The damping force is definitely proportional to velocity. Not convinced? compress a damper with your hands, it'll move slowly but you can compress it fully no problem. Then try to compress it faster, you'll get nowhere. This is because when you compress a damper you're basiclly (don't be picky Jason) making fluid move through little tiny holes. The faster the damper is compressed, the greater the resistance.

Dampers are definitely as effective opposing the bound as the rebound, but I can totally see why the rebound is foremost in your experience of knackered ones StuartB. Jason's learning motorsport engineering so he knows what he's saying, although sometimes he seems reluctant to break it down a bit for those who aren't studying a BEng

stuartB wrote:If it goes down, then bounces straight back up, with a small hiss, and stays there solid like a rock then they're alllll good.

This situation is called 'critical damping', and is what manufacturers design into new cars, and always have done. Essentially, what you're saying is correct, but using the wrong terminology sometimes brings out complaint from those of us who've done engineering.

Just a quick not on the landrover shocks. They are a bit shorter (open and closed length) than stock 300 series ones but possible not engough to cause problems

i think we're arguing the same point but im not sure

springs take the actual impact of the up/down motion, and shocks level out the bounce, i think thats what we're getting at here. correct me if im wrong

sorry, i only deal with laymans terms so i will probably offend you with wrong terminology pretty much constantly

i appreciate the engineering forum tho, great place to bounce ideas around and get corrected when im wrong



i dont come on here to offend and correct people its all about trying to work out whats wrong with my car lol

hehe, sorry, its me being picky (but it is better to start using the right terms and principles now and again ) - can't resist correcting things that I actually understand a bit about... and I'd hope other people would make corrections where due too!

@FJ sadly I don't do motorsport engineering (though I would quite like to) - I actually do something far more specific to this topic... Meng Acoustics and vibration engineering

Jason B wrote:can't resist correcting things that I actually understand a bit about...

It doesn't happen often

FWIW guys, as long as it never gets into a slanging match, I think we are lucky to have the number of people we do who are willing to learn new stuff to try and improve their cars. We certainly have a huge diversity of backgrounds.

Control theory was a large part of my degree when I did it, and the project I've been working on over the last few years, and all the maths is identical between the application I use it in and suspension as far as I can see.

For a bit more on what FJ is on about, wiki as ever rocks



and a quick read up on the "System behaviour" section on this page.. http://en.wikipedia.org/wiki/Damping#System_behavior ... should give a fair insight to the game. For suspension to rock, squiggly thing should = 1. If it's much greater than one the car is way to slow to react (which is what I think is happening on cars running landy shocks, squiggly thing is well over 1). The opposite end of the scale is Fake, with 200,000m shocks, where squiggly thing is less than 1, and it bounces forever. Then, somewhere separate, we need to get our spring rates roughly right, and we'll be on the road to win.

*squiggly thing does have a name, but I really can't remember what it is, and you may have noticed my use of engineering terms is a bit, erm, special*

well exactly - thats my point.. when they make shocks they design them in order that they take the 'wobble' out of the bounce. they have to make them stiff enough to stop the rebound yet soft enough to ideally NOT interfere with the initial bounce. hence they move upward with no resistance whatsoever but on the return journey they are "stiff." finding the fine line between the two is what its all about.

If you could design a shock that moves freely down then up once, then only provide resistance on the way down for the second time, you'd be in the money. presumably this is pretty much being done now in modern suspension setups - intelligent shocks and all that

as i say, matching your shocks to the correct springs is where the skill is

i dont care what anyone says, shocks arent designed to provide resistance to the car moving up and down (i.e. what everyone means by 'stiff') - thats what the spring is for. get them right, THEN set your shocks up accordingly

he says, sticking LR90 shocks on the back of a volvo with knackered leaf springs LOL

could you use standard 360 leafs cut and clamped to a standard 360?

also what shocks can you use in the front of a 360?

swaybar upgrades? the rears dont run a swaybar?

Whats a leaf?



Only joking.

With the wide and diverse oracle of fact and opinion stored up on v3m, i supose someone has to be at the base of knowledge pyramid. Its fun gazing up at all the technical discussions taking place way over my head.

And even i knew springs accepted the impact force, and that dampers then controled it.

Or was it the other way around?

volvosneverdie wrote:Whats a leaf?

Don't you dare start on those tree puns again

Tom

Yeah leaf it out will ya?!

No.
Im nipping this one in the bud right now.

This is all to do with the Q of the resonant system... The ratio of the reactive/resistive components. I'm studying electronic engineering, so not sure about the particularities of a mechanical system, but would I be right in thinking the springs are the resistive part - the force exerted by them in directly proportional to their displacement. The 'absorbers' on the other hand are reactive, and their force is proportional to rate of change. I think.

Jason - Where are you studying acoustics?It's something I'm very interested in and I've considered doing a masters in it once I graduate.

tommysb wrote:..but would I be right in thinking the springs are the resistive part

Not far off, the spring works like a capacitor, the damper like a resistor. All the control theory you've learn in electronics should work if you calculate everything in spice... I think I'll test it at some point.

Jason is in Southampton, where abouts are you atm?

To be honest I've not done too much control.. I opted to take microprocessors instead!

I'm based all over...just done 6 months of an industrial placement in Swindon, got another 6 months in Oxford, and then off to finish my degree in York.. but the 340 is currently at my parents' in Norwich! Quite simple really!

Jason - how familiar are you with loudspeaker design?


back on topic - So - what is recommended is 'stiffening' the spring by adding more leafs - increasing the potential energy it can store. But then also adjusting the damping to compensate?

double leaf springs + landrover shocks

unless you're taking it round mallory or snett with big concrete blocks in the boot every weekend, i dont spose you'll get even close to the potential of that setup

sounds like a challenge to me..