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Discussion Starter · #1 · (Edited)
Hi, I'm Catachan! I started a racing team called "Skeptic Racing" back when I was racing Miatas because there were so many "rules of thumb" that no one remembered where they came from anymore, and that I had doubts about. The idea of Skeptic Racing is that when we want to improve the car, or our driving, we look for existing hard data about why we should not do something that everyone else says not to do, and if we can't find it, then we try it and collect the data so we can share it with the community!

In this thread I wanted to document my process of building an MR2 Spyder for XSB. I recently purchased a car with some modifications already done to it, and I wanted to list what I had, and detail my experiences with my own improvements to the chassis. I intend to document information such as wheel and tire sizes, alignment specs, spring rates, suspension settings, ride height, and more.

I also intend to include discussions of my impressions of the car after each event. I am a member of the Central Carolinas Region of the SCCA, so most of my events will take place near Charlotte, NC.

My first event with the car was this past weekend. It was a two day event that started Saturday June 18, 2022, and finished in the afternoon on Sunday June 19, 2022.

The car setup was as follows
Configuration NameValue
Wheels17x7et45 square fitment
Tires205/45r17 UTQG 280 Bridgestone Potenza S001
ShocksFactory
Spring RatesFactory
AlignmentUnknown (I haven't gotten it on a rack yet to check)
TransmissionC60 (Celica GT 6 speed MT)
Engine1ZZ
Sway barsFactory
DifferentialLotus Elise Replica Helical Diff

DayFastest TimeSplit to Leader
175.1056.361s
276.0557.393s

Notes:
The wheels and tires were the factory wheels and tires that came with my previous race car, a 2019 30th Anniversary Edition Mx-5 Miata. They were fun to drive on, but not very performant. They are too large in diameter, and I had issues with rubbing in the front under sustained cornering. The rubbing was worst on the driver's side, which makes sense since the weight of my body would compress that side more.

Impressions:
Holy cow, this car is FUN. As you can see from my results, I am slow. I have a long way to go to catch up to the rest of my class, but wow, this car is fun. I can't stress that enough. Handling is extremely neutral, and the car encourages me to drive it more correctly than a Miata does. I noticed immediately that I was avoiding trying to trail brake into corners much more than I ever did in my Miata. Even on the square fitment of tires, the car did not feel loose, and while I was a little concerned that I would be disappointed by the MacPherson Struts in the front and the Swing axle suspension in the rear, I actually discovered that they kept the tires on the ground excellently, and the responsiveness of the car in the slaloms was like a dream.

Immediate Next Steps:
I've already ordered a few performance or safety items for the car.
  1. New Top
  2. Hard Dog Roll Bar
  3. Bronze Konig Hexaform wheels(15x8et25 front, 15x9et35 Rear)
  4. Falken RT660 tires (225/45r15 front, 245/40r15 rear)
I'm also in the process of figuring out what level of data acquisition I can get for the Spyder off of the OBD-II system on the car, so that I can collect that tasty, tasty data and share it with you! I've got a Race Capture Mk2 that I used on my Miata, so I'm hoping to get some useful proprietary PIDs off of the car for data logging. Once I have that data, I'll share my configuration information in this thread and probably a dedicated thread as well.

Future Steps:
In no particular order, I'm planning the following upgrades as well:
  • Coilovers (brand to be determined, I'm taking suggestions on brand and spring rates)
  • Racing Seats (HANS compatible)
  • 6 point Harnesses (HANS compatible)
  • Steering Wheel
  • Sway bars
  • 2GR swap (This will almost certainly be the last thing I do!)
  • Camber bolts (I may already have them but I need to check)
Thanks for reading this far, I hope you enjoy following my build process and what I report in here!
 

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It is definitely not a swing axle in the rear. MacPherson on all 4.

Everyone has an opinion on spring rates... Spirits suggests something like 15kg/mm - 25kg/mm springs depending on the circuit and tires. I like 4kg front 7kg rear, but i could see value in as much as 8kg front and 12 kg rear depending on surface and tire.

Good luck.
 

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I didn’t see where you listed the year of your car. It makes a bit of difference if you are concerned about SCCA regulations at all, since the stock rear wheel diameter and width are different starting in 03 as well as LSD only being an option in 04 and 05.
 

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It is definitely not a swing axle in the rear. MacPherson on all 4.

Everyone has an opinion on spring rates... Spirits suggests something like 15kg/mm - 25kg/mm springs depending on the circuit and tires. I like 4kg front 7kg rear, but i could see value in as much as 8kg front and 12 kg rear depending on surface and tire.

Good luck.
The spring rating is very much a function of the speed and smoothness of the surface.
And yes the tyre is a factor too as the air volume is a spring too.

Also have a look at the various spring ratings here on the sticky about that.
You will notice a striking thing in front vs rear in the TRD ones.

Lastly, Spirit values need to be interpreted with the caveat that their car is set up for pronounced oversteer. See his take on ARBs too.
 

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Discussion Starter · #7 ·
I didn’t see where you listed the year of your car. It makes a bit of difference if you are concerned about SCCA regulations at all, since the stock rear wheel diameter and width are different starting in 03 as well as LSD only being an option in 04 and 05.
The car is a 2002, but in XS-B the rules are pretty open, any wheels/tires, any engine, any transmission, any suspension, etc.

I forgot to mention the Lotus Elise Diff that's in the car, so I edited the OP to include that in the table.
 

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Discussion Starter · #10 ·
I'd like to add some downforce to the front of the car for stability at highway speeds, since it feels like the front end is lifting up off of the ground.
 

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I'd like to add some downforce to the front of the car for stability at highway speeds, since it feels like the front end is lifting up off of the ground.
You'll find that's more of an alignment issue than anything else.
 

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I'd like to add some downforce to the front of the car for stability at highway speeds, since it feels like the front end is lifting up off of the ground.
Vent the hood
Add the chin lip
- both reduce lift under front

Create some rake - reduces lift under whole car

Add a tear off ridge behind the rear lid - reduces turbulence behind the car which induces feeling of instability
Add a proper wing - works like the fletches on an arrow

Mine is under 900 kg and réally light up front but as stable as an arrow.
 

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Wow, this is exciting. I am currently competing in E Street, but will soon bump up to XS-B (Tennessee Valley Region). My Miata friends think that my car could be a class leader once it is k swapped. In a couple of months, I should have ES in the bag so I will do coilovers/wheels and start in XS-B. Fingers crossed, the new motor will be in for next season. I would love to help gather data for this new class with you. I am planning 225/245 CR-S tires on 15x9s.

My biggest competition will be my buddy with a turbo NA6 and 225 Kumhos. He regularly gets 3rd in raw time, normally behind the shifter cart and our AS national champ in his Z06. We were just talking the other day about what the best car would be for this new class since the rules are almost unlimited. Again, exciting times.
 

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Discussion Starter · #16 ·
Discovered last night that the rear toe link was wobbling at the eccentric bolt. I guess the next step is going to be to replace that, or to replace the bushing. Does anyone have any recommendations for doing that? The Megan Racing/Godspeed/etc control arms are all half the price of OEM...
 
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