Sonic is one of the fastest beings in the Earth, but being fast does not translate to strong as well. When he got the job of collecting rings, he knows that he can only do it with the help of a vehicle fast and powerful enough to carry it to wherever the rings need to be delivered. Sonic tried lots of vehicle, but there is only one vehicle that can do the job. He needs a truck to collect those rings since it could hold a lot of those heavy rings. Also, the truck could rival his speed and he would be much feel safer if he drives a fast vehicle. His enemies are always close by and they would never let him do anything that would not have anything to do with them.
Whatever, Sonic does you can almost count on it that his enemies would be there too. The rings doesn’t have to do with the enemies, but they would surely be glad if they can delay Sonic in his job. They are to self-centered and insecure with Sonic that they would be glad if Sonic would not be able to do his job because of them. That is what a villain is for and they don’t need a reason to do those things.
In this game, the idea is to collect those rings on the road. You don’t have to stop to collect those rings since the rings would be on your truck the moment that you pass through them. You do need to drive carefully since the road is tricky and is made in the mountain. It just mean that you need to be extra careful while driving since you might lose some of the rings, which you need to deliver. Actually, you might have a road accident if you are not too careful enough.