There are a couple of issues with changing wheels sizes, but it’s a question a lot of people ask. That’s because the trend towards larger-diameter, super-low profile tyres doesn’t make sense for a lot of owners. Complaints include poor ride quality, expensive tyre replacement costs and the punctures you’re experiencing.
Even though the 50-series tyres on your car are not what most would call super-low profile, they don’t feature the same depth of sidewall as a `taller’ high-profile tyre. At that point, the sidewall has to be more rigid and there’s less flex in it. Which, in turn, makes the sidewall sometimes more susceptible to copping a stray rock or even a kerbside gutter and not being able to flex to prevent damage to the rubber itself. So, in some cases, going to a smaller wheel but a tyre with a higher profile (deeper sidewall) can be a good move.
What will limit this will be the brakes on your Tiguan. Fundamentally, you need to have a wheel rim with a large enough inside diameter that it clears the brake calipers. If the wheel diameter is smaller than the brake package, you physically won’t be able to fit the new wheel-tyre combination. There are also the issues of ground clearance and speedometer calibration, both of which can be compromised with a different wheel-tyre package and, therefore, a different rolling diameter. The trick is to use, say, an 18-inch wheel and match that with an 18-inch tyre that has a deeper sidewall that gets you back to the original tyres’ rolling diameter. That will retain your speedo accuracy and your ground clearance and should also give you a tyre that’s less prone to sidewall damage and cheaper to replace if the unthinkable does happen again.
A good tyres shop should be able to help you with the necessary measurements and sizing.