How Temperature Affects Your Suspension

December 11, 2023

As the Northern Hemisphere transitions from summer to winter (with the Southern Hemisphere in reverse), you might be curious about how temperature changes can impact your suspension system. You may have noticed that during cold winter outings, your suspension feels softer and more sluggish. This article aims to elucidate the reasons behind this and quantify the effect of seasonal temperature variations on your suspension.

Some Scientific Insights

Understanding how suspension reacts to temperature changes involves grasping the Kelvin scale. One Kelvin change equals 1 degree Celsius; zero degrees mark the freezing point of water, while zero Kelvin denotes absolute zero, where molecular motion halts, and objects cease to get colder.

*Pretty sure nobody really knows how Fahrenheit works.

Absolute zero is -273°C, making the freezing point 273 Kelvin (K). A warm summer day at 27°C equals 300 Kelvin (K), a neat round number you'll notice.

Another crucial point to consider is that for a fixed volume of air (like the air within a suspension system), its pressure (a good analogy) is directly proportional to the Kelvin temperature. Additionally, the stiffness or spring rate of the air spring (how much force it generates within a fixed stroke) is proportional to the pressure inside the spring. 

What does this mean practically?

Thus, if you set your suspension at 27°C or 300K during the summer and leave it untouched, when you venture out in winter at 30K lower (-3°C or 270K), your air suspension's pressure will drop roughly by 10% compared to summer. So, if you pumped your fork to 100psi in scorching summer, it would read around 90psi when the temperature drops below freezing. Or if you set your rear shock's sag at 30%, it might now be around 33% under those conditions.

In consecutive tests, this difference is striking. However, as these extreme temperatures might span months apart, you might not notice how your suspension has softened since summer—much like not realizing how much taller you've grown until Grandma points it out.

You might consider using softer suspension in winter for enhanced traction, but remember this caveat. Or if you tuned your suspension in a warm indoor setting but plan to ride in frigid conditions, you might need to compensate—or take the chilly risk of parking your bike outside.

How Does Damping Fare?

In colder weather, damping oil thickens, increasing low-speed compression and rebound damping forces. The augmented compression damping can partly offset the softer spring rate by providing additional support. However, the increased damping combined with softer springs during rebound can lead to slower rebound speeds, potentially causing slower rebound and poorer traction in high-frequency bumps (if left unadjusted).

The impact depends on the damping oil used in the damper—more oil volume is typically more affected by temperature, although temperature's effect on high-speed damping (like hard landings) is minimal. Overall, the changes in air suspension due to temperature might be more noticeable than those caused by the damper in hot or cold weather.

When you start riding on rugged terrains, damping oil heats up—raising the temperature within the suspension spring—but this occurs only during summer and doesn't counterbalance the effects of cold weather.

How Does Altitude Come Into Play?

Advocates of coil springs sometimes argue that temperature and altitude wreak havoc on air springs while their coil springs hold steady under any condition. As we've seen, temperature's impact on air suspension is limited unless extreme temperature fluctuations occur (which you're unlikely to notice a few degrees of) and are easily explained during seasonal changes.

Regarding altitude, for every 1000 meters gained, atmospheric pressure drops by roughly 12%. So, for every 1000 meters ascended from sea level, there's an approximate 1.7psi difference in atmospheric pressure. In the context of air suspension, this influence can be disregarded. For a fork, the main effect is on the lower leg and not the spring. If the pressure outside the lower leg is 1.7psi less than inside, it would require about 5 pounds of force at each point of the compression stroke (including when the fork is fully extended) to push the lower leg into the fork. A noticeable "bottoming out" might occur soon after compression begins, hence the presence of air release valves (a.k.a. fart buttons). But note that this applies to both air forks and coil forks.

Altitude has a much more significant effect on tires. The pressure difference between the inside and outside supports them (the pressure you measure with a gauge, so you don't need to concern yourself with it). Hence, when the external pressure drops by 1.7psi, the tire pressure effectively increases by nearly the same amount, approximately a 10% increase.

Adjusting Suspension in Changing Conditions

Understanding how temperature and altitude can subtly impact your bike's suspension helps in making informed adjustments, ensuring an optimal riding experience irrespective of weather or terrain. Whether it's compensating for temperature-induced changes, tweaking sag and rebound settings, or considering tire pressures for different altitudes, these adjustments can significantly enhance your ride quality and performance.

In conclusion, while temperature and altitude affect suspension systems, the effects are generally manageable with informed adjustments. Whether you're cruising in the scorching heat or conquering icy terrains, understanding these influences helps optimize your bike's performance and your overall riding experience.

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