Originally Posted by

**erashish14**
Hi Experts,

I like to know, how **Air drag** & **Rolling friction** via Bottle dynamo can be calculated i.e. **Formula for the same**.

Actually my nephew is 15yrs old, he loves riding bicycle a lot, he carry his bicycle every where, whether its day or night,

so i'm planning to install bottle dynamo on his bicycle wheel (front & rear), which help in providing light during night while riding,

but i'm confused, did those bottle dynamos will make his bicycling harder, if yes, then how much, how to calculate that.

hence i required formulas for air drag & rolling friction calculation & other parameters which effects his cycling.

Thanks in advance

Ashish