effect on the axle load.

 

[Buckman]

That could well be what i was missing. Although the load in the car also becomes dynamic once the car is moving, the caravan applies its load a few feet further away from the centre of mass of the car so would have a greater effect on the axle load.

I guess a lot would depend on the nose weight of any trailer attached?

 

[PTA]

As the owner of a 2020 Touareg with coil springs and aftermarket tow bar I can confirm this is an issue (many complaints on Touareg Forum).
I have been "round the houses" with VW about this and have just decided to live with it.
The ACC function returns after about 180 miles of non towing.
(Should've bought one with self levelling suspension).
Annoyed!

 

[otherclive]

I have had several tow cars and none required any modification when a tow bar was fitted. Maybe this abnormality is only confined to VW? No wonder insurers ask if tow bars are fitted.

I’ve had two where I fitted MAD ancillary springs. These were a Saab 9000, and Skoda Superb estate. Both had long overhangs and in the case of the Skoda the JW tended to ground on our local speed humps. Neither had ACC but the modification made for a better ride.