Hi i am pretty new here, i was about to buy 4 used backed up wheels with 2 235/40/17, and 2 215/40/17. 80% tread, As u can see the section width are different. Does it matter? I am planning to put them on the evo.

Also do i need to balance the tires once they were put on?

thx a bunch

 

All of the numbers work together. The width also determines the tires height. The first three numbers are the width (215), the second is its height (40), and finally the wheel size (17). The height represents a % of the tires width. So, in a 215/40-17 the height is equal to 40% of the tire's tread width. If you change the first numbers (215) and not the second (40), the tire will get shorter or taller.

The diameters are different between the two. The height of your 215/40-17 is 23.8", the 235/40-17 is 24.4". This is because the height is 40% of 215mm in one tire and 40% of 235mm on the other.

Not the best idea to run a staggered tire setup on that car especially with that much difference in diameters. I'd buy another pair of 235/40's or better yet get the right OEM sized 235/45-17.

More on tire diameters Here

 

Umm... I wouldn't. The '40' in your numbers is roughly the height of the side wall. It is expressed as a percentage of the width, so we're talking about (40/100)x235 = 94mm and so on your 17 wheel, you've got a rolling diameter of 24.4"
On the other hand, you've got (40/100)x215 => 23.77" rolling diameter.
Anyway, the point is that two of your wheels are going to be bigger than the other two so the smaller ones are going to be spinning a little faster if they're on the same car. The evo's awd system is not going to take that and it's extremely likely that they're going to break.
So, don't do it. If the wheels are the same width (8.5"?) then get two new tyres at least. And yes, you will need to balance if you're changing tyres. Enen if you don't, it's always good to check since you have it off the car anyway.

p.s. tire rack has some pretty good info on tyres, you might want to start there....

Neal@tirerack beat me to it, oh well....