comparing 205/55/R16 and 205/50/17 , will the 17 inch tire be firmer than the 16 inch?
Yes.
If you are considering swapping rims:
The aspect ratio of a tire means the height of the tire's sidewall. It is the second number in the tire size, which is shown as the percentage of the tire's footprint width. This tire size measurement determines how tall a tire will be in the end.
The 205/50/17 tire has less sidewall and will result in a slightly stiifer ride, but increased response. However, the handling improvement will be negated because the rim will be heavier, creating more unsprung mass (total weight not supported by the springs on the car) Unsprung weight is bad because it takes more effort to get that weight to turn affecting handling and fuel economy.
If your rims are in good shape and you like the way the car drives, keep them. The benefits of swapping rims would not be woth the cost in my opinion. You will be fine.
Rims that I would consider if you ever want to increase handling and fuel economy are the 17" rims from a Cruise Eco model. They weigh the same as the stock 15" aluminum rims that came with my car. That swap turned what I considered to be kind of a boring car into a car that is a hoot to drive. I have the 1.8 engine and MT and flog it on occasion.. The only negative is that they are sort of ugly, but I got used to them. I put snow tires on the 15"s, and the junkyard rims were not that expensive and are good shape. For me, that was a good investment.
