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Location:
Finland
Registered:
November 2002
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How to understand "The value of damping force"
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Thu, 22 April 2004 16:04
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I have been looking around for adjustable shock and I heard that I can get TRD shocks from my local Toyota dealer in very decent price. Now I have hard time to pick right shock, mainly because I have no idea how to understand these numeric values. See here. For example: 1568/588N. First value is for stroke and second is for rebound, right? And another thing is that stiff or not? after little comparing that looks pretty average for being rear shock. Im looking stiff shocks for street and occasional track use. Car was TT132. Springs that I have in my mind are around 6kg for front and ~4kg rear for summers and 4kg front and ~2.5kg rear in snowy conditions.
Thanks!
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: How to understand "The value of damping force"
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Thu, 22 April 2004 16:12
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numeric values are newtons or kg, with 1kg=9.8N
ie for the top shock, 1372 newtons = 140kg
same for the 'reaction force of rod'....
yup, bump / rebound looks correct.
as for values... nfi  sorry 
Cya, Stewart
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: How to understand "The value of damping force"
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Thu, 22 April 2004 16:14
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CAUTION
Value in the above list shows damping force (kgf) at 0.3m/s of piston speed.
Value of damping force of adjustable type in the above list shows
4th position for 8-stage adjustable type
3rd position for 5-stage adjustable type
2nd position for 4-stage adjustable type
2nd position for 3-stage adjustable type
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Location:
Finland
Registered:
November 2002
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Re: How to understand "The value of damping force"
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Thu, 22 April 2004 16:26
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I did realize that. Thanks anyway!
Do you know what that "reaction force of rod" means in the real life, is it same as surface stiffness (my translation from Finnish word  ).
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Location:
South Australia
Registered:
July 2002
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Re: How to understand "The value of damping force"
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Thu, 22 April 2004 17:18
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Do they really have ~ 3 times weaker on rebound than on bump?
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I Supported Toymods
Location:
Sydney
Registered:
December 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 00:36
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FWDBoy you can sort of feel that the rebound force is at least twice that of the bump force by getting a shock (not installed) and pushing it in and pulling it out by hand... its heaps harder to pull / spread the shock than it is to push it together
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Location:
South Australia
Registered:
July 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 03:54
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I remember the shocks that I pulled out of my brothers rally car were very strong on rebound, maybe not as strong as on bump, but comparable, not 3 or so times weaker. But then again, a rally car can't bounce as much when it goes over a jump so I guess a fair bit of rebound damping is required.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 04:13
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There seems to be a lot of misunderstanding around of what a shock absorber actually does.
Firstly it doesn't technically make your suspension stiffer. It's primary function is to prevent your wheels from bouncing, that is to help keep the tyres firmly planted on the ground. Which is why they are better referred to as "dampers". Because the springs should be absorbing the driving shocks and the damper controls the springs.
You do not install a damper with a high damping force to make your ride stiffer. You put stiffer prings in for that and then follow it up with uprated dampers to control the bigger springs.
A damper cannot support a static load, all it can do is slow down motion. If you look at the damping specs in the TRD page you posted, one of the units given is for kgf (kilograms force) Don't get this confused with weight as it is a force. As oldcorollas pointed out earlier, at the bottom of the page it qualify's the specification by saying that it is the damping force for a piston speed of 0.3m/s. in otherwords, if you had a damper with a compressive rating of 100kgf and stood it with 100kg on top, it would sink at 0.3m/s. If it had a stroke length of 0.3m, then it would take 1 second to travel the whole stroke length.
Bare with me, there is a point in all of my dribble.
We have established that the purpose a damper is to control the spring movement and keep the tyre firmly planted on the ground. To do this it will need to resist movement that is trying to push it into the guard but still let the wheel drop back onto the ground quickly. That is the fundamental reason why there is a different rating for bump and rebound. You can see this happening on race bred dune buggies.
Unfortunatly as you are driving along, the harsher the bump, the faster the spring will want to compress and you will end up with an apparent increase in spring stiffness. This is a good reason why you wouldn't want really "stiff shockies" They need to be sized correctly so that they can maintian control of the wheels without increasing the natural frequency of the cars suspension.
The next you ask will be how do you know what rating to use. Thats a hard one because it depends on the effective spring rate of each wheel/suspension assembly, and the ratio of sprund to unsprung weight at each wheel location. You could spend a lot of time calculating these values and at best you might come close to good.
Realistically the best you can do is to get an adjustable set up that is close to the manufacturers recommendations, maybe a little stiffer if you are using uprated springs and fine tune it from there.
I haven't really helped you have I, sorry. If it was easy they wouldn't pay F1 suspension engineers lots of money would they.
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Location:
South Australia
Registered:
July 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 05:00
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Do they really have ~ 3 times weaker on rebound than on bump?
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FWDBoy you can sort of feel that the rebound force is at least twice that of the bump force by getting a shock (not installed) and pushing it in and pulling it out by hand... its heaps harder to pull / spread the shock than it is to push it together
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Isn't pulling the shock out 'rebound' btw? So rebound is usually alot stronger than bump? So the 1568/588 quoted at the start of the thread would be rebound/bump?
Yeah ppl, listen to gold28, shocks are not related to ride height/stiffness/etc!
The reason rides are made stiffer is to maintain certain contact patch (due to suspension geometry) on the road whilst cornering at speed. They are also there to reduce impulse forces on a car.
If you are putting a certain amount of force downwards on the suspension, then the system's overall height (system meaning spring + damper (sprung mass, unsprung) etc) will tend to towards an equillibrium that, in laymans terms, depends only on the strength of the spring! The damper merely controls how quickly it reaches that equillibrium, for example, say you have a very stiff bump, then as you enter the corner, the system will smoothly/slowly approach the equillibrium. You may think this is all good, but what if because of the overdamping, the car never really uses much of the outside tyre through corner entry - maybe the driver is very heavy on brakes into a corner and in this case, the driver would like very strong bump damping on the front...What if you under-damp, then it may even oscillate about the equillibrium as you wobble through the corner.
Like gold28 was saying, there are a billion factors that go into the ideal damper settings. It would be very difficult to recommend a damper setting for someone else. The best thing anyone can do before they ask about damper settings is either learn to trust the aftermarket companies to have not made stupid settings, or go and learn alot of maths and vehicle dynamics and then punch some numbers up and get an approxiamte setting that you can look for.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 05:13
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| FWDboy wrote on Fri, 23 April 2004 15:00 |
Isn't pulling the shock out 'rebound' btw? So rebound is usually alot stronger than bump? So the 1568/588 quoted at the start of the thread would be rebound/bump?
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No the bump value will be bigger, ie more mass to move at the required speed.
Bump is wheels moving up and rebound is wheels moving down.
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Location:
Adelaide
Registered:
May 2002
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Location:
Finland
Registered:
November 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 10:15
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Thanks heaps!
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Yeah ppl, listen to gold28, shocks are not related to ride height/stiffness/etc!
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Shocks should match ride height and spring stiffnes.
I ment stiff shocks as matching shocks for my somewhat stiff springs . And this is where you did get me little wrong thanks to my lousy English.
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You do not install a damper with a high damping force to make your ride stiffer. You put stiffer prings in for that and then follow it up with uprated dampers to control the bigger springs.
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Clear as water. I have read some books about suspension.
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A damper cannot support a static load, all it can do is slow down motion. If you look at the damping specs in the TRD page you posted, one of the units given is for kgf (kilograms force) Don't get this confused with weight as it is a force. As oldcorollas pointed out earlier, at the bottom of the page it qualify's the specification by saying that it is the damping force for a piston speed of 0.3m/s. in otherwords, if you had a damper with a compressive rating of 100kgf and stood it with 100kg on top, it would sink at 0.3m/s. If it had a stroke length of 0.3m, then it would take 1 second to travel the whole stroke length.
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Thanks for clarifying that.
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Location:
South Australia
Registered:
July 2002
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Re: How to understand "The value of damping force"
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Fri, 23 April 2004 16:03
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No the bump value will be bigger, ie more mass to move at the required speed. Bump is wheels moving up and rebound is wheels moving down.
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FWDBoy you can sort of feel that the rebound force is at least twice that of the bump force by getting a shock (not installed) and pushing it in and pulling it out by hand... its heaps harder to pull / spread the shock than it is to push it together
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So technically it should be easier to pull the shock out (rebound) than to push it in (bump).
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Location:
Madrid - Spain
Registered:
August 2002
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Re: How to understand "The value of damping force"
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Tue, 27 April 2004 03:32
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Yep.
Gas filled shocks will actually push themselves out anyway but thats a different story.
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Registered:
April 2004
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