TrackJunkie

Here's my calculations for determining needed helper spring rates, as taken from Jim Pasha's article at the following URL:

<a href="http://dialspace.dial.pipex.com/town/gateway/d/admc18/944t/suspension.htm#Torsion%20bars%20" target="_blank">http://dialspace.dial.pipex.com/town/gateway/d/admc18/944t/suspension.htm#Torsion%20bars%20</a>

Setup on car from which my new shocks came:
30mm Torsion Bars = 335lb spring rate (TBSR)
Helper Spring Rate = 150lb
335 + (150 * .65) = 432.5lb Desired Spring Rate

Setup on my car:
29mm Torsion Bars = 292lb spring rate (TBSR)
Helper Spring Rate = HSR
Desired Spring Rate = 432.5

Formula to Use:
292 + (HSR * 0.65) = 432.5
HSR = 216.15

So from this calculation, I should as close to 216.5lb helper springs for the rear. Does this sound right, or is there a different method that would work better?

Jay Ellis
'87 951
Lower lap times on the way...

Wormhole

I can't answer your question.
But what spring rates do you plan running up front?
I'm looking to add some helper spring as well and need to know what the correct spring rate balance should be, front to back.

Thanks
John

TrackJunkie

600 up front

Tom Pultz

If you already have 29mm torsion bars and plan to add coilover shocks you will be better off in the long run switching to a full coilover setup because the chances are very high you will have to re-index the bars anyway, so you might as well pull them since this is a track car. Once the bars are gone you can easily change rear spring rates to balance the car. Of course, if you need to leave them in because of class restrictions that's another story

Your calculations are OK, but the 0.65 factor may be a bit high. I've heard it's as low as 0.55. Not sure anyone knows for sure. I think it's somewhere around 0.6 because my car handles great with the 300 front, 275 rear + 24mm bars.

If you are going with high pressure gas shocks they will add some effective spring rate of their own. I think rear springs come in 25# increments so you'll have to pick something close. If you re-index the bars you can put adequate preload in the coilover springs so you should be able to change rates and still get the desired ride height.

BTW, the spring, sway bar, torsion bar chart at that URL contains errors. For one of the 944 turbo listings the torsion bar and front sway bar sizes are swapped and the 968 is shown with 24mm torsion bars instead of the correct 25.5mm bars. There could be other errors, that's all I recall.

DanD

I just wanted to throw this out. Here is a collection of spring rates that I gathered from the Rennlist users.

Hope this helps. It also contains front to back ratios.

<a href="http://members.rennlist.org/dan10101/944SpringRates.htm" target="_blank">Spring rates spreadsheet</a>

DanD
<a href="http://members.rennlist.org/dan10101" target="_blank">Dans Rennlist member site</a>

DanD

I also ment to add, I selected 400 front and 300 rear with the 25.5mm torsion bars (indexed real low). It works well for track (only one event so far) and seems fine for street as well.
DanD

TrackJunkie

DanD, Tom - thanks for the wealth of info! So I gather Racer21's setup is the ideal PCA legal way to get the full coil-over benefits? What is meant by "turned down", removing and re-indexing the torsion bar so much to render them useless? Also, is there a tool made to adjust coil-overs, or what types of large wrenches will do the trick?

Jay Ellis
'87 951

DanD

[quote]Originally posted by TrackJunkie:
<strong>DanD, Tom - thanks for the wealth of info! So I gather Racer21's setup is the ideal PCA legal way to get the full coil-over benefits? What is meant by "turned down", removing and re-indexing the torsion bar so much to render them useless? Also, is there a tool made to adjust coil-overs, or what types of large wrenches will do the trick?

Jay Ellis
'87 951</strong><hr></blockquote>

Jay,

(I notice I have 2 Racer22s, I need to fix that.)

"Turned down", means they put them on a laythe and make them smaller 15mm or less instead of 25mm. It makes the spring more effective and keep them legal in a class that requires the stock 'type' suspension. (seems like they would be prone to breakage)

Removing and reindexing (lower) the torsion bars would be another way of making the coil-over do more of the work. Making it easier to corner balance, spring changes and ride height corrections.

Removing the torsion bars completely would be even better yet. (but bumps you a class or 2)

There is a spanner wrench, Paragon has them for about $12. or a large set of channel locks will work, but the metal is soft and will destroy in time.

Realize, I'm pretty new to this myself, but this is the way I understand it. Anyone feel free to correct me.

Wormhole

DanD, Great job putting everything together. It will certainly make my decision easier. I'm pretty sure I want to keep the stock torsion bars and add helper springs. Looking for something similar to the M030, but with variable spring rate options. Something that will complement koni's with coil over inserts up front. Anyone know where I can find such a rear setup?



John

Tom Pultz

[quote]Originally posted by DanD:
Removing and reindexing (lower) the torsion bars would be another way of making the coil-over do more of the work.<hr></blockquote>Exactly. Most rear coilovers are high pressure gas, and they will raise your ride height without any springs installed. In order to put some static preload in the coils you need to flatten the installed torsion bar angle so the coil spring supports some of the car's weight under static conditions. This allows you to use the coil to set ride height. [quote]There is a spanner wrench, Paragon has them for about $12. or a large set of channel locks will work, but the metal is soft and will destroy in time.<hr></blockquote>My rear coilovers use steel seats but many are aluminum, so I'd recommend the special wrenches like Dan says.

DanD

[quote]Originally posted by jvc951:
<strong>DanD, Great job putting everything together. It will certainly make my decision easier. I'm pretty sure I want to keep the stock torsion bars and add helper springs. Looking for something similar to the M030, but with variable spring rate options. Something that will complement koni's with coil over inserts up front. Anyone know where I can find such a rear setup?



John</strong><hr></blockquote>


Check out <a href="http://www.halshocks.com" target="_blank">www.halshocks.com</a>
They have variable rate coil-over coil springs (as I'm sure others do.) I went with fixed rate Hypercoils from Paragon. But I used the shocks from HAL or QA1.


Check out these other threads...

<a href="http://forums.rennlist.com/scripts/rennforums/ultimatebb.cgi?ubb=get_topic&f=15&t=004446" target="_blank">Springs....spring rate...? </a>

<a href="http://forums.rennlist.com/scripts/rennforums/ultimatebb.cgi?ubb=get_topic&f=15&t=004000" target="_blank">Which springs for Bilstein coilover set-up? </a>

If you click on SEARCH a the top you'll probably find a bunch more threads..