What is the difference between CS-HG800-11 (11-34T) and CS-R8000-11 (11-28T)?

The CS-HG800-11 is the wide-range cassette with 11-34T for climbing; the CS-R8000-11 is the standard range with 11-28T or 11-32T for flatter terrain and racing. CS-HG800 uses a slightly different construction but both are Ultegra R8000 series and deliver identical shift quality.

Do I need a new chain when installing this cassette?

If your existing chain is worn beyond 0.75%, yes — fitting a new cassette on a worn chain will cause skipping and accelerate cassette wear. Always fit a fresh chain with a new cassette.

Shimano

Shimano Ultegra CasSette Sprocket, CS-HG800-11, 11-Speed (11-34T)

Name: Shimano Ultegra CasSette Sprocket, CS-HG800-11, 11-Speed (11-34T)
Brand: Shimano
SKU: CMB_WOW_ICSHG8001111134
Price: 7970.00 INR
Availability: InStock
Author: InstaSport Editorial

₹7970.00

Description

Specifications MODEL NO:CS-HG800-11 SERIES:ULTEGRA R8000 Series Average weight:335 Combination:11-13-15-17-19-21-23-25-27-30-34T Combination name(Group name):11-34T Compatible chain:HG-EV 11-speed/HG-X11 Speeds:11 Spider arm_QTY (pcs):2 Type:HG-EV