Audi C4 Avant quattro spring rates

Gaz · 01-01-17, 11:06 PM

Had a little problem with the AEL Avant quattro A6 . The spring perches on both sides were rusted and holed, and the one side had collapsed altogether and was sitting on, and rubbing against the tire.

In my infinite wisdom I decided it would be a good idea to have the spring perches cut off completely and have them converted to adjustable coil over sleeve's.

Had a few problems along the way, but right now i'm wondering what would be a good road/daily spring rate to use of the front of the car?

Really I need something close to stock A6 sport suspension so that it matches the standard rear springs on the car. Otherwise it could end up 'sea-sawing' if the front is too hard sending all the energy to the softer rears.

(if you get my drift?)

I've asked on the S2 forum but everyone seems to be saying 450/550 lbs springs !

Saying that it's a heavy car. Well, true, but that just seems far too hard to me.. Anybody else think so?

Surely the standard rates were not that hard? 450/550 lbs seems more like a race track car spring to me?

And, like I say, I don't want the rear of the car bouncing up and down like a sea-saw on country roads due to the fronts being too hard.

SO... any ideas/recommendations? Just looking for second opinion really.. And I thought the classic Audi crew might be a little more sympathetic towards setup's for everyday British road use.

Need to buy the springs asap, as my mechanic is waiting on me.. Length wise spring are probably going to be about 300 mm long and 2.5 inch wide ID if that helps at all?

cheers guys.

missfire · 02-01-17, 03:27 AM

Can your mechanic not work it out for you?

If nobody has stock rates you need to know the sprung weight at each corner ideally (i.e the weight of the shell, engine etc. everythng above the spring, not axles, wheels etc. and how that weight and forces are multiplied up by the geometry). Then work out how much extension there should be in the suspension to get the spring height and decide how much sag you want, to get your ride height. Then you divide the sprung weight at that corner by the number of inches of sag you want, to get the spring rate. (So a 500lb spring will compress one inch for every 500lb applied to it, if it's a linear rate spring, which it will be on a coilover). The irony being that the best way to work out the sprung weight is to borrow a set of known rate springs and measure the sag. And equally, an inch of travel at the spring will translate to more than that at the wheel because it's further out from the pivot point etc. so using borrowed known rate springs is by far the easiest way to get it all to work out unless you're a maths, engineering and physics guru!

So with a weight of 1000lb per front wheel, plus leverage, an educated guess or experience from the s2 forum may not be far off? Just depends how much sag you want. I'd be searching german ebay for a full kit of some kind, or maybe even better, a set of replacement stock struts?

That sounds utterly confusing reading it back but if you had a noddy car setup vertical load on the spring straight into the ground with no wishbones or arms, 1000lb per wheel and you wanted four inches of sag, you'd need 250lb springs, but it's not that simple, hence easier to work it out using someone else's springs or someone with a good returns policy, lol.

Gaz · 02-01-17, 10:53 AM

Thanks for the reply. I have tried searching for coilover kits and other suspension kits to see how strong there spring rates are, but non of them ever seem to disclose an actual spring rate.

I did originally look for replacement standard struts but second hand ones have been far away or the postage has been high according to the seller. Also got tired of waiting for a reply off one guy only to then tell me he didn't want to sell.

Days turned into weeks, weeks into months and got so fed up I decided it might be easier to convert them. Then there were snags with top mounts not fitting and with christmas and new years there has been even more delays from the mechanic now.

Anybody wanna buy an A6!!?? hahahaha. (really I'm crying inside) :/

vorsprung durch technik · 02-01-17, 02:40 PM

Quote:

Originally Posted by Gaz

Also got tired of waiting for a reply off one guy only to then tell me he didn't want to sell.

Days turned into weeks, weeks into months and got so fed up I decided it might be easier to convert them. Then there were snags with top mounts not fitting and with christmas and new years there has been even more delays from the mechanic now.
(really I'm crying inside) :/

I know that feeling,been there only a few weeks back with one guy with the S6, promises of help only to be completely let down months later putting back the head swap now until it gets warmer and i can attempt it outside myself for the first time on one of these cars.

I have no idea what the spring rates are on these are but can say they are a quite a bit more than an S2 Coupe. My 1997 2.8 C4 Quattro had a firm ride and was original factory, something a S2 nut who drove the car commented on saying how shocked he was at how firm and well controlled it felt in normal driving,i.e. no mushyness whatsoever. I'm like you i would love to know these spring rates,it was a lot easier years ago to get good info on Ford springs. Why not Audi??!

missfire · 03-01-17, 01:00 AM

No more ideas then from anyone else then? 450 doesn't seem too high? I can't access most of the s2 forum but if someone has a number you'd think there must be a reason. I thought track/super cars could be up to 900 or more? I had a look earlier too as I've got the same struts but could only find b5 rates at about 250 to 280 for sport versions. Anyway a full kit of some kind is really the way to go as, as you say, mess it up and your undampened frequency front to rear will go way out of phase to the point of car sickness.

02-01-17, 03:27 AM	#2
missfire making wooden things Classic Audi Club Member Join Date: Dec 2009 Location: cow land Posts: 8,154	Can your mechanic not work it out for you? If nobody has stock rates you need to know the sprung weight at each corner ideally (i.e the weight of the shell, engine etc. everythng above the spring, not axles, wheels etc. and how that weight and forces are multiplied up by the geometry). Then work out how much extension there should be in the suspension to get the spring height and decide how much sag you want, to get your ride height. Then you divide the sprung weight at that corner by the number of inches of sag you want, to get the spring rate. (So a 500lb spring will compress one inch for every 500lb applied to it, if it's a linear rate spring, which it will be on a coilover). The irony being that the best way to work out the sprung weight is to borrow a set of known rate springs and measure the sag. And equally, an inch of travel at the spring will translate to more than that at the wheel because it's further out from the pivot point etc. so using borrowed known rate springs is by far the easiest way to get it all to work out unless you're a maths, engineering and physics guru! So with a weight of 1000lb per front wheel, plus leverage, an educated guess or experience from the s2 forum may not be far off? Just depends how much sag you want. I'd be searching german ebay for a full kit of some kind, or maybe even better, a set of replacement stock struts? That sounds utterly confusing reading it back but if you had a noddy car setup vertical load on the spring straight into the ground with no wishbones or arms, 1000lb per wheel and you wanted four inches of sag, you'd need 250lb springs, but it's not that simple, hence easier to work it out using someone else's springs or someone with a good returns policy, lol. Last edited by missfire; 02-01-17 at 03:59 AM.

02-01-17, 10:53 AM	#3
Gaz Senior Member Join Date: Jul 2007 Location: Five Cylinder heaven Posts: 1,493	Thanks for the reply. I have tried searching for coilover kits and other suspension kits to see how strong there spring rates are, but non of them ever seem to disclose an actual spring rate. I did originally look for replacement standard struts but second hand ones have been far away or the postage has been high according to the seller. Also got tired of waiting for a reply off one guy only to then tell me he didn't want to sell. Days turned into weeks, weeks into months and got so fed up I decided it might be easier to convert them. Then there were snags with top mounts not fitting and with christmas and new years there has been even more delays from the mechanic now. Anybody wanna buy an A6!!?? hahahaha. (really I'm crying inside) :/

03-01-17, 01:00 AM	#5
missfire making wooden things Classic Audi Club Member Join Date: Dec 2009 Location: cow land Posts: 8,154	No more ideas then from anyone else then? 450 doesn't seem too high? I can't access most of the s2 forum but if someone has a number you'd think there must be a reason. I thought track/super cars could be up to 900 or more? I had a look earlier too as I've got the same struts but could only find b5 rates at about 250 to 280 for sport versions. Anyway a full kit of some kind is really the way to go as, as you say, mess it up and your undampened frequency front to rear will go way out of phase to the point of car sickness.