Never said anyone was. Directional tyres prevent you from doing 4 (or 5) wheel rotations, you can only rotate the wheels on each side. Directional tyres can be had in 15s, just not easily here as there is no demand. Look up track tyres and you will see they aren't available in low profile for a reason. The difference between a 16, a 17 and a 15 on the street will be negligible. I compete on 15s and I'm not seeing any loss in handling. But most people buy rims for show, so yes bigger rims do look better and 17s on the Corolla look less awkward than 15s. Don't forget to pay attention to the rim width, which is just as critical to handling as the rest of the specs. As for you preload question. You want to know how much they compress the spring from the factory? Zero. I think you mean height drop; If I remember correctly its -40mm at the front and -50mm at the back. As far as track tires go, another reason people put bigger rims on their cars, is because the have the ability to go wider, I currently have 7.5's instead of the stock 6, So that's an extra 1.5 inches of tread, although currently the rim itself is 2 inches bigger, It's not a bad idea to have bigger rims on a track car, that way you can fit bigger braking systems in your wheels. Most of the GT1 GT2 and some GT3 cars run bigger rims than stock* (This is referring to the GT2.GT3 classes)(They usually do fit bigger rims, But not all the time (mostly wider/lighter ones). But what about those semi light weight rims? you were talking about adding weight. Therefore making your car slower, but if you get a set of rims that weigh the same as your stock rims; its not a bad idea. I quite confused about what you are trying to say here... -You don't need to go a larger size to go wider. For example sportivo rims are 16x6. Most aftermarket ones are 16x7. Although you could get a 3 piece to -I'm pretty sure you can still fit most big brake kits under 16s on the rolla. -The reason the Carrera Cup cars run larger wheels is because they have upgraded brakes which require them to have larger wheels. It's not that they just wanted to use larger wheels for 'grip' -No matter how light you make the larger size rim, they smaller version of the rim will always be lighter. Btw the stock sportivo rim weighs 8-8.5kg. A quality lightweight rim will weigh somewhere between 6-7kg for a 16x7 (which is wider) Also in regards to tyres. I don't think you understand what radial means still. Directional, assymetric and conventonal are all terms that describe the tread on the tyre. All these tyres are constructed in a similar way; tyre is constructed about the circumference, not across the width, hence called 'radial'. My definition sucks lol :(