MCA Suspension "Traction Mod"

[norcalpb]

Originally Posted by makinen

It seems like that the spring rates matters.

Did you end up doing the 3.8k gt86 rear springs?

[grippgoat]

Could ride height change be from tightening bolts with the links at a severely not-ride-height angle?

-Mike

[makinen]

Originally Posted by norcalpb

Did you end up doing the 3.8k gt86 rear springs?

I did install 4.0k GR86 rear springs.

[Racecomp Engineering]

Originally Posted by grippgoat

Could ride height change be from tightening bolts with the links at a severely not-ride-height angle?

-Mike

I was thinking this as well. I fully replaced my trailing arm with the STI pillowball arm when I did my MCA install, which at least means the front point is free. Unfortunately I didn't measure ride height before install because I was making a bunch of changes and resetting anyway.

I wonder if tightening an OEM trailing arm with the rubber bushings at both ends while at full droop for install changes things enough (binds up) to impact ride height that much. Not sure.

- andrew

[norcalpb]

Originally Posted by Tatsu333

Nope - I was still on the stock Performance Pack suspension when I installed the MCA Traction Mod, and no ride height change occurred (I did measure before and after).

Could be the GP Sports version alters the geometry in some other way? No idea...

It totally could…maybe the new trailing arm mounting location is closer or further away relative to old mounting location causing the sag.

Originally Posted by grippgoat

Could ride height change be from tightening bolts with the links at a severely not-ride-height angle?

-Mike

To be honest I did forget to tighten with load on the suspension so this is a very interesting point. I’ll go back under soon and see if I can loosen/re-tighten with the appropriate load.

Originally Posted by makinen

I did install 4.0k GR86 rear springs.

How are you liking that spring rate? I imagine it’s similar to the oem STi springs which would mean we have another oem+ option on our hands. Did you notice a drop at all when you did your Traction mod?

Originally Posted by Racecomp Engineering

I was thinking this as well. I fully replaced my trailing arm with the STI pillowball arm when I did my MCA install, which at least means the front point is free. Unfortunately I didn't measure ride height before install because I was making a bunch of changes and resetting anyway.

I wonder if tightening an OEM trailing arm with the rubber bushings at both ends while at full droop for install changes things enough (binds up) to impact ride height that much. Not sure.

- andrew

Man this was what I was afraid of lol. But my non-educated theory would be that if I tightened the bushing’s bolt with the suspension at full droop, that the associated pre-load would actually raise the car? I have 1/4” risers getting here on Monday but I’m going to try and re-do the subject bolts before I dismantle my alignment to install the risers.

[makinen]

Originally Posted by norcalpb

How are you liking that spring rate? I imagine it’s similar to the oem STi springs which would mean we have another oem+ option on our hands. Did you notice a drop at all when you did your Traction mod?

F 2.7k BRZ springs
R 3.4k MY17 -> 4.0k GR86 springs
FSB 18mm stock
RSB 15mm Impreza or MY17

The ride height changes with loads are manageable. Before installing the Traction Mode, I was worried about the saggy butt with loads, since my rear diffuser has a small gap from the parking lot stoppers. The up-rated rear springs make it manageable.
After installing the Traction Mode, I noticed a squat angle on launches, but it disappears quickly. I think the springs suppress the squat angle.
The ride comfort is the same or softer even with the up-rated springs. But the stock Sachs dampers (from MY17) sometimes fail to dampen the oscillations from the road surface at a certain frequency (usually high freq.).
The rear is more responsive but not too much. I guess it would be too rear-biased if I used those springs without the Traction Mode. I like the current settings.

Without a spare tire or a jack in the trunk, the static ride height was not changed or only slightly changed. But the ride height changes when loaded are almost the same even with the up-rated rear springs. It means that just sitting in the driver seat could make it lower than before without changing the spring rate.

Before the installation:


After installing 4.0k springs at the rear and the Traction Mode.

[strat61caster]

@norcalpb I installed rear lca in the air, put it on the ground measured - loosened, tightened, remeasured (ride height, alignment) and saw zero difference. On this car at least having the suspension loaded when torque is negligible imho.

[norcalpb]

Originally Posted by makinen

F 2.7k BRZ springs
R 3.4k MY17 -> 4.0k GR86 springs
FSB 18mm stock
RSB 15mm Impreza or MY17

The ride height changes with loads are manageable. Before installing the Traction Mode, I was worried about the saggy butt with loads, since my rear diffuser has a small gap from the parking lot stoppers. The up-rated rear springs make it manageable.
After installing the Traction Mode, I noticed a squat angle on launches, but it disappears quickly. I think the springs suppress the squat angle.
The ride comfort is the same or softer even with the up-rated springs. But the stock Sachs dampers (from MY17) sometimes fail to dampen the oscillations from the road surface at a certain frequency (usually high freq.).
The rear is more responsive but not too much. I guess it would be too rear-biased if I used those springs without the Traction Mode. I like the current settings.

Without a spare tire or a jack in the trunk, the static ride height was not changed or only slightly changed. But the ride height changes when loaded are almost the same even with the up-rated rear springs. It means that just sitting in the driver seat could make it lower than before without changing the spring rate.

Before the installation:
Attachment 223569

After installing 4.0k springs at the rear and the Traction Mode.
Attachment 223570

Good info thanks for this. It sounds like what you did should be the minimum level of modification to compensate for the softer rear end. If my 5mm drop is permanent I've decided to go forward with the 1/4" saggy butt spacers to have the same fender to ground measurement front to rear. My rear springs are 5.1K.

It may be just the angle of your photos, but the after picture does seem to show a 5mm rear drop like mine? 5mm is extremely subtle, like 80% of 1/4 inch.

Originally Posted by strat61caster

@norcalpb I installed rear lca in the air, put it on the ground measured - loosened, tightened, remeasured (ride height, alignment) and saw zero difference. On this car at least having the suspension loaded when torque is negligible imho.

Yeah I agree. I actually just loosened all 4 of my trailing arm bolts and drove down the street and back. After tightening them all with the car on the ground my rear ride height is still 5mm lower than before the GP Sports installation.

[Racecomp Engineering]

Originally Posted by norcalpb

Good info thanks for this. It sounds like what you did should be the minimum level of modification to compensate for the softer rear end. If my 5mm drop is permanent I've decided to go forward with the 1/4" saggy butt spacers to have the same fender to ground measurement front to rear. My rear springs are 5.1K.

Remember a 1/4 inch spacer in the rear means more than a 1/4 inch change in ride height due to the motion ratio. I'm just being a jerk at this point lol.

(I don't know if the companies that make spacers keep that in mind...like if 1/4 inch refers to the spacer thickness or the resulting change in height.)


- Andrew

[norcalpb]

Originally Posted by Racecomp Engineering

Remember a 1/4 inch spacer in the rear means more than a 1/4 inch change in ride height due to the motion ratio. I'm just being a jerk at this point lol.

(I don't know if the companies that make spacers keep that in mind...like if 1/4 inch refers to the spacer thickness or the resulting change in height.)


- Andreww

Another excellent point lol. The 1/4” spacers are indeed 1/4” in height. Would you recommend not installing them? The reason I want to install them is I carry roughly 200lbs in my trunk for track days (tent, tent weights, tools) and I don’t want to worry about scraping my diffuser.

I scraped my baby pulling out of a Starbucks last week and it scarred me…

[Racecomp Engineering]

Originally Posted by norcalpb

Another excellent point lol. The 1/4” spacers are indeed 1/4” in height. Would you recommend not installing them? The reason I want to install them is I carry roughly 200lbs in my trunk for track days (tent, tent weights, tools) and I don’t want to worry about scraping my diffuser.

I scraped my baby pulling out of a Starbucks last week and it scarred me…

You'll be okay with the spacers.

- Andrew

[whataboutbob]

Originally Posted by Racecomp Engineering

Remember a 1/4 inch spacer in the rear means more than a 1/4 inch change in ride height due to the motion ratio. I'm just being a jerk at this point lol.

(I don't know if the companies that make spacers keep that in mind...like if 1/4 inch refers to the spacer thickness or the resulting change in height.)


- Andrew

https://www.mathwarehouse.com/trigon...a-equation.php

[Racecomp Engineering]

Just an FYI, the Cusco Power Brace Rear Member Side (965 492 RS) does not fit if you have the MCA traction mod...because duh...that should have been obvious.

BTW I'm selling a Cusco Power Brace Rear member side if anyone is interested. Derp.





- Andrew

[whataboutbob]

Originally Posted by Racecomp Engineering

Just an FYI, the Cusco Power Brace Rear Member Side (965 492 RS) does not fit if you have the MCA traction mod...because duh...that should have been obvious.

BTW I'm selling a Cusco Power Brace Rear member side if anyone is interested. Derp.





- Andrew

I "adjusted" mine to fit. :P