Coilover helper springs...

[bozothenutter]

Apparently for the Dutch MOT 'loose springs' is a fail.
Guess what happens when you lift my 182 on B16's......
Car is dropped 40mm as per RCCK.
Am I right in thinking longer helper springs is the hands off solution?
All longer helpers will do is loose me some 'drop' I'm not using anyway right?
Don't want to faff with the height every year.
Does its spring rate matter?

 

[Jekyll]

Yeah pretty much. They do add some poundage but it's not a lot.

So in theory, the extra length of helper spring should take up that slack once the car is lifted.

 

[Steven103]

Assuming you’re ruling out just raising the ride height a bit, a helper spring with a longer free length is 100% the “correct” answer as this is exactly what they are designed for.

Longer helpers won’t loose you any rebound travel. You’ll need to lower the spring seat a bit to maintain your chosen ride height with a new helper with a longer collided length, but the relative position of the piston rod to damper body doesn’t change therefore no change in travel. But long winded but hope that makes sense.

Double check the ID of the standard Bilstein helper. Hopefully it’s still imperial like the main spring, as although metric diameter helpers are getting more common there are very few lengths/rates available .

There’s loads of misinformation about helper springs, including from well respected journalists.

Fitting a helper spring does not affect the total spring rate in compression.

There is also an amount of rebound travel where a helper spring is still fully compressed and therefore has no effect on the total effective spring rate.

It’s only once you get to a suspension travel where the helper spring starts to open which you then have 2 springs acting in series and the total effective spring rate of the coilover massively reduces. For tarmac circuit racing with very stiff springs & low unsprung mass there’s nothing worthwhile that can be done about the reduction in spring rate.

 

[Steven103]

Just noticed you said B16 (PMS?) not B14.

I’m guessing they have pretty serious spring rates which, with a relatively low sprung mass, would mean very little precompression of the main spring when the car is on the ground. In this case the reduced total spring rate in rebound that I’m banging on about will already be happening relatively close to normal ride height, so I wouldn’t go stiffer on helper springs if I could avoid it.

Especially on the rear.

 

[bozothenutter]

Helper spring says 80-60-30, I'm guessing that is OD-ID-Rate ?
@Steven103
seems strange not to have length in there (definitely not 30mm high)

 

[JamesBryan]

Helper spring says 80-60-30, I'm guessing that is OD-ID-Rate ?
@Steven103
seems strange not to have length in there (definitely not 30mm high)

80 should be the diameter, 60 should be the length and 30 the rate.

That's how most i've seen are labelled.

 

[bozothenutter]

80 should be the diameter, 60 should be the length and 30 the rate.

That's how most i've seen are labelled.

Thanks, are they measured by outer diameter though.....weird

 

[JamesBryan]

Thanks, are they measured by outer diameter though.....weird

Inner usually.

Numbers could be the other way round? 80 length, 60 inner dia...

 

[bozothenutter]

just went outside to check...
I think it's:
80mm long
60mm ID
30 rate

that seems to match with the Eibach catalog

 

[bozothenutter]

of course nobody has a 100-60-30 spring in stock anywhere.....
Anything from 2-6 weeks quoted.....

 

[Steven103]

Metric helper springs are really difficult to find. You might have more luck searching for a "tender spring" instead. In theory they have two completely different purposes but between brands there's no consistency on what rates/lengths helpers finish and tenders start.


If I were you I'd also confirm if 30 is N/mm or lb/inch before buying. If it's N/mm it's on an awkward cusp of being a poor choice for a Clio helper but also plausible if it was intended to also be used on heavier cars or stiffer dampers. Sounds ridiculous but you can estimate the rate of a relatively soft spring with bathroom scales & a ruler. Put the spring on scales, press just hard enough until it's fully compressed, read the weight, measure the fully compressed length. Rate in N/mm = kg read from scales * 9.81 / (free length - compressed length).


How big actually is the gap between spring & spring seat when the car is on a lift? Is it only a few mm or are you this guy? https://rennlist.com/forums/attachm...springs-necessary-on-my-street-951-399-2-.jpg

Also out of interest, if you jack just one side of the car up have you ever noticed if the front ARB is stiff enough to keep the helper fully compressed?

 

[bozothenutter]

Turns out I misread the helper...80-60-30, actually was 80-60-20 🫣

the 100-60-35 I got fit fine, I'm now running dual rate at the front though.....🤣🤣🤣

 

[Steven103]

Did you ever work out if 20 or 35 was lb/inch or N/mm?

35 N/mm is genuinely about the right ballpark for a non-sport main spring lol.

If 35 is N/mm and the helper has say 70mm travel then that’s 35*70/9.81=250kg (of sprung mass) to compress the helper fully. So basically as soon as you get any weight transfer then yeah the inside front wheel becomes massively undersprung & therefore overdamped. Probably good over potholes as the wheel doesn’t have a chance to fall into the hole but possibly not ideal over track kerbs/bumps because the tyre can’t maintain contact with the road.

I measured my rear helpers on the weekend. About 2.2 N/mm. Took 13kg to fully compress them and still enough to hold the spring in place.

 

[bozothenutter]

Did you ever work out if 20 or 35 was lb/inch or N/mm?

35 N/mm is genuinely about the right ballpark for a non-sport main spring lol.

If 35 is N/mm and the helper has say 70mm travel then that’s 35*70/9.81=250kg (of sprung mass) to compress the helper fully. So basically as soon as you get any weight transfer then yeah the inside front wheel becomes massively undersprung & therefore overdamped. Probably good over potholes as the wheel doesn’t have a chance to fall into the hole but possibly not ideal over track kerbs/bumps because the tyre can’t maintain contact with the road.

I measured my rear helpers on the weekend. About 2.2 N/mm. Took 13kg to fully compress them and still enough to hold the spring in place.

N/mm mate.
I'll probably go the other way, and just get a longer main to go with the original helper...
Still wondering why Pure went with such short springs....
Probably because they couldn't get as low as they wanted?

 

[Steven103]

Forget main spring length, it's got nothing to do with this and therefore won't solve your problem.

Given that you have ruled out all of the other options (higher ride height, BC-style damper with separate height adjustment, softer main spring) the only way to solve this is a helper spring with more travel.

As a very rough guide put your car on axle stands without wheels. Measure the uncompressed length of the current helper spring (A). Measure the gap (B). Buy a new helper spring rate which has a free length longer than A+B. Add a few cm safety factor because our crystal ball can't predict what the closed length of the new helper spring will be.

Don't go stiffer than whatever the PMS helper spring was otherwise, without having all the numbers about your car to do the proper calculation, you risk the exact dual rate problem you've found.