VTECIntegra9

While going through weight transfer and roll calculations I got to thinking of how to include MY anti-roll bars into the equation with accuracy. I know you can calculate the bar stiffness based on the length, motion ratio, diameter, material, cross section, etc - this works very good with a bar with simple geometry... but what about, say, the stock front bar on the teg? It's a bit of a curly-cue in shape and the torsional stiffness would be tough to calculate without some modeling. Not to mention the motion ratio of the bar.

Anyways, I threw together a quick procedure for calculating it on the vehicle that seems like it should work well. I'm sure this is NOT the first time this has been mentioned but I didn't see any other posts up so I am going to put it on here for future reference. This includes the motion ratios already so what you see is what you have at your tire.

Please correct me if this does not make sense in any way. It is done statically with the car not rolling but we are not measuring roll stiffness, only the sway bar stiffness...however you can calculate it same as you would with wheel rate, you can use the bar rate you will measure and plug it in.

Sway-Bar Roll Stiffness = (Bar Rate[N/m])*(Track Width[m])^2/(2*57.3) in N*m/deg

You will need wheel scales (just one for this), the suspension spring removed, and a way to fix one wheel to the ground (a large friend to stand on it? or straps would work... depends on the stiffness of the bar really.

This will be performed while other measurements are being taken such as total travel, possible camber/toe change w/ travel, unsprung weight, etc.

-Measure the ride height of the car and mark the height of the chassis from the ground - you will need to block the chassis at this height.

- Remove the suspension springs.

- Disconnect the sway bar linkage from both ends so it can be moved out of the way.

- With the suspension assembled and springs removed, lower the car to its ride height and block the chassis on the end you are performing the measurement on so it can sit at ride height w/o springs to hold up the wheels.

- Place the wheel scale under the wheel and record the weight. You may also zero the scale at this point. Note the unsprung weight without the spring.

- Measure the height of the scale as your delta-d.

**You could over-inflate the tire to increase its stiffness so to negate the effects of tire stiffness....this may change your ride height position - no not under-inflate tires as this will effect your measurements**

- Now, lower the wheel and re-connect the anti-roll bar at both ends.

- Making sure the opposite wheel is fixed to the ground and is not going to unload itself from the ground, lift the wheel and place it on the scale again... You may need a floor jack under the control arm to help deflect the bar/suspension.

-Measure the weight again.

*You could raise the scale more and take another measurement and determine the non-linearity of the anti-roll bar stiffness.

That procedure should give you two weights and a change in distance (from ride height).
Bar Stiffness [N/m] = [Weight(bar) - Weight (no-bar)] / delta-d

Plug that into the roll stiffness equation above and you have the roll stiffness contribution from the anti-roll bar on that end of the car.

Hope it makes sense and if there are any errors or questions please let me know. There may be easier/better/more accurate ways of doing this but I was bored and decided to make up a method of doing it.

-Ryan / Teal