could be suspension as others have mentioned...but also..your rear tyre is obviously skimming across the ground a lil bit....move you weight back in the seat some if you can without locking your elbows...if not just lightly hold the rear brake on a bit...it will help keep the rear straighter as it skims...and if you already use rear brake...ummm...use it as a scare tactic to keep other racers from passing you into corners