Let's play 20 questions on front springs, coil over vs. torsion springs Options

[woobn8r]

What say the 914 faithful (except CWs...we know your answers)...

Have you tried coil over fronts?

What spring rate did you use?

Which rear spring did you use to balance with?

What is the main use of your car (street, Ax, sunday driver, race, combo)?

Was this set up for a four or a six (or a subie, V8, rotary, etc)?

Did you have to re-enforce the chassis around the upper front strut mount?

What were your perceived benefits?

Were there any drawbacks/ill effects?

Could you tell the difference?

Okay...I'm sure this will spawn at least 11 more questions...if not I owe ya!

So...spill it...

[Joe Ricard]

What are you trying to improve?

The only reason I would go to Coil over fronts is to increase front spring rate and to install upper and lower A-arms.
Way too much trouble

[TimT]

Have you tried coil over fronts?

Yes

What spring rate did you use?

Ive used from #250 to #650 and settled on #450

Which rear spring did you use to balance with?

ended up with #350 rears

What is the main use of your car (street, Ax, sunday driver, race, combo)?

track/race

Was this set up for a four or a six (or a subie, V8, rotary, etc)?

modified 3.2/6 short gearbox

Did you have to re-enforce the chassis around the upper front strut mount?

No

What were your perceived benefits?

Large selection of spring rates, easy to change springs

Were there any drawbacks/ill effects?

a touch more sprung weight, not able to achieve as much neg camber because spring fouls with body, however my car didn't end up needing massive camber due to very little body roll. Tire temps and handling agree

Could you tell the difference?

Yes

eOkay...I'm sure this will spawn at least 11 more questions...if not I owe ya!

So...spill it...

[woobn8r]

What are you trying to improve?

The only reason I would go to Coil over fronts is to increase front spring rate and to install upper and lower A-arms.
Way too much trouble

Originally I was thinking of the greater availability and tuneability of coil springs. Also threaded coil overs make it easy to set ride height and adjust corner balance.
Coil springs are relatively cheap to obtain and easy to change. I also do not have a chart (or formula) for rating the spring rate of torsion bars which makes tuning difficult....Moving to the coil over set up is easy....but...

Then I got to thinking that it might stress the chassis too much...I know you can do it on a tail dragger, but this is my first 914 and the chassis seems...well, fragile if not flimsey.

Other than a slight weight penalty (shouldn't be notced with a 3.2) I can't find a downside except the stress issue....(and possibly vintage or class rules)

I don't know why you would switch the Macpherson strut set up for upper control arms...that does sound like work.....

Besides I thought it'd be a good topic for discussion so we don't spend all our time bashing AA. (IMG:style_emoticons/default/alfred.gif)

[SGB]

I don't know why you would switch the Macpherson strut set up for upper control arms...that does sound like work.....

I am totally not qualified in this conversation as a non-track type, but could not one use a coil assisted strut- or strut "insert" with modification- in addition to the torsion bars to provide added springing?

[Dave_Darling]

Also threaded coil overs make it easy to set ride height and adjust corner balance.

Doesn't seem any easier to me than tweaking the torsion bar's adjusters. (And I have "coil overs"--actually adjustable spring perches!--on my "other car", so I should know!)

I also do not have a chart (or formula) for rating the spring rate of torsion bars which makes tuning difficult....Moving to the coil over set up is easy....

A quick Google search will give you the formula. There are terms for the fourth power of the diameter, and (1/lever arm of the suspension). That will actually get you "wheel rate" and not "spring rate", so you would have to do a little more conversion to get "spring rate", but wheel rate is what we should be interested in anyway.

And easy? Well, for certain definitions of "easy", I suppose...

I don't know why you would switch the Macpherson strut set up for upper control arms...that does sound like work.....

For the massively superior control of the camber curve, perhaps?


...In the tail-dragger world, at least, the consensus seems to be that the only positive reason to switch to coil springs is if you need such a high spring rate that the appropriate torsion bar won't physically fit into the A-arm.

...Sure has some good "coolness" factor, though!

--DD

[TimT]

Steve Timmins developed a chart of 911 torsion bar spring rates

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

the front data is applicable to the 914, the rear data is not applicable

a 23mm torsion bar is the largest available for the fronts and gives a spring rate of #355. If you find you need heavier springs than that youll have to go coil overs.

[SirAndy]

450lbs on scotts car, if i recall correctly ...




don't recall the rate on rogers car ...




upper strut boxes for coilovers, this is an early pic of what is now Bill P. 's "Beast" ...

(IMG:http://www.sirandy.com/pix/914/theshop/shop_005.jpg)


(IMG:style_emoticons/default/bye1.gif) Andy

[Rough_Rider]

Couple of points...

Coilovers on a stock 914 limit the amount of negative camber you can dial in. As the springs & spring perches will contact the inner suspension tower metal. As the beast pic shows to gain negative camber you must install new suspension towers.

Coilovers will increase the position of weight in suspension system. Torsion bars can't really be any lower.

Adjustment for corner balancing is a moot point as both system ares easy to reconfigure.

Only benefit is coilover springs are cheap & come in huge variety of spring weights.

Side note: F1 cars use torsion bars. The technology isn't that antiquated its just a straight spring.

[brant]

This discussion has been done over and over.
the only two reason for a front coil over are:
1) you need 400+ lbs of spring
2) you plan on changing springs every weekend to suit different tracks.

I would guess that 999 out of 1000 914 race cars out there don't change front spring rate from track to track

be honest... will you really run 2 or 3 or more different spring rates?
I doubt many will
thus it become bling factor if you don't meet one of the 2 reasons
brant

[woobn8r]

Wow, lots of great info out there!
Thanks TIMT for the conversion chart...now I have somthing to work with....

I would have guessed that 1mm increase in bar diameter would have been more than a 50lb change in spring rate...this would have left big gaps...but it's not the case according to the chart...

I suppose as I work on set up that once it is set, it is set. but getting there might involve borrowing a few bars to try out.

You guys have almost convinced me!
Great pics too!

Thanks Gents.