This is because rear shocks generate significantly more heat than front forks do so the operating temperature ranges of a rear shock is very broad.įor long term damping consistency, things like stabilizing additives and shear stable base fluids keep the oil performing like it did fresh out of the bottle. These components reduce the oxidation rate, minimize the effects of contaminants and resist permanent changes to the oil viscosity. Preventing friction and wear are important in these applications for a number of reasons. If wear starts to become excessive, it can result in increased static friction and failing parts. Reducing friction moderates heat generation and minimizes surface friction as a tuning variable making suspension tuning easier as well. Seal compatibility is fairly simple but very important. Blowing out seals is no fun and it can be avoided in most cases by selecting quality fork and shock fluids. There are exceptions, but seal compatibility is almost exclusively a function of the base fluids. Seals can be made from a variety of materials but a vast majority of suspension seals are made from nitrile rubber (Also known as buna-n, NBR, butadiene). In general, nitrile seals are affected by oils in the following ways:Īn additive people commonly look for is known as a seal swell additive. While they can certainly be useful, the mere existence of one of these additives in a formula does not make it good. Swelling a seal without counteracting that swelling at least to some degree can result in a failed seal. This is because the seals are meant to fit into a precise space and if they swell too much, they will grow too large for that space and can blow out.

The ideal situation is to have a neutrally balanced oil that does not shrink or swell the seals.

Fork oil absorber viscosity chart