Hey, Half the post's above are a load of rubbish, I won't go in to which ones!! I'm an old school rider who has been running tar on smooth rims since I started trials about 6 or more years ago. Which tar to use? The best tar to use is roofing or road tar. Don't melt it or peel it off the roads, that's just daft, I wouldn't recommend stealing it either cos you might get caught and it makes you scum. Go to any roofer/builders yard e.g Travis Perkins etc. Just ask for a block about the size of a tennis ball, you should get it for free or cheap, it will keep you going for years. How to apply the tar? Flip your bike upside down so it rests on the handle bars and seat/back tyre. Holding the seat stay or chain stay tube lift your bike up so its just on the handle bars. Then either spin the wheel or cranks to get the wheel moving. Then apply the tar to the braking surface, for best results push firmly but so hard your trying to push your bike over. The aim is to get a speckled effect like large dust or tiny rain drops. Do this on both sides of the rim. Each time you apply tar ride around and gently drag(hold half on so the pads drag the rims) the brakes for a minute or so, this helps the tar spread more evenly over the rim. Bad things and warnings!! If the tar gets too hot like by dragging the brake too much whilst riding or on a summers day it melts. When it melts it becomes very sticky like thick glue. Not always but often when you pull the brake the pads will lock on to the rim but not release. This is bad. Imagine your brake locked on at the edge of a drop off? Face plant coming soon!! Tar is bad in the wet, in the rain it turns to oil, so your brakes wont work well if at all!! Do's and Dont's Never apply tar to your front rim unless you know what your doing otherwise you'll be over the bars before you know what's hit you!! You don't want big lumps, big lines, a completely covered rim!!! Remember - It's better to use less than too much, you can always add more.