Here is my take:
For direct sunlight shots have the sun to your back and shoot during the golden hour or one hour before sunset. Still use a filtered, boxed,indirect or bounced flash. Use a tripod if no flash and hold the shutterspeed a little bit to draw in the warm glow. If the sun is behind you take the picture standing far enough back so your shadow is not in the picture.
Try shots in full shade too, use a reflector or just white board to bounce the natural light on the bike, especially effective on chrome.
Play with taking pictures in the complete dark, set the camera on a tripod set the shutterspeed to 3 seconds, maybe 2 for a bike. Squeeze the trigger and shine the light slowly across the bike, playing with this gives great pictures, or try keeping the light on one area and let the light filter over the rest of the bike. Play with the light and shutter time. This is a fun way to waste an evening. I usually hook my camera up to a PC and look as I go. For shots where you're riding to the location, take a brush to clean the tires of dirt, hide marks in dirt, bring spray mist and a microfiber clothes to touch up the bike. Look around the background for junk you can get out of the way. Shots after the rain are great because you can park your bike in a puddle and do some pretty cool reflective shots and look for fun angles.
for more art shots try to frame the picture with things in the foreground, they don't even need to be in focus. Shots through a spoke wheel showing your bike in the background looks cool or a reflection of your bike in a rear view mirror or off of a chrome bumperor shop window adds a ton of depth to a picture.
Box lights are great but expensive, a flash bounced off a white board will give 75% of the effect.
Since there is no film cost anymore just take your time and play. Review your work as you go so you can see how your lighting and settings changes effect the picture.
hope this helps-