I see few people want to touch this one.

And rightfully so. There is no perfect answer. I have been struggling with the same question all winter. The problem is no two 914's are exactly the same. And all flares are different.
The easy answer is 7's in front and 8's in back. But like DDS said, you will probably need spacers up front. I bought a set of 15" and now I am finding less variety in tire choice in 15". I probably should have gone with 16". It's hard to find a mnf'r that offers 225/50/15's and 205/55/15 to get the same diameter front and rear. Is anyone running 225/50/15's on 4 corners with 7's up front and 8's in rear??
I would love to hear what people with flares are have success with.
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'70 914 2.0
2004 Harley Davidson FatBoy
2000 FROD Exploder
'92 VW Cabrio
"some days you sand, Some days you prime"