I want to buy a different cassette. the drivetrain is Shimano 105, 11 gear 5800 system. I understand that I can simply fit an Ultegra 6800 cassette and use with the same Derailleur (105) and chain.

Is that correct?

I read from people swapped Ultegra and Dura Ace, but didn't read about 105 and Ultegra.

Yes you can use Ultegra, or even Duraace 11 speed cassettes with your 105 5800 Groupset.

Yes you can use Ultegra, or even Duraace 11 speed cassettes with your 105 5800 Groupset.

thank you

and it is ordered....Good part to check if customs show mercy