It's difficult to advise fully without knowing which Controller you are using. A good wheel is highly recommended for this Sim.
I use a G25 and find the Steering very realistic, but you may need to make some settings adjustments to fine tune it to your liking.
The Steering is usually more twitchy on Tarmac than on other surfaces.
Here are some tips that may help:
1. Go into your RBR folder, usually located in C:/ProgramFiles/SCi Games/RBR and find the file RichardBurnsRally.ini, open this up in notepad, and delete the top line that says ConstantForceMultiplayer = ... (wise to make a backup of this file just incase it doesn't work for you).
Rename PC_Inputfilter.ini to PC_Inputfilter.bak or delete completely.
2. Here is a very useful thread discussing Steering Ratios:
http://www.racedepartment.com/showthread.php?t=45114
3. Here is a link to my G25 Settings, based on the above thread advice:
http://www.racedepartment.com/showthread.php?t=46308&p=706532#post706532
With these Settings, I usually use the maximum Steering Lock under the car setup options (in-game, under Tuning).