Hi all and thanks in advance for your replies. Just picked up a 2015 Octavia MK3 and was looking at upgrading the standard 16 inch alloys i have been offered a set of 18inch Audi sline alloys. i know the centre bore is different and will require Spigot rings Tyres are 245/40/18 ET47 8.0jx18H2

They'll fit ok, but 245 section is pretty wide, maybe too wide. Standard size for Octavia Mk3 is 225/40/18.

 

235/35/18 would be a closer match.

 

Are you sure CB is different? Octavia ones are 57.1mm.

Don't forget you have the tell the car that you are running on 17" or 18" tyres - the ECU has to be reconfigured - otherwise your speedo will become inaccurate.

Edited 3 December, 20205 yr by varaderoguy

1 minute ago, varaderoguy said:

Don't forget you have the tell the car that you are running on 17" or 18" tyres - the ECU has to be reconfigured - otherwise your speedo will become inaccurate.

 

Huh?

 

As long as the overall circumference is within a couple of % there is no need to change anything.

 

E.g. 205 55 16 to 225 40 18 will require no changes. 

 

I don't even know how you could 'tell the car' or 'reconfigure the ecu' for different wheel sizes tbh, although it's probably possible to recalibrate the speedo if you fitted a massively different setup.

 

www.willtheyfit.com is a very useful site 👍

Okay - I promise I am not making this up.  You *really* do have to tell your VW/Skoda that you are changing tyre sizes.  There is a whole thread here:

https://www.vwvortex.com/threads/vcds-coding-for-alltrack-wheel-sizes.9082490/

 

Yes, any significant difference can be corrected by VCDS coding.

But you do not *really* have to tell your car via anything. Not by phone letter or telegram or VCDS.  You could & can do if you want.

Edited 3 December, 20205 yr by e-Roottoot

2 hours ago, varaderoguy said:

Don't forget you have the tell the car that you are running on 17" or 18" tyres - the ECU has to be reconfigured - otherwise your speedo will become inaccurate.

And your insurance co.

2 hours ago, pist0nbr0ke said:

They'll fit ok, but 245 section is pretty wide, maybe too wide. Standard size for Octavia Mk3 is 225/40/18.

 

235/35/18 would be a closer match.

 

Are you sure CB is different? Octavia ones are 57.1mm.

Hi thanks for the reply the centre bore on these alloys is 66.6 was going to use spigot rings to reduce this. How would the width of the tyre being too wide affect the car?

2 hours ago, danicalifornia said:

Hi thanks for the reply the centre bore on these alloys is 66.6 was going to use spigot rings to reduce this. How would the width of the tyre being too wide affect the car?

 

It'll increase the overall circumference of the wheel and tyre, affecting the speedo, and it will possibly cause rubbing against the wheelarches. Try it and see, you can always change the tyres.

 

Spigot rings should be fine, although I was under the impression OEM Audi wheels were also 57.1mm CB. Are they genuine wheels or aftermarket?

So lets remember that the car arrives from the factory on the OEM tyres and is in no way accurate. It over reads. As the tyres wear it gets even less accurate.

 

So when the new wheels and tyres are fitted the speedo might be dead accurate.  As long as you check then if it under reads then you can have a good talk with the car and tell it to get it's act together & you sort it out with the VCDS.

Edited 3 December, 20205 yr by e-Roottoot

11 hours ago, e-Roottoot said:

So lets remember that the car arrives from the factory on the OEM tyres and is in no way accurate. It over reads. As the tyres wear it gets even less accurate.

Legislation requires that when new all speedos over-read by between 0% and 10% - normally on new OE size tyres the over-read is around 5% to allow for tyre wear and different OE tyre sizes without needing speedo recalibration.

14 hours ago, e-Roottoot said:

But you do not *really* have to tell your car via anything. Not by phone letter or telegram or VCDS.  You could & can do if you want.

 

You forgot Instagram .....