Is a 1/2" smaller overall diameter ok?
 

My stock wheels/tires are: 255/45/17, total diameter of 26.03"

What would be the negative effects of replacing these with:
front: 235/35/19, total diameter of 25.47"
rear: 265/30/19, total diameter of 25.25"

For reference, stock 19s for my car come in:
front: 255/35/19, total diameter of 26.02"
rear: 285/30/19, total diameter of 25.73"

It'll be like having slightly deeper gears giving you slightly quicker acceleration and your speedo will read slightly faster then you are going.

Thanks! So there will be no long (or short) term negative impact on the car?
If it's just the speedo reading off by a few kmph, that's fine with me..

since ur 265 30 19 is smaller than 255 45 17 by 3% or so, when u accelerate hard u will activate ur abs and tcs if u have it. that can screw up gears like rear diff and tranny coz its spinning too fast according to ur gear ratio.

:suspicious: curious how that works...tcs is usually set up to detect difference in wheel speed between all four wheels. if he's replacing one tire on one side with the 3% bigger tire then yeh maybe his tcs would kick in

by replacing all 4 tires, he'll be decreasing all 4 tires at the same time, making the sensors see the wheels move at the same rate, causing no tcs/abs/broken gears. just like what phil said, it'll just be accelerating 3% faster, and showing a speedo difference of 3%

more so, his car's stock 19s front-to-rear difference on his car is 1.1% (26.02/25.73), going to his chosen tires would be 0.9% (25.47/25.25). 0.2% is most likely under the parameters for TCS/abs to kick in if it's set up to expect a certain front-to-rear wheel speed difference

just telling what i xperienced. OP can always ignore my post but let us know.