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30 mm torsion bars, wich front springs
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1051
Location: The Netherlands

PostPosted: Sat Nov 29, 2008 3:31 am    Post subject: 30 mm torsion bars, wich front springs Reply with quote

I have installed Sway a Way 30mm (massive) rear torsian bars (LBS ?).

Which LBS front springs should I use, to balance the car ?

( I don't like understeer )

Car is for track use ony.
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Sat Nov 29, 2008 4:18 am    Post subject: Reply with quote

I have asked this question of a few people, and have gotten responses ranging from 300 to 400#. I think the best approach is to install coilover sleeves (like THESE), which use a standard size race spring, which are readily available and easy to swap. That way, you can take a stab and change easily and cheaply if you don't like the result.

Oh, and they are also height adjustable, for help with lowering and/or corner balance.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Sat Nov 29, 2008 5:45 am    Post subject: Reply with quote

I liked 400's, but 350in/lb could be just as good, depending on a lot of variables (driver preference, swaybar choice etc)
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Sat Nov 29, 2008 8:45 am    Post subject: Reply with quote

I bought these special made struts:

I need to find a sping set of 60mm in diameter and a pair of helper springs.


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924RACR  



Joined: 29 Jul 2001
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PostPosted: Sat Nov 29, 2008 8:56 am    Post subject: Reply with quote

Those struts look very nice!

I'm sure you can find an equivalent metric 60mm spring in that range of spring rate (300-400). Less rate will of course allow more oversteer than the higher rates.

The other question would be length; for sure 10" long (a standard US size) will be long enough... but if you're looking for a fairly low ride height and if the spring perches can thread up high enough (and I think they might, looking at the pics), you may be able to get away with closer to 8" with the helper springs. Again, those are standard US sizes, so you'll need to do your closest metric conversion. I wouldn't try anything shorter than around 8" though, and even that might end up too low for you!
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Sat Nov 29, 2008 8:56 am    Post subject: Reply with quote

Oh yeah... 30mm isn't that big...

(mine are 34mm hollow!!!)
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Sat Nov 29, 2008 9:27 am    Post subject: Reply with quote

34mm I did not know they exist !

This is my old setup, but you can see the problem of the spring being to short. I can't find helpers springs for this size spings.
That is why I am going to a smaller 'stock' size, that is 60mm. I think the Bilstein 944 turbo cup set is the same size.


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924RACR  



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PostPosted: Sat Nov 29, 2008 11:44 pm    Post subject: Reply with quote

The 34mm's were custom-order through Paragon, about $650 IIRC, and took about 6 months to get.

Worth it though, for my racecar...
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Mon Dec 01, 2008 6:01 am    Post subject: Reply with quote

Does any one know how much LBS/ KG the rear (massive) 30mm Sway a way torsion bars are ?

Greetings,

Joost
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller


Last edited by Dutch924-racer on Mon Dec 01, 2008 6:20 pm; edited 1 time in total
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924RACR  



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PostPosted: Mon Dec 01, 2008 9:08 am    Post subject: Reply with quote

I have the wheel rate chart at work - will post it tomorrow.
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bruni  



Joined: 26 Jul 2008
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PostPosted: Mon Dec 01, 2008 8:25 pm    Post subject: Reply with quote

Quote:
This is my old setup, but you can see the problem of the spring being to short. I can't find helpers springs for this size spings.
That is why I am going to a smaller 'stock' size, that is 60mm. I think the Bilstein 944 turbo cup set is the same size.


The helper spring does not have to be the same diameter as the main spring, you just need to make an adapter that fits between the two springs that locates on the internal diameter of each spring and don't forget to use a bump stop
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924RACR  



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PostPosted: Mon Dec 01, 2008 11:51 pm    Post subject: Reply with quote

30mm rear t-bars give an effective spring rate of 335 lbs/in.

Here's the full list, for reference... source is from Paragon's old Tech Session website, before the data was lost. Thankfully I grabbed a hardcopy.

T-bar diameter (mm)/effective rate (lbs/in):
18.5 48
19 54
23.5 126
24.5 149
25.5 175
26 189
27 220
28 254
28.5 273
29 292
30 335
31 382
32 434
33 490
34 553

For rear coilovers, they have like a .56 motion ratio (according to the info I have). Here's a few data points (coil spring rate in lbs/in vs. wheel rate):

200 112
250 141
300 169
350 197
400 225
450 253
500 281
600 337
700 394
800 450
900 506
1000 562

Obviously if you're running coilovers and t-bars, just add the effective wheel rates to get the total wheel rate.

So I am currently running 553lbs/in rear wheel rate on my car, and find it effective/competitive. YMMV!
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Last edited by 924RACR on Tue Dec 02, 2008 5:25 am; edited 1 time in total
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue Dec 02, 2008 3:34 am    Post subject: Reply with quote

Interesting, so a 23.5/160# factory setup is stiffer in the front by 30% or so (Pasha recommendations of 25/210 and 26/260 are also in line with this).

This would lend credence to 400+ in the front being a good match for 30mm rears.
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Last edited by Rasta Monsta on Tue Dec 02, 2008 4:33 am; edited 1 time in total
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924RACR  



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PostPosted: Tue Dec 02, 2008 4:03 am    Post subject: Reply with quote

NO.

The information above is ONLY for rear suspension setup! Thanks for pointing that out, that was a critical piece of info I left out! I'll edit the post to make it clear. Those coil-over rates are for rear coilovers to be installed in place of the rear shocks.

The front struts have a motion ration much closer to 1:1 - typical for a front McPherson strut, somewhere around 0.9:1 IIRC.

Sorry 'bout the confusion.
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue Dec 02, 2008 4:12 am    Post subject: Reply with quote

Doesn't your info show that the effective spring rate of 23.5 t-bar is 126#? If so, then wouldn't a 160# front spring be about 1/3 stiffer?

If not, I am REALLY missing something.
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