I did some searching about tire profile sizes in the forum but most of the discussions were about fitting wider tires on the stock 18 rims.
I was wondering if anyone on the forum has increased the side profile size on these.
I love my W204 but the ride is a bit punishing sometimes as the asphalt in Brazil is kind of ****ty. Making it ride a little higher could also benefit me on some driveway entrances.
Would it be too sacrilegious from a performance standpoint to move from 265/35r18 rears to 265/40r18?

On the rear you can run 265/40x18 if running stock suspension.
I recently fitted w205 c63s wheels to my C63 estate with std suspension and the rears (9.5"x19 ET52 with 4mm spacer)came with 265/35x19 over std 255/30x19 and they fit with no scrubbing.
my old setup was 275/35x18 on E400 9" rears (same et54 as C63 wheels)


Old set up with 275/35x18

@Cwagon Why do you need a 4 mm spacer in the rear? Does it rub the strut without it?

No I was using the 4mm spacer with my old 18x9" ET54 to give an ET50 for a more flush with the guards look instead of tucked under.
If you wanted to get technical I had effectively widened the track by 8mm (2x4mm).
On the front I ran a 10mm spacer with longer bolts on 235/40x18 x 8.5" ET48 rim for a ET38 again with no rubbing.
As my C63s W205 rear rims are 19x9.5" ET56 I just decided to use the 4 mm spacer again for ET52
My current front rims are 19x8.5" ET38 std with 245/35x18 tire.

Thanks for the feedback! I'm on stock suspension so I think 265/40r18 should fit on the back on problem.
I understand that it might affect performance and speedo reading, but might improve the ride a little bit.
My car is currently running 225/40r18 in the front and 265/35r18 in the back. They're Toyo T1Rs and I think they're VERY stiff. Might be because of their age.
I'm going to go ahead and try swapping to 235/40r18 in the front and 265/40r18 in the back.

That combo should work fine and run 36psi F&R for a good comprimise between ride and handling.

Thanks for the response. Those w205 wheels look and fit well on the w204.

I was checking my tires today and saw that I have 225/40/18s on the front and 265/35r18s on the back.
The front tires are a bit smaller than the OEM size (235/40) and the back ones are wider than stock (255/35).
Do you think I'd get a decent increase in ride height/ground clearance if I went with 245/40r18s on the front and 275/35r18s on the back?
I'm not going up in sidewall height, but the wider tires (by 20mm in the front an 10mm in the back) should be taller, right?

Both the 245/40x18 and 275/35x18 are a good choice and should fit the std wheels fine.
Just check how much tire clearance you have on front to the strut.
On the rear the 275/35x18 will fit the std 9" rim and will be slightly wider and a tiny bit taller.