looking for sway bar rates and/or sway bar lever arm lengths

[Bill Verburg]

Anybody ever measure any sway bar rate?


or baring that he arm lever lengths

looking for lb/in or N/mm or such

I have some data correlating lbs/deg but w/o arm lengths it's not very useful

[stownsen914]

Speedway Engineering, a go-to for generic racing swaybars, has published the below.

https://1speedway.com/index.php?route=information/information&information_id=18

[Bill Verburg]

Originally Posted by stownsen914

Speedway Engineering, a go-to for generic racing swaybars, has published the below.

https://1speedway.com/index.php?route=information/information&information_id=18

Thanks but that's a bit too generic

the actual rate that affects the wheel motion depends on
bar diameter
bar length
lever arm length

bushes add a small tm delay but don't really affect the rate

I have rates in lb/deg but would like to also have and be able to use lb/in

I suspect that a 20mm under body 911 f will be ~110 lb/in +/- but don't really know

[jac1976]

I never thought I’d see the day when Bill was looking for an answer and not providing one.

[stownsen914]

It is generic, but for what it’s worth, I think the info you’re seeking can be derived from the Speedway Eng data and using the formula of diameter to the 4th power to compare bars of different diameters.

I used the above to pick the right size hollow 1.25” front bar to replace a 22 mm Weltmeister on my racecar. Granted, I wasn’t seeking numerical rate data, but the bar selection worked well, right down to the using calculated position on the radius arm.

Make sure you look at all the tabs on the web page I linked, I didn’t notice them at first.

[3rd_gear_Ted]

Another source

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

[Bill Verburg]

Originally Posted by stownsen914

It is generic, but for what it’s worth, I think the info you’re seeking can be derived from the Speedway Eng data and using the formula of diameter to the 4th power to compare bars of different diameters.

I used the above to pick the right size hollow 1.25” front bar to replace a 22 mm Weltmeister on my racecar. Granted, I wasn’t seeking numerical rate data, but the bar selection worked well, right down to the using calculated position on the radius arm.

Make sure you look at all the tabs on the web page I linked, I didn’t notice them at first.

hence the alternate request for lever length info

I do have the lbs/deg data but need to know the lever length to convert to wheel travel in inches

[TimT]

This was supplied by H&H way back in the day with their sway bars.

I installed bars on my911T in 1980? and I probably bought the sway bars from Tweaks

Anyway FYI

[David Inc.]

Are you looking for the actual lever arm lengths of the stock sway bar setup? "X" in the screenshot?



Well looks like I was soundly beaten to the punch.

[dannobee]

Remember, the calculations are different between factory bars and aftermarket bars due to the metallurgy and temper. Should be outlined in any of the online calculators. If you can't find them, let me know and I'll dig through my notes.


Dan

[Bill Verburg]

Originally Posted by TimT

This was supplied by H&H way back in the day with their sway bars.

I installed bars on my911T in 1980? and I probably bought the sway bars from Tweaks

Anyway FYI

I bought some used H&H for my '72 back in the day, wish i had the info sheet too

That is gold!! Thanks!!

[Bill Verburg]

Originally Posted by dannobee

Remember, the calculations are different between factory bars and aftermarket bars due to the metallurgy and temper. Should be outlined in any of the online calculators. If you can't find them, let me know and I'll dig through my notes.


Dan

yeah there are going to be several places where a judgement call needs to be made

A measurement bypasses most of them

Over on Rennlist a guy clamed a couple of bars to his bench then measured the deflection w/ a known weight, great stuff

Tim's data above is pure gold

ball park figures are fine, Not trying to put a man on the moon.

[stownsen914]

Bill - gotcha on the lever length. Speaking of levers, don’t forget to take into account the position of the droplink mount location on the A arm, I.e. 100 lbs measured at the radius arm doesn’t equal 100 lbs force at the wheel, in case that matters for your analysis.

[Bill Verburg]

Originally Posted by stownsen914

Bill - gotcha on the lever length. Speaking of levers, don’t forget to take into account the position of the droplink mount location on the A arm, I.e. 100 lbs measured at the radius arm doesn’t equal 100 lbs force at the wheel, in case that matters for your analysis.

I believe incorporating the wheel rate in any calculations solves that issue

I am mostly interested in the new design below body design but having Tim's info opens another door w/ the old style through body design

Tim's data even has the various lever arm lengths to use to convert my older data set which is in lb/deg to lb/in for comparison

[PeteKz]

I've been watching the thread. The angles of the sway bar arms on the newer style A arms, the angular difference between where the sway bar connects to the A-arm and the center of the wheel, and the flex and hysteresis of the rubber bushings makes geometric calculations suspect. I expect the only way you will get to a reasonably accurate value for the wheel rate of the sway bars will require actually measuring it at the wheel.

Unfortunately, it appears that you will have to do it for the rest of us.

[stownsen914]

Originally Posted by Bill Verburg

I believe incorporating the wheel rate in any calculations solves that issue

It depends how you calculate wheel rate. You probably thought of this, but the wheel rate you'd use for coilovers on the front of a 911, for example, will be a different than the wheel rate for the front swaybar, since the strut and the swaybar droplink attach to the A arm in different places. Similar situation in the rear.

[Bill Verburg]

Originally Posted by stownsen914

It depends how you calculate wheel rate. You probably thought of this, but the wheel rate you'd use for coilovers on the front of a 911, for example, will be a different than the wheel rate for the front swaybar, since the strut and the swaybar droplink attach to the A arm in different places. Similar situation in the rear.

911 motion ratio front is .91, rear 1.01
this is used to go from spring rate to wheel rate

It's certainly true that that the geometry of the sway bar is different, the question is how different, guess I'd need to know the distance from the sway bar mount to the ball joint, I'm guessing that in the overall scheme of things while there is a a delta it's going to be quite small

bushes introduce a tiny delta in the rate, they are more impactful; w/ a time delay, similar to using 2 different springs where there will be 2 set points

the larger issue is the effect of the other side, a single spring or t-bar only has effect on a single wheel

sways on the other hand connect the 2 sides so that both sides are twisting in opposite directions at the same time, so the question is how does this affect the wheel rate when you only care about the loaded side? My first guess is 50/50, but I don't really know.

[dannobee]

The stiffness of the sway bar isn't halved when you compute front roll couple.

If you change front springs (or whatever "spring" is supporting the body), you'll need to adjust or change the front sway bar if you want the front roll couple to remain the same by the same amount of stiffness that the springs changed (accounting for the motion ratio differences between springs and sway bars).

[David Inc.]

Originally Posted by Bill Verburg

911 motion ratio front is .91, rear 1.01
this is used to go from spring rate to wheel rate

It's certainly true that that the geometry of the sway bar is different, the question is how different, guess I'd need to know the distance from the sway bar mount to the ball joint, I'm guessing that in the overall scheme of things while there is a a delta it's going to be quite small

bushes introduce a tiny delta in the rate, they are more impactful; w/ a time delay, similar to using 2 different springs where there will be 2 set points

the larger issue is the effect of the other side, a single spring or t-bar only has effect on a single wheel

sways on the other hand connect the 2 sides so that both sides are twisting in opposite directions at the same time, so the question is how does this affect the wheel rate when you only care about the loaded side? My first guess is 50/50, but I don't really know.

Hold on he has a very good point. Two inches vertical motion of the wheel is probably only 1" - 1 1/2" of motion at the sway bar mounting point, in terms of actual deflection creating rotation in the bar.

To the bolded: That sounds about right. The sway bar doesn't care about loading of wheels, only relative wheel deflection, and the force applied would be equal to each wheel and therefore 50% of the overall stress in the bar per wheel.

[Bill Verburg]

Originally Posted by dannobee

The stiffness of the sway bar isn't halved when you compute front roll couple.

If you change front springs (or whatever "spring" is supporting the body), you'll need to adjust or change the front sway bar if you want the front roll couple to remain the same by the same amount of stiffness that the springs changed (accounting for the motion ratio differences between springs and sway bars).

Theoretically the sway bar only acts when the car is cornering. The loaded end of the sway bar twists up adding to the wheel rate on that side, the other end twists down in reaction creating the couple, if not 50/50,what is the effect?

just seems to me that equal and opposite forces are in play, similar to a teeter totter