jean Posted March 1, 2007 Report Share Posted March 1, 2007 Jon, that's a great weekend, try to make, with Alec's initiative there might be a good participation in spectators from U.K. Quote Link to post Share on other sites
marvmul Posted March 1, 2007 Report Share Posted March 1, 2007 Jean, if I may correct you, I think that most dampers, inclusive Koni Classic's, are damping on extension of the springs (= wheel drooping or body rising), and only to a small degree (about 20%) when the springs are compressing (= wheel rising). It may be academic but it can confuse people when they are checking the shock absorbers. To equalise the 2 shock absorbers on one axle, I hang them up on the ceiling (after warming them on a radiator) and check the time it takes from full compression to full extension after hooking a mass of about 30 kgs (or myself, in case of shocks for a race car) in the lower eye. To make the damping equal, the position of the adjusting screws of the two shocks can greatly differ : i.e. 1/4 and 5/4 turn from maximum. Quote Link to post Share on other sites
jean Posted March 1, 2007 Report Share Posted March 1, 2007 I must say never heard about this. As far as I know they slow down spring compression. A car with bad standard shockbsorbers can be pushed down with ease, jump back and continue the movement untill all energy is absorbed . With a good damper it's hard to push the car down, to say compress the spring, but the body will come up easily. If the damper would have the maximum damping effect on stretching the car would hit the bump stops continuously or am I so wrong Quote Link to post Share on other sites
marvmul Posted March 2, 2007 Report Share Posted March 2, 2007 Jean, maybe you are wrong indeed. I tried an adjustable Koni (not mounted on a car) this evening that was set at almost maximal damping : pushing the piston rod in the body went effortless : about 3 seconds. Pulling the piston rod out again was very difficult and took about 25 seconds. I tried an (defective! oil leak! I've a couple of them) adjustable gas Spax : compression and extension needed about the same force. Maybe gas shock absorbers are more difficult to compress because of the gas pre load, but gas preload is a spring, not a damper. If damping would occur mostly on compression and the inner wheel (ie the rear inner wheel)of a car meets a bump in a bend, it would push the car body upwards, and this movement of the car body would take much load of the outer wheel of the same axle. The inner wheel is light also when it is past the top of the bump : the two wheels of the rear axle are light then : this would upset the car very much. Quote Link to post Share on other sites
jean Posted March 2, 2007 Report Share Posted March 2, 2007 Yes Marcel this is exactly what happens when a car drives over a bump. But here inertia comes in. The car itself is very heavy and the wheel is very light, therefor you have to keep un-sprung parts as light as possible. In fact he bump will push the car upwards. The wheels being light will follow the bump with ease and move upwards quickly, on the other hand the car being heavy will follow the bump very slowly due to it's weight. The same will happen when the car is over the bump. The wheels will follow the descend quickly, unless you go too fast to allow them to come off the ground. The rest of the car being heavy continues it's path and drop down on the suspension a little later. If a car drives over a rough surface the body will remain stable as time between bumps is too short to move the body, the heavier the car is the more stable it will be, this under condition that the suspension is well balanced in relation to the weight of the car. The wheels on their side will go up and down like mad. Slowly pushing/pulling on dampers has little do do with damping capability, to see how they work you will have to push/pull in a rapid movement using a force of a few hundred kilos, in reality it's a question of inertia, the more weight the more difficult to accelerate. On road cars there is absolutely no advantage to heavily damp the down movement as this will only influence ground contact in a negative way. I fitted the Koni's I had them adjuated on centre position and the body did hit the bump stops every time whe I drove OFF a speed bump, so I adjusted them some clicks to the harder side and problem solved. Quote Link to post Share on other sites
marvmul Posted March 2, 2007 Report Share Posted March 2, 2007 Jean, your explanation is proving that you know and understand car suspension and dynamics, something I did know very well already. But dare I still doubt on your opinion about damping rates in compression and rebound of telescopic shock abosorbers and Koni's in particular. I've searched some KONI website's about 2 of their adjustable shocks : Koni Special and Koni Sport (Sport has the firmer action of the two types, both are adjustible). What did I found : -firstly : both types are only adjustible on the rebound movement (=wheel drooping or carbody rising). The compression damping rate is fixed in both these types of adjustable Koni's -secondly : the damping rate in rebound is adjustible, but always firmer than the fixed damping rate on compression : by a factor 2.5 to 4 for the Koni's Special and by a factor 2.5 to 5 for the Koni's Sport. PS : drawings are showing that the ratio between force and speed is about a straight line :so it doesn't matter if you are keeping the speeds or the forces constant to check the shocks, but I agree that a weight of 30 or 65 kgs is too low, but the closest shop that have a testing facility in my region (testing the shocks after removing them from the car) is 90km away. Quote Link to post Share on other sites
RogerH Posted March 2, 2007 Report Share Posted March 2, 2007 Hi Chaps, before Jean and Marvmul resort to fisty-cuffs may I chuck in my two penn'orth. The spring allows the wheel/tyre to smooth out the bumps (big and small). The Damper controls the spring to reduce/control the rebound effect. The amount of damping is adjusted to give the required ride quality. Most of the damping effect is (as Marvmul states) when the damper strut is being extended (controlling spring rebound). If the damper strut worked the other way around (more damping effect on strut compression) then the car body would be pushed upwards when going over a raised bump. Should I complicate things and get the tyre compression rate involved in the suspension spring rating - perhaps not. The logic of how it works is simple, the problems come when setting the car up for the required ride. There is a nice explanation on Google, log in 'Suspension Vehicle' then go to the Wikipedia entry Best of luck Roger Quote Link to post Share on other sites
wheeler Posted March 2, 2007 Report Share Posted March 2, 2007 Hi Guys Here is another website about suspension http://www.carbibles.com/suspension_bible.html looks like we all have a lot to learn! Cheers Bill Quote Link to post Share on other sites
marvmul Posted March 3, 2007 Report Share Posted March 3, 2007 Hi Chaps, before Jean and Marvmul resort to fisty-cuffs may I chuck in my two penn'orth. Best of luck Roger In Belgium, maybe it's the same story in other countries too, it seems that everyone is resorting to knifes as a first move nowadays ! Quote Link to post Share on other sites
jean Posted March 4, 2007 Report Share Posted March 4, 2007 Roger don't worry, we are very civilized people and Marcel is a good friend. Anyhow it's always good to have a nice discussion, a pub would be a much better place for such things Bill thanks for the web link, a lot of things to study Quote Link to post Share on other sites
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