After reading the cover of the box for the expansion set, it states that it will expand any 18" radius circle. I don't understand why Bachman sells the starter set with 22" radius curves but the expansion set with 18". I had to return the expansion set and buy individual tracks to make my own layout. To further confuse myself, I bought all 22" radius curves to match my starter set curves and the other pieces the Bachman e-z track catalog said I needed on page 25. When the layout wasn't working, I looked at page 3 and it said 18" radius curves are needed. I just kept buying pieces until the ends met.