It has been created by Welsh company Wild Creations, the people behind the popular ‘ball in the wall’ sculpture at Cardiff Castle for the 2015 Rugby World Cup.
It will be a focal point for Stage One of the Tour of Britain which passes County Hall on its route from Pembrey Country Park to Llandovery.
People are being encouraged to visit County Hall for photo opportunities with the giant bike in the run-up to the event, sharing their photos on social media using the hashtags #BeicioSirGar and #CycleCarms.
It is part of a big marketing campaign by Carmarthenshire County Council to promote the tour.
Over the last week people have been spotting a number of green bikes that have been dotted around the county.
Local communities and businesses are also being encouraged to get involved and benefit from the tour, with 15 town and community councils and several cycling clubs amongst those putting on their own events and decorating their streets for crowds to enjoy.
Early indications are that thousands of people will visit Carmarthenshire to catch a glimpse of world-famous cyclists – possibly including Tour de France winner Geraint Thomas – and communities and businesses are set to see a boom in trade.
Similar regions around the UK that have previously welcomed the tour have reported economic boosts of around £4million.
The giant bike is the county council’s official entry into the national Tour of Britain land art competition, where towns and villages along the route are encouraged to get creative for the ‘eye in the sky’ cameras that capture the race for ITV4.
It will stay at County Hall until late September before moving to its permanent home at the newly opened National Closed Road Circuit in Pembrey Country Park.
Cllr Peter Hughes Griffiths, executive board member for culture, sport and tourism, said: “We are thrilled that Carmarthenshire has been chosen as the start of the Tour of Britain, the biggest road race in the UK.
“We wanted to do something special to mark this special event and provide a focal point for families who are as excited as we are to welcome the tour.
“The cyclists will be racing over Towy Bridge right in front of County Hall as part of the race, so this will be a great sight for them and everyone watching the live television coverage.
“Come along to County Hall to see the bike and take some selfies with it – we’re looking forward to seeing everyone’s pictures across social media as we lead up to September 2.”
Carmarthenshire Council video –