TT victor John McGuinness believes island racers are reaching the limits of their ability to ride any faster at the Isle of Man.

The 33-year-old revealed the 1000cc superbikes, which reach speeds of between 170mph and 180mph over the Mountain Course, were already producing more power than riders could handle.

McGuinness, who holds the outright official and unofficial TT lap records, said: "There are places on the circuit where you'd be flat out only a few years ago, but you can't go flat out along there now.

"How much faster do I honestly think I could go? Not much. The bikes are so powerful now, you can end up pushing yourself over the edge.

"So more than the bike's limits, it's almost a question of knowing your own limits.

"There are some places on the course where I wouldn't push myself any further, places you go through and it's just a blur.

"You can't be thinking I wonder what's around the next corner' or that's a big lamp post, I wouldn't like to hit that' - you don't have time to make many sorts of calculations at all because you're just riding on instinct."

McGuinness romped to victory in Saturday's Superbike race but was forced to settle for fifth in the Superstock race, blaming his own lack of focus for a fifth-placed finish after having fastest in practice session.

And the Morecambe-based HM Plant Honda rider, who will be looking for a return to form in tomorrow's Supersport race, added: "I was a little disappointed, especially after the euphoria of Saturday's race.

"I'd been struggling with the stocker and I'm a little bit miffed because it's the bike I ride in the National Superstock Championship.

"I'm currently third in that championship and have been having some strong results of late but I it just wasn't my day.

"I had a really lazy first lap and to be honest a had a couple of hairy moments. You could say I lost the plot and it took me a good while before I got into my rhythm.

"After that I rode it as hard as I could but I just couldn't make any more of an inroads on the front four."

McAdoo Kawasaki rider Ian Hutchinson set a new fastest Supersport practice time to lay down his own marker for victory.

After finishing third in Saturday's Superbike race and second in the Superstock event, Hutchinson heads into tomorrow's race buoyed by clocking the quickest lap in all Supersport practice sessions on his 600cc ZX6-R machine.

Yorkshireman Hutchinson lapped the 37.73-mile Mountain Course in a time of 18 minutes and 27.04 seconds, at an average speed of 122.695mph.

Martin Finnegan, riding the Klaffi Honda 1000cc Fireblade, was fastest in Senior TT practice when he lapped in a time of 18:50.16 at an average of 120.185mph.