VW Told me that putting wrong tyres on 20" = Cruise Control Failure..

[F6T6]

Hey All,

So I recently purchased a T6 204BHP, and it previously had 20" alloys on, with 275/45/20 tyres. It soon became apparent that the tyres were incorrect as they scraped on full lock.
That I could accept, however my cruise control kept failing (from the day I bought the van) until now. I took it to VW and the mechanic said 'your ACC (Active Cruise Control) seems to be faultless when we plug it in, until we drive it then it fails. That suggests that something is causing it to fail only when the vehicle is moving. We noiticed your tyres diameter is too big, and thats likely throwing off the sensor for the ACC to work, hence it failing".

Has anybody else experienced the same?
I just ordered a set of 265/40/20 goodyears, to be installed next week... so lets see..

Looking forward to hearing peoples experience.

Thanks.

 

[ThreeBridgeT6]

Hey All,

So I recently purchased a T6 204BHP, and it previously had 20" alloys on, with 275/45/20 tyres. It soon became apparent that the tyres were incorrect as they scraped on full lock.
That I could accept, however my cruise control kept failing (from the day I bought the van) until now. I took it to VW and the mechanic said 'your ACC (Active Cruise Control) seems to be faultless when we plug it in, until we drive it then it fails. That suggests that something is causing it to fail only when the vehicle is moving. We noiticed your tyres diameter is too big, and thats likely throwing off the sensor for the ACC to work, hence it failing".

Has anybody else experienced the same?
I just ordered a set of 265/40/20 goodyears, to be installed next week... so lets see..

Looking forward to hearing peoples experience.

Thanks.

View attachment 137736

Take a look at Will They Fit - this will show how your current set-up compares to the standard OEM wheel/tyre combo. You'll also be able to see whether your new tyres will make enough difference. Your current set-up creates an 8.6% speedo error, which is pretty big in my view. The new combo will improve things, but you'll still be over 4% out. I've no idea what tolerance ACC has, but you'll be able to experiment on the site to find something that works. Don't forget your offset too - this can contribute to rubbing, not only of arch liners but also door cards on sliders. I have 9.5J ET35 all round on mine and the fronts, wearing 275/40s are only just in line with the arch.

 

[Dannyb6467]

There are loads of members who have OEM wheels sitting in the garage too, why not actually try a set and see if this issue remains.

 

[Dellmassive]

ACC uses the ABS wheel speed sensors.....

So it's possible that rotation speed is slower with larger wheels?

Though I thought vw had a set of official 20's now? . . . What size tyres are on those?

.

 

[dubber36]

My understanding is that all speed and distance recordings are done off the wheel speed sensors. Providing that all the wheels have the same (give or take a bit for tyre wear) circumference, then all should be happy. A larger circumference will cause the speed sensors to under read against reality, but the van has no way of knowing what reality is. It bases its calculations on the information it receives. So if you set the CC at what the van believes to be 50mph, it has no reason to assume it's doing anything other than that.

 

[Dellmassive]

More info....

Acc & City Braking - How Its Done -

ACC & City Braking - How Its Done - what is it? Adaptive cruise control (ACC) Adaptive cruise control (ACC) is a speed control system with intelligent control of the vehicle speed. The system accelerates and decelerates comfortably. Adaptive cruise control is a combination of a speed and...

www.t6forum.com

.

 

[j4ckal]

ACC uses the ABS wheel speed sensors.....

So it's possible that rotation speed is slower with larger wheels?

Though I thought vw had a set of official 20's now? . . . What size tyres are on those?

.

275/35r20 is the only official vw size, hence not suitable for t32's.

275/45r20 is a huge tyre, I'd change them anyway regardless of whether it was giving a fault or not.

 

[Ali-G]

And bear in mind that you probably won't find a 275/35 tyre load rated for a T32.

 

[j4ckal]

And bear in mind that you probably won't find a 275/35 tyre load rated for a T32.

I'd just added that into my post as you replied

 

[Gavinda]

If the wheel diameter is greatly oversized, then I suppose the speed the ACC system reads from the wheel sensors will not match the speed at which the radar sensor is closing on the vehicle in front?

 

[j4ckal]

That's one big tyre.

 

[DXX]

I’d be more concerned about the rubbing, according to Gov.uk that‘s a Major defect.

(f) A tyre fouling a part of the vehicle

Major

MOT inspection manual: cars and passenger vehicles - 5. Axles, wheels, tyres and suspension - Guidance - GOV.UK

Axle, wheel bearing, wheel and tyres, tyre pressure monitoring system (TPMS), and suspension (including springs, shock absorbers, and suspension arms and joints) rules and inspection for car and passenger vehicle MOT tests.

www.gov.uk

Every insurance policy I’ve read says that the vehicle must be maintained in a roadworthy condition.

 

[Deleted Member]

I run 265/40/20 and a 50-60mm drop and no acc issues at all so I think you may be being fobbed off.

 

[Bigsidavies]

I’ve got 275/40/20 but no ACC.
My cruise control works perfectly fine.

 

[mmi]

VW and the mechanic said 'your ACC (Active Cruise Control) seems to be faultless when we plug it in, until we drive it then it fails.

Any chance to get the actual fault codes?

 

[Robert]

Hey All,

So I recently purchased a T6 204BHP, and it previously had 20" alloys on, with 275/45/20 tyres. It soon became apparent that the tyres were incorrect as they scraped on full lock.
That I could accept, however my cruise control kept failing (from the day I bought the van) until now. I took it to VW and the mechanic said 'your ACC (Active Cruise Control) seems to be faultless when we plug it in, until we drive it then it fails. That suggests that something is causing it to fail only when the vehicle is moving. We noiticed your tyres diameter is too big, and thats likely throwing off the sensor for the ACC to work, hence it failing".

Has anybody else experienced the same?
I just ordered a set of 265/40/20 goodyears, to be installed next week... so lets see..

Looking forward to hearing peoples experience.

Thanks.

View attachment 137736

Just adjust your K value in your Instrument Cluster to achieve displayed speed a little bit above the real speed.
There are a lot mobile phone apps showing GPS speed, Google Maps included.
Once your adjustment is completed your ACC issue will never come back again.

 

[Robert]

Any chance to get the actual fault codes?

There is no fault code stored in module 13. While driving with ACC activated the fault shows up as a warning text message in the Instrument Cluster only when "specific" speed is exceeded. Usually around 90km/h = 56mph.
At that point ACC gets deactivated but surprisingly once the vehicle speed is reduced the fault disappears and ACC can be reactivated again.

Basicially when ACC is active, module 13 reads vehicle speed directly from ABS(03) and also from IC(17) if there is too much difference than it is interpretated as abnormality and ACC produces immediate fault and deactivates cruising.

 

[The Bear78]

If the wheel diameter is greatly oversized, then I suppose the speed the ACC system reads from the wheel sensors will not match the speed at which the radar sensor is closing on the vehicle in front?

I imagine this wouldn't matter as the closing speed is also dependent on the speed of the vehicle in front. That is, the ACC would just assume that the vehicle in front is going slower than it is but still hold distance and match speed as required?

 

[Gavinda]

I imagine this wouldn't matter as the closing speed is also dependent on the speed of the vehicle in front. That is, the ACC would just assume that the vehicle in front is going slower than it is but still hold distance and match speed as required?

Yes, I thought about that after I posted but, who knows what algorithms these systems use or how smart they might be trying to be?

 

[GFos]

Hey All,

So I recently purchased a T6 204BHP, and it previously had 20" alloys on, with 275/45/20 tyres. It soon became apparent that the tyres were incorrect as they scraped on full lock.
That I could accept, however my cruise control kept failing (from the day I bought the van) until now. I took it to VW and the mechanic said 'your ACC (Active Cruise Control) seems to be faultless when we plug it in, until we drive it then it fails. That suggests that something is causing it to fail only when the vehicle is moving. We noiticed your tyres diameter is too big, and thats likely throwing off the sensor for the ACC to work, hence it failing".

Has anybody else experienced the same?
I just ordered a set of 265/40/20 goodyears, to be installed next week... so lets see..

Looking forward to hearing peoples experience.

Thanks.

Hi - did fitting the 265/40/20 tyre solve the problem with the ACC? Cheers, Graham