Aftermarket swaybar sizing for longhoods

[Tremelune]

I have a 1970 911T with no sway bars. It weighs 2400lb with a driver and full tank of gas. The torsion bars are stock, at 19/23.

I'd go with stock sways (15mm), but they're not cheaper and they're not adjustable, and they're harder to source, so I was looking around at aftermarket alternatives...They seem to be designed for much heavier cars that came stock with 19mm or 21mm sways, and I think I would rather be under-swayed than over...

How do I gauge the stiffness of these bars (and what would be appropriate)? Is there a way to make an apples-to-apples comparison? If I knew the "softest" settings were softer than stock 15mm bars, it'd be easier, but there's no "spring rate" numbers I can look at for any of these things...

Car is a canyon carver that sees lots of crappy city roads and potholes...It's exceedingly rare for me to be sliding tires such that there is understeer or oversteer for me to think about.

[HarryD]

My mostly stock 1973 (Turbo T-bars) has 19 mm adjustable sways (Weltmeister) front and rear. They work great (I autocross and HPDE) and provide that extra bit of control you want.

[gtc]

I asked a similar question years ago (comparing through body to underbody sway bars) and didn't get a straight answer. But if you are comparing two through body sway bars, all you should need is the lever arm length and bar diameter for both to make a reasonable comparison.

[Trackrash]

My '71 came with no sways when I got it. I put on 19mm sways with the fronts being adjustable. Worked well and seemed to be a good match with the stock torsions and koni red shocks.

[Cory M]

You should reach out to Tarett Engineering. Their standard bars are 22 mm but they have made 19mm as well in smaller batches. They have a very wide range of adjustment.

[Tremelune]

I believe the Tarett bars are the ones Elephant sells? They suggested I go with 21mm, but then were very surprised by the weight of my car...Evan says that 19 and 21 are almost the same at their softest setting. I dunno.

[doswald]

I'm in the same boat with my '71T, except I've upgraded torsion bars to 21mm front and 26mm rear. Is there a rear 15mm adjustable sway available? How does the rear 19mm adjustable sway on its softest setting compare to a fixed 15mm?

Thanks for the help!

dho

[HarryD]

Originally Posted by doswald

I'm in the same boat with my '71T, except I've upgraded torsion bars to 21mm front and 26mm rear. Is there a rear 15mm adjustable sway available? How does the rear 19mm adjustable sway on its softest setting compare to a fixed 15mm?

Thanks for the help!

dho

I have same size torsion bars on my 1973 with Weltmeister adjustable 19 mm sway bars. I have had no issues and my handling is neutral.

[Bill Verburg]

Originally Posted by Tremelune

I have a 1970 911T with no sway bars. It weighs 2400lb with a driver and full tank of gas. The torsion bars are stock, at 19/23.

I'd go with stock sways (15mm), but they're not cheaper and they're not adjustable, and they're harder to source, so I was looking around at aftermarket alternatives...They seem to be designed for much heavier cars that came stock with 19mm or 21mm sways, and I think I would rather be under-swayed than over...

How do I gauge the stiffness of these bars (and what would be appropriate)? Is there a way to make an apples-to-apples comparison? If I knew the "softest" settings were softer than stock 15mm bars, it'd be easier, but there's no "spring rate" numbers I can look at for any of these things...

Car is a canyon carver that sees lots of crappy city roads and potholes...It's exceedingly rare for me to be sliding tires such that there is understeer or oversteer for me to think about.

When tuning the suspension for handling of the 911 first get the T-bars right(assuming that the wheel/tire package is optimal)

for street use it's hard to justify going beyond 20/26 or 21/26

then tweek w/ the sways

balance f/r isn't hard to do, the big thing is the amount of body roll which causes all sorts of bad thing to happen, how bad depends on your speed, the road specifics and individual taste

The idea of sways is merely to control body roll and hence negative suspension responses to cornering on smooth roads

going too big makes any rough road use worse no matter the smooth road balance, it's similar to going too big w/ t-bars

What you are looking for is a minimal leash placed on body roll in corners, w/ as little input as possible the rest of the time.

Other things that limit body roll are the geometry of suspension components at the installed ride height, lower the car a little and rack spacers are needed, lower more and the spindles will need to be raised, the effect of this is to reduce the lever arm causing roll. If not implemented the lever arm on lowered cars is increased causing more roll for the same suspension spec.

Once the suspension geometry is as good as can be arranged then do the t-bars for balance, again 20/26 or 21/26 max for street use

then the smallest sways possible to limit any residual objectionable roll on smooth roads

the lighter the chassis the smaller the bar necessary and again way better to err small than to err big

[doswald]

Thank you for the responses Harry and Bill. I'd like to stay focused on Tremelune's initial question. Taking Bill's statements, "the smallest sways possible" and "better to err small than to err big", which is a better fit for a longhood: nonadjustable 15mm; or adjustable 19mm on the lightest setting?

dho

[Bill Verburg]

Originally Posted by doswald

Thank you for the responses Harry and Bill. I'd like to stay focused on Tremelune's initial question. Taking Bill's statements, "the smallest sways possible" and "better to err small than to err big", which is a better fit for a longhood: nonadjustable 15mm; or adjustable 19mm on the lightest setting?

dho

for most people and w/ stock t-bars for street use it's 6 of one 1/2 dozen of the other, the adjustable gives you more flexibility but few actually need or want to use that feature

Back when I had my '72 I put H&H Carrera adjustable on it w/ stock, never touched them after the install, this was w/ stock t-bars 7& 8x 15s 205/55 an 225/50 tires

[3rd_gear_Ted]

Here are T- bar to coil over rates for G-body cars as measured by the S.A.E. students who got dynamic with Steve Timmons.
You can also use the Sway away calculator to determine sway bar rates

911CoilConv

https://swayaway.com/tech-room/torsion-bar-wheel-rate-calculator/

[Tremelune]

Originally Posted by doswald

which is a better fit for a longhood: nonadjustable 15mm; or adjustable 19mm on the lightest setting?

The tricky bit with non-adjustable 15s is...where do you get a set in good shape for the same money as the adjustables?

[Cory M]

Originally Posted by doswald

Thank you for the responses Harry and Bill. I'd like to stay focused on Tremelune's initial question. Taking Bill's statements, "the smallest sways possible" and "better to err small than to err big", which is a better fit for a longhood: nonadjustable 15mm; or adjustable 19mm on the lightest setting?

dho

The answer is... yes.

Really there is no perfect answer. We don't even know what kind of tires the car is on. Every driver has different preferences. A rough ride or stiff suspension is very subjective. I adjust my sway bars at practically every track day to tune the handling, so I value the adjustability. I've only adjusted the bars on my street car a few times in a few years. Probably best to just buy what you can find and try it out. Stock sway bars are likely fine here.

[Bill Verburg]

The thing w/ sway bars is that the stiffer it is the more it reduces grip at that end of the car, They take load from the inside wheel, and transfer it to the outside wheel. The more load transfer, the less grip.

Ideally you want an active sway bar that adjusts itself to conditions, These are becoming more common these days, barring that no bar or the least intrusive bar is desired unless, there is so much roll that geometry of the wheel wrt the chassis and ground goes out the window and reduces grip even more

Get the wheels/tires right get the suspension springing right, get the shocks right get the bushes right get the basic alignment spec right and then use the smallest least intrusive bar possible