Does Ambient temperature affect gas shocks?

[autobonrun]

I'm researching switching to gas shocks and would like to know if anyone has found that the ride height or stiffness of Bilsteins is affected by temperature?

I know that the specific volume of a gas is very much dependent on temperature, while a hydraulic liquid is not. In gas filled cylinders, the internal pressure increases with temperature.

Is the effect in shocks so small that it is of no consequence? Does anyone know what type gas is used to fill the Bilstein shocks? I may be able to calculate the effect if I knew what gas was used.

I don't want to analyze this to death, but I know the ability of my hood shocks to support weight changes summer to winter, even if they aren't leaking. You guys in California don't have the big seasonal temperature changes we do in the Midwest.

[rscupper]

OK, everyone can slap me here because I have no clue what I'm talking about. Let me guess and otherwise surmise:

Gas shocks are nitrogen filled. I think this may be true as most similar applications in the aviation industry are so charged - I'll leave it to you to figure the rates of change throughout the various temp ranges. Note that nitrogen generators and other sources are fairly common at air bases; therefore, one can assume that aircraft struts also leak and need refilling periodically.

I don't know the how fluid-filled struts would behave vis-a-vis gas types, but I'm ASSUMING such a phenomenom is considered in the structural/functional engineering of both systems (who said that?). I vote for gas for weight savings - perhaps, though, at a functional disadvantage?

Racer types could comment here, please. I don't have a clue.

[dickster]

from my motor cycle experience i would say yes. it is in the quality of the shock to compensate for it. thats why some race shocks are very, very, expensive.

richard

[89911]

They do effect the gas shocks holding up your hood. Cold weather=holding hood up with head.

[autobonrun]

Richard, I followed up on your comment and think I have the answer. I was mistaken thinking that the shock absorbing was done by the gas. Perhaps gas shocks is a misnomer as they still contain hydraulic fluid that does the actual damping. The gas charge is only used to prevent the shock from foaming if the temperature increases, thus maintaining consistency. Ambient temperature change should not affect the ability to prevent foaming because the pressure is so high and it would take huge reductions in the pressure to prevent the gas from performing this function. Racing conditions could however produce the temperatures that could change the damping characteristics.

The stiffness associated with the gas (mono) shocks has more to do with the internal design of the shock than the gas charge. I've attached the Bilstein link which helps explain.

Looks like I can switch to the Bilsteins.

http://www.bilstein.com/products/basics.html

[RoninLB]

Educated answers so far. My experience with Bilsteins on cold, 40 deg. and lower, is that they are a little hard for a couple of miles. I believe the friction warms them up. On hood lid I open and close it slowly.

[BKOMAR]

I may be comparing apples to oranges here...but I have found that my Bilsteins on the Porsche seem stiff on cold mornings and a bit lower in ride height (feels like), in comparison to the Boges in my Quantum Syncro which dont seem to feel ANY different regardless of the temp. Everything ELSE feels different though, especially the vinyl seats (Porsche) on those 10- 20 degree mornings *sigh* After a few miles the Bilsteins loosen up and are more compliant. Brian

[masraum]

hmm, Sutobonrun, the gas does have an affect on the handling characteristics of the shocks at least a little. With hydraulic shocks the fluid just slows the movement of the shock on compression or extension, but with gas charged shocks the gas actively opposes compression and will return the shock to its extended position after the shock is compressed. There is still fluid present to do the same job that it does in normal hydraulic shocks, but the gas does also have some affect on the characteristics of the shock.

Switching to gas shocks can actually raise your vehicle(I've read of and seen people switching and then having to have their car lowered some to return to original height). I think cold weather would cause them to work more like plain hydraulic shocks the same way the hood shocks are affected by cold.

This mostly from my understanding of things and my experience, so I could be wrong.

[KTL]

I don't know about the temp. change affects as my car hibernates in the salty Midwest winter. Just changing out the stock Boges for the Bilstein sports in the rear caused my car to resemble a '68 Chevelle. Looks like crap.

[RoninLB]

Bilstein definately raises the car a little over non gas shocks. I think I read in PANO or Excellence it is 50 lbs per shock lift.

[Clark Griswald]

Any change in pressure will be small.

Consider that each corner weighs about 700 lbs average front and rear.

Secondly, consider that each high pressure gas shock is providing only about 40 lbs lift. The remaining 660 lbs is supported by the spring at that corner.

If the shock lift changes by say 20% (that is a lot!) it's still only 8 lbs. 8 lbs out of 700 is about 1.1%.

A gallon of gas weighs about 6 lbs. So burn through 5 gallons of fuel and you have a similar change in ride height.

Also consider that the shock itself generates heat. Shocks convert kinetic energy into....Heat... So the shock itself will heat up while you are driving.

Has anyone noticed their car riding taller in the saddle after a run due to warmed up shocks?

Also, keep in mind that the reason for having gas shocks is to prevent foaming (aeration) of the shock oil. It is not to create spring rate or lift.

[RoninLB]

Clark--you assume a linear curve in gas shock lift. Maybe, I don't know. Autobonrun asked about temp. change effects in gas shocks, nothing specific. BKOMAR is dialed in to his suspension. This may need a technical professional answer.

[dickster]

just to give an example of what i was referring to in my earlier post.

i have a triumph daytona sports bike. i changed the original damper (rear) for an ohlins unit. the old damper used to feel very different depending on the temp. outside. it was best described as inconsistent.

when i changed to the ohlins unit the handling became noticably (night/day diff) more consistent whatever the weather (and i live in uk so temp. is up/down all the time).

it actually says in the ohlins literature that the damper will compensate for temp. itself.


hope that helps!

richard

[autobonrun]

Originally posted by richardnelson
just to give an example of what i was referring to in my earlier post.

i have a triumph daytona sports bike. i changed the original damper (rear) for an ohlins unit. the old damper used to feel very different depending on the temp. outside. it was best described as inconsistent.

when i changed to the ohlins unit the handling became noticably (night/day diff) more consistent whatever the weather (and i live in uk so temp. is up/down all the time).

it actually says in the ohlins literature that the damper will compensate for temp. itself.


hope that helps!

richard

Was the old unit hydraulic or gas? I assume the new unit is gas?
If your answer is that they are both gas, that would mean that any tempertature compensation is a function of the internal design of the unit. If your original unit was hydraulic, I'm not sure what the hell it means. RoninLB may be correct, a Bilstein engineer may be in order to totally answer my question. I'll fire off an email to Bilstein and ask the question. If I get an answer, I'll post it here.

[dickster]

just checked and both are gas.

so yes, you are correct - its seems that the build quality/design of the shock determines how much it will be affected by temp.

(obviously a race shock (which costs mega amounts) is designed to run at high (race) temps without fading).

but the diff. between the shocks on my bike are amazing. when i first bought the bike i asked a dealer that races triumphs what he would recommend as upgrades. he said the only changes he would make would be to the suspension, and it will be transformed - best £600 i've spent on bike stuff....

regards

richard

[Roland Kunz]

Hello

Yes shock absorbers have a operation temperature and will not work to well ( or at all ) if they are to cold or to hot. However some driving will work some heat into them and they work like they should. If they get to hot your driving style needs other shocks.

OK the benefits and how from gasshocks are aviable in any comercial flyer from the companys, best is to drive them to find out. But a good desigened oil shock can outperform a simple made gas shock. So gas filling isn´t a sign from quality.

Grüsse

[Early_S_Man]

While the 'de Carbon' patent high-pressure monotube shocks (like Bilsteins and others) can reduce aeration of the hydraulic oil at high temperatures, the oil viscosity is still affected by temperature. Even at highway speeds ... in wintertime conditions the shocks never reach the normal operating temperatures that you see in the summer! So, it is normal to expect a bit harsher ride in the winter.

[911pcars]

Ever notice how close the rear shocks are to the heat exchangers? (at least on the early 911s). I'll get around to measuring the heat from the exhaust system. If it's higher than, say 300 degrees, I'm sure it affects the jounce and rebound specs as well as longevity.

Sherwood Lee
http://members.rennlist.org/911pcars

[autobonrun]

Here's the email I sent to Bilstein, Germany. If I get a response, I will post it here. If I don't, I tried.


++++++

I am a member of an active Porsche technical website in the US . Many of us are switching to Bilstein shocks from the standard hydraulic shocks. There are a few technical questions I hope one of your engineers can answer so I can post the reply for others interested in Bilsteins to see.

I would like to know:

1) Is the purpose of the gas fill only to prevent foaming of the hydraulic fluid or does it actively contribute to the damping; if so in both directions of travel?
2) How does Bilstein compensate for changes in shock temperature (either from ambient conditions or racing) such that the performance is consistent? I would think the gas pressure would change with temperature.
3) Are Bilsteins more stiff than say Koni's or Boge's because of the gas charge or because of some other internal design.
4) Is there a quantified percent difference in stiffness between the Bilstein HDs and the Sport Shocks.
5) Lastly, is there a Bilstein recommended setup for Porsche 911's (eg. HD front, Sport Rear).

Your answers will be greatly appreciated.

[RoninLB]

Autobonrun....Great work. They better reply or send me the address and picture of the guy who is disrespectful to all of us. Also, I hear that cows in Kansas serve milk and cookies for New Years parties. Is that true??