Does anyone knows what's the biggest size rims i can put on my datsun 1200 fastback? I need the dimensions.Any info on this ?

All depends on how much work you wanna do.
I think around 14 inch wheels with 60 series tyres are as big as you can go without mods
.
WIth Stanza struts and a small amount of guard massaging, I got 195/50 R15's on my coupe.

People have fitted bigger ones though. I'll let them tell you what they did

I have a set of 16 x 6 running 40 profile
no mods needed thats on a ute though
have had no scraping of the guards and think I might upgrade to 17s when the rubber dies but they are new so it could take a while.

That 45USN Datto 1200 had 17" Vault Krystals, i imagine alot of work to fit them...

duno why u'd wana go much bigger than 15 anyway, but.... im runnin 14s with 60's on stanza struts with a bit of neg camber and the ute is lowered a bit so had to panel beat the very front corner of the guards in to stop scrubbing on full lock, and ive rolled the guards as well cos it was gettin a bit close.

no offence to those who like the huge wheels, but i rekon for a car the size of a 1200 17's are a bit overboard.

good luck though mate, whateva floats your boat

have you ever seen 17's on a 1200 before? 15's look big on them im not shour of your background, some are the type that 26" rims on pimped out hummers with 5 tonne of audio :p... spose if you like it go for it.. i personaly havent seen too many 1200 with 17's, but i know that at least one guy has 17's i have seen a pic of it on here before..

the old coupe i had was running 13x7 with 225/60 on the rear
the rim had 110 mm from inner rim to internal bolt face

From what has been posted it looks like 17inch wheels are possible, but there are so many variables,what fits on one guys car wont fit on anothers.

If you want the biggest rims possible you are probably not the sort of guy who would be happy with a stock ride height either,and as soon as you lower your car the rims that did fit dont.

If you are after an older style deep dish rim you will most likely have to pump the guards but the same size rim in a front wheel drive offset may fit without modification.

I've seen 18" and 17",but really you only want 15"s.

I've got 15" on my ute and they don't scrape BUT they are too big for the look of the car, I had 13" mags before and they were much better