Hi. What is the maximum front&rear disk sizes for stock calipers on an Octavia 2 1.9 TDI? 
The front calipers should be FS-III and the factory disk size is 280mm .

The rear ones are CII 38 and are coming with 255mm disks.

Now, what are the maximum disk sizes I can fit in? Or do I have to change the calipers to fit the RS sized disks (312mm front/ 272-286 rear)

My understanding is if  the front strut diameter is 50mm then you are stuck with small rotors unless you change the hub carrier and strut to 55mm.  Then you'll need 312mm rotors with VRS/GTI calipers and caliper carriers and minimum 16" rims

 

Can;t help with the rears - sorry.

 

If you are overheating the brakes & boiling fluid then you might consider better brake pads, better brake fluid and some ducting to direct air onto the calipers better

Thank you!
No, they are not overheating (yet). But in March/April I plan to go for a Stage 1 and also upgrade my brakes (I have to change them anyway by then). 
I know about rim size, I was planning to get 17" rims anyway.
The conclusion is that I have to swap for RS calipers. Probably a better idea is to sell it and buy an RS

6 hours ago, BMV94 said:

The conclusion is that I have to swap for RS calipers. Probably a better idea is to sell it and buy an RS

Unless you can DIY everything and have access to cheap parts from a donor car.

 

Buy the RS and you get better seats, better suspension and more power straight away.

 

I've modded my 1.8tsi Elegance a fair bit but at the end of the day it's still a 1.8tsi Elegance.