Larger Tyre options with ACC

P

paulbishop2

New Member
Hi.
Time to replace the boots. Has anyone fitted 275/40/20 tyres to T6.1 with ACC ? Whats the largest size tyre you can go without it throwing up a fault on the dash?
Thanks in advance
 
I have that size on a T6 with ACC and it works fine. I'm unsure what error you could get?

Only difference should be the speedo will change if increasing the rolling diameter from stock. I find 30 on the clock equals 30 on satnav so need to be cautious of a smaller room for error with speed cameras.
 
I purchased it recently and it has 255/40/20 which are 7% larger than stock. I put it in to VW as it keeps throwing up an ACC error and they said it was due to the tyres being too large a circumference (it thinks it is doing 50mph by the speedo but the sensor says its going faster and it then throws up an error the dash.) I had 275s on my last T5 and they were great. Do you know what width and offset your rims are?

Cheers
 
Interested in this... I've got a T6 (2018) with oversized tyres. I don't get an error message but my speedo is out by +8% so when speedo says 60 I'm doing about 64.5 according to sat nav... I've spoken to VW engineers and there's no way to reprogram the vehicle to inform it you've got bigger tyres. Other manufacturers allow this via ODB2 etc... Will have a play with the winter tyre setting and see if that makes a difference.... thanks for the suggestion @temporarysecretary
 
TWB-Mark said:
Interested in this... I've got a T6 (2018) with oversized tyres. I don't get an error message but my speedo is out by +8% so when speedo says 60 I'm doing about 64.5 according to sat nav... I've spoken to VW engineers and there's no way to reprogram the vehicle to inform it you've got bigger tyres. Other manufacturers allow this via ODB2 etc... Will have a play with the winter tyre setting and see if that makes a difference.... thanks for the suggestion @temporarysecretary
Click to expand...
100% a T6 allows you to add 5mph to the Speedo with this setting.
 
Lots of Sensor faults. Is that because it thinks there is a fault, as wheel sensor doesn't match radar sensor whilst driving?

tempImageF73qpf.png

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TWB-Mark said:
Interested in this... I've got a T6 (2018) with oversized tyres. I don't get an error message but my speedo is out by +8% so when speedo says 60 I'm doing about 64.5 according to sat nav... I've spoken to VW engineers and there's no way to reprogram the vehicle to inform it you've got bigger tyres. Other manufacturers allow this via ODB2 etc... Will have a play with the winter tyre setting and see if that makes a difference.... thanks for the suggestion @temporarysecretary
Click to expand...
You can adjust the Speedo reading on the t6. You just need an obd tool capable of accessing the instrument cluster and adjust the k-number. All info can be seen here

Just tweak it one digit at a time and try it. If you go too far it will trigger an acc fault. I'm running 20's and GPS reading 70mph results in Speedo reading about 74 or there abouts.

Just heed the advice in the above link regarding tweaking things on a t6.1
 
temporarysecretary said:
Scrap that. It appears it's just a warning too.
Click to expand...
Yes absolutely. I was full of optamism as I jumped in my van, tweaked the Winter Tyre settings and drove down the A2 to test it... ha ha! Yes it's just a speed warning, nothing more but gave me an excuse to go out for a drive ;) :slow rofl:
 
paulbishop2 said:
I purchased it recently and it has 255/40/20 which are 7% larger than stock. I put it in to VW as it keeps throwing up an ACC error and they said it was due to the tyres being too large a circumference (it thinks it is doing 50mph by the speedo but the sensor says its going faster and it then throws up an error the dash.) I had 275s on my last T5 and they were great. Do you know what width and offset your rims are?

Cheers
Click to expand...
I have a similar problem. 255/55/18 tyres on a new T6.1. Speedo under reads by about 10% and ACC is unavailable more than half the time. Just been to VW Van Centre, which said a diagnostic check on the ACC blames the wheel/tyre size. They recommend reverting to the original size wheels and tyres, which for cost reasons if nothing else I'm reluctant to do.

Was thinking of having someone with VCDS recode the wheel circumference but being put off by threads below that say that in T6.1 it's irreversible.

So havering between getting smaller tyres (may be tricky as I have all season ones, and expensive), smaller rims and tyres (even more expensive) or being brave and finding someone to recode. Any more up to date news on the coding issue or do people think that's still irreversible?
 
tomdavy said:
I have a similar problem. 255/55/18 tyres on a new T6.1. Speedo under reads by about 10% and ACC is unavailable more than half the time. Just been to VW Van Centre, which said a diagnostic check on the ACC blames the wheel/tyre size. They recommend reverting to the original size wheels and tyres, which for cost reasons if nothing else I'm reluctant to do.

Was thinking of having someone with VCDS recode the wheel circumference but being put off by threads below that say that in T6.1 it's irreversible.

So havering between getting smaller tyres (may be tricky as I have all season ones, and expensive), smaller rims and tyres (even more expensive) or being brave and finding someone to recode. Any more up to date news on the coding issue or do people think that's still irreversible?
Click to expand...
Surely it can't be possible that you could recode it but then be irreversible?

The code is either modifiable or it isn't?

I'm sure someone will be along shortly to tell you it's doable and reversible.
 
Some things can be genuinely write once for security. The chips are built with electronic fuses and once the value has been written the fuse is blown disabling the write capability.

eFuse - Wikipedia

en.m.wikipedia.org en.m.wikipedia.org

This is used for things like security keys and protecting the actual code in the ECUs - there are many modules that are shipped "blank" and you can only write once.
 
tomdavy said:
I have a similar problem. 255/55/18 tyres on a new T6.1. Speedo under reads by about 10% and ACC is unavailable more than half the time. Just been to VW Van Centre, which said a diagnostic check on the ACC blames the wheel/tyre size. They recommend reverting to the original size wheels and tyres, which for cost reasons if nothing else I'm reluctant to do.

Was thinking of having someone with VCDS recode the wheel circumference but being put off by threads below that say that in T6.1 it's irreversible.

So havering between getting smaller tyres (may be tricky as I have all season ones, and expensive), smaller rims and tyres (even more expensive) or being brave and finding someone to recode. Any more up to date news on the coding issue or do people think that's still irreversible?
Click to expand...
I've got 255/55r18 Falken wildpeak's fitted with no issues and my speedo is only 4% out on a 2021 T6.1. Mathematically 255/55r18 tyres will cause Speedo to under-read by a shade over 6%.What tyres do yoj have fitted to have that sort of variance?
I've had no issues with ACC.
 
@tomdavy What wheel size was originally fitted to your van?
@Samro What wheel size was originally fitted to yours?
Speculating, but on T6.1, I wonder, could it be down to the original wheel circumference variant programmed from the factory?
From my research (currently looking at tyre options on 18” and irreversibly reprogramming theT6.1 wheel circumference), 17” vans are programmed with wheel variant 3 and 16” vans are programmed with wheel variant 1.
With variant 3 being closer to the larger rolling diameter of the 255/55r18, could it be that it’s within the tolerance of whatever the van is doing for ACC to work, but that variant 1 is just outside of the tolerance?
 
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