Originally Posted by
79pmooney
I never thought about aluminum rims expanding on rim braked downhills. Makes sense. Also never heard of spokes popping because of that expansion. It does bring to mind the advice of years ago of keeping spoke tensions well below allowable max for the rim and hub flanges. I've never been a fan of max tension spokes. This is another reason I'll stay off that band wagon. (My primary reason- very tightly laced wheels can go quite out of true with spoke breakage. I like the idea I can bring the bike to a stop still upright after one or more spokes are gone.)
It's a confluence of bad: Aluminum has a high coefficient of thermal expansion, small diameter rim (20"), so less heat sink, and short spokes, so less elasticity. In my case, also add only using rear brake on that descent, because front rim sidewalls were more worn and I was trying to baby that. A particular small wheel bike company hypes their 20" wheels as "stronger"; Sort of. Stronger rim "hoop strength", so less likely to dent from impact. Short spokes are more rigid, but you don't want that, you want longer and more elastic, that is the driver for double-butted spokes, thinner diameter in the middle, away from bending loads on ends.