Saddle setback 

The slacker your seat tube angle is, the farther away your saddle gets from your BB. 

Some bike brands, Norco for example, will correct for this by changing the seat tube angle for different sized frames on the same model bike. But the majority of brands do not. So, your XS frame ends up with the same angles and the XL. With the same Seat tube angle and saddle set in the same position, you’ll see a very large difference in setback.  

Saddle setback is an important part of bike set up and this calculator will help you find the right spot. 

How far behind your BB you are will effect power output, ergonomins and comfort. Use this calculator to help set your saddle position.

Hint: Just beacuse the UCI says you have to keep it a minumum distance from your BB, doesn’t mean you need to follow that rule on your own bike.

All lengths in mm.