To add more detail to the other solution: pick "Solo", "Quick Race" from the Menu. Select "Snaefell Mountain Course" track and pick "Tourist Trophy" beneath track selection. Select time of day of preference and hit the
button to confirm. On the next screen select your bike and again hit
to confirm. You will be racing on the longest track in the game. It takes on average 20-25 minutes to complete 1 lap and there are 6 laps in this race. I would advise going for
at the same time and following the solution for that achievement on your first or second lap (except race setup), and you will get
while going for this if you don't already have it. You will need to complete 2 laps (40-50 minutes) in total so get ready for that and enjoy this really delightful ride that makes you feel you're watching Eurosport.
Just when you are finishing lap #2 and approach the finish line to start lap #3 you will see a flashing gas icon indicating your bike needs service. Slow down after crossing the start line as the other guide suggests to about 35 km/h, and look out for the pit stop entrance on the left under a white-and-black checkered banner, just before that tall tower. If there were any riders just in front of you the chances are you'll see them there being attended to. Pull in slowly until a cutscene begins with the crew taking care of your bike. At this point the achievement should appear, and you can either continue to finish the race (between 2 and 2.5 hours total) or quit.