explain tire size fitments

[idanity]

explain tire size fitments / staggered / stretching etc. my current is falken zieks ze512's and worn.
225x45x17 direct fit, no spacers, no rubbing
wheels are 17x7 +42mm offset (no spacers/ rubbing)
grouind control coilovers 500/350

what i want is
FALKEN Azenis RT-615 94Ws or FEDERAL SS595RS-R 94W

225x45x17 front
235x45x17 rear

i know this will bring slight understeer upon what is already a perfect handling machine. but how much ?

please explain why i see many people who are running wheels (17x7.5) with tires 215x40x17 (basically why are they stretching the rubber ?
is there a rule to fallow ?

also.
what is the widest tire we can run in the rear w/out seeing any rubbing or requiring spacers

[braytonia]

A 215/40 on a 7.5 isn't that much of a stretch... And people usually stretch tires because it means less tire flex but in turn makes for a horrible ride. But I come from a world where people stretched tires just to fit the rubber in the wheel wells. And the biggest tire you can fit in the rear... That I'm not sure its all trial and error I guess.

Examples of a ridiculous stretch... Left- 175/45 on a 8inch wheel and on the right a 215/45 on a 10 inch wheel.

[idanity]

so by that (very silly looking) standard,
if i install 235's on a 7" wheel, i would have less sidewall strength, or roll-over ?

[braytonia]

so by that (very silly looking) standard,
if i install 235's on a 7" wheel, i would have less sidewall strength, or roll-over ?

235s on 7inch wheels would look a little funny almost like monster truck tires. But you wont roll over, youll just feel the tire roll if you drive hard.

[StereoInstaller1]

If you really like the "overstuffed" look, get Nexxen.

My 215/40/17s were over an inch wider than the set they replaced n the same size.

[idanity]

If you really like the "overstuffed" look, get Nexxen.

My 215/40/17s were over an inch wider than the set they replaced n the same size.

havent seen them.
i have narrowed down 2 types of tires
FALKEN Azenis RT-615 94W vs. FEDERAL SS595RS-R 94W

if i decide on 225 all the way around, i will get Azenis's,
if staggered, the federal,
only b/c i cannot find the azenis's in 235x45x17,
and they are lighter.

thanks for the replies.