An old bike? seriously? put some more effort dude!
a kidney could worth up to 1 million dollar, pull off that kidney from your body and convert it to bitcoins, that is what i called as a real effort haha you can get up to 130 bitcoin with a single kidney sold to the needy.
Where can it be, so I can do it right away. LOL. In our country, a kidney will only worth $5-10k USD if converted to USD.   
 
on a serious note , taking risk by selling stuff -a non necessary- stuff that is better choice rather than letting your stuff stay there losing value , you can switch it of to a productive , progressive one like bitcoin investment.
there is no harm to do it, as long as not something you are using it urgently in your daily life like a house.
it could be a high risk , you can not afford to lose it and i think that is a bad choice.
It's true, it would be better to have an investment where you can see it grow than an asset that is decreasing its value over time. Though a bike is an asset where you can use anytime as a mean of transportation.