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

[renfield90]

I am pretty sure jackets have been won on a square setup (heck, Heitkotter won with off the shelf V3s which I think are inferior to the T2). People who really want to maximize their setup are not going to stay there but it is a good predictable package for people who want to bolt on an upgrade and not think about it too much. RCE needs to make money and they can do that by appealing to the widest range of customers possible. Having worked with an aftermarket shop before, let me tell you it's way harder than it looks.

[Racecomp Engineering]

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.

Yes it's squared, but the motion ratio for a 2nd gen is not 0.75, it's closer to 0.78. Either way, what some are aiming for is called "flat ride" which is in reference to natural frequencies. I wrote this little thing to help explain that:

https://www.instagram.com/p/B6TKG6Un...RlODBiNWFlZA==

Flat ride or even wheel rates is one approach to setting up a car's suspension, one that was developed initially for comfort on cars with soft springs/dampers and lots of travel. It is definitely considered by actual motorsports engineers, but it's not the only consideration. These cars have very different front and rear suspension designs and geometries and limitations and some odd quirks. Formulas are guides, or starting points with which we try to work through a whole bunch of other compromises with the car and application.

There are advantages and disadvantages to square spring set ups for these cars, and a big advantage is that for most people they are easy to drive fast on track with stock swaybars and reasonable alignments. For some, stiffer rear spring rates feels good and works better for their application. And that's totally cool, there's never going be 1 set up that works for every car and every driver and application.

Heck, I run 5k/6k on my car and it kicks ass for a fun primarily street car...but it would be faster around a track with 6k front springs, even if that throws off the formula.

- Andrew

[ruturaj001]

Originally Posted by Racecomp Engineering

Yes it's squared, but the motion ratio for a 2nd gen is not 0.75, it's closer to 0.78. Either way, what some are aiming for is called "flat ride" which is in reference to natural frequencies. I wrote this little thing to help explain that:

https://www.instagram.com/p/B6TKG6Un...RlODBiNWFlZA==

Flat ride or even wheel rates is one approach to setting up a car's suspension, one that was developed initially for comfort on cars with soft springs/dampers and lots of travel. It is definitely considered by actual motorsports engineers, but it's not the only consideration. These cars have very different front and rear suspension designs and geometries and limitations and some odd quirks. Formulas are guides, or starting points with which we try to work through a whole bunch of other compromises with the car and application.

There are advantages and disadvantages to square spring set ups for these cars, and a big advantage is that for most people they are easy to drive fast on track with stock swaybars and reasonable alignments. For some, stiffer rear spring rates feels good and works better for their application. And that's totally cool, there's never going be 1 set up that works for every car and every driver and application.

Heck, I run 5k/6k on my car and it kicks ass for a fun primarily street car...but it would be faster around a track with 6k front springs, even if that throws off the formula.

- Andrew

Thank you, I went trough it and would look up older posts as well. My goal is to have a best setup for learning if that makes me slow even then it's not a problem. I think I do not want to go very fast, that's why I am using 225 SX2s and moderate camber (no coilovers yet). I am just understanding things and might ask stupid questions. I plan to get coilovers in future but still time isn't the goal, feel is.

[Tomyyyu]

Originally Posted by Racecomp Engineering

Yes it's squared, but the motion ratio for a 2nd gen is not 0.75, it's closer to 0.78. Either way, what some are aiming for is called "flat ride" which is in reference to natural frequencies. I wrote this little thing to help explain that:

https://www.instagram.com/p/B6TKG6Un...RlODBiNWFlZA==

Flat ride or even wheel rates is one approach to setting up a car's suspension, one that was developed initially for comfort on cars with soft springs/dampers and lots of travel. It is definitely considered by actual motorsports engineers, but it's not the only consideration. These cars have very different front and rear suspension designs and geometries and limitations and some odd quirks. Formulas are guides, or starting points with which we try to work through a whole bunch of other compromises with the car and application.

There are advantages and disadvantages to square spring set ups for these cars, and a big advantage is that for most people they are easy to drive fast on track with stock swaybars and reasonable alignments. For some, stiffer rear spring rates feels good and works better for their application. And that's totally cool, there's never going be 1 set up that works for every car and every driver and application.

Heck, I run 5k/6k on my car and it kicks ass for a fun primarily street car...but it would be faster around a track with 6k front springs, even if that throws off the formula.

- Andrew

Got it. So I ended up following 949’s suggestion on ride height and rake. Granted my wheel diameter is smaller than the one he mentions in the article. https://www.949racing.com/supermiata...lignment-info/

I’m now on:

- 7/9k springs
- Ride height (floor to futhermost) part of jack points
- Front Right: 5 9/16”
- Front Left: 5 7/16”
- Rear Left: 5 12/16”
- Rear Right: 5 14/26”
- Rake: 5/16” or ~8MM
- Measured with:
- No driver
- A052 (245/40/17)
- 17x9 +45 RPF1
- 8/12 gallons of gas

Question for @for preload, I just used the spring perch and moved it my desired ride heights. So what has me confused is if preload, droop, and bump travel need to be adjusted on these KWs? Does preload need to be adjusted too?

It seems based on this article:
https://suspensionsecrets.co.uk/coil...ght-correctly/ they mention that KWs use just spring perch adjustments so preload, bump, and droop are all already factored in when they are built. Which if true, that’s a cool feature, sure does make the end users life easier.


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[Racecomp Engineering]

Originally Posted by Tomyyyu

Got it. So I ended up following 949’s suggestion on ride height and rake. Granted my wheel diameter is smaller than the one he mentions in the article. https://www.949racing.com/supermiata...lignment-info/

I’m now on:

- 7/9k springs
- Ride height (floor to futhermost) part of jack points
- Front Right: 5 9/16”
- Front Left: 5 7/16”
- Rear Left: 5 12/16”
- Rear Right: 5 14/26”
- Rake: 5/16” or ~8MM
- Measured with:
- No driver
- A052 (245/40/17)
- 17x9 +45 RPF1
- 8/12 gallons of gas

Question for @for preload, I just used the spring perch and moved it my desired ride heights. So what has me confused is if preload, droop, and bump travel need to be adjusted on these KWs? Does preload need to be adjusted too?

It seems based on this article:
https://suspensionsecrets.co.uk/coil...ght-correctly/ they mention that KWs use just spring perch adjustments so preload, bump, and droop are all already factored in when they are built. Which if true, that’s a cool feature, sure does make the end users life easier.


Sent from my iPhone using Tapatalk

Correct, adjust ride height with the spring perch. This adjusts preload + bump + droop. You don't really have to worry about preload. As you adjust ride height, you're trading bump between droop travel.

You have a range of ride heights that work and KW + RCE and other coilovers that don't have the adjustable lower mount tend to have more total travel. You can think of them as already preset to a proper length. Nothing inherently wrong with coilovers that let you adjust the lower mount, just have to do it right (many don't and even some manufacturer's don't know how to do it right).

- Andrew

[Tokay444]

Be sure to also corner balance.

[Tomyyyu]

Originally Posted by Tokay444

Be sure to also corner balance.

I’m going to do an event first. So was thinking let’s just align and go for it. Before I spend ever more cash corner balancing. I don’t have scales.


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[Tokay444]

To get that far and then not complete the puzzle seems like doing yourself a disservice if you ask me.

[Tomyyyu]

Originally Posted by Tokay444

To get that far and then not complete the puzzle seems like doing yourself a disservice if you ask me.

Fair enough. Just gotta find a place that does both.


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[Tokay444]

If your alignment shop doesn't corner balance, I wouldn't waste your money on their alignment.

[Tomyyyu]

Originally Posted by Tokay444

If your alignment shop doesn't corner balance, I wouldn't waste your money on their alignment.

Yeah was reading around that you should disconnect end links when you align. And when you align you shift weight around (?). So corner balance is naturally part of the process.


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[Gearhead23]

You should be sitting in the drivers seat when the alignment is done. That is what my guy requires. That 130 to 200 lbs of driver weight does make a difference.

[Tomyyyu]

Originally Posted by Gearhead23

You should be sitting in the drivers seat when the alignment is done. That is what my guy requires. That 130 to 200 lbs of driver weight does make a difference.

Yup. Found a place that will align and corner balance. They will use gym weights to get my weight in the drivers seat.


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[ruturaj001]

Originally Posted by Tomyyyu

Yup. Found a place that will align and corner balance. They will use gym weights to get my weight in the drivers seat.


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How much is the quote estimate?