CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[Wepeel]

Originally Posted by Dimman

Any math beyond quoting some numbers they read will terrify people. Heh...

I put together a spread sheet for my own use, but my unsprung weight figures are estimates, as are the motion ratios I use. But it still gives me a better idea of how different spring rates can affect different cars.

About the struts, I've been using 1:1, what are the actual points we need to use?

For the struts the motion ratio primarily comes from the spring angle. Caster is nominally 5.6 degrees, SAI is nominally 15.5 degrees, so use the cosine of the larger angle for the motion ratio (.964).

[ZDan]

Originally Posted by Wepeel

For the struts the motion ratio primarily comes from the spring angle. Caster is nominally 5.6 degrees, SAI is nominally 15.5 degrees, so use the cosine of the larger angle for the motion ratio (.964).

There's also scrub radius to consider. I.e., how close is the intersection of the steering axis with the ground to the tire centerline? Positive scrub radius would act to further reduce the ratio, negative scrub radius would make it closer to 1:1. Search did not reveal FR-S scrub radius, but apparently McP struts do often have negative scrub radius. So maybe it's 1:1 after all...

[enwave]

I absolutely LOVE the stock suspension setup on the BRZ, but believe the wheel well is just a little but large... I've read around a ton, but I can't seem to find what people in my situation are doing.

Is my best bet to japanparts the STI springs for best hope of preserving the existing stock feel? Or are there other great springs with a similar spring rate and 15mm drop?

[Dimman]

Originally Posted by Wepeel

For the struts the motion ratio primarily comes from the spring angle. Caster is nominally 5.6 degrees, SAI is nominally 15.5 degrees, so use the cosine of the larger angle for the motion ratio (.964).

Originally Posted by ZDan

There's also scrub radius to consider. I.e., how close is the intersection of the steering axis with the ground to the tire centerline? Positive scrub radius would act to further reduce the ratio, negative scrub radius would make it closer to 1:1. Search did not reveal FR-S scrub radius, but apparently McP struts do often have negative scrub radius. So maybe it's 1:1 after all...

I've got three entries in my spreadsheet for calculating wheel rate and frequency. I use coil rate, a modifier for mounting angle and the leverage of the control arms. So in MacStruts the leverage is 1, and the mounting angle reduces effective coil rate slightly. (I've got a graph in a book somewhere for how much angle reduces effective coil rate.)

So that should be close enough?

[CSG Mike]

Originally Posted by eckoflyte

Question regarding Ground Control camber plates. We know that these allow the strut to be mounted higher, in effect lowering the car without sacrificing bump travel. From a geometry point of view, what would be the difference in lowering the car using the threaded shock bodies or using the GC plates? They both allow the car to be lowered without reducing shock bump travel.

There is no difference. I only allows for more travel.

[CSG Mike]

Originally Posted by OICU812

I'm hoping rce and CSG mike will make a thread like this for alignments and what's safe and workable. I realize people say use what works thing is there are people far more experienced with multiple setups ie: wheels sizes, tires,etc...

Alignments are highly subjective. As with ride quality, what one person may consider acceptable (ride quality and/or tire wear) may be totally different from what another person may consider acceptable.

For example, I daily drive my s2k with this alignment:

Front:
-3.5 camber
6.5 caster
0 toe
Rear:
-3.5 camber
5/32" total toe-in

My last set of RE-11 lasted 7 track days and 18k miles with that alignment (and constant tire rotation). That wear may not be acceptable to some, and far better than expected for others. Is it an alignment I would use on a FR-S/BRZ? No.

The CSG BRZ's alignment is currently:

Front:
-3 camber (via coilovers and camber plates [included with Tein SRC purchased from us])
0 toe
Rear:
-2.4 camber (natural camber from the drop)
0 toe

This is the alignment we recommend to experienced drivers that expect to see 6 or more track days per year with some street use.

However, as previously stated, alignments are highly subjective, and my recommendations will vary. The more data and feedback you can provide me, the better I can recommend changes. However, there is no right or wrong. What may work for me may not work for you, and vice versa.

[CSG Mike]

Originally Posted by CSG Mike

Front:
-3 camber (via coilovers and camber plates [included with Tein SRC purchased from us])
0 toe
Rear:
-2.4 camber (natural camber from the drop)
0 toe

Before today's alignment
Front
-4 camber
1/16" total toe-in

Rear
-2.75 camber
5/64" total toe-in

Change came from altered ride height and tolerances with the installation of the latest revision of the CSG-Spec Tein SRC.

Latest specs as of today:

Front
-3 camber
0 toe

Rear
-2.75 camber (natural from ride height drop of -1.4")
0 toe[/QUOTE]

[Wepeel]

Originally Posted by ZDan

There's also scrub radius to consider. I.e., how close is the intersection of the steering axis with the ground to the tire centerline? Positive scrub radius would act to further reduce the ratio, negative scrub radius would make it closer to 1:1. Search did not reveal FR-S scrub radius, but apparently McP struts do often have negative scrub radius. So maybe it's 1:1 after all...

For a strut, the wheel offset/scrub radius shouldn't have any effect on the motion ratio, since the balljoint can't carry any moment and the spindle is rigidly attached to the strut. Offset will have affects on the tension/compression force going through the lower arm and the bending moment on the strut though.

However, for something like a swing axle, wheel offset will have a definite effect on motion ratio.

[Wepeel]

Originally Posted by Dimman

I've got three entries in my spreadsheet for calculating wheel rate and frequency. I use coil rate, a modifier for mounting angle and the leverage of the control arms. So in MacStruts the leverage is 1, and the mounting angle reduces effective coil rate slightly. (I've got a graph in a book somewhere for how much angle reduces effective coil rate.)

So that should be close enough?

That should be good; don't forget to square the cosine of the angle (just like you would square the leverage).

Also FYI, motion ratios for the rear: 0.78 measured for the spring, 0.59 measured for the bar. I've got some calcs for wheel rates/frequencies for front and rear due to springs and bars, but that's probably better suited in the Suspension Modeling thread.

[ZDan]

Originally Posted by Wepeel

For a strut, the wheel offset/scrub radius shouldn't have any effect on the motion ratio, since the balljoint can't carry any moment and the spindle is rigidly attached to the strut. Offset will have affects on the tension/compression force going through the lower arm and the bending moment on the strut though.

Different scrub radius does affect the leverage ratio and motion ratio on a strut. More positive scrub radius (or lower wheel offsets) gives the wheel greater leverage on the spring, reducing the wheel rate for a given spring rate. The balljoint doesn't have to carry any moment, it's just a part of the overall mechanism.

[OICU812]

Originally Posted by CSG Mike

Alignments are highly subjective.

However, as previously stated, alignments are highly subjective, and my recommendations will vary. The more data and feedback you can provide me, the better I can recommend changes. However, there is no right or wrong. What may work for me may not work for you, and vice versa.

Ok fair enough and understood, example looking for advice on is:

FR-S
1-1.25" drop tops to retain stroke and function

Rear 18x9.5" - 255/35/18 Michelin Pilot Sport A/S
Front 18x8.5" - 225/40/18 Michelin Pilot Sport A/S

Suspension: KWV3 with Vorshlagg front plates and Rear Stance LCA (have read and noted that Vorshlagg plates add a degree of caster.) not sure what stock is and how much the vorshlagg affect goals on front camber etc?

Goal driving: DD/ Street & Spirited /5% autocross

Guess: -2 degrees camber in rear with zero toe
Guess: -.5 degrees camber in front with zero toe


How would that work or any advice based on that setup?

Lastly if it were 18x9.5" and 255/35/18 tires all way around what would you then reccomend given all other data same?

[448hpsti]

Originally Posted by CSG Mike

Before today's alignment
Front
-4 camber
1/16" total toe-in

Rear
-2.75 camber
5/64" total toe-in

Change came from altered ride height and tolerances with the installation of the latest revision of the CSG-Spec Tein SRC.

Latest specs as of today:

Front
-3 camber
0 toe

Rear
-2.75 camber (natural from ride height drop of -1.4")
0 toe

[/QUOTE]

Why on earth were you running toe in up front???

[Wepeel]

Originally Posted by ZDan

Different scrub radius does affect the leverage ratio and motion ratio on a strut. More positive scrub radius (or lower wheel offsets) gives the wheel greater leverage on the spring, reducing the wheel rate for a given spring rate. The balljoint doesn't have to carry any moment, it's just a part of the overall mechanism.

Agree to disagree. If you work out the FBDs of the linkages (mainly the strut/spindle linkage) it's easier to see how the resultant force through the spring is independent of the lateral location of the applied vertical load.

Where the offset does make a difference is in lateral force applied at the strut top (and hence the tension in the lower arm).

[CSG Mike]

Originally Posted by 448hpsti

Why on earth were you running toe in up front???

It wasn't intentional...