Get a tougher gear on Shimano GRX, 11-34T, 2x11 I have a new 2021 Cube Nuroad Race gravel bike with Shimano GRX, 11-34T, 2x11.
I am used to riding a road bike, and find on the new one I don't need the easiest gears on the hills, but could use a tougher gear on the downhill as I can't get any power down when descending. (I have switched the 40mm tyres for 32mm tyres while the weather is still not half bad in the UK).
I have never messed about with the cassette on a bike, switching gears etc, and was wondering how to go about it. Do I need to buy a whole new cassette? What cassettes are suitable and compatible?
Thanks
Edit:
Some useful suggestions. For more information, it is not just pedalling down serious slopes that I run out of gears, but on not very steep descents and occasionally on the flat if my speed is up. Though it seems what I need is to switch out the chain rings.
You cannot get a higher gear ratio by replacing the cassette. The 11 tooth sprocket is the smallest you can get on a compatible cassette. (Systems with 10 tooth sprockets exist but use a different freehub design).
The issue is that you have 46/30 tooth sub-compact chainrings (I looked up specs here). Which are giving you the low ratios. This is common on gravel bikes as they have larger diameter tires run at lower pressures and are designed to negotiate rougher surfaces. A road bike typically has 50/34 or 52/36 tooth chainrings.
If you want higher gear ratios you have to get larger chainrings. GRX 2x11 cranks only come in the 46/30 size. You may be able to find larger rings made by another manufacturer that fit the GRX crank, or you get a whole replacement crank with larger rings.
If you still want to know how cassettes fit on hubs see this Park Tool video. There are a few standards for the freehub that the cassette fits on. Shimano's HyperGlide II is dominant and also used by SRAM. Campagnolo has their own standard. Systems that permit 10 tooth sprockets like SRAM XD and XDR are becoming more popular. In addition to the freehub attachment the cassette sprocket tooth range has to fit inside what the rear derailleur can handle. This includes the max sprocket size and 'total capacity' (difference between chainring tooth counts plus difference between largest and smallest sprocket tooth counts).