Wheel swap

I very much doubt it cayuga duck. Copen standard wheel size is 165/50 R15 so the 185/55 16 will be way too big. There are other posts here on tyre size and a link to a good tyre size comparator website, just do some searches in the forum.

 

take a look at something like - http://www.rimsntires.com/specspro.jsp

the basics are - your original wheels are

4 x 100
15x4.5
ET45

Tyres
165/50 15

So, as well as the wheels needing to be 4 x 100 - you can then drop in the size of other wheels and tyre combo's and see how different they will be from standard.

If the Suzuki ones a 4x100 that's a start - but you'll need the width, ET and bore details as well to be sure. The other issue tends to be that the Kei cars go for uncommon sized tyres. On a 16" rim, those 55 profile tyres will end up with too large an overall diameter compared to your originals (Australian states have a limit you have to meet) - in Qld it's +15mm. With that large a diameter change - as well as reduced clearance under your guards - your speedo is out by a few % (hence the regulations).

I just went through all of this last month getting new wheels and tyres. I looked at all of the local wheel store options, stock wheels from others cars etc - but few had close to the Copen Kei car specs. (close to ET45 is not common - and I wanted to avoid rubbing and guard rolling etc).

I ended up getting a set of Weds wheels from Japan (a massive collection of Kei-car friendly wheels there of course) - and found one brand of suitable size tyres on the market in Australia (I needed 165/40 R16's to fit my 4x100 16x6 ET45 wheels)

 

Too big. You will need something like mine, 195/40-16. And i have a steering angle decreser (english?) installed.

 

stick with 15" if you can and drop the car a little. I ended up choosing 17" wheels for mine and im now having to cut and mod a lot of the car to fit on to it properly have a look here https://www.copenworld.com/vb3/showthread.php?t=2695&page=2 this is when i first put the wheels on. I couldn't get a full turniing circle as they was rubbing. now started flairing the arches but there is a lot of man hours thats gone into it. Ive now measure mine and its possible to fit 18" wheels on but to play it safe im sticking to 17" for the bumps and so on. I also use a 205/40/17 tyre which is a nice smooth ride to me