can anyone answer this ?

 

Yep, 17s went straight in to mine.

 

On the skyline Australia Forum I just read:
"165mm, same size as the rear ones, plenty of space on the backside, the plastic cradle the front ones sit in may need a little trimming for aftermarket speakers"

On the German Forum they also said some measures between 16-17 cm
So I would take the 17cm ones and give it a try =)

 

Front and rear ?

What colour are your front speaker mounts ? as I've got a slight felling mine have been changed as I've had a quick look and they look to small for 17's and I found a wanted thread of someone who was after some and the ones they posted a pic of were white plastic whereas mine are black and look wooden ???

 

fitted all the speakers, had to go for 13cm front and 17cm rear, 17's wouldn't have fitted in the front without modifying.

 

The factory size for the R34 is 6" ( commonly called 6.5") front and rear.
Unless you're fitting entry level speakers, some trimming of the factory speaker pod is common for ANY car!

....and for the record -
R33 is 6" front and rear
R32 is 6x4 front, 6" rear

 

Can you confirm 6" front door and rear deck speakers for ALL R34? Regardless of model?

I am about to order some replacement speakers. I like using Crutchfield but of course they don't have the info for Skylines