Recently one of our more active users contacted us with a decent amount of frustration. He is an avid mountain biker outside of Bend, OR. Per the area, things get a little wet on many rides. He is consistently having issues with his bike feeling ‘slow’ or as if he is trying to ‘ride through sand’. We consulted him on the issue, which was made easier because this particular user had already replaced bearings a few times hoping to fix the issue. He was missing one lesser understood aspect that we were happy to help him out with – all seals are not created equal and are for sure not the same.
We will need to break this down a bit, but I promise to not get too technical (that is what this page is for). We need to generally cover; nomenclature, design intent, and a bit on materials. Most bearing companies, vast majority in the bicycle industry, use similar nomenclature.
- RS is a seal that is light-contact
- RH has a heavier contact
- RZ would be non-contact
- Z would be for a shield
- Y, K, or other brand specific nomenclature may also be seen for specific materials
RS for radial ball bearings is by far the most utilized in precision classes from zero to Abec 5 or so. It has a light contact to handle many potential contaminants, but the light contact creates minimal rolling resistance as well. This can be an important combination of attributes for a multitude of applications, including the many types of bicycles. RH is a heavier contact seal, usually designed in the range of 3-5 times more interference on the inner race than the RS seal. The obvious benefit of this is the greater efficiency at keeping out smaller contaminants and liquids. The flip side of that benefit is the greater rolling resistance, at least for the initial run in time – see Side Note below. The RZ seal is non-contact on the inner race. This is utilized for higher RPM applications and generally higher precision applications. Both higher RPM and precision within most applications go hand in hand. So does the fact that these types of applications generally have more extensive barriers/protections from contamination ingress into the bearings. Z stands for a metallic shield, non-contact on the inner race as well. Shields can be used mostly interchangeably with the RZ seal. The decision between the RZ and the Z is generally a personal preference, but sometimes because of the contaminant type. This brings us to the ‘specials’. Some specials for seals fall into this category. Viton, double contact, single contact, different holding methods, etc. all do have some effects – the definition of the ‘some’ is what is up for debate. For the bicycle industry, common Nitrile Butadiene Rubber is just Jim Dandy. Bicycle applications do not see 150°C[ °F] or any chemicals that will react with this common rubber – don’t be upsold. These materials and difference for sure have their place and their needs, just not an upsell in the bicycle industry.
As per our rainy-day mountain biker in the North West, we switched him to some RH seals and he hasn’t had an issue since. Too boot, he didn’t notice any extra rolling resistance with the 4 bearings his 2 hubs required! (which is usually the case with our users).
As always keep the questions coming. We are here to help and educate.
Until next time – Ride Safe!
Side Note: All contact seals made of any material will slowly wear. The standard Nitrile Rubber may wear a bit faster than a more costly Viton, et., but they will both wear nonetheless. What this means is that the highest sealing efficiency along with the highest rolling resistance will be right after installation. As the bearing is rotated/used, both the sealing efficiency and rolling resistance will decrease over time. This is both expected and not a big deal – seals don’t last forever, but generally longer than the bearing!