This is the roll center, suspension pickup, and steering angle modification thread.

[PoorMans180SX]

Originally Posted by Z33dori

is there an equation to figure this out?

b/c if you run the camber plates up top rotated for caster, then you would need to do all the camber at the bottom. Obviosuly the best idea for this is adjustable LCA, but for me right now is not much of an option. I just dont wanna cut myself short on camber.

Well most coils will let you pull 2.5ish degrees of camber, so any extension of the lca will give you more. You'd probably have to find a lot of angles to figure this out without doing it. Someone with an adjustable lca should be so kind as to take a couple measurements.

I've seen guys with 25mm extensions running 7 degrees of camber, so unless you want that much, I'd stick with 15mm.

[brainfood]

Originally Posted by IThaJokaI

It would be as simple as making a bracket to adapt the wilwood to the bigger rotor, any machinist with half a brain could do it.

I know it would be a simple bracket but as common as z32 rear brakes are and the fact that you are buying knuckles that have brackets for the 2nd caliper already seems silly to have to make another bracket but if that's what has to be done. May be the difference in buying these or dw/era1 because you can keep the z32 ebrake on those.

[brainfood]

Also would love to see a picture of the arms from the rear of the car with Pbm knuckles installed. Please anyone that already ordered a set

[az_240]

Originally Posted by brainfood

I know it would be a simple bracket but as common as z32 rear brakes are and the fact that you are buying knuckles that have brackets for the 2nd caliper already seems silly to have to make another bracket but if that's what has to be done. May be the difference in buying these or dw/era1 because you can keep the z32 ebrake on those.

Only thing that sucks about using the z32 e-brake with either of those knuckles is you have to flip the e-brake assembly upside down. When you do this the e-brake doesn't work as well.... still okay for parking... not so good for drift.

To help fix this I sent my e-brake shoes to Porterfield to have them relined with their new RD-4 race compound. Way cheaper than Project Mu shoes and should be a better compound. I should get them back next week.

If I still can't get the wheels to lock with minimal effort I may just go with PBM/hydro.

Also it's hard to find coils that will even work with these dw knuckles in the rear for s14. S14 dw rear coils go to 70cm so that gives you an idea of how tall the coils need to be. Axle boots can also be a problem depending on what ruca/traction arms you have and how low you are. I noticed my friends s13 axle boots are smaller than my s14 boots so might have to trade him

[brainfood]

^ thanks for the info keep me posted I've never had a problem with stock pads on z32 ebrake but it makes sense that it doesn't work as well as stock after it's flipped.

The thing for me is it's for my street car with full interior and a hydro wont look as clean as a stock ebrake. I don't mind running a line lock for ebrake but I haven't seen any clean hydro setups with full interior and center console. Mounting it under the radio would be fine but I have a double din nav so it's like trying to cram 10lbs of shit in a 5lb bag.

[godrifttoday]

is pbm max coming out with a front knuckle? not a modified one?

[az_240]

Originally Posted by brainfood

^ thanks for the info keep me posted I've never had a problem with stock pads on z32 ebrake but it makes sense that it doesn't work as well as stock after it's flipped.

The thing for me is it's for my street car with full interior and a hydro wont look as clean as a stock ebrake. I don't mind running a line lock for ebrake but I haven't seen any clean hydro setups with full interior and center console. Mounting it under the radio would be fine but I have a double din nav so it's like trying to cram 10lbs of shit in a 5lb bag.

Yeah I'm in the same boat.... trying to keep the stock look with full interior. Will post how it goes when it's back together.

[brainfood]

Has anyone tried to mount to add hydro under a stock/modified center console?

[kewilso3]

Can we get back on topic now?

[thefro526]

Originally Posted by IThaJokaI

The z32 rear caliper/rotor should bolt right on, like stock. But you would need to make a bracket to adapt the wilwood to the bigger rotor.

Originally Posted by IThaJokaI

It would be as simple as making a bracket to adapt the wilwood to the bigger rotor, any machinist with half a brain could do it.

I sort of figured as much, but I was hoping that there was some sort of COTS part that could make it work.

Seems like it might almost be worth buying the PBM rears at $400 then cutting off the brake caliper mounting points and running George's dual Z32 bracket for an additional $270 or whatever it is. Comes out to be $670 for a dual caliper rear, which is still cheaper than ERA-1 or DW... Might take this route.

[brainfood]

Originally Posted by kewilso3

Can we get back on topic now?

Yes one more question how does it feel? Work well?

[PoorMans180SX]

Originally Posted by thefro526

I sort of figured as much, but I was hoping that there was some sort of COTS part that could make it work.

Seems like it might almost be worth buying the PBM rears at $400 then cutting off the brake caliper mounting points and running George's dual Z32 bracket for an additional $270 or whatever it is. Comes out to be $670 for a dual caliper rear, which is still cheaper than ERA-1 or DW... Might take this route.

First, you won't need to "cut off the brake caliper mounting points" as they're flush on the knuckle.

Secondly, you can't find a machinist to make you two brackets for less than $270? And you want to run two anchor weight calipers back there?

Make the bracket, run a wilwood. No sense in doing it more expensive and heavier.

[GKTECH]

Hey guys, we haven't posted on here for a few years now however you'll be seeing more of us in the near future once we've got our distribution center setup in the States.

The reason for my post is to ask your opinions on a design for a billet 7075-T6 aluminium knuckle that we're working on.

At this stage here is where the design is at:

- body and mounts to be machined from billet 7075-T6 aluminium, spindle material to be 35CrMn (TBC pending FEA tests)
- All threads going into main unit to have threaded inserts
- Direct bolt on design for S13, S14 and S15's (provision for both 12mm and 14mm knuckle to strut mount, provision for different taper for LCA ball joint, and 2 different spindle sizes to suit either S13 or S14/S15)
- 40mm drop spindle
- As the design currently sits (still needs to be run through the FEA and optimized) currently weighs in at 2.1kg's. The stock S13 unit weighs 3.3kg's, stock S14/S15 unit weighs 3.8kg's and the Drift Works unit weighs a whopping 3.9kg's
- The design caters for interchangeable brake caliper mounts
- The design caters for interchangeable tie rod mounts (so far we have 2 designed; standard and DW style)
- Provision for ABS sensor (not shown in images below)
- Ability for stock brake dust cover to slip over base of spindle



Just to show you the possibilities of what our new billet 7075-T6 aluminium modular knuckles will have have a look at this

(Again, please note that this is NOT the finished product, FEA's and optimization of the design still needs to occur).

With the ability to swap out tie rod mounts you can completely change the feel and drive of your car. We can see in this image the stock arm Vs. the DW arm, the DW arm will give about 18% quicker steering than the standard arm.

You’ll also notice the DW position is further outboard than the standard position. This will give you less Ackermann effect, so the inner and outer wheels will steer at nearly the same angle, rather than having the inner wheel steer tighter than the outer wheel.

That said, the possibilities are endless. One idea that we're toying with is to have the CAD files to the mounts (both caliper and tie rod) available to the general public, this would mean that people with the skills to play around with their own mounts could do so with relative ease.



The questions:
- What is this design missing from your "ideal" knuckle?
- Someone has brought to our attention that we should be using a standard radial caliper mount, what is common in the US (we reside in Australia and it's not so common over here)


Thanks for your input in these early stages to help us improve on our design prior to production

Regards,
Greg

[GKTECH]

P.S I deliberately haven't mentioned the price because I don't want this to seem like a for sale ad, this is not for the purpose of selling, more so development.

[thefro526]

Originally Posted by PoorMans180SX

First, you won't need to "cut off the brake caliper mounting points" as they're flush on the knuckle.

Secondly, you can't find a machinist to make you two brackets for less than $270? And you want to run two anchor weight calipers back there?

Make the bracket, run a wilwood. No sense in doing it more expensive and heavier.

I might've (probably) been wrong on the caliper mounts, I assumed they'd need to be cut off just like they would need to be on a stock knuckle. I always figured that the new mounting points of the calipers would've interfered with the original caliper mounting brackets. Might not be the case with the PBM knuckle.

As far as the bracket goes, I could have them made for the cost of material, if not for free if I asked for a favor (I work with a machine shop on a daily basis) and wanted to go that route, but then I'd need to CAD them up myself (not really a big deal, just a few hours of my time) and wait for them to get machined. I'd much rather buy something that's already figured out.

As far as running the wilwood, when I checked the site, it didn't seem like the style used on the PBM knuckle came in a size that'd work with the Z32's rear brake thickness (probably do, I just couldn't find them). In terms of expense, it doesn't seem like it's that much more expensive, IIRC, the rotors that George runs on his Dual Z32 kit are more than $25 cheaper than an oem Z32 rotor, and a pair of rear Z32 calipers are what, $100 vs $260 per pair of wilwoods, in the end, I'm ~$100 more expensive than the PBM setup, without much more additional work. (I figure the $100 of additional expense is less than what my time is worth to design the brackets and the cost of the material to make them)

I think you're right on weight though, the setup I'm looking at would probably be heavier, although I couldn't see it being much more than stock knuckle with a similar setup.

[DC Dan MAX USA]

Originally Posted by CaBS

Do you have any pictures of the Pro Grip front and rear knuckles? What kind of dollars are they? I was hoping to keep the drum brake handbrake setup too but I'm guessing there is not enough room for it with the drop spindle?

The GP sports adjustable ones are discontinued apparently. I was talking to a drifter mate of mine in Japan and he said he'd seen a few failures of the adjustable type and never any of the cut/shut ones.

no I dont have pictures, its the same exact look with a longer (uncut) steering arm $400 + shipping

There is no grip and drift specific rear knuckle, Im sure the grip guys just wont use the dual caliper mount.

The reinforcement of the RLCA mount prevents the use of the Z32 drum.

Originally Posted by IsBettyBish

If I can even tell a difference between the poly and spherical bearings (which i'm sure 80% of people can't)

People spend a good deal of money making everything solid and spherical, it makes no sense to finish off the build with some bushing knuckles.

Originally Posted by Z33dori

if you run the camber plates up top rotated for caster, then you would need to do all the camber at the bottom.

Remember that you can run less static camber with reduced caster. You will have a better contact patch at lock because the caster is not amplifying the the camber and you will even have better straight line braking contact patch. Therefore being so concerned with adding toms of camber on the lower arm is really not an issue when you reduce caster at the top plate.

Originally Posted by brainfood

Also would love to see a picture of the arms from the rear of the car with Pbm knuckles installed. Please anyone that already ordered a set

prototypes have been on my car forever
then

now

Originally Posted by godrifttoday

is pbm max coming out with a front knuckle? not a modified one?

working on it. we know that for some its not convenient to send in their parts to get modded.

Originally Posted by brainfood

Has anyone tried to mount to add hydro under a stock/modified center console?

Originally Posted by az_240

Yeah I'm in the same boat.... trying to keep the stock look with full interior. Will post how it goes when it's back together.

customers 240

My daily driver

Originally Posted by thefro526

I might've (probably) been wrong on the caliper mounts, I assumed they'd need to be cut off just like they would need to be on a stock knuckle. I always figured that the new mounting points of the calipers would've interfered with the original caliper mounting brackets. Might not be the case with the PBM knuckle.

As far as the bracket goes, I could have them made for the cost of material, if not for free if I asked for a favor (I work with a machine shop on a daily basis) and wanted to go that route, but then I'd need to CAD them up myself (not really a big deal, just a few hours of my time) and wait for them to get machined. I'd much rather buy something that's already figured out.

As far as running the wilwood, when I checked the site, it didn't seem like the style used on the PBM knuckle came in a size that'd work with the Z32's rear brake thickness (probably do, I just couldn't find them). In terms of expense, it doesn't seem like it's that much more expensive, IIRC, the rotors that George runs on his Dual Z32 kit are more than $25 cheaper than an oem Z32 rotor, and a pair of rear Z32 calipers are what, $100 vs $260 per pair of wilwoods, in the end, I'm ~$100 more expensive than the PBM setup, without much more additional work. (I figure the $100 of additional expense is less than what my time is worth to design the brackets and the cost of the material to make them)

I think you're right on weight though, the setup I'm looking at would probably be heavier, although I couldn't see it being much more than stock knuckle with a similar setup.

The stock diameter (brembo replacement) disc is light and works great $38ea, so does the OEM foot brake caliper with performance pads, and the wilwood dual piston part#120-9689 is a really cheap price $100ea. + pads for a light dual piston cnc billet new part. All of this stuff just works perfectly, we offer the setup this way because its the best bang for the buck. Are you so in love with the Z32 parts that you are willing to do all that to rework our stuff? If used Z parts really that valuable sell it used if you already have it and let that pay for your brand new parts. However if you are a fabricator and just enjoy making cool stuff, im sure its nothing to make some new brake mounting tabs & weld them up - you have no limitations on what you can customize.

[marks14]

I think I figured out how to explain my logic without making a wall of text. Comments are more than welcome. In by no way am I trying to bash PBM, when I talked to dan on the phone he was very helpful with my questions, and I'm planning on ordering rack spacers + other items in the very near future. PBM is always constantly trying to think of new ideas.

Originally Posted by DC Dan MAX USA

-This is the picture that you get almost any time that you mention ackerman on our cars. This picture says that if you keep your LCA pickup point, and your tie rod pickup point an equal horizontal distance as stock you will keep stock ackerman. This would be true if your KPI (kingpin inclination angle) was to be vertical. KPI in s-chassis for the front is defined by the ball joint and upper coilover mount. If any of you have been under your car you know that your tophat of your coilover is not directly above your balljoint. In s-chassis the KPI is tilted inwards (because the tophat is more inwards twards the center of the car than the balljoint).

-For a car that has a vertical KPI, 0 ackerman would be when the outer tie rod pickup point is directly behind the KPI (or balljoint). To add or remove ackerman you move this outer pickup point horizontally (perpendicular to the KPI) to the inside of the car for positive ackerman (toe out at full lock), or to the outside of the car (toe in at full lock) on s-chassis. The key here for ackerman, is the perpendicular distance of the outer tie rod pickup to the KPI when looking from the front or bck of the knuckle.

-On s-chassis' the KPI is angled in at the top, and for all intensive purposes we will say that the KPI is along the shank of the balljoint (the red line). To adjust ackerman, we do the same thing as stated in the previous bullet point (move the tie rod pickup point) and the perpendicular distance to the KPI effects ackerman in same way as a car that has a vertical KPI. The blue line below shows my line of no change in ackerman because the perpendicular distance to the KPI stays the same along that line.


Now if you just extend your shank to space your LCA down you will add ackerman to your car because when you add that spacer your LCA is still the same length and the spacer pushes the knuckle towards the inside of the car, which in turn pushes the outer tie rod pickup point towards the center of the car, which in turn increases its perpendicular distance to the KPI, thus adding ackerman. The way to solve this issue is to Lengthen your LCA ~(spacer_height)*sin(KPI_angle_from_vertical). This will keep your lower ball joint on the same axis (red line) keeping the original KPI, which will not effect ackerman.

[C. Anderson]

Is there an ideal length for rear traction arms on s13's?

[nieko]

Not really, bro. The traction rod length is going to depend on your particular ride height, camber/toe settings and personal preference of how you want the car to feel.

[Motary]

GKTECH - the drop would be nice at 60mm, most S chassis are lowered around that much in the front and for drifting it would be sweet to have 0 KPI so you wouldnt have weird positive camber in drifting without running huge negative camber, which will decrease with steering angle increase

[PoorMans180SX]

GKTECH - yeah what Motory said. I like the changeable arms.

Dan at PSM - I'm excited for the forged knuckle! Same specs as a pro knuckle, or is there more drop there? Maybe it's just an illusion from the smooth look.

Mark- While your thinking is logical, you are missing one thing. Spacing the LCA down increases the horizontal distance between your tie rod pickup and ball joint. If you draw a line down the two towards the rear of the car, THAT is your ackerman. There is no way around increasing your ackerman with a spaced ball joint besides modifying the steering arm. Sorry.

[GKTECH]

Originally Posted by Motary

GKTECH - the drop would be nice at 60mm, most S chassis are lowered around that much in the front and for drifting it would be sweet to have 0 KPI so you wouldnt have weird positive camber in drifting without running huge negative camber, which will decrease with steering angle increase

Hi there, thanks for your reply.

I agree that most people probably would lower their cars 60mm's, most coilovers lower the car to some degree anyway so unless we had coilovers that were to match the 60mm drop spindle, then it wouldn't work but I certainly hear what you're saying.

In regards to the KPI/SAI, on the revised version of the design (which we should have finalized within a few days) we will go one better than what you have requested, we will have adjustable KPI. Much like the MSI billet uprights seen here: MSI Billet Aluminum Uprights (Lots of pics) - Subaru Impreza WRX STI Forums: IWSTI.com

We're more than open to ideas as we are in the early stages of the design. That said, we should be finished within 2 weeks or so before we start getting these on to the track.

[C. Anderson]

So what are the effects of lengthening and shortening the traction arm?

[GKTECH]

Originally Posted by PoorMans180SX

GKTECH - yeah what Motory said. I like the changeable arms.

As above, we'll have adjustable KPI/SAI

[nieko]

The design and everything looks pretty damn awesome, the biggest chalenge is offering them at an affordable price. Most S-Chassis people in the US are either: not serious enough, don't care enough, are kids with not money, or just flat out bums.

[GKTECH]

Originally Posted by nieko

The design and everything looks pretty damn awesome, the biggest chalenge is offering them at an affordable price. Most S-Chassis people in the US are either: not serious enough, don't care enough, are kids with not money, or just flat out bums.

We've had quite a few emails in regards to the price, at this stage our target price for a kit is $599 with the option to purchase additional/different steering arms at $99/pair.

The kit will include everything required to get you going and car specific too, or mix and match (ie. you choose at the time of ordering which LCA ball joint you're running, which strut your running for either 12mm or 14mm bolt holes, you choose the spindle you want etc. etc.)

We don't yet have distribution setup in the US however we will in the very near future and until then, we will have DHP, UPS, USPS and FedEx accounts setup within the coming weeks to cater to US orders.

Greg

[GKTECH]

Sorry, just to clarify that price is in AUD (AUD vs USD is around parity at the moment anyway) however that price includes 10% tax which you won't have to pay so the price for US customers is expected to be a bit less than $550/pair + freight ($100 or so max as they'll be under 5kg's a pair)

[PoorMans180SX]

Sounds like a pretty awesome deal!

[GKTECH]

The target price is a little ambitious however it is what we're aiming for.

Greg

[DC Dan MAX USA]

Originally Posted by PoorMans180SX

Dan at PSM - I'm excited for the forged knuckle! Same specs as a pro knuckle, or is there more drop there? Maybe it's just an illusion from the smooth look.

same spec. just smoothed out. Right now we are machining a logo on the flat space under the spindle.