Ignore the "top 5" in the achievement description. You get this achievement when your best lap time for every track is below a certain cutoff for that track. This cutoff isn't shown anywhere, but on the Records screen, the word "RECORD" will appear above lap times that qualify. You only need one record per track, not for every vehicle type. The achievement unlocks after you quit out of the last qualifying race.
Here are my own record times. They aren't the actual cutoffs, and slightly worse times will qualify as well. For Opencross and Waypoint, there are probably several seconds of leeway; for Supercross, there's probably less than a second in most cases.
Nationals
Clearwater - 02:03.66 ATV
Copper Valley - 02:20.52 ATV
Crawley Creek A - 01:18.22 MX
Crawley Creek B - 02:10.85 ATV
Del Sol - 01:46.94 ATV
Greenfield - 02:17.36 MX
Kittery Point - 01:53.66 MX
Lakewood - 02:01.90 MX
Pine Lakes - 02:37.93 ATV
Split Oak A - 01:37.34 ATV
Split Oak B - 02:03.38 MX
Sutherlin Valley - 01:29.69 MX
Supercross
Bridgeport - 01:18.19 MX (according to Mister Buds, 01:18.99 also qualifies, but 01:19.04 doesn't)
Capital City - 01:07.44 MX
Columbus - 01:27.48 MX
Denton - 01:11.66 MX
Foothills - 01:24.93 MX
Harris Park - 01:00.75 MX
Jefferson - 01:11.93 MX
Norton - 00:59.60 MX (according to n1ckKz, 01:01.31 also qualifies)
West Stone Gardens - 01:19.99 MX
Wilford - 00:53.12 MX
Bridgeport was the toughest track for me.
Supermoto
Clearwater - 01:38.74 ATV
Crawley Creek - 01:43.15 ATV
Del Sol - 01:31.14 ATV
Del Sol - 01:41.07 Trophy Truck
Greenfield - 01:27.84 ATV
Pine Lakes - 01:46.94 ATV
Pine Lakes - 01:48.35 MX
Split Oak - 01:22.05 MX
Split Oak - 01:30.46 ATV
Split Oak - 01:33.21 Trophy Truck
Opencross
Coppper Valley - 02:19.16 Sand Rail
Kittery Point - 02.22:54 Sand Rail
Kittery Point - 02:23.60 Offroad Buggy
Lakewood A - 02:24.18 Trophy Truck
Lakewood A - 02:29.46 Offroad Buggy
Lakewood B - 03:35.76 Trophy Truck
Pine Lakes - 01:57.95 Offroad Buggy
Pine Lakes - 02:02.48 Sand Rail
Sutherlin Valley - 02:21.65 Offroad Buggy
Sutherlin Valley - 02:23.87 Sand Rail
Minimoto
Edgewater - 01:07.34 MX Mini
Specter Arena - 00:50.09 MX Mini
Endurocross
Fairview Arena - 01:16.71 MX
Lincoln Memorial - 01:07.36 MX
Waypoint
Del Sol - 01:54.99 Sand Rail
Greenfield - 02:40.00 Sand Rail
Kittery Point - 01:21.32 Sand Rail
Split Oak - 01:48.86 Sand Rail
Sutherlin Valley - 02:31.06 Sand Rail
Freestyle (The game incorrectly displays "RECORD" and my best scores in the Best Combo column. The following are best scores, not best combos.)
Clearwater - 21,200 MX
Copper Valley - 15,000 MX Lite
Del Sol - 18,720 MX
RBW Center - 28,156 MX
Southbend - 26,020 MX
Sutherlin Valley - 26,502 MX
THQ Spectrum - 29,334 MX
West Lake Arena - 19,415 MX
Tips for Supercross
Set up a custom event with one All-Time rider, examine his lines and rhythms in the replay, and try to mimic them.
In a turn, take the outside line whenever you need more speed to clear the next jump or some whoops.
Use preload only for the jumps that need it. Not all of them do.
Right before you land a jump, use the clutch for half a second. This provides a significant speed boost.
Performance tuning: I used Pro settings, 90% speed (because the speed boost from using the clutch lessened as I tuned toward acceleration), 60% hard suspension, and 60% hard tires (soft enough that I could make turns without letting off the gas).
Tips for Lakewood B Opencross
Use a trophy truck. (I used the gold one.) A sand rail seems to be slower by a few seconds.
I'm not sure how much performance tuning actually matters, but here are the Pro settings that I used: 75% acceleration (speed isn't the limiting factor here), balanced suspension, 66% soft tires. You might want to try even more acceleration.
Every (and I mean every) corner can be taken without letting off the gas. For the sharpest turns, start way on the outside and begin the turn early.
Use the clutch in mid-air for a significant speed boost when you land: Press LB after you leave the face of each jump, and release LB right before you land.
While in mid-air, pull the left stick down or up to align your truck with the terrain before you land. The front of the truck has a tendency to dip down, so most of the time you'll be using the left stick to pull the front back up. Doing this is particularly important in the first part of the course (before the ravine). Otherwise, the uneven terrain will cause your truck to bounce all over the place.
On the second of the two big hills, I started along the right side and aimed to land about in the middle. On a good landing your speed won't drop below 35-40 mph. (Below 30 mph is bad.) Remember to use the clutch before landing.
The record time cutoff appears to be 03:36.00. I didn't get the record with 03:36.xx but got it with 03:35.76. On this run, I didn't use any pre-load; I didn't want to be in mid-air any longer than necessary.