Cold temps and fork sag

Hi People,

Prob a daft question but here goes. Does the cold weather have any effect on air fork sag/pressure. Cold = more or less dense air????
I checked the pressure last night just before I went and all was well, but whilst on route I noticed the fork was compressed more than it normally is when riding normally. They felt OK and returned back to 150mm when I got off but it just pecked my head a little. I forgot to check pressure when I got back as the Mrs had sorted out tea.

They are 2010 Rev Teams

Ta

I know the post is about forks but i've found this warning for shocks so maybe it affects both.

here

air pressure in sealed unit drops a small amount when it's cold, but i don't know if it would be enough to affect the feel of the shock

Humm, it did feel as though I'd wound the forks down to say, 130mm but they still worked fine and the RRP guard seemed slack, thats how I noticed the drop really.

I can't claim any scientific basis to this but I have observed that air forks tend to get a bit saggy in the cold. Yesterday a friend and I were out in about -15 and both our forks (Manitou minute and an 09 Reba) felt like they'd lost half their pressure after about 15mins. It's something I've always noticed in my Manitous during winter, and they are well taken care of and regularly serviced.

I'm convinced there must be something with the seals shrinking (I assume) and letting air out somewhere, but I'd be interested to hear a real explanation (I've never experienced anything like the mojo link).

I've noticed my '07/08 Reba's feeling somewhat 'wooden' in the cold but feeling far more responsive indoors (where i keep my bike).

Its the oil in the damper more viscous when cold.

I've been in the shed fettling the steed for tomorrow and checked the air in the forks and it's the same as the other day, -5psi ish due to filling the shock pump. I've alresdy done the how much does it alter the volume when fitting scenario, so know its about that.

So as they didn't feel wooden, but seemed to have more sag. I'll conclude that it is in fact a result of the denser cold air

Air contracts about 8% by volume from 20c to 0c, so your sag, if only dependant on air, would drop by 8%. I honestly don't think I would notice this.

The damping will also feel a bit sluggish, but only for a while as I would expect the oil to soon warm up as the shock operates, as will the air so I think you should get your sag back. Its worth knowing that the air spring provides some damping too..

Air contracts about 8% by volume from 20c to 0c, so your sag, if only dependant on air, would drop by 8%. I honestly don't think I would notice this.

That kinda makes sense then. Cycling at anywhere past -10 (plus wind-chill) would probably make at least 10-15% extra sag, and the fact that the damping is working cos of the rapid small-bump nature of snow (around me at least) makes the fork feel under-pressurised. I checked my forks after the ride mentioned above and they hadn't lost air like I thought, so this seems like the most likely answer.

yep kind of all true oil more viscous due to temp, air pressure will be a bit lower, and can drop as much as 25 psi depending on shock pump/hose length pressurizing from valve to gauge.
However as you ride the fork will warm up as it moves obviously if really cold and wind chill e.t.c will have a bearing on how much.
Seals may stiffen and loose some sealing properties too, showing if there is a minor fault in seal that only appears in extreme conditions.

Cycling at anywhere past -10 (plus wind-chill) would probably make at least 10-15% extra sag

[pedant]wind chill won't make a difference to an inanimate object once it is down at the ambient temperature[/pedant]

(sorry, got an exam on weather and winds tomorrow…)

this may be unconnected but motor bikes suffer with something similar and is caused by the relationship between compression and rebound damping. more rebound than compression causes the spring to become more compressed under load as the oil doesn't return to the neutral position quickly enough. most high end kit compensates for this and therefore this may be a compete red herring but it's one effect that i have witnessed….

hungry monkey – Premier Member

Cycling at anywhere past -10 (plus wind-chill) would probably make at least 10-15% extra sag

[pedant]wind chill won't make a difference to an inanimate object once it is down at the ambient temperature[/pedant]

(sorry, got an exam on weather and winds tomorrow…)

Hungry Monkey You'll do all right in that exam.

I think the others may have something in the stiff seals too. I wonder how much work any of the bike companies have put in to the effects of low temperature on bikes and components..

the damper oil is cold so the fork won't rebound as readily and as a consequence sits further into its sag. It should stop once you've given the fork a bit of stick and the oil has warmed up. all bike dampers warm up an bit anyway regardless of the outside temperature.

(edit) I reckon…

adstick, thanks for adding some weight to my opinion…

try reducing the amount of rebound damping as if we are right this will fix it or reduce the effect…

Zactly. I'm fairly sure the temperature would have bugger all effect on the air spring, and the effect is apparent on both air and coil shocks.

[pedant]wind chill won't make a difference to an inanimate object once it is down at the ambient temperature[/pedant]

(sorry, got an exam on weather and winds tomorrow…)

That's alright, it just shows you know what you're talking about, unlike my random guessing based on some poorly (un)remembered high-school physics from 15 years ago 🙂

Good luck with the exam.

I'll have a go a winding back the rebound when I go out tomorrow.