please explain coil overs

[aftermath]

I know the answer is in the threads somewhere....
Corect me if im wrong ( Im a computer guy, not mechanically inclined ).
A coil over is a shock\spring combined? Can it be used to adjust ride height instead of tinkering with torsion bars?

I have a car that I want to replace the suspension, or tweak the torsion bars, etc, why do more people not upgrade the suspension to coil overs? Does this allow one to get rid of torsion bars altogether? I know some re-enforce things for coil overs.

Can someone explain the basic changes to the car, the benefits, and maybe why more people dont go this route?

Or point me to a thread where its all explained.

Thanks

[Bill Verburg]

Coil overs are indeed a shock/strut w/ a concentric coil spring. Some, but not all, incorporate height adjustment collers
This set has a wide range of adjustment

This set has a small range of adjustment on the front but none on the rear

All 911s from '89 up(964.993,996,997) have coil oversuspension stock

Older 911s can be fitted w/ them but there are somerissks and drawbacks to using them where they weren't designed in.

As you indicated one of the best potential features of coilovers is height adjust-ability, a second is a wider range of spring rates.

[aftermath]

Do they allow you to remove torsion bars?
Is there a good thread on the steps to re-enforce the car to allow for the install\use of coil overs?
Doesnt look like Pelican sells them either.
What are the risks\drawbacks? Is it cost prohibitive to switch to coil overs if your replacing the suspension anyways? I get the impression people would like to upgrade but they dont, why? Cost?

[Quicksilver]

Yes it will mean that you do away with torsion bars but it also means that you are supporting the weight if the car by the shock mounts. This means you will need to reinforce the car. It isn't a trivial project.

[randywebb]

A third is the ability to use differential spring rates based on the amount of displacement of the suspension - see the thinner, differently wound "ends" of the purple springs that Bill posted.

Today, Porsche uses a lot of such tricks - the newr cars depend on the rubber stops for some susp. compliance according a 2-part susp. test in Pano - it was done by an MD and an engineer IIRC -- about 2 years ago. Worth reading.

[hobieboy]

I'll let the expert chime in but this is what I understand...

Besides ride height & spring rate that Bill talked about, some system also have adjustable rebound/damping rate. All these are features not easily (or possible) done with torsion bar.
I think most shy away because of price.

Wrt chassis reinforcement - I'm on the page that the suspension point was not designed to take "vertical" load. So, can you remove the torsion bars? Yes. Will it cause long term issue, IMHO, yes. I have heard there are many out there who did this without reinforcements and have no problems. But I'm not comfortable with the idea.

[Bill Verburg]

Originally posted by hobieboy
I'll let the expert chime in but this is what I understand...

Besides ride height & spring rate that Bill talked about, some system also have adjustable rebound/damping rate. All these are features not easily (or possible) done with torsion bar.
I think most shy away because of price.

Wrt chassis reinforcement - I'm on the page that the suspension point was not designed to take "vertical" load. So, can you remove the torsion bars? Yes. Will it cause long term issue, IMHO, yes. I have heard there are many out there who did this without reinforcements and have no problems. But I'm not comfortable with the idea.

Adjustable shock rates, rebound or compression, have nothing to do w/ coil overs.

Koni, Leda and Fox all have adjustable 911 dampers for t-bar suspension.

Not all coil overs include adjustable damping either, the higher end products from Bilstein(PSS9), JIC, Moton etc. do. But there are many that do not like Bilstein HD. Yes, the multi adjustable systems are very expensive and not for everyone.

Coil overs for 911 started as helper springs to get higher rates than could be obtained form t-bars alone.

[Zeke]

Easiest definition: coil (spring) over (shock). If you look around in the archives a bit, you will see conversions. Some of the reinforcement recommended is not all that difficult for a fabricator of modest talent. Many times, though, this conversion accompanies installation of a multi point roll cage and the suspension points in question here are picked up into the cage structure. This gives the car a lot less body flex as well as the needed reinforcement. After all, a real trick set up on just a street car may be lost in terms of the added performance. A significant amount of work for only the ease of adjustment.

Some threads posted in the past were authored by "Tyson Schmidt." Refer to "BBII" in your search. (BTW, I don't mean to infer that Tyson is of "modest talent." Quite the contrary.)

[Jack Olsen]

There is pretty much zero benefit to making the change unless you are racing the car. Coils allow stiffer spring rates than the thickest torsion bars. Going that stiff doesn't make much sense for street use. Plus, coils reduce wheel and tire clearance in the front, and require dropping the engine and welding in reinforcements around the rear crossmember.

For track use, the advantages are: easy and quick height adjustment, the ability to quickly change springs out, and (as mentioned above) the ability to run stiffer spring rates than available torsion cars allow.

People who do it for the bling factor confuse me. I got rid of my coils in the front in order to fit wider wheels and tires.

[randywebb]

"People who do it for the bling factor confuse me."

- And you live WHERE???

It's the Bling Center of the Universe. How can you be confused?

[Brant]

Regarding the pro's and con's
here are a few:

con
- generally not legal for stock type racing
- moves weight higher up in the chassis and increases the amount of unsprung weight
- alot of expense for zero gain if you continue to use streetable spring rates
- I would argue that the front ride height is as difficult or perhaps more difficult to adjust with a coil over.

pro's
- bling
- alows quicker spring rate changes. In fact this is one of two only REAL arguements for using a coil over. If you go to a track event and swap your spring rates 2 or 3 times a weekend, then yes you want a coil over
- REAL arguement #2, coil over spring rates come in a greater range and selection.

converting a street car to coil overs puts you into the bling catagory and causes racers to laugh behind your back
brant

[lfot]

Originally posted by Brant
converting a street car to coil overs puts you into the bling catagory and causes racers to laugh behind your back
brant

hahaha

but don't you need the coil-overs so that your ginormous wing won't look out of place on you '93 civic?

[Zeke]

Well, I'm not laughing at anyone who undertakes such a project. Maybe the thread starter is unaware of the fact beginning with the 964 model, the 911 had coil springs. Still does. And, the 914 had them in the rear from 1970. The earlier 911 just wasn't designed for them, not that they aren't an improvement, properly installed.

Now, I have to ask about the dynamics of the coils aside from being able to have much heavier ratings. It seems to me that the torsion bar is limited to a certain set of characteristics, whereas the coils have become rather sophisticated in design using progressive winding, etc. From my vantage point, today's coil springs are not your father's springs.

Can some engineers help on this perspective?

[lfot]

Originally posted by milt
From my vantage point, today's coil springs are not your father's springs.

Can some engineers help on this perspective?

I'm curious as well, however, the thread starter was asking about their car. To this point it seems the real answer is that you'd be getting into the land of diminishing (or completely negative) returns if converting a torsion based suspension for a street car.

my 2¢
Now...

on to the engineering!

[randywebb]

Look up, young Jedi....

Originally posted by randywebb
A third is the ability to use differential spring rates based on the amount of displacement of the suspension - see the thinner, differently wound "ends" of the purple springs that Bill posted.

Today, Porsche uses a lot of such tricks - the newr cars depend on the rubber stops for some susp. compliance according a 2-part susp. test in Pano - it was done by an MD and an engineer IIRC -- about 2 years ago. Worth reading.

[Shuie]

I put them on the rear of my car for no good reason. My intention was to get a spring that was the equivalent of my old 28mm t-bars, so I think the springs are 225lb. Call it bling, or whatever, I could care less, I just wanted them. They are lighter than a strut/t-bar setup and easier to adjust. Its an easy enough mod for the next owner to undo if they don't like it.

[dentist90]

You can get more progressive spring rates (ie non-linear) from coil springs. This would be of more benefit on the street, though. Small bumps and dips in the road would be absorbed by the tighter windings, while full support would only be provided under extreme cornering or braking. I would think for track use you would want fairly stiff spring rates at the sacrifice of a comfy ride over washboard surfaces.
Changing ride height with torsion bars isn't overly difficult. Getting your corner balance back is. But changing the springs to stiffen the ride is a fair bit easier than changing torsion bars (again with the corner balance issue).

[garibaldi]

Me in my younger, stupider days...decided it would be a great idea to install coilovers on my 77 911 turbo, but not just any setup, I yanked everything out and did ERP 935 spring plates in the rear, monoballs on all the joints from and back, Smart Racing 31 mm sway bars from and rear, with Bilstein RSR threaded shocks and struts with RSR valving and 425/550 springs.....and didnt reinforce anything....oh, and all on a daily driven 2400 lbs 400 hp 930....and did I mention that I live in the tri state area...about 20 minutes from manhattan...so the roads are tip-top around here. Needless to say, the first time I pulled into a steep driveway, I literally tore the rear sway bar mount clen off the chassis, and then this other time at 1 am in the middle of the ghetto in Newark, I went over an expnasion joint in the road that busted the entire rear upper shock mount inside the engine compartment off the chassis and sent the top of the rear shock piston poking through the rear firewall and suck the ass of the car down so the tire was resting on the underside fo the rear flare. So reinforce I guess is what Im trying to say....or drive on a pool table

[mmastro]

Originally posted by garibaldi
Me in my younger, stupider days...decided it would be a great idea to install coilovers on my 77 911 turbo, but not just any setup, I yanked everything out and did ERP 935 spring plates in the rear, monoballs on all the joints from and back, Smart Racing 31 mm sway bars from and rear, with Bilstein RSR threaded shocks and struts with RSR valving and 425/550 springs.....and didnt reinforce anything....oh, and all on a daily driven 2400 lbs 400 hp 930..............So reinforce I guess is what Im trying to say....or drive on a pool table

I took that advice, too. when I talked to you regarding coil overs! Ha Ha Ha! But I DID reinforce the $hit out of the rear towers.

I still am running this same setup on my 77 930 and couldn't be happier! On the track it feels stuck to the race surface...on the street I do suffer from the-not so-maintained roads in LA, but who cares? I don't! Rear torsion bars were always a royal pain in the a$$ to adjust ride height.

Bling? ok,.... laugh behind my back.....I wouldn't hear you anyway over my fire-belching exhaust!

Cheers!

[Brant]

So are you guys adjusting your ride heights once a week?

perhaps changing your spring rates every weekend?

that extra reinforcement weight makes it hard to hit 1837#

brant