track suspension info needed... Options

[Jeroen]

Hey all,

Gathering suspension parts for my track car and I'm trying to make up my mind

I'd like to go with yellow adj. Koni's.
Does anybody now up to what spring rate the yellow Koni's can handle?

Should I go for torsion bars (22 or 23mm)
I can have the struts modified for coilovers for about the same money I'd need to spend on the t-bars
Coil over springs are pretty cheap and I wouldn't be stuck with just one spring rate

Any info on springrates in relation to the weight of the car?
I'm aiming for about 1750# for the car and was thinking about starting with 275 or 300# rear springs

Does anybody know the spring rates for the front torsion bars?
I've been looking into it, but different sources quote (very) different rates (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)
Anybody running big front t-bars (22 or 23mm), what springs are you using in the rear?

I know, lots of questions, but I'm trying to figure out my options, so any advise is welcome
Right now I'm looking at too many unknowns to make a decent guestimate

thanks...

Jeroen

[brant]

I've lost it now and its probably the same one you've already seen.. but there once was a comparison table on pelican that showed the torsion bar diameter = xxx lbs.

I've always run 22mm front bars (about 15years of DE and wheel to wheel combined). I've tried rear spring in 200/250 and now 275with my non running -6

I know others use 23's but I was strongly steered away from these by my builder AJ... He believes that you can over spring and loose traction.

he runs aero on his rear with very high spring rates around 400lbs to compensate for the aero yet still runs 22's on his front. (probably a 1700 lb car also)

he builds ton's of coil over race cars and admittedly is a very good driver himself. The funny thing is that he is faster than many of his customers in his 2.2L -4 car with torsion bars.......

[Jeroen]

QUOTE (brant @ Jan 7 2005, 06:50 PM)

I've lost it now and its probably the same one you've already seen.. but there once was a comparison table on pelican that showed the torsion bar diameter = xxx lbs.

found it... or rather (and that's the problem) them
got 2 lists and they vary pretty wildly

here's what I found

List 1 (front t-bars):
21mm - 173#
22mm - 210#
23mm - 250#

List 2 (front t-bars):
21mm - 249#
22mm - 298#
23mm - 355#

quite a difference (IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif)

[brant]

wow.. big difference..
I think I've always understood the 210# for the 22's...
I've always understood the first list was accurate and came from a reputable source...
but what source I don't know.

bump

[TimT]

http://instant-g.com/Data/911CoilConv.html

here is a table of coilover/torsion bar conversions.

[John]

I don't know if that is imperical data or if it is theoretical.

It wouldn't be too tough to calculate.


We have used 22mm torsion bars in front with 350# rear springs for at least the last 10 years on the track. The front is softer than the rear and we balance it with the front sway bar (I don't recall the size, but it is fairly big).

This winter, we have changed over to 23mm torsion bars and will initially set the sway bar to full soft to start....

[john rogers]

Your question should get lots of replys??? I use 23mm front t-bars and 300# rear springs and have adjustable Koni shocks on all four corners. I also use a front and rear sway bar with a GT limited slip. This has worked well since the car runs on Goodyear slicks and is great on tracks that are smooth but it is hell on a rough surface such as we raced on in Tacate Mx last year. Our rule of thumb was to go just stiff enough on the rear to keep the inside front wheel planted in very tight corners and so far has worked well.

[airsix]

The part of the question nobody is answering is what range of spring rates are the available off-the-shelf shocks designed to opperate within. I am highly interested in the answer to that question.

-Ben M.

[brant]

QUOTE (airsix @ Jan 7 2005, 01:37 PM)

The part of the question nobody is answering is what range of spring rates are the available off-the-shelf shocks designed to opperate within. I am highly interested in the answer to that question. -Ben M.

Ben,

still not answering your question...
don't know the answer really...

went with this though:

[drew365]

Jeroen; My setup is:
Front - 22mm hollow torsion bars, adjustable Koni shocks, 23mm Smart Racing sway bar.
Rear - 400# Eibach springs on adjustable perches, Bilstein shocks, 16mm Weltmeister sway bar.
My car weighs about 2000#. It is very stiff and neutral with little to no body roll. My front bar is usually about the mid point and my rear bar is near full soft. I make small adjustments for different tracks but usually no more than 1/2" on either sway bar.

[Jeroen]

QUOTE (TimT @ Jan 7 2005, 08:37 PM)

http://instant-g.com/Data/911CoilConv.html here is a table of coilover/torsion bar conversions.

Yep, that list is quoted as "list 2" above (for ease of comparison, I left the wheel rates out)
As a side note, it lists the rear wheel rates (taildragger rear t-bars) higher than the spring rates. Thought that was odd...

[TimT]

Jereon.
My top secret suspension set up is:

Front: Bilstein RSR raised spindle struts
450# springs
19mm sway bar

Rear: Bilstein RSR shocks
350# springs
sway bar disconnected

The p/o told me he had the shock revalved, but Im not so sure of that..when I bought the car it had 650 front 600 rear springs.. and hand some handling "issues"

Ive got my car dialed in the way I like it, its very nuetral, corners very flat. I do have some concerns about to much weight transfer under hard braking... curing that is this years project!

[lapuwali]

I've never really spent much time on car suspension, but I spent a ton of time and money on bike suspensions. The key issue there was getting the answer to Ben's question: spring rates for the available shocks. On a bike, anyway, these always had to be considered as a pair. If the shock wasn't adjustable, there was a fairly narrow range of spring rates that worked. Go outside of that, and the shock could no longer control the spring (if too high), or the damper set the performance more than the spring (if too low). A too low spring rate relative to rebound damping also got you a jacking effect, where the spring wouldn't fully extend the shock again after compression, and a series of bumps would give lower and lower ride heights until the shock bottomed out.

The mass being sprung and damped mattered, but was essentially the same for most bikes (the rider made a bigger difference than one bike or another, assuming the same rear suspension design). I would expect Koni or Bilstein could provide these numbers, esp. on a simple coilover setup like the rear of the 914. For the front, they'd need to know the geometry of the system to get the effective rate of the torsion bar at the damper.

btw, wild guess here, but the two lists of torsion bar to weight numbers might be wheel or damper rates, which are probably different front/rear on a 911 (different length of lever arm between t-bar and damper or wheel). A longer lever gives a lower effective rate for a given size torsion bar.