A cheap upgrade for the bikes would be smooth 1.5" wide tires from the bike shop. Follow the gear and brake adjustments on the Park Tool website, and you will be able to get plenty of fun out of the Walmart bikes. I have a Cat Eye and a Planet Bike LED lights on my bike (about $20 each 10 years ago), but I also bought LED flashlights for $2 each at the $ store, and I put them on the handlebars with elastic bands.