Posted on 15th Feb 2014
Many people know that on a standard Shimano and Sram freehub body notches can occur over time. This is because the splines on the Shimano and Sram freehub bodies and cassettes are not very deep. The cassette material is made out of a hard steel material (with some cogs being made out of titanium on the higher end models). The freehub bodies are made of aluminum on our wheels, which is a softer material. The constant impact of the cassette against the freehub body can wear grooves into the freehub body.
This is a bad thing, right?
Contrary to what most people think, these grooves or notches are not a bad thing. They can end up being bad if the grooves get deep enough to throw off the alignment of the cogs next to each other. This can affect your shifting as cassettes have the gears placed in strategic position to ensure crisp shifting. However, when there are small grooves, this means that your cassette is bedding itself into the freehub body in multiple locations. Vibration is a killer for metal parts interacting with each other and when your cassette has multiple contact points with the freehub body, it cuts down on the vibration of the cassette. This greatly increases both the chain and the cassette life.
How can I prevent the notches from getting really bad?
Going along with the eliminating vibration, making sure your cassette it tightened down very good will prevent cassette from being able to wiggle back and forth. Whenever notches occur it's going to be the cogs in the middle of the cassette as that's where the least amount of side force is. If the cassette is not tightened down enough, these middle cogs will have room to wiggle back and forth a bit. This will allow the cassette to bed itself into the freehub body much worse than if everything was tightened down completely.
Check below at these pictures
The notches on this hub are really bad. This was from a wheel where the cassette was not tightened down very well. The cassette could wiggle back and forth in the middle and this wore groves into the freehub body.
This is one of my personal wheels. It has thousands of miles on it under all types of riding including a lot of climbing and sprinting. I tighten down my cassettes very tight and this helps to minimize the notching. Small notches like this are actually beneficial to cassette and chain longevity.
Is there any other solutions?
There are freehub bodies that have a steel strip in place of one of the splines. The thinking behind this is that the cassette will move against the harder steel strip instead of the alloy splines, preventing any notches from occurring. This is a good solution for preventing the notches from happening, but it does mean that your cassette now only has one contact point with the freehub body. This can hamper the longevity of both your chain and cassette.
Using a titanium freehub body is another option, although titanium is a very expensive material and very hard to machine down into a freehub body. A few hubs do come standard with a titanium freehub body, but also come with a higher price tag. This is the best option though for completely eliminating the notches and also keeping good longevity for both cassette and chain.
Making sure you tighten down the cassette and that all the necessary spacers are in place is an excellent and very cost effective solution. It just requires a little elbow grease, time to work those skinny cyclist arms :-)
All prices are in USD.