Hi, first of all welcome to Pakwheels. Awesome, so you're a Belta owner aswell. What is model year of your particluar Belta? I am really glad you like the car so far, could you give us more details and maybe post some pictures of it so we could get a good idea of how your Belta is like.
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Spacers are a big no, they do raise your inital vehicle height but at the same time your shock absorbers and springs get damaged. The stock tire profile of the 1.0L Belta is 165/70/R14 if you don't want a really big difference in your overall drive quality then I would suggest you go for 185/65/R15 at max which is the tire profile for the 1.3L with 15'' alloy rims it won't make the suspension a tad bit stiffer because the suspension of the 1.0L and 1.3L varients are the same although the 4WD being an exception.
What 1.3L Belta did you drive? The one with the 2SZ-FE or the one with the 2NZ-FE? The ride quality of the 1.0L and the 1.3L are pretty much the same, but the 1.3L varient has more overall power as compared to the 1.0L varient ofcourse and the fuel economy of both isn't that much of a difference either. That roaring sound you hear when you gun the car is of the CVT gearbox, at full accleration it changes gears at higher RPM's. I've experienced it with the 1.3L varient aswell because it comes with a CVT gearbox too.