The BMX can be found at the north-east corner of the dirt track in front of the sloped bank. Get on the bike to start the trial.
The BMX is better at taking corners than the Quad bike, but much slower than the Sanchez, so you can pretty much just keep peddling at all times apart from on the tight turns and you won't need to brake at all.
Course 1: Target Time: 1 minute 25 seconds
You should be able to take the first turn around the sloped bank without slowing down and without needing to use the bank to help you turn. Ease off the pedalling once you drop down into the ditch after the next right turn by the hump. Level out as you jump the next hump, then stop pedalling again as you come out of the ditch to turn right going back to the start line.
Course 2: Target Time: 1 minute 30 seconds
Stop pedalling briefly as you turn after the double sloped banks, then ease off the pedals again as you come down from the second mound so that you can turn left at the bottom. You should be able to take the next left turn without slowing down if you start turning early enough, then jump the hump to start the next lap.
Course 3: Target Time: 1 minute 20 seconds
You can to do this course without slowing down at all. Start turning at the first sloped bank as early as possible to take the long 180-degree turn in one go. After the mound leave turning until just before you hit the sloped bank so that you get the right path to the next marker and take the whole turn in one go.
Course 4: Target Time: 1 minute 35 seconds
Again, you should be able to do this course without taking your finger off the pedal button. After the first the first turn keep to the left of the track so you can get a good right turn into the ditch. Level out as you jump the hump over the next ditch. After the next turn at the sloped bank is a hump. Jump this hump and you're onto the next lap.
Course 5: Target Time: 1 minute 45 seconds
Another no-go-slow course. After the first two right turns you'll hit a hump. Level out as you jump and then turn right around the next bends. You'll then jump the hump and be on the next lap.
Course 6: Target Time: 1 minute 40 seconds
The first turn looks quite tight, but you can take it without slowing down. Ease off the pedals once you get to the checkpoint on the sloped bank though, as you need to take a sharp left turn just after this to climb back up to the mound. Stop pedalling before you get to the bottom of the mound to take the tight right bend, then turn right around the long sloped bank and back up to the starting line.
Course 7: Target Time: 1 minute 35 seconds
Bear left around the three sloped banks, then level out after you hit the hump and drop into the ditch. Turn around the next sloped bank then head back up for the next lap.
Course 8: Target Time: 2 minutes 40 seconds
Slow down as you get to the first turn, it's a tight one. Jump the hump, turn around the next two slopes then stop pedalling to take the tight left turn at the bottom of the second mound. Slow down again for the next turn, then bear around the long sloped bank and back to the staring line.
You've now completed all of the time trials, so we'll now work our way around the west island finishing off the remaining side missions, red balloons, unique jumps and rampage missions.