Originally Posted By Spanner Juggler
Originally Posted By Rog
My car was built in 2005 and also has the blue springs (but not as clean as yours). I’ve always suspected my front end was a bit on the hard side. You can barely move it by pushing down at the front. A couple of months back Peter B got underneath with his tape measure and concluded my lowers had about 20mm of compression shocked2 I think he said it was comparable to the stiffness of an F1 car! So I’m eagerly awaiting my kingpins to developed slack so I get in there and play.


Not being able to manually move the front much is totally normal, try any other car and you will see the same. As for measuring the lower rebound spring....little exercise for you, if you have a front bumper grab the stays and do your best impression of a weight lifter and try and raise the car, or use a jack in the middle. Let it go and measure the lower springs.....now push the front down and repeat and you will find there is a considerable difference. The cars 'stick' either high or low by at least 20mm depending on how it was parked, did you roll to a stop, did you dab the brakes, did you power into the parking place more? Its all down to the 'stiction' in the kingpins and bushes and if you saw a car with kingpins and no stub axles and wheels assembled you would see the angle the pins sit at (corrected in geometry by the stub axle face not being parallel to the bush tube)....all a normal part of the geometry. Don't let a characteristic of the car sway you into thinking the rebounds are under load, an excellent video posted on here (somewhere) of a car driving down the road showed the rebounds have a massive gap above them most of the time anyway making a bit of a nonsense of this worry about preloading the rebounds. Of course you want smooth interaction between the kingpins and bushes but if it ain't broke why fix it?


I am a bit confused by your statement "the rebounds have a massive gap above them most of the time anyway making a bit of a nonsense of this worry about preloading the rebounds". My understanding is/was that standard rebounds are always under load and this is quite excessive as they are around 375lb springs, and that only when the top spring is under load and compressed through hitting a bump or during hard cornering does the bottom rebound spring become unloaded. This as I understand it produces a non linear suspension effect where the initial suspension is at the total of the rebound 375lbs plus the lbs force of the top spring, so that when the rebound becomes unloaded the suspension effectively immediately drops to the lbs force of the top spring becoming much softer and this can then effect the handling of the car. So the suspension goes from hard to soft and back to hard when going through a rough time or hard cornering. One approach as I understand it to address this issue is to replace the top springs that are around an inch shorter and to then shorten the rebound spring so that when the car is at rest the rebound spring is just touching the bottom of the stub axle and is not compressed. By shortening the top spring the ride height remains the same and all the suspension is now linear due to the top spring being the main component and and bottom spring now truly acting as a rebound spring. Obviously rebound is also controlled through the the shock absorbers as well depending on what they are and how they are tuned. My understanding is that this approach is/has been used on race and road cars to some success. In fact it is an approach I will be taking with mine when I come to replace the king pins, I will raise the top spring rates by about 20lbs with 1 inch shorter springs, shorten the rebounds having assembled them and measured the amount to remove. and I will then tune the shock absorbers for the rebound rate, possibly using Quantums if I can afford it, or maybe with some minor mods to the AVO adjustable for bump and rebound.

Please tell me if I am missunderstanding something here?

Last edited by AJSki2fly; 10/12/15 11:45 AM.
Adrian

Buggered Off, to a modern none leaky car, heart's still ticking