flibble
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| posted on 31/8/10 at 06:35 PM |
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coilover springs question (just curiosity!)
I fully realise I know bugger all about car suspension but whilst looking up which springs to buy from merlin/rally design I ended up wondering why
they seem to be such comparatively heavy (lightness is good afterall!) and tightly wound affairs as opposed to the normal tintop springs which
I'd have thought were of higher poundage?
 vs
qsn2uOBBMfDN1vSIg~~_35.JPG)
Just curious 
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mangogrooveworkshop
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| posted on 31/8/10 at 06:49 PM |
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Buy them from here
http://www.dfaulknersprings.com/spring_tester.htm
Its where they get them from
cheers pat
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philw
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| posted on 31/8/10 at 06:56 PM |
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quote:
Originally posted by mangogrooveworkshop
Buy them from here
http://www.dfaulknersprings.com/spring_tester.htm
Its where they get them from
cheers pat
Merlin motorsport are actually cheaper than Faulkners
Must try harder
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mangogrooveworkshop
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| posted on 31/8/10 at 08:04 PM |
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quote:
Originally posted by philw
quote:
Originally posted by mangogrooveworkshop
Buy them from here
http://www.dfaulknersprings.com/spring_tester.htm
Its where they get them from
cheers pat
Merlin motorsport are actually cheaper than Faulkners
well stone the crows
never new that cool going to get some softies for the rear
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ReMan
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| posted on 31/8/10 at 08:13 PM |
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quote:
Originally posted by flibble
I fully realise I know bugger all about car suspension but whilst looking up which springs to buy from merlin/rally design I ended up wondering why
they seem to be such comparatively heavy (lightness is good afterall!) and tightly wound affairs as opposed to the normal tintop springs which
I'd have thought were of higher poundage?
Just curious
Yes interesting
I expect for a more linear rate, but I'm up for a better explanation
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MikeCapon
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| posted on 1/9/10 at 07:41 AM |
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It’s a bit early in the morning (for me) but here’s a short(ish) explanation.
A spring is really just a long bar of metal which bends and unbends each time the spring compresses and opens. The only difference with a spring is
that your long bar of metal is wound into a spiral of sorts.
All metals have an elastic limit. In other words you can bend your bar of metal a bit and it will spring back to its original shape. Bend a bit too
much and it will stay bent or ‘take a set’. Different metals and metal alloys have different elastic limits. Soft metals like lead have a very low
elastic limit. Steel alloys used for springs, once tempered have pretty high elastic limits.
The primary characteristic of a spring is its rate. In other words how much it will compress with a given load applied to it. You can make a spring of
the same rate and length with all sorts of different designs (wire diameter and number of coils). Back to your steel bar. A short bar made out of
thick wire is very hard to bend so has a high rate. A long bar made out of thin wire is easy to bend so has a low rate. By varying the wire diameter
and the bar length the same rate spring can be made different ways.
As an example you could in theory make a 250 lbs/in spring using each of the following designs:
6mm wire with 2.7 coils
7mm wire with 3.8 coils
8mm wire with 5.6 coils
10mm wire with 12.5 coils
The number of coils is directly related to the length of your steel bar.
For a spring of the same length, the thinner the wire, the lower the number of coils, and the greater the movement available in the spring. Thin wire
+ few coils equals lots of space between the coils to be taken up before the coils touch and the spring becomes “coilbound”.
Back to the elastic limit you can see that with thin wire + few coils you will be bending your steel bar a long way. The stress imposed taking the
spring close to coilbound will be more than enough to go beyond the elastic limit and your steel bar will become permanently bent. The effect on your
car’s springs will be that the spring takes a set and the suspension will lose its ride height.
Manufacturers of aftermarket springs sold by people like Merlin, Rally Design and Faulkner will (should) calculate the stress at the point just before
coilbound and choose a design (wire diameter and number of coils) that ensures the metal is not taken beyond it’s elastic limit hence the large number
of coils in most of these springs.
More exotic materials and production methods can produce springs with higher elastic limits but these become pretty expensive. Look at springs from
someone like Eibach as an example. Material choice and heat treatment is a pretty critical business. Apart from the danger of a spring taking a set, a
harder material with a higher elastic limit will also become prone to breakage. There are a few tin tops prone to this.
Finally the springs you see on tin tops are the result of a whole different design process. Firstly the numbers involved mean that the manufacturer of
the spring will have a wire drawn to the exact size needed. Every gram of metal means money and weight. (Money adds up over thousands of cars.) This
avoids the compromise faced by aftermarket spring manufacturers who will only have a number of different ‘stock’ wires to play with.
The major difference with a tin top spring though is that the spring designer will know the exact movement that the spring will be subjected to. The
spring will never be compressed by more than the amount needed to fit the spring plus the movement in the shock itself. This means that the spring
never gets anywhere near coilbound and the stresses are lower. If you take a spring from a tin top and compress it to coilbound it will almost
certainly take a set.
Last of all and just out of interest, tin top spring rates are surprisingly low. The last car I worked with was a FWD weighing just under 1000kg and
the rates for tarmac rallying were around 250lbs/in at the front and 110lbs/in at the rear. Lots of preload and shocks with a high compression rate
have a lot to do with this.
I hope this helps to explain a bit. Please ask if I haven’t made anything clear enough.
Cheers,
Mike
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interestedparty
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| posted on 1/9/10 at 08:06 AM |
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It's good to have Mike here- not only does he know his stuff, but he also knows how to explain it AND actually goes to the trouble of writing a
long and clear post like that for our benefit.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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ReMan
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| posted on 1/9/10 at 10:59 AM |
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Yes nice one Mike.
Mind you, back to the OP question, and the example bics, I'd have thought there was some room for a comromise that does reduce weight for a 7
application
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MikeCapon
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| posted on 1/9/10 at 11:20 AM |
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Thanks interested party. I was just really, really pleased that for once there was a question I knew the answer(s) to
And ReMan yes of course there is a possibilty of a compromise that would be best suited to a seven. It's just that people aren't
interested enough for it to happen. You'd need a small spring manufacturer to get interested as the quantities are very small if you wanted a
'bespoke' spring. The vast number of different types of 'seven' reduce the numbers again.
For the time being though, the best you can do is fit the shortest and therefore lightest spring that will physically fit on your shocks and offer
sufficient movement (stroke) for the movement of your suspension.
If enough people were interested I could try and organise something with a colleague who makes springs in Sheffield (where else!) who can make small
quantities for sensible money.
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Liam
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| posted on 1/9/10 at 11:57 AM |
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Regarding those original pics, if those tintop springs are anything like the ones on my tintop, they are much thicker, much larger diameter and much
heavier than the coilover springs. There's a big difference of scale between those pics! The 1.9" coilover springs we use on our cars are
actually probably among the most compact and lightest springs used in road cars.
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ReMan
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| posted on 1/9/10 at 12:22 PM |
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quote:
Originally posted by Liam
Regarding those original pics, if those tintop springs are anything like the ones on my tintop, they are much thicker, much larger diameter and much
heavier than the coilover springs. There's a big difference of scale between those pics! The 1.9" coilover springs we use on our cars are
actually probably among the most compact and lightest springs used in road cars.
I'd disagree.
My small tintop's coils are about the same wire gauge as my & springs...
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flibble
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| posted on 1/9/10 at 04:32 PM |
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Blimey that was quite a comprehensive answer there Mike, encompassed pretty much all my wonderings in one go cheers!
KevD
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