The contests for all three drivers' titles in the Porsche Carrera Cup GB are really hotting up as championships moves to Silverstone for rounds 15 and 16 over the weekend of 29/30 August. Tim Harvey currently heads the overall title race, while Robert Lawson tops pro-am1 and Robin Clark leads pro-am2, but all three battles are very finely balanced.Over 20 examples of the stunning 911GT3 Cup car will gather at Silverstone for two more races, and the Northampton circuit is something of a home venue for Porsche as it plays host to the superb Porsche Driving Experience Centre.In the overall standings, Tim Harvey (Red Line Racing) and Tim Bridgman (Team Parker Racing) are the key title contenders and they head to Silverstone split by only four points – in Harvey's favour. Bridgman clawed just one point back in the course of the previous race weekend at Knockhill, so it is going to be a tense run-in to the title. "As each meeting goes by, it becomes tighter and history suggests it will probably go down to the wire," said Harvey.However, Michael Caine (Motorbase Performance) and James Sutton (Red Line Racing) are still chasing the title and a bad weekend for Harvey and Bridgman would bring Caine and Sutton right into contention. Meanwhile, young Carrera Cup scholarship winners Tom Bradshaw (Team Parker Racing) and Lewis Hopkins (Red Line Racing) are getting quicker and quicker and could yet join the big four over the closing races of the season.In the pro-am1 category, the competition is just as intense as Robert Lawson (JHR) battles to hold on to a series lead he has held since Oulton Park at the end of May. Lawson is having a superb debut season in the Carrera Cup, but he has a gaggle of rivals and it is Glynn Geddie (Team Parker Racing) who is coming up strongly. A superb double win at Knockhill has brought Geddie to within 13 points of Lawson. At the end of round 10 at Croft in June, Geddie was 39 points adrift of Lawson.But the pro-am1 battle is not just about Lawson and Geddie. In particular, Ollie Jackson (Motorbase Performance) and Tony Gilham (Red Line Racing) are well in contention, while Derek Pierce (JHR) will be quick and Michael Leonard (Team Parker Racing) rejoins the battle after missing the Knockhill weekend. New into pro-am1 this weekend will be Liam Griffin in another car from the Motorbase Performance squad.The points' situation in pro-am2 is also attracting a lot of interest and there has been some great racing in the category over recent race weekends. Robin Clark (Parr Motorsport) continues to head the standings, but his lead is under attack from Bob Lyons (Celtic Speed), Paul Hogarth (IN2Racing) and Glenn McMenamin (Parr Motorsport) and with scores to be dropped, it's going to be a close battle to the title.Round 15 of the Carrera Cup GB is scheduled for 4.20pm on Saturday after qualifying on Saturday morning. Round 16 will start at 1.15pm on Sunday and is expected to go out live on ITV4 during the afternoon's BTCC programme.