It runs 18 x 11 +30 wheels, so that's 69mm extra extension on the outside edge per side compared to stock wheel size.

The RX8 is only 19mm less front track width than an 86 although it does use a slightly wider wheel which would have a small effect on the arm position.

I will be purchasing the entire front end of a RX8 very soon so would be happy to share some measurements.

Unless you've already measured and know that the attachment points are the same distance apart as on the FRS/BRZ (or have measured the arm lengths), seeing the stock arms doesn't tell you anything. If the attachment points are further apart it'll be wider with the same length arms too.



69mm = 2.72", that's way less than the extra width.

These are the only measurements I have found of the RX8 suspension at this stage, they give an idea but not very accurate.

https://photos.google.com/share/AF1Q...cxMURkaTc0MG5B


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I purchased a pair of RX8 front uprights tonight, I was planning to buy the whole front end but I could not find one for the money I was willing to spend.

While I was there the guy was nice enough to let me take some measurements of the RX8 control arms. As it turns out if you compare the distance of the lower control arm inner pivot across to the face the wheel bolts to for the BRZ and the RX8, the RX8 is actually only about 19mm longer.

Anyway I am pushing ahead with my conversion from mac strut to double wishbone. I won't hijack this thread any longer so if you want to follow the progress then keep an eye my build thread for updates.

The RX8 uprights are now mounted on my BRZ, for the most part the double wishbone conversion is complete. I have extended my wheelbase by 35mm mostly so that the steering rack will clear the crank pulley since the rack is now in front of my Honda K24 engine.

https://i.imgur.com/k0rdcVw.jpg?1

Wow.. Beefy control arms much? looks like roll case size tubing. 1 1/4 at least.

Yes it is 1.25"

Most roll cage is 1.5" with a 1.75" main hoop.

The shock must mount directly to the lower control arm so strength is needed. You could use a smaller tube with chromoly but I prefer to work with mild steel.

Why the preference over chromoly? Cost? Material characteristics? Keep the progress coming!

Mostly the material characteristics, my day job is as a material scientist so I have a pretty good understanding of this. I am not a professional welder, if you follow my build thread you would see I only began welding about 6 months before starting the project, all self taught, reading, youtube tutorials etc. Chromoly weighs the same as mild steel but it is stronger so you can use smaller tube, thinner wall to save weight. The downside is you must weld it following strict guidelines, your welding technique must be on point or you can end up with brittle welds. Mild steel is much more forgiving to weld so I see less risk in using it and I take the weight penalty.

You taught yourself to weld to do this project.. I'm impressed. I'm a bit of a welding hobbyist myself. Takes a lot of balls start chopping up a car and welding it together without prior experience. Appreciate you're sharing your handiwork.

:cheers:

I have no background in engineering or physics or any kind. I can do basic math and I’m just trying to learn to get the proper coilovers setup by having numbers guide/help me. Natural frequency, motion ration and such. Just reading through the whole thread and all intrigues me and that is why i’m posting. Not trying to derail the thread or cause any trouble. If I offend anybody, I am sorry and i can delete this post right away, just let me know.

I came across this website but they are using a different car and trying to plug in numbers that is already posted in this site. Thank you so much and you guys are awesome! Not really sure if I can use the formula that the guy had in there but i don’t have the numbers like axle weight and wheel weight. Could this be applicable in our car?

https://drivetribe.com/p/lets-talk-s...TuOW5CN4C8x7JA

That approach (choosing suspension frequencies first) is a good first step in setting up a car. It's just a first step and there's much more to think about. That analysis did not mention swaybars for example, which can contribute a significant amount to roll resistance.

There are a lot of "rules of thumb" but none of them are perfect! Decent starting points though.

- Andrew

It is giving me numbers that I'm like "wait I don't want those frequencies in my setup" but I don't have all the numbers needed and like you said there is more factors that is in the equation. Thank you though for your input. I appreciate it!

The best suspension frequencies are the ones that help you get around a track the fastest. :)

Many top level suspension engineers are not that concerned with some of the usual flat ride suspension frequency "rules of thumb".

- Andrew