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finding spring rate - JW
02GF74 - 28/9/06 at 08:18 AM

I have a coil, 7.5 turns, 291 mm (11 1/2 in) long, wire dia. 10 mm, and I.D 70 mm (2 3/4 in).

It has stamped JW on it.

It was fitted to that most respected of British supercars: the Triumph Dolomite

Now I am guessing Rover/Triumph/BL/Whoever would not be making their own coil springs but buy them from a spring manufacturer so in theory there is a whole plethora of springs in this size (coil diameter).

The JW is either the manufacturer or more likely a code for the spring rate.

Does anyone know of a website - spring makers etc. that can give the spring rate for this spring, ideally using the 2 letter code? Or a website with spring data that I can use to extrapolate the rate?

Alternatively, is there a formula that calculates spring rates - I think I have all the data except for the material; but let's assume it is regular springy steel stuff.

Ta.

NS Dev - 28/9/06 at 08:21 AM

do you have a press or pillar drill and some bathroom scales?

If so, put the spring on the scales under the drill or press, compress it an inch and read the scales.

02GF74 - 28/9/06 at 09:09 AM

no scales but I did stand on it and got someone to measure, and get it to be in the range 125 - 150 lb/ins.

(I'll borrow some scales & remeasure)

The second test was to measure the other spring fitted to car in free air and "when on the ground" (i.e. jack up under axle until chassis is hust off the stand).

Free length = 291
Fitted length = 250 (I have thought how can measure this better)
Compress by = 41

Change in length when loaded 15 mm
Total change in length = 56 mm

using 150 lb/ins, supported weight = 150 kg

using 130 lb/ins, = 130 kg

From SVA, rear axle = 282 kg.
Or 141 kg per side.

Now english axle, brakes, shafts etc is gonna be about 50 kg, wheel + tyre is 15 kg (my estimates) or about 40 kg per side.

So adding the unsprung mass, then I get 190 or 170 (cf measured 141).

close but still a few kgs out.

The point of all this is to see what is needed to get the rear end lower. There is a rubber buffer between bulkhead and top of spring shroud with 2 shaped washers that I reckon removing will give me about 25 mm - it is bad idea to do that as the top of the spring will move against the bulkhead but I could fit a thinner rubber buffer? (or I could cut the top of the mount and use a plate held by bolts that can be raised/lowered to adjust ride height)

Basically I think the set up in shock/spring is good enough so no need for new springs or shocks.

Comments?

mookaloid - 28/9/06 at 09:10 AM

Just a thought - would these be any good to you?

linky

from this thread

Cheers

Mark

02GF74 - 28/9/06 at 09:15 AM

quote:
Originally posted by mookaloid
Just a thought - would these be any good to you?

linky

from this thread

Cheers

Mark


thanks but not; too short (I need 15 inch) and a bolt type end on the top instead of an eyelet.

mookaloid - 28/9/06 at 09:27 AM

quote:
Originally posted by 02GF74
quote:
Originally posted by mookaloid
Just a thought - would these be any good to you?

linky

from this thread

Cheers

Mark


thanks but not; too short (I need 15 inch) and a bolt type end on the top instead of an eyelet.


ok I was thinking they might be reasonably priced

Cheers

Mark

NS Dev - 28/9/06 at 12:14 PM

quote:
Originally posted by 02GF74
no scales but I did stand on it and got someone to measure, and get it to be in the range 125 - 150 lb/ins.

(I'll borrow some scales & remeasure)

The second test was to measure the other spring fitted to car in free air and "when on the ground" (i.e. jack up under axle until chassis is hust off the stand).

Free length = 291
Fitted length = 250 (I have thought how can measure this better)
Compress by = 41

Change in length when loaded 15 mm
Total change in length = 56 mm

using 150 lb/ins, supported weight = 150 kg

using 130 lb/ins, = 130 kg

From SVA, rear axle = 282 kg.
Or 141 kg per side.

Now english axle, brakes, shafts etc is gonna be about 50 kg, wheel + tyre is 15 kg (my estimates) or about 40 kg per side.

So adding the unsprung mass, then I get 190 or 170 (cf measured 141).

close but still a few kgs out.

The point of all this is to see what is needed to get the rear end lower. There is a rubber buffer between bulkhead and top of spring shroud with 2 shaped washers that I reckon removing will give me about 25 mm - it is bad idea to do that as the top of the spring will move against the bulkhead but I could fit a thinner rubber buffer? (or I could cut the top of the mount and use a plate held by bolts that can be raised/lowered to adjust ride height)

Basically I think the set up in shock/spring is good enough so no need for new springs or shocks.

Comments?


why do you "need to get the rear end lower"???

Is it because the car doesn't handle correctly?

If not, why not?

Rear damping on live axle sevens is absolutely critical, saving money on dampers a complete false economy in this area.

If the dampers are the wrong length, you need the right length ones.

If they are the wrong rate, you need the right rate ones (and that's damper rate not spring rate)

02GF74 - 28/9/06 at 01:10 PM

quote:
Originally posted by NS Dev

why do you "need to get the rear end lower"???

Is it because the car doesn't handle correctly?

If not, why not?

Rear damping on live axle sevens is absolutely critical, saving money on dampers a complete false economy in this area.

If the dampers are the wrong length, you need the right length ones.

If they are the wrong rate, you need the right rate ones (and that's damper rate not spring rate)


it's all to do with SVA fail - rear link foling on chassis. there more I think about it, the more I don't think they do so all these post have been wasting your time - sorry - but sometimes it hlps to think aloud as got comments.

In short, I need to convinve the SVA man that the arms do not foul on the chassis - if I jack one rear wheel up, then surely that is as far as the axle will drop so surely that is proof!

I hear what you are saying about damper - this is the one in t he f27 plan so I guess they looked/build a few so not some random choice.

NS Dev - 28/9/06 at 01:58 PM

ahhh, right, gotcha!

The normal tests for fouling are take both springs off, then jack the car up letting the axle dangle, then lower it onto the bump stops both sides, then jack one end of the axle up high enough that both wheels come off the ground (thus giving full twist on the axle)

The bump/droop stops on the dampers should be enough to prevent fouling under all those conditions.

If you can do all the above, take pictures of the tests and show the examiner, I can't see how he can then fail you.

chriscook - 28/9/06 at 05:50 PM

You can calculate a spring rate pretty accurately there are quite a few calculators online that do it - google 'spring rate calculator'. You'll probably need to measure the wire diameter with calipers tho.

The material used in coil springs is pretty standard stuff. It just gets complicated if the spring is variable rate.

Bob C - 28/9/06 at 06:55 PM

Here's my calculator - seems to do the biz with all the springs I've tried. Certainly good for a 1st approximation
Bob

02GF74 - 29/9/06 at 08:33 AM

quote:
Originally posted by Bob C
Here's my calculator - seems to do the biz with all the springs I've tried. Certainly good for a 1st approximation
Bob


looks like units are in inches? - is coil diameter internal/external or midway along coil. (look like O.D.)

wire = 10 mm
turns = 7.5
I.D = 70.

(I remeasured again and it is around 125 lb/in)

DarrenW - 29/9/06 at 10:11 AM

There are some notes on the spreadsheet to explain the units etc. Yes - inches. Im sure coil diameter is always OD.

Bob C - 29/9/06 at 12:49 PM

I've always assumed diameter of middle of coil.
Bob

DarrenW - 29/9/06 at 02:34 PM

Some interesting data here about coil springs but unfortunately doesnt seem to say if we should use mean diameter or OD.

http://www.acewirespring.com/coil-specifications.html

It does say how to determine spring rate. Nats idea of drill press and scales using the formula on the site should give accurate result.