quote Originally posted by cvxjet: I have been into handling since I was into cars.... I have been thinking of how suspension works for a long time...

Okay, I'd love to get your (and anybody else's) feedback on how replacing OEM rubber sway bar mount bushings with poly bushings affects handling. I've been led to believe for years here that poly sway bar bushings would help stiffen the suspension. When I stated this in a well known Subaru forum, I was "schooled" by a member there who insisted that rubber bushings effectively increased the sway bar's diameter (compared to poly) due to the rubber bushings "gripping" the bar. In all the years I've been here at PFF, I don't recall this argument ever being put forth.

The fella who wished to "school" me appears to be educated on the matter, but I'm also familiar with the expression... bullsh!t baffles brains.

I'd appreciate it if several of you could have a look at This thread. My user name there is Vancouver98STi, and the action picks up at post #8 (although I first appear in post #4). My nemesis in this thread is mrsaturn7085.

quote Originally posted by mrsaturn7085: ...the factory bar twists the rubber bushing in place. Aftermarket urethane allows the bar to freely spin in the mount. The rubber resists twisting which increases effective diameter slightly. Free rotation in the bushing (urethane/bearings) reduces twisting resistance.

Once the discussion on this starts, it goes on quite a bit... but I believe it's entertaining, and maybe even informative!

Have I been mistaken all these years? Please let me know.

[This message has been edited by Patrick (edited 12-07-2017).]

Good question that you asked about the actual amount of surface movement of the sway bar at the mounts. It's about 1/8" for the average sway bar.

You might want him to up the input loads and allow the rubber bushings to deflect as they normally would in a car, ie, the side going up crushes that rubber bushing and vice versa on the other side, adding non-effective deflection to the equation. 10 NM is about 7 ft.lbs which is a very small force. Resisting 2 degrees of roll in a 3000 lb car with a centre of gravity that is 17" above the ground, a weight distribution of 53/47 with a 5% front roll resistance bias and has a track width of 72" while acting through a motion ratio of 0.5 is the range you want to ask about. Then ask how much reduction in force the crushed rubber bushings would account for compared to non-compressed bushings under the same conditions, and what the relative sway bar diameters would be to compensate for that crush.

I'm curious to see what he comes up with; could be that he's right.

Eliminating the sway bar mount deflection and also the end link deflection by using urethane or solid material allows the sway bar to be effective as soon as the car starts to roll. While the different durometers of rubber available can be used to tune the sway bar effectiveness via compliance, I prefer to go the simpler route and sidestep the issue by getting rid of the rubber. I don't think he would disagree with that.

[This message has been edited by mender (edited 12-07-2017).]

[This message has been edited by cvxjet (edited 12-08-2017).]

quote Originally posted by Patrick: Once the discussion on this starts, it goes on quite a bit... but I believe it's entertaining, and maybe even informative! Have I been mistaken all these years? Please let me know.

Patrick,

No way! The theory that it increases diameter because the rubber "grips" the bar would probably cause such a small amount of difference it wouldn't even be measurable. On that note, even if it did make a difference in the slightest, it would only be a verrrrrrrry temporary phenomenon; as the rubber "gripping" the bar has such a small contact area that it would slip rather rapidly. (I.E. putting a skinny bicycle tire on a 400 HP Corvette, fatter tires are needed for the forces exerted) One should also assume that the sudden flex of the softer rubber would cause part of the bushing to lose contact with half the bar, on the loaded side of the bushing mid turn...

It's nonsense IMO. If he wants to make that claim then I need more evidence than just a theory of what probably happens under ideal conditions.

More "what ifs"; take for example a 35mm sway bar will flex the same amount as a 35mm sway bar every time, no matter the bushing it's sitting in. by that similar logic, one can argue that we can simply weld together a bunch of beer cans and use that as a driveshaft. This theory will obviously not work, the cans will fail and twist into a mangled mess the second you press the gas pedal; why? Because the amount of metal used is too thin are not strong enough to handle the force, the only way to combat that is more thickness, IE strength to deal with the forces exerted here. While not exactly the same point he is trying to make, a rubber bushing "gripping" the bar won't make the bar twist any less, the only thing to do that would be more metal, a 37mm sway bar, for example, 2mm more metal of which will flex less every time compared to the 35mm.

I'm rambling at this point. What a terrible example. I hope you get my point, though.

------------------
"Discord"
Red 1988 GT under restoration!

Let's Go Mets!

( ͡° ͜ʖ ͡°)

Just an update; I made a 1/2 inch spacer for the front stabilizer bar frame mounts, which angled the bar from the previous 12 degrees to 15 degrees.....The car turns in great and has extremely mild DTO...




I can hardly drive the car at the moment because of Drug-induced Lupus; The doctor prescribed Omeprazole for my acid-reflux, so now I cannot go out in the sun at all and my joints are all wrecked......Supposedly, I will recover 6 months after stopping the drug.........8 months and still no improvement.....

[This message has been edited by cvxjet (edited 01-24-2020).]

You are welcome GTO........I think it makes the car much more enjoyable to drive- The steering just feels much quicker (It is still heavy at parking speeds)

I forgot to mention that moving the bar down would interfere with the front crossmember braces- So I bought Rodney's braces which are stronger yet smaller in cross-section....

[This message has been edited by cvxjet (edited 01-25-2020).]