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Jun 15, 2011 15:59:42 GMT
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Hi all, one of the coilover springs on my Audi has snapped so I want to replace them (all) - I've looked on Rally Design first up and they list 116 variations of length & spring rate!  I can easily narrow that down to the right length by measuring whats on there at the moment (when unladen) but I'm hoping for some advice on what is a sensible spring rate for a very low family estate? I guess too hard & I'll be biting through my tongue but too soft & I'll be constantly bottoming out  In this instance, low really does mean low..  Thanks ;D |
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Jun 15, 2011 16:03:12 GMT
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Borbet T's? Lovely  Try finding a bit more serious company who let's you switch springs until you find what suits you. If you send them a spring they can measure it for you and you can go from there |
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Jun 15, 2011 16:13:20 GMT
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You can calculate the rate if the old springs with a few measurements: www.pontiacracing.net/js_coil_spring_rate.htmAs a rough guide, The ones on my mk2 golf FK coilovers work out to be around 300lb/ft. I had 180lb springs on the front of my old grey 106 and they were loads too soft. |
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RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
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Jun 15, 2011 16:45:22 GMT
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You can get a rough idea by measuring how much the spring compresses when you put the cars weight on it. Just divide the weight on the spring (in lb's) by the movement in inch's and you'll have it's spring rate. Ok you'll have to guestimate the weight on the wheel you're measuring, but it'll get you somewhere close.
This is assuming the cars not being supported by the bump stops, and that the springs are free length before you put the weight on them of coarse.
There are various mathematical methods of calculating the necessary spring rate, but they'll either involve information you don't have easy access to, or will still need you to guess how hard you want the ride.
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Jun 16, 2011 11:19:20 GMT
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Have a read through the first few pages of Seth's Hillman thread where he made the coilovers and showed how to calculate the spring rate and ride height he wanted. I have a feeling he may have done it on paper to prove that it really is quite simple, but also used an online calculator.
Is there nothing stamped on the old ones, Andy?
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...proper medallion man chest wig motoring. |
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Jun 18, 2011 21:03:05 GMT
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There's a great book called race and rally car source book that is packed with info on how to calculate lots of stuff for your car...
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Koos
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Jul 12, 2011 12:34:14 GMT
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Thank you all for your input, and sorry for the slowness of my response - I haz done measuringz:
Compressed: 12cm
Uncompressed: 15.5cm
Vehicle weight: 1820kg (according to plate)
I like Robin's solution - that's maths I can handle ;D How do I approximate the weight on a spring from the total weight? I'm thinking 45:55 weight distribution / 2?
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,790
Club RR Member Number: 34
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if you want to know for certain, nip down the local scrappy/weighbridge and give em a drink to measure your noseweight and tailweight.
again though it still wont be an exact art, some people just prefer a firmer ride than others, or have less suspension deflection to use. generally speaking, i find an oversprung car better than an undersprung one, especially when its really low. it can be a bit rattly/harsh on big hits, but i find that better than it being really bouncy and crashing through the travel and bottoming out.
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Dez, that would be my preference too and TBH that's basically how it is now & I'm happy with how it rides. Not really bouncy, doesn't crash or bottom out, but pretty savage if you hit something big. So I guess what I want is the springs as they are now, but the same on both sides & not snapped. MATHS!!  Springs Compressed: 12cm = 4.73" Uncompressed: 15.5cm = 6.11" Difference = 3.5cm = 1.38"Car Weight Total: 1820kg = 4013.1lb Front @ 55%: 1001kg = 2207.2lb Corner Weight: 500.5kg = 1103.6lbSpring rateWeight on spring / movement = 1103.6 / 1.38 = 800!! Really?!  |
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Jul 13, 2011 10:05:56 GMT
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Didn't realise that old barge was still about. I put the coilovers on it for a mate about 3 years ago and thought the car would of worn through by now lol iirc the coilovers cost him about 800 quid so I'm surprised a spring has broke. Saying that I suspect after I fitted them he probably went at it with a grinder to get it lower, he was/is obsessed with lows
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muttley racing ftmfwmf
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Jul 13, 2011 10:19:16 GMT
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Y0! Nice to hear a bit of history Yeah, as I understand it the coilovers are £820 FK Konigsports and to be fair they really are very good - the ride is excellent. And yes, the springs have been cut in pursuit of epic lows, but one of them has actually snapped as well - after 3 years I don't think that reflects badly on their quality  My plan is to buy replacements in the cut length - assuming you can actually get 6" 800ft/lb (WTF!!) springs? Rally Design only go to 7" 600 rate..  EDIT: Yes you can, easily ;D |
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Last Edit: Jul 13, 2011 10:25:21 GMT by HARDCORE
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Jul 13, 2011 10:25:57 GMT
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those figures don't sound too far out of the ballpark given how daft low you want it, a friend of mine is running prototype AST Sportline 1 and 2 dampers on his Phase 2 V70 T5, current front spring rate is just over 500 Lb/in and its only sat 30-40mm lower, it weighs quite a bit less than your Audi at 1415kg!
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Jul 13, 2011 11:01:40 GMT
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muttley racing ftmfwmf
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rob0r
East of England
Posts: 2,743
Club RR Member Number: 104
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Jul 13, 2011 11:36:34 GMT
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Random comment... Faulkners have more spring choice than Rally Design and aren't far off the price.
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E30 320i 3.5 - E23 730 - E3 3.0si - E21 316 M42 - E32 750i
ETC
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stealthstylz
Club Retro Rides Member
Posts: 14,960
Club RR Member Number: 174
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Jul 13, 2011 11:45:08 GMT
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Find somewhere local with a spring tester and get them to measure what is on. There's a oval race shop near me that does mine.
Matt
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Jul 13, 2011 12:15:17 GMT
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MATHS!! Springs Compressed: 12cm = 4.73" Uncompressed: 15.5cm = 6.11" Difference = 3.5cm = 1.38"Car Weight Total: 1820kg = 4013.1lb Front @ 55%: 1001kg = 2207.2lb Corner Weight: 500.5kg = 1103.6lbSpring rateWeight on spring / movement = 1103.6 / 1.38 = 800!! Really?! ^^^^^^ This is why when I did it on the Volvo, I guessed  luckily I guessed about right and it sat on 8" long 250 lbs spring was a little soft but was generally okay. Sorry I can't be of much more help....... lets face it I put Transit springs on my Sierra, over kill |
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Sierra - here we go again! He has an illness, it's not his fault.
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Jul 13, 2011 12:19:23 GMT
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Random comment... Faulkners have more spring choice than Rally Design and aren't far off the price. I got mine from Faulkners, just remembered HC what diameter are your springs? I've got some 2.5" (not 2.25") coilover springs knocking around your more than welcome to have them if you want? |
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Sierra - here we go again! He has an illness, it's not his fault.
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VIP
South East
Posts: 8,299
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Jul 13, 2011 13:42:35 GMT
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MATHS!! Springs Compressed: 12cm = 4.73" Uncompressed: 15.5cm = 6.11" Difference = 3.5cm = 1.38"Car Weight Total: 1820kg = 4013.1lb Front @ 55%: 1001kg = 2207.2lb Corner Weight: 500.5kg = 1103.6lbSpring rateWeight on spring / movement = 1103.6 / 1.38 = 800!! Really?! I think you'll find a B4 Audi 80 doesn't weigh nearly 2 tonnes... |
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Jul 13, 2011 13:43:58 GMT
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Indeed! Sounded mental to me too, hence all the ' really?' and 'WTF?'.. Methinks I looked at the wrong weight on the plate! EDIT: WHS^^ I phail!  |
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Last Edit: Jul 13, 2011 13:46:02 GMT by HARDCORE
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VIP
South East
Posts: 8,299
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Jul 13, 2011 13:52:35 GMT
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Carfolio kerb weight of a 2.0 B4 Avant is 1270Kg.
Round it down to 1200 for adjustment of unsprung weight.
Putting that into the calcs gives you a figure of 526lb, so I'd round it to 550lbs.
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I can easily narrow that down to the right length by measuring whats on there at the moment (when unladen) but I'm hoping for some advice on what is a sensible spring rate for a very low family estate? I guess too hard & I'll be biting through my tongue but too soft & I'll be constantly bottoming out 
My plan is to buy replacements in the cut length - 
luckily I guessed about right and it sat on 8" long 250 lbs spring was a little soft but was generally okay.
