They will probably fit, but they won't be ideal due to all of that extra tire height. It will more than likely throw off your MPG and the way the SX handles. It might even mess with the traction control, but I haven't heard much (or looked into it for that matter) about how the Kia traction control system reacts to tire changes.

It is understandable if you want to try to get another winter or so out of them, so go ahead and give it a shot.

 

Do the bolt patterns match up?? If so, than try it, because you can always remove them if they get too bad.

 

Your speedometer will read about 6.25% too slow. Which means at 60mph your speedo will read about 56.5 mph which also means your odometer will be off by 6.25%. Gearing will be screwed up a bit most likely hurting fuel economy, acceleration, and braking. Tires may rub on the wheel wells but I think that's something that you'll just have to test fit and find out.

You can do it...most people wouldn't recommend it... for the reasons listed above. Personally I bet it'll look pretty good if you're into the rally look. I have an 89 honda civic wagon as my other car and guys are putting 27" tires in place of the stock 23.6" tires for off road handling and looks on that car and they say the car still drives fine so a big jump in tires might not bother you so much, but I don't think anyone knows yet how the forte will handle it.

 

Tire's tread life and traction are often discussed for obvious reason; not as often talked about, but just as important, is how a tire's stiffness must be considered part of the suspension system. *Assuming* that the 16 and 17 tires are constructed similarly and used for similar purpose (i.e. 4 season tire, or summer tire, or whatever) I would think that the 16 inch tire, with its higher profile, meaning more rubber, will likely mean ride will improve, but handling will suffer.

As someone else has mentioned, the SX is designed with 215/45/17 tire, unless the ride bothers you that much (I think it's perfectly fine and fun!), I would leave it as is. The car must have gone under hours and hours and hours of testing at Kia; unless a change shows improvement convincingly, either subjective by trusted/experienced drivers, or objectively with faster track time, I don't believe in drastic changes to the suspension system.

If you want to experiement, then the first step IMHO is to try better tire; for example for sure I will give the Continental ExCon DW (not DWS) a try once these stock Good Year's wear out. However it is, the same equation applies: more likely if ride improves, then handling will suffer. This is the classic tradeoff and there is rarely an exception. If for some reason the Continental has better ride AND handling - a possibility since the stock tire is so cheap, I would consider us to be very lucky!

 

I don't mind the ride at all actually, these othe tires I have are just for the winter. It makes sense that more rubber on the tire leads to a better ride, but the handling would lose some of its fun, but in the winter, it's not exactly a big deal. I'm just hoping to squeeze out a few winters more on the tires, before having to replace them is all.

 

^^^I see what you are trying to do. Thanks for the clarification.