Autox Spring rate help, Too Stiff? Options

[nolift914]

Is my Autox 914 too stiff?
I am currently running the PO setup, the 914 was set up for club racing with front and rear coil overs. The front is at 330lbs/in which I believe is the equivalent to 25MM torsion bars and the rear is at 230. The 914 is a 4 weighting approx 1780lbs with bias ply slicks. I plan on switching to Dot-R radials. I have always thought for autox go soft on springs and big on bars. Does the paddock crowd have any suggestions for a setup. The autox sites in NYC tend to be on the rough side. I was thinking either 175 lbs/in in front and 140 lbs/in rear or 200 lbs/in front and 180 lbs/in rear.

[Randal]

Is my Autox 914 too stiff?
I am currently running the PO setup, the 914 was set up for club racing with front and rear coil overs. The front is at 330lbs/in which I believe is the equivalent to 25MM torsion bars and the rear is at 230. The 914 is a 4 weighting approx 1780lbs with bias ply slicks. I plan on switching to Dot-R radials. I have always thought for autox go soft on springs and big on bars. Does the paddock crowd have any suggestions for a setup. The autox sites in NYC tend to be on the rough side. I was thinking either 175 lbs/in in front and 140 lbs/in rear or 200 lbs/in front and 180 lbs/in rear.

Currently running 19mm torsion bars with a smart racing bar, with the smallest diameter bar they offered. Had under-steer until I went to the lightest smart racing bar. Front shocks are Koni's set to almost total soft. Rear springs are 240# if I remember correctly. They might be #225, but will check.

With Avon's no under-steer at autox's or hilllclimbs. I'm 100# ligher than you.

Are you going to Dot-radials to make a class?

[J P Stein]

MY 914 weighed 1700 to 1780 lbs depending on ballast.
Most AXs were run on a venue that was rough as a cob.
Ride height was 4 1/2 to 5 inches measured from the dough nuts.
21 mm front T bars.
275/300 lb rear springs.
22mm (effective) front AR bar set half hard....none at rear.
Revalved Bilstein shocks......soft on rebound.
Slicks, Cantis in front, 10inch straight sides in rear.
Worked OK on smooth venues also.....but not ideal.

I drove a similar 914 track race car set up for the big track at PIR (which is billiard table smooth) on this same venue......skippng from pillar to post it was uncontrollable.

[Woody]

My current AX setup is similar to what JP used to run. I have 21mm tbars, a 22mm swaybar, 250 rear springs and 225/275 A6s. 1850 pounds. Its a very predictable car.

[J P Stein]

There are some mine fields with a suspension set up like I related..

A stiff shassis is needed to *make the suspension do its work*......I'm talkin' bridge stiff. A stock chassis will flex all over hell and make handling inconsistent.

To help the suspension do its work, low friction bushings....not cheep derlin/poly whatever, are needed.

Over 200 lb rear springs can/will cause cracking aound the un-reinforced rear towers long term.....the rougher the venue, the quicker this happens.

Enjoy (IMG:style_emoticons/default/biggrin.gif)

[nolift914]

Is my Autox 914 too stiff?
I am currently running the PO setup, the 914 was set up for club racing with front and rear coil overs. The front is at 330lbs/in which I believe is the equivalent to 25MM torsion bars and the rear is at 230. The 914 is a 4 weighting approx 1780lbs with bias ply slicks. I plan on switching to Dot-R radials. I have always thought for autox go soft on springs and big on bars. Does the paddock crowd have any suggestions for a setup. The autox sites in NYC tend to be on the rough side. I was thinking either 175 lbs/in in front and 140 lbs/in rear or 200 lbs/in front and 180 lbs/in rear.

Currently running 19mm torsion bars with a smart racing bar, with the smallest diameter bar they offered. Had under-steer until I went to the lightest smart racing bar. Front shocks are Koni's set to almost total soft. Rear springs are 240# if I remember correctly. They might be #225, but will check.

With Avon's no under-steer at autox's or hilllclimbs. I'm 100# ligher than you.

Are you going to Dot-radials to make a class?

I am currently running in PCA class M01 and SCCA FP, I am looking to move away from the Canti's due to the limited availability. Cant find soft compounds.
Going to either Radial slicks or Dot-R autox tires. I found this chart listing the front torsion bar spring rate

SIZE ( mm) SPRING RATE ( Lb/in)
18.8 110
21 173
22 210
23 250
24 296
25 350

I believe I have 330lbs / springs on the front which by the chart would be the equivalent to 24.5mm bar, which seems stiffer than those listed in this thread from 19mm to 21mm.

There are some mine fields with a suspension set up like I related..

A stiff shassis is needed to *make the suspension do its work*......I'm talkin' bridge stiff. A stock chassis will flex all over hell and make handling inconsistent.

To help the suspension do its work, low friction bushings....not cheep derlin/poly whatever, are needed.

Over 200 lb rear springs can/will cause cracking aound the un-reinforced rear towers long term.....the rougher the venue, the quicker this happens.

Enjoy (IMG:style_emoticons/default/biggrin.gif)

J P

I should have given more details of the 914's current setup, In addition to the front and rear coil-overs on Bilsteins, the front struts have raised spindles. front and rear Elephant racing polybronze bearings, Reinforced rear trailing arms and lower console, full 8 point cage. no reinforcement on front and rear shock towers. Front sway bar (Weltmeister) and no rear bar.

From the setup's listed everyone is softer in front between 125lbs to 175lbs and stiffer in the back 225 to 275. (IMG:style_emoticons/default/confused24.gif)

[mskala]

I believe your chart is accurate from my memory of 21mm calculation.

Anyway, what do I know, I've never driven anything other than the 914
in anger, but here is my opinion. Yes, you should have the front softer
or equal springs to rear. Since your car is not a street car, overall
stiffer is better, except when the surface gets too bad. Understeer is not
your friend, and can be tuned a bit with the front bar. Also, unless you
have a co-driver, with such a light car it may be difficult to heat up the
tires if you go with something wide for your semi-flares. We do a group
of 4 runs and the first 2 for me are only for heating. If lucky the pressure
goes up by ~4psi then I know I'm in business (with dot-r).

Here is my setup, which I'm pretty happy with as a street car.
Torsion bar: 20mm (yes, these are occasionally available)
Rear spring: 180
Front sway: 19mm weltmeister, set kinda in the middle after tuning
Rear sway: none
Front shock: koni adj
Rear shock: Bilstein non-adj (perch adjustable)
Wavetrac limited slip
about -2deg camber all over
lowered slightly, no spindle change
Wheel: 7.5x16 Fuchs-center, BBS rim
Tire: Kumho V710 215/40/16
No flares
Weight: stock but no tar on interior (~2050)
Engine: 2.2L 'E' six

[nolift914]

I believe your chart is accurate from my memory of 21mm calculation.

Anyway, what do I know, I've never driven anything other than the 914
in anger, but here is my opinion. Yes, you should have the front softer
or equal springs to rear. Since your car is not a street car, overall
stiffer is better, except when the surface gets too bad. Understeer is not
your friend, and can be tuned a bit with the front bar. Also, unless you
have a co-driver, with such a light car it may be difficult to heat up the
tires if you go with something wide for your semi-flares. We do a group
of 4 runs and the first 2 for me are only for heating. If lucky the pressure
goes up by ~4psi then I know I'm in business (with dot-r).

Here is my setup, which I'm pretty happy with as a street car.
Torsion bar: 20mm (yes, these are occasionally available)
Rear spring: 180
Front sway: 19mm weltmeister, set kinda in the middle after tuning
Rear sway: none
Front shock: koni adj
Rear shock: Bilstein non-adj (perch adjustable)
Wavetrac limited slip
about -2deg camber all over
lowered slightly, no spindle change
Wheel: 7.5x16 Fuchs-center, BBS rim
Tire: Kumho V710 215/40/16
No flares
Weight: stock but no tar on interior (~2050)
Engine: 2.2L 'E' six

Thanks for the info, you were very quick at the Zone 1 autox. I was having a hard time trying to get heat in the the tires and was looking forward to trying to close the gap on day 2 before the apparent issues.

[J P Stein]

There are several spring rate for torsion bar charts floating around.
This is the one I use.


Front Rates
Torsion Kw (lb/in) Ks (lb/in)
Dia (mm) (Wheel) (Spring)
16 77 90
17 97 112
18 122 138
18.5 137 154
19 152 170
20 187 207
21 227 249
22 273 298
23 327 355

[Randal]

Right, no soft compounds with Canti's.

Before you go to radials check out the soft compound Avons. They are expensive, but they work. Also believe the real soft Avon's have more tread on them to start out.

[nolift914]

Right, no soft compounds with Canti's.

Before you go to radials check out the soft compound Avons. They are expensive, but they work. Also believe the real soft Avon's have more tread on them to start out.

I took a look, what compound do you run A11 or A24

[J P Stein]

R35 Hoosiers always worked for me. There was most always a string of "others" behind us. It's all in the set up.

[nolift914]

R35 Hoosiers always worked for me. There was most always a string of "others" behind us. It's all in the set up.

I will take a look for the r35's , running the r45's now can't get them hot.

[Downunderman]

With 330 on the front and 230 on the back the thing must understeer like a pig. If you want to keep the 230's on the back I would drop the fronts to 190. The theory being that the spring rates should reflect the F/R weight distribution which with a teener is roughly 45/55 (on a six at least, don't know what a four is, but cant be much different).

[Randal]

Right, no soft compounds with Canti's.

Before you go to radials check out the soft compound Avons. They are expensive, but they work. Also believe the real soft Avon's have more tread on them to start out.

I took a look, what compound do you run A11 or A24

I'm running A45 for both autox and hillclimbs. Magic actually. Perfect for light weight 914's.

Good idea to decide on front tire size you want (narrow or wide) then ratio your weight balance to the rear tire. In effect you end up with every inch of tire with the same weight, i.e., just like F1. Smaller in front is better.

You're concerned about getting heat into tires, so run narrower tires in the front.

[ChrisFoley]

With 330 on the front and 230 on the back the thing must understeer like a pig. If you want to keep the 230's on the back I would drop the fronts to 190. The theory being that the spring rates should reflect the F/R weight distribution which with a teener is roughly 45/55 (on a six at least, don't know what a four is, but cant be much different).

You have to look at wheel rates to make a valid comparison.
The rear wheel rate is higher than the spring rate.
The front wheel rate is lower than the spring rate, as shown in the chart above.

[J P Stein]

Next time some expert tells you what spring rate your T bar are do this simple test.
Plop your ass on the front fender. How much do you weigh and how far did the fender drop?......WARNING: If enough sand is pounded up your ass, the fender may go down more. (IMG:style_emoticons/default/blink.gif)

[nolift914]

I guess my question is what spring rate is equivalent to a 21mm torsion bar for a 914 with front coil-overs and what is equivalent to 19mm.

[J P Stein]

Looking at the supplied chart the answer would 21mm=250 in lbs & 19mm=170. Did your mom have much trouble toilet training you?

These numbers are approximates.

You'll not find an easy path to 914AX Nirvana without *actual testing*. This involves spending money for parts and then trying them out......or you can set back and seek more data.

[Randal]

Speaking of research, have you asked Tom Provasi how he had the car set up when it was a big autox winner?