MTFCI Forum

Flaps - your missing their real purpose

Posted By: John F. Regan <Send E-Mail>
Date: 8/1/03 20:51

In Response To: Duct tape for rim flaps??? (Doc)

While flaps will certainly keep you from harming the tube during installation, that is not their main purpose. Their main purpose also is not to provide protection against the rough part of the rim per se but to prevent the inner tube from ever going there so as to prevent the tire bead from damaging the tube during driving.

I am in a very large chapter of the MTFCI with over 150 member families and we get lots of Ts out on tours. It is most obvious over the years that those who do not use flaps or those who used to not use flaps are the ones who have all the flats but not from installation and actually not from the rim rubbing either since these folks all use tape of some sort on the rim. The main purpose of the flap is to prevent the clincher tire from pinching and rubbing a hole in the inner tube. Without flaps the inner tube is stretched across the bead and down in the trough of the tire and against the rim. If you look close at punctured tubes that have been on flapless wheels you will see that the tube always has a hole along the inner diameter but just off to the side and you will also see a line where the clincher bead has been rubbing on the tube each time the tire is forced to the side as when turning a corner. The tire itself will rub a hole in the tube at the point where the tube is stretched tight over the bead edge of the clincher tire. With flaps the tube never is stretched over the bead edge because the flaps go up along the side of the tire and as the tube is inflated the flap is squeezed against the inside side wall of the tire and thus forms a bridge over the tire beads and the tube never gets into the trough of the tire beads. I have seen numerous times when folks seem convinced it was an installation error that pinched the tube but those same people have flats again and again. I had 3 flats my first 2 years touring and I was super careful during mounting and I had smooth rim surfaces. A tire man explained to me what was going on and it sounded logical. I put in flaps on those same rims and nothing else and have never had a flat since and the tires are just about worn out now.