You can use this method of racing to earn around 7,000 Reputation Points every two minutes. Note that you'll need a friend to do it and possibly at least two cars (excluding motorbikes) in your garage. We say "possibly" because some people have reported it not working if they have less than that number of cars... Anyway, here's the steps:

1. Either you or your friend need to host a Criminal Records online race. You can find this under Jobs in a lobby.
2. Make sure you setup the rules for the race as pictured further below. This is important.
3. Then invite your friend in (or they invite you), choose any vehicle that you want and start the race.
4. Note that you don't really need to beat your friend, it might get you a few extra RP but it's not really important.
5. Just keep racing and you should be able to earn around 7,000 RP every 2 minutes. You are awarded the RP at the end of every lap.
6. At the end of the race simply choose to replay it.

Thanks TwoDynamicHD