Uneven Ride Height

[EuropaTC]

Brian's equation will get you close to the rate but I didn't see where it accounted for the squared and ground end. One of my engineering books says to take off two coils for ground and squared springs but I tried to calculate the rate of one of my springs and wasn't satisfied with the results (sorry I can't provide details, it was some time ago).

I'd love to take credit for those sums, but I just copied it from a book....

As I understand it you only consider active coils so you ignore the first loop at either end which contains roughly half a coil of flattened steel. I generally count up the lot and take off 2.

It is critical to get the number of coils even down to part coils - for example you could have 10.5 active coils, don't round it up to 11 or down to 10. The more coils you have the lower the error you have because it's the bending over the whole length of the wire - think of it as unravelling the coils into a straight rod.  If you've only 10 coils then you've a short  rod so 0.5 would mean 5% but on 20 coils it's obviously a lower error.

Taking ito account the part coils, the equation has been fairly accurate when I've checked against new, known springs where it's easy to get an accurate measurement of wire and coil diameters. Not perfect, but good enough within a few %.

Brian

[BDA]

Brian, I in no way meant to be dismissive of your equation or post. (I think you know that.) I was only relaying my experience. If the spring does not have squared or ground ends, the calculation is very straightforward.

I won't quibble with your assertion that your calculation is close. I only remember that I was disappointed with the calculation I did and I really don't remember much beyond that such as how far off I was or how I counted the coils.

[EuropaTC]

Brian, I in no way meant to be dismissive of your equation or post. (I think you know that.)

No BDA, I didn't consider your comment as negative, I actually thought you were giving me credit for the maths equations....   which may have been possible many, many years ago but is sadly  so far beyond me now that I'd consider such an equation as "magic" 

The problem I found with cross checking calculations vs measurements was being very critical on measuring the wire/coil diameters. I played about with a spreadsheet going slightly up or down with the numbers and it can make a heck of a difference, much more than I thought at first.     In the end, like all the other sums I've done on suspension & brakes I treat them as comparative rather than absolute and just to give an idea of where I'll end up.  (and if it's likely to be a disaster !)

Brian

[BDA]

I'm glad you didn't consider it negative!

I know what you mean about equations! When I go to refresh my mind on simple engineering equations, I get lost very quickly! I think to myself, this used to be so simple! 

[Nukski]

Thanks BDA,
     For the additional test method. I used Brian's formula and got 103 lbs which makes sense because 100 was the factory spec. It would be logical that these springs were likely cut down from factory 16 coils to the current 11 coils.
     But now that I got the second shock off I see that the one with the perch adjusted all the way to the bottom(drivers side) has a free length 1/2 inch longer(see pic).
     I'm going to take advice of most on this thread and order 2 new front springs of known quantity. Ray from RD Ent. was very helpful on the phone so I'll go with his recommendation, 10 inch @ 115 lbs.   Just hope it does't lower the front too much since the current ones are over 11".
      Will let you know how it works out.
Bruce
70' Europa 0318R

[BDA]

If the PO cut 5 coils from the original springs the new rate would be significantly higher than the stock rate (possibly in the neighborhood of 30% higher). Of course, that's somewhat academic now since you're going to order new springs. 10 inch springs shouldn't lower the front too much and if it does, you can raise it by adjusting the spring perches higher.

Do you know if the shocks have been adjusted (likely stiffened)? I think I mentioned earlier that with stiffer springs, it might require an increase in shock stiffness. It would be helpful to know the "click" adjustment. But driving and what you are comfortable with is what will determine how to adjust the stiffness of your shocks (see my earlier post concerning basic rules for shocks.

While you're waiting for your new springs, you might take a look at your rear springs. Then when you get the front shocks and springs back on your car, you can think about what you might need to balance the car. Softer rear springs will tend to decrease oversteer (and increase understeer), harder rear springs will tend to increase oversteer (and decrease understeer). This is relative to the springs in the front so, for example, if your rear springs are stock, you would likely have more understeer. You'll have to take some corners pretty hard to get a feel for how the balance is. You may decide that you want new rear springs, too. You should also see how it handles on the highway. If it feels like it wants to wander on the highway, stiffer shocks would likely help that condition.

Good luck and let us know how things go!

[EuropaTC]

Hi again Bruce,

Well, you've got to the bottom of that little problem, there's certainly something adrift with those springs !

I think BDA is right though, you'd expect more than 3lbs from a 5 coil reduction so either the previous owner didn't start off with original springs or there's something else wrong.  For reference I ended up taking 2 coils off mine and they went from 140 to roughly 160lbs. (the calcs were 141lbs as received, 159lbs modified)

10" will be fine for ride height with adjustable platforms, mine are 9" albeit with a much higher spring rate.   

From the manual the standard S2 is 100lbs so 115lbs is closer to the TC spec, but the extra poundage won't make a dramatic difference because it's working at an angle which reduces the leverage.  Looking at the manual the standard S2 rear is 72lbs against 75lbs for the TC with it's slightly different weight distribution so I reckon it's good advice from Ray, it should work fine with adjustable dampers.

But while you're going to the trouble of sorting out the front I would think seriously about BDA's suggestion of rear springs.

Again they aren't expensive and you will have the peace of mind in having a matched set. If the DPO cut those front springs I wouldn't have any confidence that the rears were standard. And there's nothing worse than a Lotus with duff suspension !

Brian

(you'll note how quickly we on this forum are to spend your pocket money on cars    )

[Fotog]

Brian:  You say "From the manual the standard S2 is 100lbs so 115lbs is closer to the TC spec, but the extra poundage won't make a dramatic difference because it's working at an angle which reduces the leverage.  Looking at the manual the standard S2 rear is 72lbs against 75lbs for the TC with it's slightly different weight distribution so I reckon it's good advice from Ray, it should work fine with adjustable dampers."

I'm a little confused.  You're mentioning two numbers that are associated with the TC, 115 lbs and 75 lbs.  What are those? Front and rear, respectively?  (I admit I haven't tried to look; I'm just responding to your post).

And while you're discussing springs, how do you all remove them from the dampers?  Brian?, Bruce?  Others?

I'm anticipating getting into this down the road, and I don't want to buy tools that won't work.  Might as well benefit from your experience and knowledge.

Vince

[BDA]

Yes the TC spring rates are 115#/in in the front and 75#/in in the rear.

The front springs require some creative methods to compress them to take them off. Some have used ratcheting straps to squeeze the interior coils so you can take the spring off (didn't you show pictures of the springs off your front shocks?) There is a keeper or collar at the top with a cut through it so you can take it off the shock. When the springs are compressed enough, you'll be able to take the keeper off.

I've posted pictures of my spring compressor. A long time ago, I had steel plates cut for a compressor design based on the stock shocks and springs (which you are unlikely to encounter now). I just adapted it for using the smaller diameter springs we use now. I use threaded rod with a threaded union. It's been a long time since I built it so I don't remember how I made the hooked parts. They are obviously not completely threaded. The red stuff is the stuff you can buy to dip your pliers handles in to cushion them. I used this so as not to scuff up the paint on the spring. You could file or grind the threads off a section of threaded rod to replicate that part. It's pretty obvious how it works. The bottom of the stock goes in the hole in the plate, the hooks hook to the coils near the top of the spring. I think I used the threaded unions because my threaded rod wasn't long enough. Other than the plate, you should be able to find everything at a hardware store and you could probably replace the plate with something else from a hardware store too. 

[jbcollier]

+1 on BDA's suggestion to disassemble and check the rear springs as well.  One lister had uneven front ride height and the problem was traced to the rear springs.

[EuropaTC]

I'm a bit late responding and I see Jim's already sorted out the confusion on spring numbers.

As for fitting them, I said mine are 9" free length at the front and I didn't need a compressor. I just wound the platforms as low as they'd go and the springs fell in place. You might be equally lucky with a 10" free length.

Otherwise we all seem to have our own, custom built compressors because the original springs have loads of coils and quite a bit of pre-load so not all conventional spring compressors will work. I have a set that's very chunky and robust but useless for standard Lotus springs because the clamps are too thick.

Brian

[Fotog]

(didn't you show pictures of the springs off your front shocks?)

That wasn't me.  But thanks, fellows.  Especially the pictures, but the descriptions are invaluable too. 

Vince

[BDA]

Oops! Sorry! I hope you get your springs off without drama!