sway bars?

[J08M3]

[lucid]

Guys, please keep the tone in check, and let's get this back on topic. Thanks.

[jml]

Originally Posted by doba_s

What are his thoughts about swaybars ? have you asked him yet ?

He said something was coming soon, but that he focused on putting together a nice set of coilovers (Moton Street sports) first.

[HP Autosport]

E9X chassis don't work well with big anti roll bars. If you really want to reduce the body roll a bit, start with the E93 front and rear anti roll bars, then go to a good coilover system with higher but proper spring rates down the road.

[doba_s]

Originally Posted by Orb

The Dinan bar is from 335i so they have taken a big friggen bar to make a 3 wheel wonder and now stuck it on M3.....what can I say but tell Dinan to stick it up their as#.

This is performance with massive sacrifice and insult to every member here.

Orb

How is the M3 bar is from 335 when 335s bar is 26.5mm and m3s is 28.5mm ? Can you explain it ? Do you know something we dont ?

AD

[Orb]

Originally Posted by doba_s

How is the M3 bar is from 335 when 335s bar is 26.5mm and m3s is 28.5mm ? Can you explain it ? Do you know something we dont ?

AD

You can't compare the BMW bars easily since they are variable diameter and thickness. Only a few of us know what the rates are. The e92 M3 bar is on average 26.5 mm and e93 M3 bar has small section at 28.0 but it is thinner. The rear bars are 23 mm on the rear on e92 and 23.5mm on e93. The e93 bars are scaled to handle the extra weight and 1% difference in weight biasing. A 335i bar is 26.5 but has a narrow section that drops its rate considerably over a M3 bar.

The Dinan bar is solid 28.5 mm monster is really stiff. The spring rate for M3 front roll bar is about 230 lb/in and the Dinan bars is about 420 lb/in. In roll it is 2x the rate.

All the e90/e92 M3 and e92 bars are interchangeable just like most if the suspension part.

Orb

[swamp2]

Originally Posted by Orb

You can't compare the BMW bars easily since they are variable diameter and thickness.

Aren't they actually hollow as well?

[Orb]

Originally Posted by swamp2

Aren't they actually hollow as well?

Yup, the thickness changes through out the length.

Orb

[lucid]

Originally Posted by Orb

The spring rate for M3 front roll bar is about 230 lb/in and the Dinan bars is about 420 lb/in. In roll it is 2x the rate.

What are the spring rates you are quoting exactly? How are they obtained? Why are they in lb/in? Are these approximations for linear wheel motion? How about torsional stiffness? Thanks.

[Orb]

Originally Posted by lucid

What are the spring rates you are quoting exactly? How are they obtained? Why are they in lb/in? Are these approximations for linear wheel motion? How about torsional stiffness? Thanks.

I have suspension calculated and validated so what do want to know? The sway bar is a torsion spring so that is why it is a rate but you know this!! For this car, the motion ratios are close to 1 front and rear.

There is nothing difficult about calculating the roll bar spring rate with a high degree of accuracy. However, calculating the OEM bars is a destructive exercise.

The bar stiffness is governed by the modulus of rigidity (G)....it is a given for spring steel.

Orb

[lucid]

Originally Posted by Orb

I have suspension calculated and validated so what do want to know? The sway bar is a torsion spring so that is why it is a rate but you know this!! For this car, the motion ratios are close to 1 front and rear.

There is nothing difficult about calculating the roll bar spring rate with a high degree of accuracy. However, calculating the OEM bars is a destructive exercise.

Orb

I meant why is the rate not expressed per radians since we are talking about a torsion spring and not a compression spring.

[Orb]

Originally Posted by lucid

I meant why is the rate not expressed per radians since we are talking about a torsion spring and not a compression spring.

You are right of course and should be in (ft-lb/degree) if we just had the bar only.

The equation used is from Fred Puhn and is expressed in lb/in. This doesn not include the motion ratio.


K (lbs/in) = (500,000 D^4 \ (0.4244 x A^2 x B) + (0.2264 x C^3))

A - Length of end perpendicular to B (torque arm - inches)
B - Length of center section (inches)
C - Length of end (inches)
D - Diameter bar (inches)

It is good enough but not perfect.

BTW, in the end I ran this in Ansys as non linear FEA problem.


Orb

[swamp2]

Originally Posted by lucid

I meant why is the rate not expressed per radians since we are talking about a torsion spring and not a compression spring.

The simple answer is that the lever arms on the end of the bar essentially turn the torsion of the center section into a roughly linear spring as measured at these arm ends. The arms obviously move in an arc but you can still approximate this with the tangential force component and it is roughly linear. What really matters in the calculation of the torsion bar effect on the suspension (on the unequal compression of the left/right side) is this "linear" rate at the ends of the arms.

[lucid]

Originally Posted by swamp2

The simple answer is that the lever arms on the end of the bar essentially turn the torsion of the center section into a roughly linear spring as measured at these arm ends. The arms obviously move in an arc but you can still approximate this with the tangential force component and it is roughly linear. What really matters in the calculation of the torsion bar effect on the suspension (on the unequal compression of the left/right side) is this "linear" rate at the ends of the arms.

Yes, that is what I meant by "approximations for linear wheel motion?" in my original question, but you expressed it better than I did.

Since we are talking suspension here, I am not all that comfortable with how the car handles during high speed turns. What are people's opinions on this?

[Orb]

Originally Posted by swamp2

The simple answer is that the lever arms on the end of the bar essentially turn the torsion of the center section into a roughly linear spring as measured at these arm ends. The arms obviously move in an arc but you can still approximate this with the tangential force component and it is roughly linear. What really matters in the calculation of the torsion bar effect on the suspension (on the unequal compression of the left/right side) is this "linear" rate at the ends of the arms.

Thanks....the real differance is only a few precent. The only thing to add is that there is a motion ration but in this case it is 1^2 for the rear and 0.96^2for the front so the wheel and bar rates are are close to the same.

Orb

[HP Autosport]

Originally Posted by Orb

The Dinan bar is solid 28.5 mm monster is really stiff. The spring rate for M3 front roll bar is about 230 lb/in and the Dinan bars is about 420 lb/in. In roll it is 2x the rate.

That is a great upgrade if you are looking for more understeer!

[jml]

Originally Posted by HP Autowerks

That is a great upgrade if you are looking for more understeer!

May not be the case. The E46 actually responded in the opposite way (counter intuitive). With a strut design the negative camber falls off quickly as the body rolls, resulting in lost grip after turn-in (after the weight transfers). Keep the car flatter really helps a lot - but my sense is that the E90 may not respond in quite the same way, though it does have a front strut.

[HP Autosport]

Originally Posted by jml

May not be the case. The E46 actually responded in the opposite way (counter intuitive). With a strut design the negative camber falls off quickly as the body rolls, resulting in lost grip after turn-in (after the weight transfers). Keep the car flatter really helps a lot - but my sense is that the E90 may not respond in quite the same way, though it does have a front strut.

You are correct, the E36/E46 cars liked a big front bar to keep roll induced camber change under control. And that was what we thought at first and experiment with it, but it only made the understeer worse on the E8X/9X cars. At the end springs were used to reduce the understeer and slight increase in anti roll bar diameters to fine tune the handling balance.

[jml]

Originally Posted by HP Autowerks

You are correct, the E36/E46 cars liked a big front bar to keep roll induced camber change under control. And that was what we thought at first and experiment with it, but it only made the understeer worse on the E8X/9X cars. At the end springs were used to reduce the understeer and slight increase in anti roll bar diameters to fine tune the handling balance.

Good to know!

[Eugene-TAIWAN]

Originally Posted by HP Autowerks

Where are you trying to go with your car?

Front is 28mm vs 26.5mm
Rear is 23.6mm vs 20 mm

Still tubular steel and very light in weight. Aftermarket anti roll bars will be very heavy, perhaps twice the weight like we have seen in the 135/335i ones from H&R, UUC, etc.

Harold

Do you or have your tried it?? on an E92 M3???
I just want to know if it works for sure. so I no return problems at all.

[e46e92love]

Originally Posted by lucid

Since we are talking suspension here, I am not all that comfortable with how the car handles during high speed turns. What are people's opinions on this?

How did this question not get addressed?

Also, Orb, do you know how the "spring rates" of the e92 f & r sway bars compared to those of the e93? I know there is a difference in thickness, but what is the actual applied difference? Also, rememeber when answering I'm not an engineer so if you start quoting formulas my brain might cease up and cause drool to drip out the side of my mouth

Cheer,
e46e92

[Eugene-TAIWAN]

Originally Posted by e46e92love

How did this question not get addressed?

Also, Orb, do you know how the "spring rates" of the e92 f & r sway bars compared to those of the e93? I know there is a difference in thickness, but what is the actual applied difference? Also, rememeber when answering I'm not an engineer so if you start quoting formulas my brain might cease up and cause drool to drip out the side of my mouth

Cheer,
e46e92

Yes, I agree that formulas are a pain. All I want to know if the e93 sway bars are a direct bolt on to the e92 chassis.
and ofcourse the car has a lot of body roll during high speed turns.