Bike hoses and the like… made of butyl rubber, which is a synthetic rubber consisting of a polymer of the substances isobutene and isoprene. Both of these substances are classified as carcinogenic in category 2, but since they are polymerized it is considered that there is no risk in this context… such rubber should not be used in jewelery to avoid unnecessary exposure to these substances.
It would be wise to read this article, do some further research, and decide for yourself whether you want to work with rubber bicycle inner tubes.