Author Topic: Spring Rates  (Read 5054 times)

DGoose

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Spring Rates
« on: April 16, 2014, 09:30:24 »
I've ordered a set of adjustable spax dampers for my 1994 Ace and would like to fit with new, uprated, spring rather than the 20 year old units currently attached to the car.
   
   Can anybody advise factory rates ?
   
   If I knew the OEM spec this may save me having to send the existing units for test.
   
   In my opinion both front and rear springs need to be a bit stiffer on this particular car and Neal from Redline PE has suggested 170Lb (x4) rears but we are struggling with the fronts.
   
   Any thoughts / suggestions /observations most welcome.
   
   Cheers,
   
   David

shep

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« Reply #1 on: April 16, 2014, 17:06:26 »
That's got to be one for John Abel!

3.5 Pints at the Bar

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« Reply #2 on: April 16, 2014, 20:19:04 »
If you get stuck for data, it is possible to measure and calculate the rate of a helical spring provided that it is not variable rate, tapered, etc. (it's a while since I've seen Ace front springs). You need 3 measurements:
   
   "N", which is the number of free turns of the spring (i.e. not counting the end turns that don't flex).
   
   "R" (inches), which is the mean radius, measured from the axis of the spring to the centre line of the wire. It's easiest to get this by measuring the outside diameter of the whole spring, subtract the wire diameter, then halve the answer.
   
   "d" (inches), which is the wire diameter (this needs to be measured accurately because the rate varies with d to the 4th power).
   
   The equation is:
   
   (d x d x d x d x 187500) divided by (R x R x R x N)
   
   The answer is in pounds per inch, calculated for steel springs.

Nev

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« Reply #3 on: April 17, 2014, 17:31:15 »
From the notes I have on file from the previous owner of mine, the front springs are 10" open, 600 lb rated and 2 1/4" ID.
   They are from the Ford RS Cosworth Sierra.

Max Allan

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« Reply #4 on: April 18, 2014, 10:42:43 »
If the setup on my 94 Ace (No 44) was typical of cars leaving the factory the front springs were coil bound long before hitting the bump stops causing the suspension to “crash” driving on all but the smoothest roads (not easy to find in these days of prolific potholes!). Matters were made worse by the ride height, which was too low. Therefore to commission new springs using data from the existing ones will not sort the problems.
   
   Because the steering and ride on my car was so awful I set about systematically going through steering and suspension geometries, making improvements where possible. Changes to suspension included relocating front and rear dampers, manufacture of longer stroke Koni’s, spring spacers to raise rear suspension and new front springs supplied by Coil Springs (1989) Ltd.
   
   I don’t recall exactly the data Saturn Works needed to make the new springs, because this all happened a long time ago. However, I don’t remember them requiring anything particularly technical - I think it was outside diameter, free length and “compressed” length when at normal ride height.
   
   www.coilsprings.co.uk    coilsprings@saturnworks.fsnet.co.uk

hawk289

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« Reply #5 on: April 18, 2014, 12:36:12 »
Max is spot on, the car is coil bound by standard. I'm changing my spring and dampers as we speak, removing a few turns and getting heavier springs. The cost of springs is not bad (Merlin will do a set for £50) it will be down to the drivers experience. Recommendation, if you are happy with your current set-up then take both springs, important both to Merlin and they will tell you the Lbs then match with new, it should be simple.

DGoose

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« Reply #6 on: April 22, 2014, 09:18:13 »
Thank you all for the input.
   
   As with most things AC nothing is entirely straightforward is it !
   
   I was hoping to stick with similar spring lengths and diameters but to increase the spring rate by 10% or so.
   I could cope with a firmer ride and the higher spring rate would presumable help to negate the occasional bottoming out of the springs on pot holes etc.
   
   Once again, thanks for the advice I'll let you know how things progress.
   
   David

AC Ace Bristol

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« Reply #7 on: April 22, 2014, 19:55:54 »
.
   David.
   
   
   Will you have the new spring set up fitted  prior to Shelsley Walsh Hill Climb on 3rd & 4th May..[?], or are you running old set up, whilst contemplating new spring rates and lengths.  [?].
   
   Keith..[:)]

DGoose

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« Reply #8 on: April 23, 2014, 13:50:46 »
Hi Keith,
   
   The rear springs and height adjustable shocks are being put together this week so I would hope to get them on to the car and set up before Shelsley.
   
   Fronts will have to wait until I have the time to strip it down and send the original springs for testing.
   
   David

DGoose

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« Reply #9 on: June 12, 2014, 13:06:51 »
New springs / dampers now fitted.
   
   We have increased front rate from 450lb standard to 475lb but using a fractionally longer spring with one less coil, this has eliminated the occasional crash from the front as the springs bind over potholes etc.
   
   
   [/URL]
   
   [/URL]
   
   Rear springs below are uprated from 150lb standard to 175lb but retaining standard length.
   
   [/URL]
   
   Overall impressions are favorable, ride is obviously a little firmer than before but straight line stability is improved and cornering ability, which was already very good, now inspires even greater confidence.
   
   
   Incidentally if anyone has considered using alternative alloys here are the original offset and center bore spec from OZ racing:
   
   Original wheels: OZ Exclusive.
   Rim: 7.5j x 16
   Offset: ET33
   Center Bore: 63.4mm
   PCD: = 5 x 112
   Stud size: M12 x 1.5

3.5 Pints at the Bar

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« Reply #10 on: June 13, 2014, 23:30:39 »
I'm glad to hear that the mod works well. I'm amazed that the spring binding problem existed to start with, but there is usually a reason for everything. Of course, if you had leaf-springs, you would not have that bother :)

David S

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« Reply #11 on: November 11, 2014, 08:46:31 »
Had the wheels balanced yesterday only to be told one wheel dented and one dented and twisted - so not repairable.
   
   Looking through the older posts for discussion on wheels and required specifications, the reply DGoose gives the specifications for the 16 inch wheel, the question I have is this the same specification for the 17 inch wheel?

Max Allan

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« Reply #12 on: November 11, 2014, 23:35:17 »
Hi David. Bad news you have two scrap rims!
   
   I don’t know the technical spec of the 17 inch rims. However, if it’s of any help my car was originally fitted with standard 16 inch five spoke rims as fitted to all 1995 cars, but were changed to 17 inch TSW Imola rims by the Factory when originals were damaged shipping the car back from 1995 Detroit Motor Show. When I bought the car back in 2000 the spare was still fitted with an original five spoke rim.
   
   I therefore think it reasonable to assume both sizes fit, so share same hub dimensions.

DGoose

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« Reply #13 on: November 12, 2014, 15:24:22 »
Hi David S
   
   If switching to 17" rims of the same width (7.5j) the offset and all other specifications would be the same as the standard 16" wheels.
   
   Standar rim: 7.5j x 16
   Offset: ET33
   Center Bore: 63.4mm
   PCD: = 5 x 112
   Stud size: M12 x 1.5
   
   The 17" wheels I fitted to DE1017 use wider rims, 8" front & 9" rear so the ofsett requirements are quite different.
   
   Probably stating the obvious but if you increase rim size you would use a lower profile tyre. The calculator below gives a very reassuring visual reference.
   
   http://www.willtheyfit.com/index.php?width=225&aspect=50&diameter=16&wheelwidth=7.5&offset=33&width2=225&aspect2=45&diameter2=17&wheelwidth2=7.5&offset2=33#content
   
   It would seem quite likely that there are a few spare wheels out there somewhere as several cars have been scraped or modified from standard, it may be worth speaking with John Able the club registrar.
   
   If you do have to swap your wheels there would be plenty of takers for the originals along with the centers which are very difficult to obtain.
   
   Regards,
   
   David G

David S

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« Reply #14 on: November 13, 2014, 10:08:13 »
Max and David,
   thanks for your quick replies the wheels are 17*8 front and rear with 235/45 front and 255/40 rears.
   I can find no other information, so for the PSD, would be safe to say the cars all had a standard 5*112?
   
   If so leaves the offset, David can you let me know what you used for offset on the 8" and 9"
   
   I will of course in the mean time contact John Abel
   thanks again for help