Lotus Elan

Front springs and ride height

PostPost by: Roy Gillett » Fri Oct 15, 2010 4:18 pm

Hi,
I wonder if some of the theorists out there can help me.

The ride height on my +2 130 seems to have sagged recently as I have started grounding on split road humps that it used to clear without problem. On checking I found that the measured ride height under the front cross member had dropped by about an inch from the 6.5 inches I set it to a couple of years ago. Rear ride height under the diff shelf by the way was still spot on.

As I have Protech front dampers with adjustable spring platforms I decided to wind the ride height up.

Having moved the lower spring platforms up by 0.45 inch and done a shake down ride I find the ride height has only risen by about half an inch. I was expecting more.

My question is : Is there any linear relationship between how much I raise the spring platforms and how much the ride height increases? And was I wrong in expecting the ride height to increase by significantly more than the amount that I wound up the spring bases?

Help please!

Roy
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PostPost by: john.p.clegg » Fri Oct 15, 2010 4:34 pm

Roy

Why would you think that?The springs are at a slight angle so the vertical component would be slightly less than the platform change...

John :wink:
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PostPost by: Higs » Fri Oct 15, 2010 4:36 pm

It is basically linear. To support the load the springs will need to be compressed the same amount as before (i.e. the same length). Therefore, if you raise the spring platform by 0.5", the spring will "push" the top mounting up by the same amount (to keep the spring length the same).

The only other effect is the angle of the spring/damper. Raising the spring platform will produce slightly less vertical height change because of this. If the angle from vertical of the damper is 30 degrees then the the increase in ride height will be just over 85% of the platform movement.
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PostPost by: elansprint » Sat Oct 16, 2010 8:05 pm

Roy are the plates that the shocks mount to on the front chassis turrets OK as the front can sag when these break free.
Ian
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PostPost by: Roy Gillett » Mon Oct 18, 2010 7:24 pm

elansprint wrote:Roy are the plates that the shocks mount to on the front chassis turrets OK as the front can sag when these break free.
Ian


Thanks Ian
I have just checked the chassis turrets and the wishbone ends of the shocks and all seems well. I think the springs have just 'given' a bit. Unless anyone out there has a better explanation.

But thanks for the feedback

Roy
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PostPost by: gerrym » Tue Oct 19, 2010 6:49 am

Roy, the front springs are both highly stressed and inherently unstable and liable to buckling. You may have a failing spring. With the buckling, the springs may be dragging on the outer shroud and/or inner shock body. Also are you sure that the bump stops were not partially supporting the load. These are all non linearities in the system which mean that one inch does not translate into the (sin angle) * one inch vertical ride height increase.

Regards
Gerry
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PostPost by: bill308 » Thu Oct 21, 2010 1:33 am

Roy,

If the adjustable spring platforms have more adjustment available, use it, that's what they are for. At some point the springs may sag to such an extent that you could encounter coil bind. Absent this, use the adjustment. Of course if something is broken you need to rectify it. But you already checked and aparently all is well.

All springs sag given enough time. Springs made of better material, sag less.

Bill
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