Spring rate advice Options

[BlueRidge914]

I’d be grateful for some spring rate advice for my vintage race 914.
It’s a narrow body 2L six, 205/50 tires all around. Front torsion bars with adjustable sway bar. Rear is Bilstein Sports with adjustable spring perches, and a fixed sway bar.
My personal preference leans to a relatively softer spring all around.
Any recommendations for both torsion bar size and rear spring rate?
Thanks!
Gavin
VARAC #58

[brant]

What diameter front torsion springs do you have?

We run 911 front torsions which are bigger than -4

I currently run 21mm hollow front with 275lb rear

Brant

[BlueRidge914]

It was more than twenty years ago since I installed the front T-bars and rear springs (shocks and struts have been replaced), and I can’t recall what rates they were Brant. I think the springs are 250. I’d like to go hollow and move from 2.5” to 2.25” rear springs, no helpers as the rear sway bar keeps the back end flat.
Your combination sounds good. Still on the soft side that I prefer relative to current practice of going stiffer .
Thanks Brant

[slivel]

I believe that you get performance gains by going as stiff as possible but not so stiff that you are bouncing over rough pavement. Stiffer helps to prevent front end dive under braking and rear end squat under acceleration while keeping the balance close to what the chassis has statically.

The tracks that I frequented were pretty smooth and I did not feel like changing out my suspension from track to track. Final race configuration for my car had 450 front and 400 rear. The car and driver are now retired and I have softened the suspension by using stacked springs giving me a progressive rate.

For what it's worth, I'll attach my spec sheet and a suspension worksheet.
 1975_Porsche_914rev16.pdf ( 69.19k ) Number of downloads: 1871

 Suspension_for_914_world.pdf ( 200.22k ) Number of downloads: 2217

[yeahmag]

What type of racing? What tires? Do you have an LSD?

[BlueRidge914]

Tires are 205/50x15 all around, treaded - no slicks, as per vintage race rules.
WaveTrac in the gearbox.
Tracks are mostly fast and smooth (CTMP Mosport home track), but also some shorter, bumpier tracks.
I’m not unhappy with the car’s handling, but since it’s all I’ve raced for so many years, I may not know what I’m missing. But it’s time for a refresh anyway.
I’m not aiming for big changes like Vons and 935 style fronts, but what works for spring rates on a generally original suspension setup.
Thank you!

[campbellcj]

I believe that you get performance gains by going as stiff as possible but not so stiff that you are bouncing over rough pavement. Stiffer helps to prevent front end dive under braking and rear end squat under acceleration while keeping the balance close to what the chassis has statically.

The tracks that I frequented were pretty smooth and I did not feel like changing out my suspension from track to track. Final race configuration for my car had 450 front and 400 rear.

Mine was set up for primarily track use along similar principles and IIRC has 22mm hollow 911 t-bars and 350 rears (may be 300 or 325). Very flat and stable on track (or canyons), but nearly intolerable for street use.

[BlueRidge914]

That is great advice - thanks. And sort of what I was thinking.
One more race, then probably 22mm hollow bars and 300lb rear springs (keeping the rear sway bar) over winter. I’ve raced this car 25 years, and I don’t think big changes would make it any more fun for me.
Gavin

[yeahmag]

I think what Chris says is a good place to start. Treaded tires, even race tires will produce less grip than slicks. I'm running A7's, 450's, a stock rear sway bar, and custom Penske shocks on mine for autocross and I like it. Might try to lower the spring rate a bit to something like 350-400 now that the bar is in and the shocks actually do their job.

[Thorshammer]

There’s a bit more to consider when choosing spring rates.

What bushings/bearings
Are the rear trailing arms reinforced properly (and that’s not by wrapping them in 10+ lbs of perforated steel)
The anti roll bars: what are they riding in, and how well do they rotate and is their geometry reasonable
Are the shocks standard off the shelf… remember, if the rebound isn’t matched to the spring rate, there can be a some negative heave effect. So, in some cases, if you can’t control the heave, due to an insignificant damper, choosing a spring rate that matches the damper, will yield better performance overall

However:

21/225 or 21/250 works nicely IMO

[BlueRidge914]

There’s a bit more to consider when choosing spring rates.

What bushings/bearings
Are the rear trailing arms reinforced properly (and that’s not by wrapping them in 10+ lbs of perforated steel)
The anti roll bars: what are they riding in, and how well do they rotate and is their geometry reasonable
Are the shocks standard off the shelf… remember, if the rebound isn’t matched to the spring rate, there can be a some negative heave effect. So, in some cases, if you can’t control the heave, due to an insignificant damper, choosing a spring rate that matches the damper, will yield better performance overall

However:

21/225 or 21/250 works nicely IMO

Thanks for this.
So to answer your questions:
Rear trailing arms were reinforced around 30yrs ago the add sheet metal way. Is the other way you refer to the method Tangerine uses ie cut open and reinforced internally?
ARB in front is the Elephant hollow adjustable with teflon bushings. Rear is a stock OEM bar. All set up at least 20years ago.
Shocks front and rear are Bilstein Sports. Fronts were custom valved by Rebel, also many years ago. Spindles raised 19mm with Rebel bump steer kit. Small steering rack lift.
Solid monoballs front and rear. Front is Rebel adjustable.
21mm solid front torsion bar with Rebel solid bushings.
Rear springs are 275lb 2 1/4” adjustable perch, helper springs, thrust bearings.
I’ve raced this car 25 years with basically the same setup. So I don’t know what I may be missing!
I have contemplated the Rebel 935 style kit, but don’t know if that’s worth it (for me - a true vintage, vintage racer)
Any thoughts about what I might change/upgrade?
Much appreciated.
Gavin

[slivel]

So to answer your questions:
Rear trailing arms were reinforced around 30yrs ago the add sheet metal way. Is the other way you refer to the method Tangerine uses ie cut open and reinforced internally?
ARB in front is the Elephant hollow adjustable with teflon bushings. Rear is a stock OEM bar. All set up at least 20years ago.
Shocks front and rear are Bilstein Sports. Fronts were custom valved by Rebel, also many years ago. Spindles raised 19mm with Rebel bump steer kit. Small steering rack lift.
Solid monoballs front and rear. Front is Rebel adjustable.
21mm solid front torsion bar with Rebel solid bushings.
Rear springs are 275lb 2 1/4” adjustable perch, helper springs, thrust bearings.
I’ve raced this car 25 years with basically the same setup. So I don’t know what I may be missing!
I have contemplated the Rebel 935 style kit, but don’t know if that’s worth it (for me - a true vintage, vintage racer)
Any thoughts about what I might change/upgrade?
Much appreciated.
Gavin
[/quote]

If you make a significant change, be prepared to spend some time in development mode. If the car feels balanced and predictable, why change? You say that your vintage racing organization limits your tire so that is a major constraint. If your tire data shows even wear and temps across the tread, I would say you have optimized your setup. If your organization allows for changing suspension pickup points, you probably could achieve better performance but at the cost of being in development mode. For racing I observed a big improvement when I went to the Elephant poly bronze bushings on the rear. Soft bushings deform under side load during cornering and give unwanted changes in toe. It wasn't clear if you had done the rear of your car with high performance bushings. My shocks are also Bilstein's and were custom valved by Bilstein. I worked with one of their shock engineers and they rebuilt all four corners for me. Unfortunately they don't provide this service any longer.

[BlueRidge914]

[quote name='slivel' date='Jan 31 2026, 03:17 PM' post='3243045']
So to answer your questions:
Rear trailing arms were reinforced around 30yrs ago the add sheet metal way. Is the other way you refer to the method Tangerine uses ie cut open and reinforced internally?
ARB in front is the Elephant hollow adjustable with teflon bushings. Rear is a stock OEM bar. All set up at least 20years ago.
Shocks front and rear are Bilstein Sports. Fronts were custom valved by Rebel, also many years ago. Spindles raised 19mm with Rebel bump steer kit. Small steering rack lift.
Solid monoballs front and rear. Front is Rebel adjustable.
21mm solid front torsion bar with Rebel solid bushings.
Rear springs are 275lb 2 1/4” adjustable perch, helper springs, thrust bearings.
I’ve raced this car 25 years with basically the same setup. So I don’t know what I may be missing!
I have contemplated the Rebel 935 style kit, but don’t know if that’s worth it (for me - a true vintage, vintage racer)
Any thoughts about what I might change/upgrade?
Much appreciated.
Gavin
[/quote]

If you make a significant change, be prepared to spend some time in development mode. If the car feels balanced and predictable, why change? You say that your vintage racing organization limits your tire so that is a major constraint. If your tire data shows even wear and temps across the tread, I would say you have optimized your setup. If your organization allows for changing suspension pickup points, you probably could achieve better performance but at the cost of being in development mode. For racing I observed a big improvement when I went to the Elephant poly bronze bushings on the rear. Soft bushings deform under side load during cornering and give unwanted changes in toe. It wasn't clear if you had done the rear of your car with high performance bushings. My shocks are also Bilstein's and were custom valved by Bilstein. I worked with one of their shock engineers and they rebuilt all four corners for me. Unfortunately they don't provide this service any longer.
[/quote]
Your point that if it works well, why change is right on - and far too sensible! Our prep rules have changed from a 1972 cut off to build to what was available up to 1979.

Regarding rear suspension: I also have Tangerine solid trailing arm brackets, and Rebel hollow pivot shafts for bushings.

I need treaded tires, and currently run Nittos. The new Hoosiers sound fantastic, but at twice the price I can’t justify it. Maybe someday.
Thanks for the input.
Gavin

[Thorshammer]

Ok,

The next step is a leap in faith, also in money. I would consider this two ways. General improvement, or a full assault.

General improvement: reduce unsprung mass, reduce friction in all joints, properly strengthen areas.

-Tangerine racing builds some outer suspension mounts, that do not flex. The stock units flex a great deal
-again TR for a set of proper trailing arms. His research was proper, and as we discussed the issues, and my experience with motorcycle swing arms, and how we used to pass tubing through the arms, and weld, he built fixtures, and really came up with proper solutions that have been tested and confirmed, they are right.
-Find, buy, build, copy the Shine Racing services Nadella needle bearings. When Dick Shine (his real name) built these, it addressed a multitude of issues, strength, friction
-not sure what your rear bar is rotating in, but the links need to be heims, and the main bar must rotate without friction… but we never ran them… ever

Front:

-Get rid of the torsion bars. And go to coils
-the front suspension a-arms also need needle bearings… shine again, if you can find them… otherwise, the ERP stuff, is nice, as is Tarrets (Ira has done a great job with his company)
-front sway bar: key piece of kit: I like the .100 wall speedway bar mounted in needle bearings. Some key fab here, pay attention to the angles.

Now.. if price is not a concern:

Tractive dampers… although their customer care sucks, their product is extremely well performing.

Raise the rear suspension pickup points 3.0 inches… TR has a kit
Ask if TR will reclock a set of trailing arms to alter the IC…. Some blind trust in what he did 20+ years ago… it’s right, it works… you will find the same concept in the Finch/Hotchkiss/Kirby 914.

300 lbs fronts, 300 lbs rears…

Slicks…

[brant]

Ok,

The next step is a leap in faith, also in money. I would consider this two ways. General improvement, or a full assault.

General improvement: reduce unsprung mass, reduce friction in all joints, properly strengthen areas.

-Tangerine racing builds some outer suspension mounts, that do not flex. The stock units flex a great deal
-again TR for a set of proper trailing arms. His research was proper, and as we discussed the issues, and my experience with motorcycle swing arms, and how we used to pass tubing through the arms, and weld, he built fixtures, and really came up with proper solutions that have been tested and confirmed, they are right.
-Find, buy, build, copy the Shine Racing services Nadella needle bearings. When Dick Shine (his real name) built these, it addressed a multitude of issues, strength, friction
-not sure what your rear bar is rotating in, but the links need to be heims, and the main bar must rotate without friction… but we never ran them… ever

Front:

-Get rid of the torsion bars. And go to coils
-the front suspension a-arms also need needle bearings… shine again, if you can find them… otherwise, the ERP stuff, is nice, as is Tarrets (Ira has done a great job with his company)
-front sway bar: key piece of kit: I like the .100 wall speedway bar mounted in needle bearings. Some key fab here, pay attention to the angles.

Now.. if price is not a concern:

Tractive dampers… although their customer care sucks, their product is extremely well performing.

Raise the rear suspension pickup points 3.0 inches… TR has a kit
Ask if TR will reclock a set of trailing arms to alter the IC…. Some blind trust in what he did 20+ years ago… it’s right, it works… you will find the same concept in the Finch/Hotchkiss/Kirby 914.

300 lbs fronts, 300 lbs rears…

Slicks…

So much of those modifications are not legal in many vintage clubs
I second the roller
Bearings

[yeahmag]

I ran the rear roller bearings and greatly prefer the Rebel Racing teflon rears (and fronts). The fretting ends up wearing the needles and races and introduces slop. I' haven't had that issue with the teflon ones and I'm running A7's. LOTS of side loading happening.