Guys, I think you need to think long and hard about lowering your tyre index without supporting information from VW, you are just asking for trouble
from your insurer if you cannot justify your rational with hard evidence.
On my Audi A4 I went from a load index of 95 XL to 94 XL when I fitted winter tyres last winter, Audi UK couldn’t give me a definitive answer when I emailed them
(maybe I got the wrong person or dept.) A local dealer helped out; interestingly the Audi website now have a useful online tyre configurator
http://www.audi.co.uk/owners-area/audi-tyres/online-quotation.html that shows different spec’s depending on wheel size/tyre size (which I think is similar to what the dealer used to confirm my tyres were suitable)
My car came with 235/40 R18 95Y summer tyres. However, If I drop to 17” it recommends 235/45 R17 93W but also recommends a load index of 94W on a couple of brands (because I was fitting winter tyres I went with a slightly thinner tyre 225 which is good practice and allows for snow chains to be fitted)
If I drop to 16” it recommends 205/55 R16 91V but also 215/55 R16 93V (for the wider tyre) If I drop to 15”
(not sure they’ll fit over the brakes?) it recommends 195/65 R15 91H but also 205/65 R15 95H (wider tyre)
So there is variance on the load index issue; that said it appears to increase as the width of the tyre increases, I’m happy with the information I’ve got from Audi that I can safely run a 225/45 R17 94 winter tyre on my Audi A4.
I just think you’ll have a battle
on your hands with any insurer trying to convince them that using a lower Load index of 88 instead of 92 on your golf Gti/Ed30 when the width of tyre and size of wheel, are not being altered.