best way to travel with a bike?

wellbeloved747 Posts: 406
edited September 2012 in Road general
i am looking to go up to my Grandmas house soon an wanted to take my Allez to cycle around the London area what would be the best and safest way to carry the bike on the outside of the car. we have a volvo s60 and the bike with luggage will not go inside so how should i carry it. i have roof bars for the car so could anyone reccoment some fairly cheap roof carrying thig.