997gt3north

I thought I would start a new tread, my old PASM revalve thread almost finished ( a few more posts about Tenders vs Helper Spring shortly).

I jumped into my revalve, a bit naive, but have now done so much reading on Rennlist and many other sites about Spring Rates, Tender Springs, Helper Springs, Linear Springs, Progressive Springs, when to use Tenders versus Helpers, the use of Progressive Helpers, etc, etc, etc - no wonder race teams carry cabinets filled with springs.

The other reason I have been thinking a lot about this is a few posts on Rennlist that I found about 'Tender Springs' - everyone should do a search on this topic - it leads to a few really technical suspension physics discussions for the really interested + I have been very interested in the tread about a Rally type progressive spring rate suspension setup being very good at Sebring.

So, given that I have been extremely happy with my re-valve setup, I thought it may be useful to broaden the topic about a re-valve (or very likely not necessary) type spring change on the OE shocks that may work very well at Sebring and yet may also work at smoother tracks.

I'll start with 2 tender springs that I have come across that I think are worth mentioning

Both come from this link and are Eibach - pg 37 - see Tender Progressives

http://performance-suspension.eibach...16_catalog.pdf


I don't have enough time currently to post all my thoughts now, this will take a few days to go over everything, but I will start off with there are a few things that will at first seem counter intuitive when you use Tender Springs in combination with Main Springs and the same logic applies about Progressive Tenders and further when you use these in combination with linear Mains.

The punch line is, if you have a 250# Tender with a 900# Main, the Tender Spring when it comes into play at Wheel Droop (inside wheel lifts at apex) does not act like a 250# spring as you may initially think. The reason is that the 250# Tender is going to be pushing against another spring (the main 900# spring) so it will act like a softer spring than it's 250#.

The formula for how it will act until it coil binds is

(Main Rate x Tender) / (Main Rate + Tender Rate)
(900 x 250)/(900+250)
= 195#

The higher the main spring rate, the close the actual tender rate will be to actual but it will always be less - just accept this fact - it gets easier after a few days thinking about it and then becomes obvious.

Back to Sebring / bumpy tracks and whether we can do anything from a 'home brew' perspective, using your stock shocks, to keep it subtle over the bumps with Tenders / Progressive Tenders and then add firmer Mains to improve things like front dive under braking, etc and yet still make the car work when you visit smoother tracks.

I think it is worth a discussion, I understand the 'Just buy a Moton, KW or Ohlin package' - I just want to broaden the discussion. In my opinion, my re-valve has been a monumental success so I think it is likely very possible to re-use the stock shocks (revalved or not), with the correct tenders and mains to make a better bumpy track car.

The other reason that I think it is likely very doable is that for TUV approval reasons, Porsche has to make sure at all possible ride heights available on their supplied shocks, that the springs provided remain fully seated (the long soft front spring and the crazy rear spring used on mk1s). Another interesting fact is that for those with 2007 vs 2008 gt3s and RSs, at one point the rear shocks went from fully threaded to only the lower 1/3rd being threaded - for very stiff rear main spring setups with tenders and certain ride heights, this rules out using 5-6" mains and requires 7" to be safe.

I'm going to post a bunch of stuff in the coming weeks, links etc, but the goal is to see / discuss if there might be an easy tender / main spring combo swap out with the addition of a 60mm rear spring top hat that might make for a fun / useful experiment.

The 2 initial candidates that I have come across are Eibach Progressive Tenders

Part # 050-060-0040/0120

This is a 228/385 progressive tender
Free height is 4.1 inches - block height is 2.2 inches
Supports when compressed 854#s (front corner weight supported by spring on a gt3 is around 600#s)

Using the math above, this Tender Spring while a 228/385, actually acts like a 143# until this section closes and then jumps to 385#s. So a 228/385 is really a 143/385.

Now, let's say we want to use this Tender Spring in combination with a stiffer main spring that can help resist the front dive in a brake zone - let's say 2 possible candidates are a 400# and 600# Main.

When we do this, we again change the Progressive Tenders characteristics as there is yet another spring to push against which further reduces the actual spring rates until each section fully compresses.

So, a 228/385 with a 400 or a 228/385/400 actually behaves like a 105/196/400 and a 228/385/600 behaves like a 115/234/600


If you think about the above 2 potential front spring combinations

105/196/400
115/234/600

it actually presents some interesting choices - just for reference, the front spring rate on a 997mk1 is basically spot on 234#s.

As I mentioned earlier, this 228/385 part supports 854#s. What this means is that given the front spring has to hold approximately 600#s, you will in the above choices be riding around normally on the middle # (196 or 234), when you go for hard brakes you will get (400 or 600) and when you get into unloading bumpy situations the tire will first 'reach down' and touch with a softer (105 or 115). There is no magic here for if your ram into a hard curb, you will quickly move into the (400 or 600#) range but on rebound will land initially far softer than a firmer typical 600/800 f/r after market setup.

I believe both set ups would likely work on a stock shock without any revalving necessary - another choice would be combining it with a 500 or 550 main spring - these would equate to

228/385/500 - acts like - 111/217/500
228/385/550 - acts like - 113/226/550

Again, think of these 3 measurements above as bumpy / normal / braking.


The other Progressive Tender Eibach part is

050-060-0060/0150

Info
343/857 Progressive Tender
4.6 inches compresses to 2.4 inches
Supports when compressed 1124#s (rear corner weight supported by spring on a gt3 is around 900#s)

Possible rear setups

343/857 with a 750 main - acts like 184/400/750
343/857 with a 850 main - acts like 190/426/850
343/857 with a 950 main - acts like 195/450/950

(you basically ride in the middle zone until you side or side/rear load the rear by an additional 200#s and then, for example in a corner and during trackout, another 350-500#s would come to the rescue)

997gt3north

The rear shock on a 997mk1 is 600#s and an mk2 is 660#s as a reminder. From my work so far on revalving and normal and firm settings, the shocks can handle 150#s on either side of their range without issue.

Another possibility for the rear is to just Replace the existing useless permanently coil bounded rear with a higher spring rate tender that would hold a significant part of the rear car's weight so the Tender will come into play more often. Swift springs, as an example offers a 336# tender that supports 616 pounds of weight (remember, the rear of the gt3 is about 950 of sprung weight). If you replace the rear spring with 550/600/700/750 mains you would get

336/550 - acts like 208/550
336/600 - acts like 215/600
336/650 - acts like 221/650
336/700 - acts like 227/700
336/750 - acts like 232/750

Basically, the 336/650 for mk2 car's should feel exactly like stock but be more compliant over bumps as any decent bump would momentarily unload 350#s and that would get the progressive tender to soften the landing.



More to come


Paul

Nizer

Should be an interesting thread.

I'm curious if there's a "transition-effect" trade-off in going the helper spring route. Transition-effect is my term and I'm sure there's a correct one in the suspension world, but think of it like turbo lag. Is there an noticeable inflection in handling when suspension transitions from helper to main spring?

Hoping the Exe-tc folks jump in as well given their very different approach - soft spring, stiff damper.

utkinpol

not sure what is a hidden reason behind it but in majority of samples i saw tender springs were never stiffer than 200lbs, usually at 150lbs - same as mine or 0lbs. and it also considered a 'street noise reduction only' measure and for pure track cars shops do not put them in at all.

997gt3north

Actually race cars with enough spring travel (cup cars) that use high main spring rates use Tenders, not Helpers with very low rates, so that 'transitions' from droop (tender zone) to main spring is not an overly abrupt effect. There are also other non-intuitive reasons tenders are used. There is a great post if you search 'Tender Springs' (I will post it later when I re-find it) that addresses a specific somewhat non-intuitive suspension leverage effect concerning roll-center - and why they are also preferred over non use / weaker Helper Springs.

997gt3north

Yes there is. If you want the benefit of higher spring rates, it comes with the challenge of managing these transitions - if the car's suspension travel range is large enough, given the spring rate, to unload the much shorter travel of the main spring.

As an example, on the rear of my 997gt3 with a 900# rear main spring and a stock ride height (will be going 10mm lower shortly), at rest the main spring is compressed just over 1 inch - but the rear suspension travel to full droop is 2.5 inches - therefore, you have to choose someway to manage this - let the spring unseat, use a low helper rate, use a higher rate helper tender to fine tune this process.

<----- see my suspension picture (this is with wheel off so full droop is very slightly lower - you can see the tender is non-blocked and it's affect will be felt on transition back to main spring load)

utkinpol

it`s an interesting topic - i saw a 996 cup car on a lift at my mechanics shop and with wheel suspended it had one single spring and no space between lower and upper hats and spring - everything was tight.

but that car sits very low and obviously those springs do not have much of a travel, so, who knows.

997gt3north

There are so many ways to set up a car - and that is why I thought it was a worthy topic. I have seen cups with and without tenders - but I really want to keep this discussion to our street ride height / likely spring range / suspension travel range setups.

As you can see, with my 900# rear spring at stock ride height, there is an approximate 2" droop range that has to be managed somehow - my front with a 600# spring, soon to be 700#, gets fully unloaded at stock ride height by about 8mm - this will only get larger with higher spring rate and very slightly lower ride height. This has to be managed somehow - either with nothing, helper or higher rate tender.

It was all the above facts and research and the Sebring Rally suspension setup that started all my researching - I really do think that there is likely a way to help a stock gt3 work better at a bumpy track like Sebring with different springs and tenders and make it still work perfectly fine on smoother tracks - this is partly, but not specifically because PASM allows 2 modes in addition to the other issues mentioned. It is also potentially useful if anyone wants to do Rally / Hill climb type driving and just swap out the springs for the event.

997gt3north

some useful rennlist threads - worth the 20 minutes when you have the time - if you are interested

https://rennlist.com/forums/944-turb...tender+springs

https://rennlist.com/forums/996-gt2-...tender+springs

https://rennlist.com/forums/racing-a...tender+springs

https://rennlist.com/forums/996-turb...tender+springs

https://rennlist.com/forums/racing-a...tender+springs

https://rennlist.com/forums/racing-a...tender+springs

https://rennlist.com/forums/racing-a...tender+springs

https://rennlist.com/forums/944-turb...tender+springs

Mvez

Interesting. Since that's how the stock rear spring already works, it would be perhaps informative to find out the rear spring rates on the new 4.0 RS, since it now supposedly has helper springs in the rear (per the articles I've read).

997gt3north

So, after you have absorbed the above, my idea for a potential Sebring / Bumpy track spring setup with all OE non-revalved dampers is:

1) let's take a 3200# car
2) 650# at front corners, 950# at rear corners
3) add 200# driver and just for argument add evenly to each corner
4) car with driver is 700# front corners, 1000# rear corners

Front Setup
- 228/385 progressive tender with 400 main (228/385/400 acts like 105/196/400)
- with this setup, 400# main kicks in at 854#s or 150#s more than corner weight with driver

Rear Setup
- 343/857 progressive tender with 750 main (343/857/750 acts like 184/400/750)
- with this setup, 750# main kicks in at 1124#s or 124#s more than corner weight with driver
- so, both front and rear mains kick in at very similar increases (125-150#s)


If we now compare this setup to stock

Normal driving (Front, Rear)
(196, 400) vs (234,600)

Braking and Accelerating (Front, Rear)
(400,750) vs (234,600)

Bumpy Transitions (Front, Rear)
(105, 184) vs (234, 600)

These very low f,r (105,184) rates would only be used momentarily at droop to soak up the initial 1" of droop travel

That's my idea for a bumpy track setup with the OE dampers - both softer and yet firmer when you need it - and the dampers would be within their comfort range - and you will also have the 2 PASM settings to experiment with.

You could purchase the 2 tender springs, 2 main springs, spring dividers and the Tarett 60mm rear spring hat for less than $500. If you can do your own install you would then have to pay for an alignment.



Paul

tcsracing1

all french to me

Izzone

Paul,

Love your posts.....there are still a few engineering geeks like me out there

Better question, are you shipping your car down this winter for Sebring?

997gt3north

Randy,

I would love to.
I wrote this post with you in mind - I don't want you to spend money on a cheater $$$ suspension to beat Peter when I know you can do it with a 'stock' suspension - save your money for that sequential shifter.

Send me an email at

mail at pauloneil dot com with your contact details

Will try and get Sebring in this winter


Paul

997gt3north

I wanted to highlight one of the pages from one of the links I posted - this page runs through a logic experiment that explains how roll resistance can have a dramatic and counter intuitive effect when an untendered main (the inside wheel) stops being compressed

https://rennlist.com/forums/racing-a...pension-3.html