Hondo6

The disc could indeed be thinner than a rear sprocket - though you'd still want it to be thick enough to do its job. 10- and 11-speed rear sprockets are already down to 1.6mm thick. Would 0.5mm be enough? 0.75mm? Dunno.

The problem I'd see would be the actual fabrication if done as part of a monoblock cassette like the Presta/Edco/SRAM monoblock variants. These are machined out of a single piece of steel (some with larger rear cogs may have one or two alloy cogs attached in lieu of the largest 1 or 2 cogs being part of the steel monoblock to save weight). In the case of the Presta, that is CroMo steel.

Therein lies the problem IMO. Unless you wanted to machine it separately and attach it, it would require a larger billet. And that larger billet would require more time to program and machine. It would also generate more wear and tear on the CNC machinery, particularly the cutting heads, and would generate more waste steel millings.

Significant? Perhaps - or perhaps not. But a manufacturer would have to take that into account and price the cassette with protector disk accordingly higher. (Well, they would if they wanted to stay in business over the long term. Otherwise, maybe not. )

My guess is that an add-on - maybe one added via rivets to the largest cog - would turn out to be far more practical to manufacture. Dunno if it would sell or not.

Related, but different subject: ran across this. It seems to be a niche product aimed at the downhill biking community. It apparently replaces the largest 3 sprockets on a10-speed cassette that normally uses a spider to hold the three largest sprockets.

Not my style, but it does have a certain . . . different look. And while it appears pretty thick, since it's alloy it's not all that heavy (<50g).





Link: https://www.ebay.com/itm/25285625378

No endorsement of product intended; no experience with the vendor. Link provided for info only.