The achievement description is wrong.
You need to win the SUPERBIKE TT (Tourist Trophy).
It's 3 laps qualifying, 6 laps in the actual race.
Before properly attempting this I would practise on the supersport TT first. It's 1 lap qualifying and 4 in the actual TT. If you can't win that you'll likely have difficulties on a superbike.
I use the SUTER MMX 500 which I was able to purchase after placing in the top 3 in the SUTER invitational. It's a pretty fast and well rounded bike.
My 1st attempt was 110 minutes and 59 seconds (I won by about 20 seconds).
2nd attempt was 110 minutes and 20 seconds (won by about about 40 seconds).
3rd attempt was 109 minutes and 40 seconds (I won by literally about 4 seconds).
Probably crashed on average about 1.5 times per lap.
I aimed to beat 55 minutes and 30 seconds after 3 laps to give myself a chance to finish below 111 minutes.
You need to pit every 2 laps (don't exceed 37mph when going into the pits, you'll be disqualified. If that happens though you can dashboard then load the race back up but it usually becomes buggy so just don't.
Make sure to qualify in 1st and in the actual race you don't want to let any bikes overtake you. You don't need more obstacles and the AI can wipe you out easy anytime.
They will be somewhere behind you the whole 6 laps. Just keep focus and don't crash too much.
Extra tip* don't full throttle coming out of corners just half throttle until you get going a bit an then straighten up. It's very easy to lose grip. Also when braking hard try and approach corners perfectly straight. If you are at an angle and brake hard you'll probably say hello to a crash..
Learn the track. Know where you can go flat out and where the nasty corners are I.E. ballacraines, douglas road corner. parliament square, guthries memorial, the bungalow etc.
Your gameplay settings should be semi-pro. Turn off screen shake and wind blindness or whatever it's called (hell).
Good luck! I advise coffee or some energy drink. Can be nice to turn the engine volume down a bit.