I have noticed on old wire spoke airheads there are divots around the rim, but the are not evenly spaced. Whats the reason for this?
I've been told it is a safety feature to keep the tire on the rim in case of a flat. I assume that its true........can anyone back that up?
I have no knowledge of this for certain, but I imagine they are part of the manufacturing process used as a way to hold the rim from the internal side, once it has been rolled and welded. It would be interesting to watch the entire wheel making process from flat steel bands to a finished rim, for example, when are the spoke holes and dimples put in? After rolling, or before? I'd imagine afterwards,,,anyone watched rims being made?
It's called a "drop center rim" and the ding-things prevent the bead from dismounting when you have the tire go flat. Read up at Duane's Website: http://www.w6rec.com/duane/bmw/5dents/index.htm
They're not all the way around the rim because... ... it would negate the reason for the dropped center, making it difficult or impossible to mount a tire. Take a look, and you'll see they're evenly spaced from the valve stem. The valve stem itself probably acts as one of the humps. Duane does talk about it on his site. And it is a safety thing I've only seen on BMW wire wheels, intended to keep the tire on the rim should it suddenly deflate.
I have heard that they are to prevent the bead from breaking but I never have been able to figure out how those little dimples could accomplish such a task. I just don't see how they could, since they don't protrude far enough from that part of the of the rim to even touch the bead. And then the spacing......?
No, I don't see any way they could prevent the bead from coming loose! But they could help prevent the tire from dropping into the well and coming off the rim entirely.
They keep the bead from dropping into the center all the way around the rim in the event of a flat. It works well---just try to dismount a tire the wrong way!. It's in your manual---You have to start spooning at the divots so the bead can drop into the well on the opposite side of the rim. If you start opposite the divots there is no way to get the tire off. Try it.
That makes sense, glad you- all cleared that up for me. I do wonder though, why don't any of the other wheel manufacturers think it is such a good idea? Maybe there are some others doing it, but I don't recall noticing. Are there?
so if that is correct, then why are they not on the rear wheel as well then? I asked BMW why they are there, they said they don't know
Correct. They are on all the BMW wire wheels made for tubes, front and back: as mentioned above, just try to get the tire off without getting the bead down into the center where there are NOT divots while you spoon away on the opposite side.. they ARE effective... !!
