Inside rear wheel unloading

[Magpie]

Maybe this will help. The solution I have been talking about is a spring that is closed under normal load. Anyway I'm going to order longer springs for the front if the 10/7 combo works.

However I have another solution to try as well, hopefully at the MX5/Porsche car clubs combined track day.

http://forums.nasioc.com/forums/showpost.php?s=451317ce539fb0def9bf9122f3619c07&p=10952302&postcount=1
Tender vs Helper springs

Helper and tender springs are both made from a flat wire spring that are designed to completely compress. In Whiteline's view, the difference is mainly in the application of the spring and at what point they close in the chosen application. This is obviously dependant on spring load, where a helper spring is generally known to close BEFORE normal load is applied, and a tender spring is generally known to close AFTER normal load is applied.

So, a helper spring in one application may be used as a tender spring in another application. For the same application, a helper spring generally will be softer than a tender spring.

Whiteline uses helper springs for a number of reasons.

- Simplicity. In a tender spring system, the specifications of both main spring and tender springs are absolutely critical for the system to work properly.

- Noise. In a helper spring system, as the helper is closed at normal ride height, there is minimal spring noise. In a tender spring system, the tender is designed to close during suspension compression potentially creating noise.

- Spring rate tuning. In a helper spring system, it is very easy to change springs for tuning purposes. In a tender spring system it is a much more complicated process, and will require both new main and tender springs.

- Vehicle corner weight tuning. In a helper spring system, adjusting the height of the spring platform directly effects the height of the main spring. In a tender spring system, platform adjustment compresses the tender spring and main spring at the same time.

We believe that using the term "spring pre-load" is a bit of a misnomer and misleading. Its important to note that changing the height of the spring platform does effect the spring load at full droop, but when the car is on the ground (suspension loaded) the total spring load for all 4 springs is the same, it cannot change. The spring rate remains the same, it too cannot change. The only thing that can change is the ride height.

Regards,
Wojtek..

[project.r.racing]

All I keep reading is incorrect preload. If the springs are becoming uncaptive, then they do not match the damper travel. Spring perch is in the incorrect position.

Getting a 40mm longer spring wont change anything. Cos you'll just place the spring perch 40mm lower to get the same ride height. You'll only get up to 40mm more extra travel.

Unless the spring perch is screwed all the way up the damper and had no adjustment left?

[Magpie]

project.r.racing the coil overs are setup to maximise suspension travel. I agree that the spring length does not match the

The springs/bumpstops were removed, reinstalled into the car, wheel put on then jacked up to ensure that the wheels did not touch the side fenders when at full compression/steering lock. The length of the shock was adjusted to ensure that the tyre did not foul the fenders. This sets the correct length of the shock, accordingly ALL the available travel is being used.

The coilovers on the front are set at a length of 435mm and there is 127mm of travel (excluding bumpstops) available. Whereas in the rear there is only 70mm of suspension travel.

The spring perch is in the correct position for my chosen ride height/corner weight and the travel of the shock.

[pepejesus]

The issue is with stiff springs in a light car at a low ride height, you simply won't be able to compress the spring enough to allow for the springs to be captive at full droop travel. Tender/helper springs solve this problem by providing a lower rate spring that is fully compressed (in coil bind) when the car is at rest, but that will provide enough spring to extend the damper at full droop where the normal spring has fully extended itself.

Longer springs won't help. You will either have a higher ride height with the longer spring, or you will end up setting your perch lower by the difference between your old short spring and your new long spring, giving you the same ride height and the same amount of uncaptive droop.

You either put up with the fact that your springs are uncaptive at full droop (and effectively give away some droop travel) or you run a tender/helper spring.

Suggest having a read of this thread: http://www.miataturbo.net/race-prep-75/who-not-running-helper-spings-87330/

Particularly this part:"if you have say a 700# 6" long spring and you adjust the perch to get your ride height at a preferred value you end up with say 1.5" of gap between the spring and the perch when its unloaded. If you replace that spring with an 700# 8" long spring then re-adjust the perch to get the same ride height. you will have the same 1.5" gap between the perch and the spring when its unloaded. its just that your adjustable collar will be set 2" lower on the shock body to achieve the same ride height.

The only way you are going to change that is by going to a lower spring rate or having a section of the spring operate at a lower spring rate such as a helper spring."

[Magpie]

Thanks for the post, I'll read the link soon.

Using examples from King Springs catalogue I now have more questions....

The BC Racing springs are 62 dia and the closest in the required lengths on King Springs are 65 dia.

65 dia 180mm 10kg/mm has a compressed length of 80mm total spring travel is 100mm
A 200/250mm have travel of 107 and 142mm.

Therefore I could be loosing up to 27mm of suspension travel as the spring fully compressed length is less than the amount of travel in the dampers. Further the bump stops are not really being utilised, they are 38mm long. So when at the limit of travel on the front it is riding on fully compressed springs. Helper springs will not help as they will further reduce suspension travel!

Spit balling but a 250mm Spring and a helper spring will have a combined travel of 126mm when they are both fully compressed. But a total length of 320mm.

The solution is to have a spring that uses the full amount of damper travel, but keeps the spring captive.

[pepejesus]

The solution is to have a spring that uses the full amount of damper travel, but keeps the spring captive.

With the important qualifier of 'with heavy springs that the static load of a light car will barely compress, at a very low ride height.'

A long spring is not the answer with stiff springs and low ride heights.

Tell me how your 1000kg car will compress a 10kg/mm spring long enough to be captive at full droop down to a 4 - 5 inch pinch weld height.

The answer is it won't, and you'd end up screwing the perch further down the shock body to get the ride height you want, and guess what is now happening at full droop? It's no longer captive.

A tender/helper spring gives you the ride height you want, with the spring rates you want, with the bump/droop split you want, all with the spring being captive and giving you the full range of droop travel.

Going back to your previous post -

3. Shock length (coilovers)
a. Most appropriate method of setting shock length should be used. That is as per MCA method.
b. If spring becomes uncaptive at full droop then a helper spring maybe sufficient to 'push' the inner wheel back in contact.
Note: King springs make 2 x helper springs at 1.25/4.0 (kgs/mm) which compress from 70mm to 16/20mm.
c. Correct spring length should be used in preference to helper springs

This is correct EXCEPT point C. Correct spring length should be used IN COMBINATION WITH helper/tender springs. Long springs are NOT the solution nor are they a substitute for correct length springs plus a helper/tender. A spring long enough to be captive at full droop is NOT the correct length spring for a light car with a stiff spring at a low ride height.

Go back and read what madjak has said earlier in this thread, he has gone through the exact same thing you have and he's 100% correct with what he's said.

And after trying (and failing) with an 8" spring he landed on a 7" spring + tender/helper, he said he should have ideally gone with a SHORTER 6" spring plus a helper/tender!

[Magpie]

Again thanks!

Will be arranging some helper springs in the near future.

Suspension is not simple

[RS2000]

You either put up with the fact that your springs are uncaptive at full droop ........

In the instructions that come with their coilovers, MCA state that this is not a problem.
The bottom adjustment (threaded body in bottom mount) is adjusted to give max wheel travel & the spring seat is adjusted to give ride height.
I have 11/7 kg MCA reds valved for the track, & the rears are totally uncaptive at full droop, but only by about 4mm.
Unless I jump kerbs, the suspension does not reach full droop on the track. If I do get a rear wheel airbourne, the design means the springs can only seat properly when landed.

Cheers

[Dan]

You either put up with the fact that your springs are uncaptive at full droop ........

In the instructions that come with their coilovers, MCA state that this is not a problem.
The bottom adjustment (threaded body in bottom mount) is adjusted to give max wheel travel & the spring seat is adjusted to give ride height.
I have 11/7 kg MCA reds valved for the track, & the rears are totally uncaptive at full droop, but only by about 4mm.
Unless I jump kerbs, the suspension does not reach full droop on the track. If I do get a rear wheel airbourne, the design means the springs can only seat properly when landed.

Cheers

Yeh, MCA use a spring locator to make sure the spring gets back into position after it compresses again following it becoming unentrapped. Not really applicable to people without MCA's like in this case though.

I'll agree it is a cool feature, I was just dropping my car down the other day and thought that I was pretty lucky having MCA's

[madjak]

[quote="pepejesus"
Go back and read what madjak has said earlier in this thread, he has gone through the exact same thing you have and he's 100% correct with what he's said.

And after trying (and failing) with an 8" spring he landed on a 7" spring + tender/helper, he said he should have ideally gone with a SHORTER 6" spring plus a helper/tender![/quote]

On the front I'm currently running 12.5kg springs @ 7" with no tender. Tenders are on the rear with 5" springs. I _should_ be running a 6" 12.5kg spring with a tender on the front but I figured two sets of springs was enough $ wasted. It works fine as it is... tenders would be better again though.

On the track I'm often in the air. I tend to bounce off kerbs a bit so I wouldn't really like to run uncaptive springs even with the MCA style.

Really if budget isn't an issue get tenders on all 4 corners. You get far more droop (ie +50mm) with no downsides. Shorter main springs are lighter anyway so you get an extra bonus. If you can't afford 4 then run them only on the back over the front as having the extra droop on the back helps with grip. Be aware, if you experiment like me then you'll end up spending lots on springs doing a trial and error fitment.

Magpie, I have a pair of eibach race springs on the shelf. 8" 750lbs 2.5". For $10 shipping you can see how they go on your car... they might work but my guess is you'll find your car will be 30mm too high... my shocks didn't have enough adjustment amd maxed out.

[Magpie]

Madjack, thanks for the offer I will send you a PM.

I should remember one of my previous posts "post less and keep your thoughts to yourself"... This is an academic discussion as I'm not making radical changes to the car, focus is on driver not changing the car!

Before jumping on the bike this morning I looked at the front suspension in light of Madjack's offer of 8" springs. The 8" are 20mm longer than my current springs (not looking at the spring rate).

Other factors to consider - the spring perch can be lowered about another 50mm (at full droop) only as the upper ring will foul on the upper control arm. The amount at full compression needs to be measured to see what the gap is, this could be a limiting factor.

BUT, to fully compress a 10kg spring (65mm Ø) with 100mm of 'movement' would take 1,000kg! This is not possible hence it is pointless having 127mm of travel if it will never be able to be used. However it is better to have the springs limit the damper travel than the damper itself, the springs act as a safety margin to avoid damage to the damper.

Another BUT, adding helper springs will only limit more of the suspension travel at full bump as they will add to the total compressed length.

The academic issue is that the fully compressed spring length (coil bind) needs to be taken into consideration when deciding on springs. The focus seems to be on spring rates and not taking into account suspension travel and spring length variables.

IMG_1297[1] by Eipeip, on Flickr

[Dan]

On the track I'm often in the air. I tend to bounce off kerbs a bit so I wouldn't really like to run uncaptive springs even with the MCA style.

Really if budget isn't an issue get tenders on all 4 corners. You get far more droop (ie +50mm) with no downsides.

How do tenders give you 50mm of droop over an uncaptive Spring?

Wouldn't the unsprung weight pull it down to max droop when the spring becomes uncaptive?

I guess a spring would be more controlled? I was curious about this when I got my MCA's as it feels strange leaving a spring uncaptive.

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[The American]

Are there two scenarios to tune for depending on which is your greater problem?

1) unloading the inside on corners
2) unloading both wheels while leaping off things

I would have thought that helpers would help a lot with scenario two, but for scenario one, the resistance to droop provided by the ARB would have a lot to do with how helpful the helpers were?

[plohl]

For an academic discussion this thread has little math.
You can calculate "preload" for a given ride height based on corner weights, motion ratio, spring rate, shock free length, spring length, spring rate... nothing too complicated.

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[Magpie]

For once I have avoided the maths plohl. I'm going back under my bridge and get on with driving the car and not playing with it.