We're going to take a look at what happens to your suspension when the ambient temperature increases...
So, there are a few things to consider here. Your suspension has oil and gas (air) inside, both of which will change as their temperature increases. But how does this affect performance? Let's take a look:
First up - Gas, or Air in most cases. As temperature increases, gasses expand.
If you have an air fork or an air shock and you setup your sag/adjusted your air pressure at say 18°C and then you go riding in 26°C, the air is going to expand. Because that air is sealed into a chamber, that expansion causes the pressure to increase.
The result? A firmer fork/shock which means you now have less sag.
How to avoid this? It's simply a case of re-setting the pressure to the same pressure that you set it to when setting your sag at a lower ambient temperature.
Hang on a minute, you might say, what about the Gas in your shock's reservoir/piggyback? Won't things expand and increase in pressure too?
The answer is yes, but there's less to worry about. Firstly, most of these will have nitrogen in there. Nitrogen is more inert. This means it doesn't expand as much as air does with a given increase in temperature. Secondly, the increase in pressure in this small chamber has very little effect on the performance of the shock, in just about any modern shock. This is due to the chamber being compressed a very small amount through the full stroke of the shock. Most shocks are not easy to adjust the IFP pressure too, so it's really not worth worrying about.
Second - Damper oil. As temperature increases, oil gets thinner. In a damper, this equates to less damping force. So it sounds easy right? Just close all the dials a click or 2 and it will be the same?
It's not quite that clear-cut, sorry! Different damper designs will react differently to thinner oils and different oils will get more or less thin, at a given temperature increase.
Some damper designs will only really be affected through the low speed range of damping, in which case a click or 2 firmer on your low speed adjuster will get you back to your normal feel. However, others may be affected throughout the range and may only have 1 adjuster, so it's going to be a compromise. The best thing to do is try a click firmer, where you can, and see how it rides.
Some damper oils are very high quality and some, not so high quality! Part of an oil's specification is something called Viscosity Index, or VI. This is a measurement of how much thinner an oil gets as the temperature increases. The higher the number, the less the oil thins with temperature increase, therefore giving you more consistent performance. So, dampers that use a high VI oil will change very little as temperatures increase. This is great, you may not have to change a thing! On the flip side, an oil with a low VI will change performance quite dramatically as the temperature increases.
Third - Lower leg lube. As above, oils with a low VI can change dramatically with temperature increases. All lower leg lubes have a low VI number, so they change quite a lot with temperature.
But hang on, this is only a lubricant and it's not in a damper, so how does it change performance?
Well, it's all about surface tension and the resulting force. In your lowers, the lube creates a film that sits between the stanchions and the bushings. This prevents wear and allows the fork to move with less friction than if there were no lubrication. However, the thicker the oil, the more it wants to hold itself together to those 2 surfaces (surface tension). So as the stanchion moves through the bushings, the oil between has to move. This creates a measurable force.
As the oil gets thinner, this force gets less, so your fork will feel different. If you ride all year round, in big deviations of ambient temperature, you may want to consider changing the thickness of your lower leg lube for different times of year, to keep the feel similar. That said, some oils are better than others, so you may not need to. But it's worth a consideration.
Hopefully, this gives you more of an insight into how/why your suspension can feel different when the temperatures rise. As we mention, this is very variable, depending on the design and oils used. But if your suspension is feeling different this time of year, taking on board the info above can help you hone in on your preferred feel.
Thanks for reading and if you have any feedback or suggestions for future articles, please drop us an email.
Happy riding!