Suspension gurus - Critique my plans, please...

[fanaudical]

I'm planning on rebuilding my suspension this coming winter and figured I'd start planning/buying parts now.

Our subject is a '75 Targa 911S with factory Koni's and otherwise stock suspension, running 195/65R15's on all corners. It's equipped with 20mm sway bar front and 18mm sway bar rear. I have no idea which torsion bars are installed. I doubt the suspension has ever been touched except for repair of a broken rear sway bar mount. This is a 2.7l car that I've rebuilt; it weighs just under 2600 lbs loaded with passengers last time I had it on a truck scale.

The car gets used for "fun" - weekend drives on twisty roads, occasional road trip, almost zero track time. Road quality in the PNW is deteriorating.

I've read through many of the suspension rebuild threads here (all great info).

My current plans:

Shocks: Keep the Koni's; maybe upgrade to the Koni Sport's with the externally-adjustable rebound knobs to allow some easier suspension tuning. My understanding is that it is less expensive to purchase new shocks than attempt rebuild of the existing shocks.

Bushings: Use Elephant Racing rubber bushing for the front A-arms. Use Powerflex street bushings for the rear trailing arms.

Sway Bars: Keep the stock sway bars but rebush with Powerflex street bushings.

Steering: Replace the tie rods with the turbo tie rod kit.

Rear: Replace the existing non-adjustable rear spring plates with some adjustable spring plates from a later 911.

Front: Am considering replacing the stock upper strut mount with Rennline monoballs (just so this is bulletproof).

Alignment: Following all this, I'll get it as close as I can in the garage and then submit to a local shop that is good at this stuff for corner balance/alignment.

My questions:

Does anybody have any recommendations on the Koni Classic vs Koni Sport decision? I've read here that the Sports may be too stiff (even when set to soft) for older 911's.

In the event I pull the torsion bars and find enough corrosion to warrant replacement, are there any suggestions for which bars to use?

Any comments/suggestions on the rest?

Thanks for the help.

[RSTarga]

Originally Posted by fanaudical

I'm planning on rebuilding my suspension this coming winter and figured I'd start planning/buying parts now.

Our subject is a '75 Targa 911S with factory Koni's and otherwise stock suspension, running 195/65R15's on all corners. It's equipped with 20mm sway bar front and 18mm sway bar rear. I have no idea which torsion bars are installed. I doubt the suspension has ever been touched except for repair of a broken rear sway bar mount. This is a 2.7l car that I've rebuilt; it weighs just under 2600 lbs loaded with passengers last time I had it on a truck scale.

The car gets used for "fun" - weekend drives on twisty roads, occasional road trip, almost zero track time. Road quality in the PNW is deteriorating.

I've read through many of the suspension rebuild threads here (all great info).

My current plans:

Shocks: Keep the Koni's; maybe upgrade to the Koni Sport's with the externally-adjustable rebound knobs to allow some easier suspension tuning. My understanding is that it is less expensive to purchase new shocks than attempt rebuild of the existing shocks.

Koni's were not available on a Targa, but I like them. Don't go sport. Just buy new.

Bushings: Use Elephant Racing rubber bushing for the front A-arms. Use Powerflex street bushings for the rear trailing arms.

I used Elephant rubber for all bushings the sport stiffness.

Sway Bars: Keep the stock sway bars but rebush with Powerflex street bushings.
see above

Steering: Replace the tie rods with the turbo tie rod kit.
great upgrade

Rear: Replace the existing non-adjustable rear spring plates with some adjustable spring plates from a later 911.
Very nice upgrade, get some off a newer 911.

Front: Am considering replacing the stock upper strut mount with Rennline monoballs (just so this is bulletproof).

Use the elephant rubber strut mount.

Alignment: Following all this, I'll get it as close as I can in the garage and then submit to a local shop that is good at this stuff for corner balance/alignment.

My questions:

Does anybody have any recommendations on the Koni Classic vs Koni Sport decision? I've read here that the Sports may be too stiff (even when set to soft) for older 911's.

In the event I pull the torsion bars and find enough corrosion to warrant replacement, are there any suggestions for which bars to use?

On an early Targa don't go above the stock Torsions at the front use the 24.5 or 25 at the rear.

Any comments/suggestions on the rest?

Thanks for the help.

I did all the above on my 73 since our roads are miserably rough. I love the ride, very sporting, not too stiff. put my comments in your quote, sorry.

[fanaudical]

Thanks for the input.

Interesting comment about the Koni's not being an option on the Targa. The car came to me with Koni's on all four corners and S calipers up front. I've never done the COA. I guess it's possible that somebody refitted those...

[tirwin]

Can't help you on the Koni's but I think the adjustability factor sounds like a plus on paper.

I have 21/28 t-bars. My suspension is very similar to Craig_D's setup. If you have not read his thread you should put that on your reading list.

This morning I drove through the North Georgia mountains with a 997 S, a 996, a Cayman and a supercharged M5. My ol' SC hung in there for the most part. I feel pretty certain that there is no way the original suspension would've allowed me to drive like I did today.

The two things that I think I am the most pleased with was the decision to do a digressive curve on the Bilsteins and to raise the spindles to get full suspension travel. I don't know if Koni's can be done on a digressive curve or if you can buy them that way. I am really impressed by how I can hit a bump in the road and the car is not unsettled.

[HarryD]

Originally Posted by fanaudical

I'm planning on rebuilding my suspension this coming winter and figured I'd start planning/buying parts now.

Our subject is a '75 Targa 911S with factory Koni's and otherwise stock suspension, running 195/65R15's on all corners. It's equipped with 20mm sway bar front and 18mm sway bar rear. I have no idea which torsion bars are installed. I doubt the suspension has ever been touched except for repair of a broken rear sway bar mount. This is a 2.7l car that I've rebuilt; it weighs just under 2600 lbs loaded with passengers last time I had it on a truck scale.

The car gets used for "fun" - weekend drives on twisty roads, occasional road trip, almost zero track time. Road quality in the PNW is deteriorating.

I've read through many of the suspension rebuild threads here (all great info).

My current plans:

Shocks: Keep the Koni's; maybe upgrade to the Koni Sport's with the externally-adjustable rebound knobs to allow some easier suspension tuning. My understanding is that it is less expensive to purchase new shocks than attempt rebuild of the existing shocks.

Before you commit, check both options. Many of us like the Bilstiens. HD fronts and sport rears is what I have on my 911.

Bushings: Use Elephant Racing rubber bushing for the front A-arms. Use Powerflex street bushings for the rear trailing arms.

Are you sure you need to replace the front bushes? My car has 160,000+ and my local suspension guru saw no need to replace. I installed Neatrix on my rears about 30k ago and they seem to be fine.

Sway Bars: Keep the stock sway bars but rebush with Powerflex street bushings.

No idea on this.

Steering: Replace the tie rods with the turbo tie rod kit.

I did this when I first bought the car to replace my damaged tie rods. Great improvement.

Rear: Replace the existing non-adjustable rear spring plates with some adjustable spring plates from a later 911.[

Why? Are you existing spring plates in need of replacement? For ordinary use, you don't need to address this that often.

Front: Am considering replacing the stock upper strut mount with Rennline monoballs (just so this is bulletproof).

Why waste the money? You are not racing. Stock suspension parts are just fine for your planned use.

Alignment: Following all this, I'll get it as close as I can in the garage and then submit to a local shop that is good at this stuff for corner balance/alignment.

I like Rothsport for this.

My questions:

Does anybody have any recommendations on the Koni Classic vs Koni Sport decision? I've read here that the Sports may be too stiff (even when set to soft) for older 911's.

In the event I pull the torsion bars and find enough corrosion to warrant replacement, are there any suggestions for which bars to use?

I went to Turbo bars to reduce squat in my car an prevent rubbing in my lowered car. Otherwise, stick with stock.

Any comments/suggestions on the rest?

Thanks for the help.

I suggest you chat with Steve Weiner.

[Driven97]

Originally Posted by fanaudical

Sway Bars: Keep the stock sway bars but rebush with Powerflex street bushings.

I know I've posted this in a few threads, but it's one of the more important lessons I've learned with my car. If you're going to do poly swaybar bushings, you must fit them. They're shipped too large in case of a recessed mounting surface. If you try to just bolt them in, you'll clamp down on your swaybar and it will bind. A rubber bushing can deflect, poly not so much. That'll equal crap ride and handling. This is how bad mine were for a year:



Sand those babies down so that they're not squeezing the bar, it should rotate as free as butter when bolted all the way down. If you don't want to sand them, you can drop some washers in between the bracket and the chassis to spacer it out.

[chrismorse]

Originally Posted by fanaudical

I'm planning on rebuilding my suspension this coming winter and figured I'd start planning/buying parts now.

Our subject is a '75 Targa 911S with factory Koni's and otherwise stock suspension, running 195/65R15's on all corners. It's equipped with 20mm sway bar front and 18mm sway bar rear. I have no idea which torsion bars are installed. I doubt the suspension has ever been touched except for repair of a broken rear sway bar mount. This is a 2.7l car that I've rebuilt; it weighs just under 2600 lbs loaded with passengers last time I had it on a truck scale.

The car gets used for "fun" - weekend drives on twisty roads, occasional road trip, almost zero track time. Road quality in the PNW is deteriorating.

I've read through many of the suspension rebuild threads here (all great info).

My current plans:

Shocks: Keep the Koni's; maybe upgrade to the Koni Sport's with the externally-adjustable rebound knobs to allow some easier suspension tuning. My understanding is that it is less expensive to purchase new shocks than attempt rebuild of the existing shocks.

Bushings: Use Elephant Racing rubber bushing for the front A-arms. Use Powerflex street bushings for the rear trailing arms.

Sway Bars: Keep the stock sway bars but rebush with Powerflex street bushings.

Steering: Replace the tie rods with the turbo tie rod kit.

Rear: Replace the existing non-adjustable rear spring plates with some adjustable spring plates from a later 911.

Front: Am considering replacing the stock upper strut mount with Rennline monoballs (just so this is bulletproof).

Alignment: Following all this, I'll get it as close as I can in the garage and then submit to a local shop that is good at this stuff for corner balance/alignment.

My questions:

Does anybody have any recommendations on the Koni Classic vs Koni Sport decision? I've read here that the Sports may be too stiff (even when set to soft) for older 911's.

In the event I pull the torsion bars and find enough corrosion to warrant replacement, are there any suggestions for which bars to use?

Any comments/suggestions on the rest?

Thanks for the help.

Hi fanaudical,

Most guys seem to be going away from the poly, especially for a street car, quieter, less NVH. I'm doing ER rubber F/R.
At 80k miles of previously sedate driving in mild climates, I found my dad's coupe to have badly worn rubber bushings that allowed one front bar to be badly damaged. I/m going with 21/27 torsion bars. That is about a 60% increase. You may want to stay with stock or go up about half that amount, (try talking to Chuck at ER.)
I also have the 20/18 Carrera bars, but to facilitate corner weighting, I am going to an 85 bar with adjustable ER drop links, (same size bar, but adjustable links).
I am guessing that going to height adjustable spring plates, you will break even, given the time savings when corner weighting.
Turbo tierods are the new standard.
I will be running bilsteins HDs. Going to a more sporting Koni may detract from your ride, but the adjustability would be nice if you are going to ever drive the car more aggressively.
I am going with a sport rubber top strut mount. I decided not to go with the PB or Monoballs to keep the ride more civilized.
Similarly, I will be using sport hardness trailing arm bushings, not monoballs.
Roads in Humble County are going to hell too, so I am going with stock (Euro) height, not lower.

As long as you are in there, you might as well:
Overhaul the steering rack.
Rebush the pedal cluster.
Do the wheel bearings.
Overhaul the brakes.

Chris

[fanaudical]

Thank you very much for the all the input and suggestions.

I'll have to look up about the digressive curve for shocks and look at CraigD's thread.

I don't know if my rear spring plates are worn and require replacement, but I do figure that it will be easier to rebush a second set of plates at my leisure as well as reduce some effort during corner-balance work. My thought is that little upgrades like this can only add value to the car.

I'm going to rebush the front "while I'm in there". Suspension was about the only thing I didn't touch when I reassembled the car. I really wish I had taken the time to do the suspension when I had everything else apart.

Regarding the front upper strut mount, I guess I thought that since the cost of monoballs was not much more than "quality rubber" that the monoballs may be an improvement to ride quality. I guess that they may make ride quality a bit harsher. I'll have to think about this one more.

Torsion bars are still a bit of a mystery to me. I would like to bring the car down to Euro ride height (it's at stock US height now). Do the stock bars work OK at Euro height with a somewhat lighter car?

[Craig_D]

Hi Fanaudical, I'm a little pressed for time at the moment, so I don't have much input at the moment.

Here is a link to my post that I think you may find helpful: '78 SC Elephant Racing Suspension Upgrade

Note: I had the spherical upper strut mono-balls (ER's) and I suggest going with ER sport rubber. I'm not terribly familiar with Targas, but the mono-balls increased the NVH (Noise Vibration Harshness) a lot. Riding over cement road would make the car buzzzzz and didn't add any appreciable crispness to the turn-in or overall handling. I switched out to Elephant Racing sport rubber strut bushings and I love them.

Sways - I would also suggest ER sport rubber bushings all around, and would suggest replacing the stock rear end links with Tarett drop links (available from our host). These made a noticeable difference in crispness and reduced initial body roll from the rear of the car.

Torsion bars and strut inserts/shocks are a matched system. It is best, by far, to save your pennies and go into this having the shocks and springs matched to each other. I'm not very familiar with Koni's in 911s, but I worked with Chuck Moreland at Elephant racing to match my setup for balance. Up front Bilstein strut inserts with a digressive damping curve and 30mm raised spindles matched to 21mm hollow torsion bars. The rears are Bilstein HD shocks with 28mm hollow torsion bar. I'm running stock '88 Carrera (G50) sways with sport rubber and Tarett drop links.

I'm also running on Dunlop Direzza II tires on 7/8x16 Fuchs and the car's weight is 2477 lbs.

I attacked my project with the goal of improved performance everywhere for canyon carving and occasional DE track days, balanced with retaining as much comfort as possible. Success is that I love driving it, and my wife loves being a passenger. I hope this helps.

Cheers,

- Craig_D

[tirwin]

Originally Posted by fanaudical

Thank you very much for the all the input and suggestions.

I'll have to look up about the digressive curve for shocks and look at CraigD's thread.

Are your current struts Bilsteins? If so, talk to Chuck Moreland at ER about re-valving your existing ones on a digressive curve. It is about the same cost (I think it's even a little cheaper) than new ones. Like Craig said, you want to match them to the stiffness of the t-bars. Chuck can advise you on that.

Originally Posted by fanaudical

I don't know if my rear spring plates are worn and require replacement, but I do figure that it will be easier to rebush a second set of plates at my leisure as well as reduce some effort during corner-balance work. My thought is that little upgrades like this can only add value to the car.

If you are tracking the car or AX a lot and you want to experiment then that is really where the value comes in being able to have adjustability. Getting the old bushings off is perhaps my least favorite 911 job ever and I've replaced the headliner before. The spring plates aren't really going to wear out but it is so much easier to put fresh bushings on new spring plates from a time/labor standpoint.

Originally Posted by fanaudical

I'm going to rebush the front "while I'm in there". Suspension was about the only thing I didn't touch when I reassembled the car. I really wish I had taken the time to do the suspension when I had everything else apart.

Regarding the front upper strut mount, I guess I thought that since the cost of monoballs was not much more than "quality rubber" that the monoballs may be an improvement to ride quality. I guess that they may make ride quality a bit harsher. I'll have to think about this one more.

I would listen to Craig's advice here and go rubber instead of monoballs for the upper struts.

Originally Posted by fanaudical

Torsion bars are still a bit of a mystery to me. I would like to bring the car down to Euro ride height (it's at stock US height now). Do the stock bars work OK at Euro height with a somewhat lighter car?

Tread lightly into lowering (speaking as someone who has gone below Euro height). Much has been discussed on this topic in other threads. Lowering changes the control arm geometry which induces bump steer and limits suspension travel. Some lowering is ok but you can also quickly go down a path of diminishing return where the costs increase and the value to you decreases rather quickly.

[Driven97]

Originally Posted by tirwin

Tread lightly into lowering (speaking as someone who has gone below Euro height). Much has been discussed on this topic in other threads. Lowering changes the control arm geometry which induces bump steer and limits suspension travel. Some lowering is ok but you can also quickly go down a path of diminishing return where the costs increase and the value to you decreases rather quickly.

^Very true!

Remember, this is original ride height:

From the C&D road test of a 1978 911SC.

And an '84 Carrera:


Most of us have our cars way, way below ideal height. Suspension geometry suffers, travel suffers, and as a result ride & handling suffer. But it looks good so we lower.

[Trackrash]

Koni classic vs Koni sports? Definitely go with the sports. My experience is there isn't much difference EXCEPT you won't have to REMOVE the shock with the sports to adjust them.

As far as torsions go, you will want bigger. No, you will NEED bigger. I would recommend 21/26 for a street car. If you are going to track or AX then even bigger.

Also, one of your sway bars SHOULD be adjustable.

If you really want to upgrade your handling upgrade to SEVEN inch wide wheels. Seriously.

Otherwise I think you are on the right track.

[RSTarga]

On an Targa for street, you do not want or need Sport shocks at the front, 21 Tbars at the front are too much.
Especially for bad roads.
He wants a street setup for bad roads, if you go stiff, you just bounce from bump to bump. Actually less roadholding.
Maybe the best shocks are the Bilstein HDs at the front and Sports rear.
Don't go below Euro height.

[tirwin]

Originally Posted by RSTarga

On an Targa for street, you do not want or need Sport shocks at the front, 21 Tbars at the front are too much.
Especially for bad roads.
He wants a street setup for bad roads, if you go stiff, you just bounce from bump to bump. Actually less roadholding.
Maybe the best shocks are the Bilstein HDs at the front and Sports rear.
Don't go below Euro height.

Personal opinion here based on my limited experience. I did a lot of reading and sought advice here before going to a 21/28 setup. I was fearful that I was going to make my ride too harsh. That was not the case. In fact the ride quality was a HUGE improvement over the old setup. Why? I think there are 2 reasons.

First, it's hard to compare new components to old worn out components. My old suspension needed a refresh badly.

The second is that I think having my Bilsteins re-valved by Chuck to match the t-bars makes a huge difference.

The lesson I learned is that you have to treat the entire suspension as a system and if you choose the components of the system well, you can get a good result.

[Driven97]

Chuck did a decent job on my front valving but I was very disappointed by how much he missed with the rear. Scrapping his rear valving was one of the better things I've done with my car for both ride and handling. IMHO, YMMV, and all that jazz.

28mm rears, assuming you have a not significantly lightened car, *should* be very reasonable. That's near the bottom of the range of ride stiffness for a modern sporty car.

Even the factory front torsions, however, are somewhat on the stiff side as far as ride is concerned. Moving to just 21mm ones makes them 166% as stiff as OE on top of that.

[fanaudical]

Thanks again for all the input. I learned a few things here that I need to research some more. I hadn't that considered transmission of road vibration increases with the monoballs.

That ride height pic looks very similar to my car. I always think my Targa is standing too tall. I don't intend to go below Euro height (I do like some clearance for the areas in which I drive).

Is there an easy way to determine which torsion bars are installed without disassembling everything first?

[tirwin]

Originally Posted by Driven97

^Very true!

Remember, this is original ride height:

From the C&D road test of a 1978 911SC.

And an '84 Carrera:


Most of us have our cars way, way below ideal height. Suspension geometry suffers, travel suffers, and as a result ride & handling suffer. But it looks good so we lower.

Here's my below Euro height for visual comparison purposes.

[Craig_D]

Originally Posted by Driven97

^Very true!

Remember, this is original ride height:

From the C&D road test of a 1978 911SC.

And an '84 Carrera:


Most of us have our cars way, way below ideal height. Suspension geometry suffers, travel suffers, and as a result ride & handling suffer. But it looks good so we lower.

This is somewhat mis-information. Sorry, but the American market ride height was RAISED passed optimum because of bumper height regulations in the US requiring the cars to be raised above Euro spec, and spacers added to fill in the gap in the front struts.

Next, and Tirwin understands this, that raising the spindles lowers the car (by raising the front wheels) while maintaining optimal travel, steering and suspension geometry.

Raised spindles was how the factory lowered their RSR race cars while keeping the proper steering/suspension geometry.

If you're lowering your car without raising your spindles, then yes, you can put yourself into sub-optimal geometry territory. Making a rally 911? ...lower the spindles to raise the car and keep optimal geometry along with longer travel.

Look at what the Porsche factory did when they raced their RSRs with raised spindles.

[Driven97]

Originally Posted by Craig_D

This is somewhat mis-information. Sorry, but the American market ride height was RAISED passed optimum because of bumper height regulations in the US requiring the cars to be raised above Euro spec, and spacers added to fill in the gap in the front struts.

US cars were raised 75-82 only, 83 was back down to ROW ("Euro") height per the Porsche 911 Red Book. So the black '84 pictured is indeed Euro height. White car is in the weird US raised range.

[RSTarga]

I never understood why the Feds mandated bumper height without making it standard across all licensed vehicles. We have pickups running around here where the bumpers are eye level for us. Don't understand how that can be legal for street use, but at least here in Texas, it is.
Scary to think what about head on with one of these.