The wheels do affect the size of the bike, a little. 29er wheels make the bike sit higher as the hub is higher vs a 27.5 wheel. The wheel size really depends on riding style. 27.5 wheels tend to feel more playful and quicker. 29ers roll over things better and take a tad bit more effort to get them going. Best to google or YouTube the differences so you can make your own choice on what wheel you might like better.