Yeah i have read that +40 is around perfect and i am just curious to see if the 5mm is that big of a deal that will make or break my overall wheels fitting or not...
I have just fitted 18x9 +35 with 245 45 18 to my 13 wagon. its not lowered. rears are fine. fronts poke a tiny bit, maybe 5mm at most.
So I would say that you will have some issues with 10 inch wide wheels and 35 offset which will end up being 12.7mm wider than 9 inch wheels with the same offset.
So with 40 offset the 10 inch wide wheels will be 7.7mm wider so you will need to account for 12.7mm at the top of the wheel taking into account the assumption the poke I have is 5mm.
You would need some serious camber (bolts may work) and stretch to come close to making them fit though I am sure its possible.
Lets assume you make up 5mm with guard rolling.
You then have a net 7.7mm to deal with. for that you will need camber.
So assuming you have a 235 35 20 tyre you will have an approx. rolling diameter of 673mm which gives a rolling radius of 336.5mm.
Using maths and shit to make up 8mm using camber you would require 1.362 of additional negative camber than I have which is approx. 0.55 so that gives a total of 1.912 degrees of negative camber. I don't believe that is possible with camber bolts so you would likely need strut top camber thingys.
but that doesnt take into account the actual range of additional camber you will need to add because the lower the car goes the more additional negative camber you will need to add to reach the final figure of 1.912.
so say lowering the car by 40mm reduces negative camber by 0.5 degrees you would in theory need to have an additional 2.412 degrees to reach the actual reading of 1.912.
I am no expert on suspension geometry by any means but thats how I see it.
sorry for the long winded disjointed discussion but thats how my mind works im afraid!