GR86 - Understeer Alleviation - RCE Tarmac 2 (7k square setup)

[Spuds]

Originally Posted by cmiovino

RCE SS-1's (6k springs, even), with their camber plates up front, OEM ones in the rear.

Vorshlag vs RCE/KW camber plates won't make a huge difference in height between the two, comparing the two setups in terms of height should be very much the same.

I think that's way too low for T2s on the vorshlag plates. I recall that the RCE camber plates for SS raise the perch up a bit right? The vorshlag perches are actually lower than stock, meaning you lose bump travel. Anything below 13" is not going to go well at all.

[Spuds]

Originally Posted by strat61caster

949’s ride height suggestions have a lot to do with their damper design droop/bump lengths, it shouldn’t be gospel, but I think it’s a great starting point.

@Spuds do you have the big oem tapered bolt in the upper hole of your strut? You have to use some level of camber bolt, even just the smaller oe bottom bolt to get past -4 degrees of camber even when the struts are slotted.

You know, that would certainly explain the camber problem. Yes, just used the OE bolts in the proper locations.

[Tomyyyu]

Originally Posted by strat61caster

949’s ride height suggestions have a lot to do with their damper design droop/bump lengths, it shouldn’t be gospel, but I think it’s a great starting point.

@Spuds do you have the big oem tapered bolt in the upper hole of your strut? You have to use some level of camber bolt, even just the smaller oe bottom bolt to get past -4 degrees of camber even when the struts are slotted.

And I think we should put out a PSA for people to not blindly following 949's guide. XIDA's rear shock has 7mm more travel than us, and that made a huge difference.


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[Breezio]

Originally Posted by Tomyyyu

And I think we should put out a PSA for people to not blindly following 949's guide. XIDA's rear shock has 7mm more travel than us, and that made a huge difference.

Yes. Plus their guidance is geared towards track driving. A great track setup is not a great autocross setup. And vice versa.

[Spuds]

FYI, raised the car, particularly the front end. 341/346mm, up from 336/342. It drives completely different now. Roll center, bro.

Also added a rear sway bar, but honestly the front end steering change is more pronounced.

[ZDan]

Originally Posted by Spuds

FYI, raised the car, particularly the front end. 341/346mm, up from 336/342. It drives completely different now. Roll center, bro.

Also added a rear sway bar, but honestly the front end steering change is more pronounced.

If raising the car a bit significantly improved front grip, I'm still *guessing* (even more so) it was more of a front bump travel issue!

Raising the front of the car raises front roll center, which would increase lateral weight transfer up front if rear ride height were left the same, which should give more understeer (all other effects ignored for the moment). But of course raising the rear does the same thing in back, and it's really the F/R weight transfer distribution that affects handling balance.

I forget though, for which type suspension does roll center height move more with ride height changes, strut or multilink?

[Racecomp Engineering]

Our SS1/SS2/SSR camber plates should give you more bump travel at a given ride height vs the Vorshlag plates, but the Vorshlags give you caster and I think you can get a little more camber.

Bump travel in the rear is not nearly as much of a problem as people used to think IMO.

- Andrew

[Racecomp Engineering]

Originally Posted by Spuds

You know, that would certainly explain the camber problem. Yes, just used the OE bolts in the proper locations.

Using the "OEM crash bolt" is almost automatic for me at this point...easy and reliable 0.5 degree is nice to have.

- Andrew

[Spuds]

Originally Posted by Racecomp Engineering

Our SS1/SS2/SSR camber plates should give you more bump travel at a given ride height vs the Vorshlag plates, but the Vorshlags give you caster and I think you can get a little more camber.

Bump travel in the rear is not nearly as much of a problem as people used to think IMO.

- Andrew

For future reference are the SSx plates compatible with Tarmac coilovers? (it's not obvious to me lol)

[Spuds]

Originally Posted by Racecomp Engineering

Using the "OEM crash bolt" is almost automatic for me at this point...easy and reliable 0.5 degree is nice to have.

- Andrew

Bottom hole or top slot?

[Racecomp Engineering]

Originally Posted by Spuds

For future reference are the SSx plates compatible with Tarmac coilovers? (it's not obvious to me lol)

Yes.

Originally Posted by Spuds

Bottom hole or top slot?

The "OEM crash bolt" is essentially using another set of the OEM lower bolts in the top hole/slot. The standard OEM bolt for the top hole has a shoulder which takes up space and prevents you from tilting the hub inwards more.

- Andrew

[ZDan]

Originally Posted by Spuds

For future reference are the SSx plates compatible with Tarmac coilovers? (it's not obvious to me lol)

So be aware that with the SS plates you will likely lose some front camber as the strut protrudes up above the interface with the srut tower.
My car is kinda asymmetric, I was only able to get -3.2 degrees at the front left *with* factory camber bolt in the upper holes. Could probably could get around -3.8 at front right.

But for mid-corner front grip I'd rather have -3.2 camber *with* adequate bump travel than -4.5 with the outside front being overloaded due to being hard on the bumpstop... Also 330mm front ride height = no problemo...

[900BRZ]

Originally Posted by ruturaj001

Hmm, looking up, this looks right, it is squared. I just started researching in to the topic and I agree that square spring rate doesn't make sense on twins. I was using @900BRZ 's blog.

https://900brz.com/posts/gr86-vs-brz

Looking at your numbers, we would be staggered by a much larger margin when trying to have square wheel rate. 60% stiffer in the rear.

Thanks for the mention and correction. I’ve updated the post.

[ruturaj001]

Originally Posted by 900BRZ

Thanks for the mention and correction. I’ve updated the post.

We all are learning. Your blog is how I got introduced to the topic and really like your organized approach. I wish someone would pick up your research and put it to good use, like improving their oil coolers like you did with upgrades. Companies making profit from these don't seem to have put as much effort as you did.