I have replaced topmounts, wishbones track rod ends and arb droplinks and still knocking from shocks so I will have to splash out on a set of bilsteins soon. I can't decide whether to lower the car or not but aside from this if I decide not to lower it should I replace the old standard springs with new standard springs? and if so why? Do springs get softer or weaken over time and thus affect handling?

I don't think it would be enough to notice. You don't see your ride height change over time.

Springs can sag a bit over time, but not by a massive amount.

I don't think you will have a big issue with using the original springs with the new dampers though.

cheers guys, Unless someone convinces me otherwise I wont change my springs when I change my shocks, although its nice to have all new bits, if there is no benefit then why bother with the expenditure! Anyone else have an opinion on this?

Nope they will be the same as they left the factory.
Hook's law sees to that.

Gareth

but if the springs are old i would get some new ones, in the last 5 months 3 coops including mine have snapped a spring.

snapping springs can't be good! so I guess corrosion and metal fatigue comes into play?? any engineers out there?

make that four coops

one of my fronts snapped (original) just before christmas, mileage around 100k


Paul

yup, my front drivers spring snapped at about 100k as well Seems to be a built in fault...lol

it seems like this should be pointed out too when people are looking at coops with around 100k on them.

So I guess what your all trying to tell me is that I am better off buying new springs aswell as dampers! So be it, hope my credit card can handle it!!

Um, no it doesn't; Hooke's law only describes the extension of a spring while Young's Modulus is in operation; once the yield point is reached it's a new ball game.

Springs definitely *can* lose their temper with age and become effectively less springy. Also, corrosion and wear affect the properties to.

That said - when I replaced everything else I put the original 150k mile springs back on the front.

I replaced my dampers, drop links, top mounts, bearings, track rods, wishbones, except the springs. Have had no problem at all. My car has done 140K.

That's a bit misleading Neil.
As you say as long as the yield point is not reached the stress/strain graph will remain linear.
If I compressed a car spring fully it will return to its original length. Therefore the yield point will not have been reached. If the yield point has not been reached then the spring constant will not change.

I had this argument a few years back and I proved that a car spring does not reach yield point and obeys hooks law even at full compression (no gaps between coils).

If there is no corrosion, and the spring is free from manufacturing defects, it will always have the same spring constant that it left the factory with.

Gareth

but there often is..

Yes, but remember that if the corrosion has changed the spring constant, then the ride height would be lower.

X=F/-k
Where X is extension (in this case compression), F is the Force (weight of car), and -k is the spring constant.

Therefore it is physically impossible for springs to go (soft) IE, lower spring constant; without having a very noticeable reduction in ride height.

Perfectly true, Gareth. You can't be at the same height with a different spring rate unless the supported mass or the spring length has changed.

You don't reach the yield point in compression - you get coil bound instead (hence variable rate springs have a different coil pitch so the binding occurs gradually and the spring becomes proportionally and gradually stiffer).

But springs can still suffer metallurgical changes over time, though they will of course show a reduced ride height. Like the twenty-year-old ones I took off my kit last week; uncompressed they have the same height, same diameter, same gauge metal - but the old ones rode an inch and a half lower.