Spyder rear suspension

[Jason1]

Hi guys

Does anyone know what the free length and the rate of the MK1 Spyder rear suspension springs??

Mine are both broken and Spyder say they no longer stock them and have no information on them. On the up side; they say I can upgrade to the MK2 version if I grow tied of my first born

If anyone knows if the dampers are standard from another car that would be helpful too.

Thanks

Jason

[steveww]

Those are not the normal Lotus rear suspension items. I can not help you with the spring rate or free length however looking at the dampers they look like standard racing items. Have a look through the Demon Tweeks catalogue and you will see items very similar. Given that Spyder are a small volume manufacturer they would have not gone to the expense of having something custom made. They look a little like the Lotus front units? I would give GAZ or SPAX a call and see what they have.

[Jason1]

Cheers

Just cleaned up the damper and it is Koni, I am trying to get the spring off so I can see the serial number on the damper but it is all rusted together.

It looks like there is a lock nut under the spring platform and then the top should spin off of the damper shaft.

Can anyone confirm how to dismantle these dampers? I have tried bashing the top around and it will not spin off.

Thanks

Jason

[Foxie]

Jason,

I can't advise on dismantling your dampers, but here is my experience.

When I fitted Spyder chassis and IRS to my Plus 2 around 8 years ago, I also ordered Spax adjustable shocks and springs to match. All the springs gave too high a ride height even with full adjustment on the shocks. The top bushes were still loose with the nut tightened to the end of the thread on the shock top. I ordered replacement and higher rated springs from Demon Tweeks. These were only available in max 12". The rear springs were too short. They could not supply spring spacers more than 1" or so , so I got some made up locally to required height.

I have found that replacement springs are nearly always pot luck regarding height/rate, and I have often ended up cutting them to suit.

Sean Murray

[rgh0]

Jason

Spring rate of your springs is easy to calculate if you know the wire diameter the spring outside diameter and the number of working turns of the coil.

Spring rate = k (lbs/ in)
Steel modulus of elasticity= G = 11500000 (psi)
OD= outside diameter of spring (inch)
d = spring wire diameter (inch)
n= number of coils


R= radius of centre line of coil = (OD-d)/2

K = G x d^4 / 64 x n x R^3 (lb/inch)

where d^4 means d to power 4 and R^3 means R to power 3


If you work in metric the formula is the same
but
k= spring rate ( kg/mm)
G= 8070 kg/square mm
all other dimensions in mm

Required free length can be be calculated from the rear suspension load based on car weight and spring length at normal ride height and the geometry of how the spring supports the load, i.e. The angle from the vertical and the lever arm of the spring versus the wheel. I dont know the Spyder suspension geometry details but if you can take a photo with some dimensions it can easily be worked out also.


regards
Rohan

[Jason1]

I just got the spring off, it is 11 inches

That's a short spring and it has the flat ends so it has not been cut down.

The shocks are Koni 80R-2549.

Does anyone know where I can get these from? I have looked on Demon Tweeks site and the lowest rated spring seems to be 160 lb. I have googled 80R-2549 but no luck

Jason

[Foxie]

Rohan,

I have used this formula to calculate spring rates of various springs I have fitted to my Plus 2, and compared the results to careful practical measurements. I have listed these below. The calculated results I have got were between 5 and 30 percent greater than the measured values. So although the calculated results are in the same order of magnitude, I would not consider them reliable enough for fine tuning suspension.

I also did a calculation for converting front and rear spring rates to actual wheel rates on the Plus 2, but don't have it to hand at the moment. Have you figures for these ?

Rate calculated 98 91 137 159 123 122
Rate measured 94 84 104 125 110 102

Sean Murray

[Foxie]

I just got the spring off, it is 11 inches

That's a short spring and it has the flat ends so it has not been cut down.

Jason

When I cut springs, I grind the ends to a tapering flat, and realign them. It's hard to tell if they have been cut or not.

Sean Murray

[stuartgb100]

Hi Jason,

I'm a little worried about how short that spring seems. Isn't the original something like 16 inches long.

Also, there's no guarantee that the Koni damper is correct, either.

You may just have inherited a PO's best guess/bodge?

Why not try and take a little of the uncertainty out of the equation before parting with hard earned cash? How about a chat with Koni:

Koni is a POTN.com affiliate. For all enquiries please contact POTN.com on the details below.

POTN.com
POTN ltd
1st Floor
6 Duncan Close
Moulton Park
Northampton
NN3 6WL
United Kingdom

Tel: 0845 3459755
Fax: 0870 7583106

e-mail: [email protected]

AND a chat with someone on the racing side, eg Tony at TTR ?

(no disrespect to anyone else on the forum intended) but a verbal chat over the phone might be a good idea, and you can always post up the outcome for Rohan/Sean and others to comment upon ?

Regards,
Stuart.

[rgh0]

Sean

With good quality springs I normally get calculated and actual measured rates less than 10% difference and unless your running a formula one car this is probably close enough. Most drivers, even a lot of professionals, struggle to actually feel a spring rate difference of less than 50% in how the car handles according to a friend who does suspension development for Koni in Australia for a lot of the top race teams.

Conistent wire diameter and coil diameter and accurate measurment of these parameters are critical given the power these are raised to, this turns a small error or variation into a big difference.

I have the conversion for the Elan between spring and wheel rates but not the plus 2. I am away on business for the next few days but can work out the plus 2 numbers on the weekend for the standard plus 2 suspension geometry if you want it.

regards
Rohan

[Foxie]

Rohan,

I'd be interested in in your results, whenever you get time.
Thanks

Sean

.

I have the conversion for the Elan between spring and wheel rates but not the plus 2. I am away on business for the next few days but can work out the plus 2 numbers on the weekend for the standard plus 2 suspension geometry if you want it.

regards
Rohan

[Midlife]

Jason, Leda are very good and are only in Witham so not far from you.

Doug

[Jason1]

Cheers

Just up the road from me.

I am talking with Tony Thompson at the moment, he does not think much of the Spyder suspension. He is looking into the alternatives, I'll see what his conclusions are.

Thanks

Jason