According to the VW owners manual for a late 2L the original tyres were 185SR14 which is what I have on mine (just checked)
Of course to maintain your rolling diameter you need to know what the diameter is. Miy 185SR14s are 25.5 inches dia. That is what your new tyres should be. Just ask the supplier.
Even better is this, which advises also about the chnage in your speedo reading if you get it wrong. You can compare any size to another. http://www.etyres.co.uk/tyre-size-calculator.htm
Can anyone tell me what size of tyres I can run on 14" rims ,lowered 1 spline at the rear with the van sitting a little lower at the front ,on saying that the engine ain't in yet ?