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Discussion Starter · #1 ·
Hey all, I'll be doing a TT conversion on my project Stealth ES next winter.

I'm looking at BC Racing coilovers. The digressive valve series in particular.

This is just a fun street project car. I'm planning on running 10 psi with a good tune. For traction, I'm running 265 width tires on 18*9.5 inch rims, a quiafe, and solid front and rear motor mounts (poly side mounts), and want to install coilovers this spring.

I live in Michigan and want to daily drive the car when the weather is nice.

What spring rates I should run for my application? I know that FWD 3S came stock with a firmer rear spring than front. Should I duplicate the stock ratio?

Thanks.
 

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1994 Mitsubishi GTO Twin Turbo MR
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Honestly, if you're looking at it from just a driving aspect - stock is probably the way to go. It's a little more floaty/cloud-like but super comfortable (can't speak for a N/A chassis though.)

Ultimately, it's going to depend on your application for spring rates and what you want out of the car in terms of feel, and what you want it to do. As you can't "just choose" a spring rate and call it good, because they impact the car's feeling. It's a difficult answer, because everyone likes their vehicle to feel a certain way when it does a certain something.

If you drive your car normally, the only difference you would know is that it feels physically stiffer. If you do any TA, AutoX, Drag Racing, canyon carving, etc. You can tune the feel out if you notice you understeer too much or liftoff oversteer, oversteer, etc.. (Note: Springs aren't the only thing to tune feeling!) That's how you'll get the best approximate gauge on what spring rates you want.

Only way to know is to try it out, and see if you like it.

Otherwise if you just want coilovers to drop the car, and cruise with, it's probably not really worth discussing spring rates.
 

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Discussion Starter · #3 · (Edited)
Thanks for the reply. Geat points.

Once I'm done with my build I do plan on some occasional drag racing and autox. I get that tuning springs is a process. I'd just like feedback on a good starting point.

I want to drop the car to get rid of the 4x4 look, but mostly I want stiffer springs to handle launches when I put the turbos in.

I did some deep searching and 10k/8k is what I've seen recommended by knowledgeable NA guys that have done the TT conversion for street driving, even though stock NA has firmer rear springs than front. I believe them but I'm curious why maintaining the stock ratio isn't a good idea with coilovers.

Anyway, I realize you'll get better results with dedicated setups, but I'm looking for a DD that can handle decent roads and nice weather that I can take to the strip sometimes or carve corners with. I don't mind compromising for a jack of all trades setup.

Based on my reading it sounds like ohlins are my best bet, but they're out of my budget, so BC racing coilovers with digressive valving at 10k/8k is a good second option.

That sound about right?
 

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1994 Mitsubishi GTO Twin Turbo MR
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Thanks for the reply. Geat points.

Once I'm done with my build I do plan on some occasional drag racing and autox. I get that tuning springs is a process. I'd just like feedback on a good starting point.

I want to drop the car to get rid of the 4x4 look, but mostly I want stiffer springs to handle launches when I put the turbos in.

I did some deep searching and 10k/8k is what I've seen recommended by knowledgeable NA guys that have done the TT conversion for street driving, even though stock NA has firmer rear springs than front. I believe them but I'm curious why maintaining the stock ratio isn't a good idea with coilovers.

Anyway, I realize you'll get better results with dedicated setups, but I'm looking for a DD that can handle decent roads and nice weather that I can take to the strip sometimes or carve corners with. I don't mind compromising for a jack of all trades setup.

Based on my reading it sounds like ohlins are my best bet, but they're out of my budget, so BC racing coilovers with digressive valving at 10k/8k is a good second option.

That sound about right?
I have 8Kg/6Kg and they're perfect for my setup (which my plan is exactly like yours, a little bit of everything.) It is stiffer than stock, but firm, planted, and holds up well against squatting at the track.

I can't say I've tried different suspension, but some folks I know run 12-16kg and it rides like a brick so, that would be one thing I'd be wary about.
 

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Discussion Starter · #5 ·
That's great feedback! Thanks, man. You're right, I think lighter springs would be better for a DD.

So here's where I get hung up.

Stock spring rates for first gen (lbs/in) are:

AWD 218 front, 157 rear

FWD 168 front, 196 rear

If my math is right that means stock ratios are:

AWD 1.4:1 F/R

FWD .86/1 F/R

So going by maintaining stock ratios, 8k/6k makes perfect sense in your application being AWD. Also transferring weight to the rear is way less of an issue for you. lol.

For my application it would seem I'd want 7k/8k to maintain the stock ratio.

I read that a lot of autox guys who run a FWD LSD actually prefer a higher rear spring rate for handling. I'll also be running an LSD on my car.

IDK. 7k/8k would be damn close to the stock ratio to stock but I know jack about suspension. lol. I was hoping to get feedback from some suspension gurus.

I'm leaning towards either 7k/8k or 6k/8k, or possibly even 8k/8k.

If I hated it, how hard would it be to change spring rates? At what point do the dampers have to be revalved?
 

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If I hated it, how hard would it be to change spring rates? At what point do the dampers have to be revalved?
You would have to swap out the spring (or have them create a new spring with the specs you need.) To my knowledge, spring rate is completely bound by how the spring is created. As in you cannot make a 8kg spring 12kg, nor can you make a 12kg a 3kg spring. A 3kg spring is 3kg, 8kg is 8kg, so on and so forth.

I'm not a professional by any means on suspension, just a lot of research and book knowledge.

However, all of the hypothesis, theory, and math behind it all is subjective - because not every car is the same. And ultimately it's only going to really affect the car when you're reeeaaally pushing it to it's limit.
 

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Discussion Starter · #7 · (Edited)
You would have to swap out the spring (or have them create a new spring with the specs you need.) To my knowledge, spring rate is completely bound by how the spring is created. As in you cannot make a 8kg spring 12kg, nor can you make a 12kg a 3kg spring. A 3kg spring is 3kg, 8kg is 8kg, so on and so forth.

I'm not a professional by any means on suspension, just a lot of research and book knowledge.

However, all of the hypothesis, theory, and math behind it all is subjective - because not every car is the same. And ultimately it's only going to really affect the car when you're reeeaaally pushing it to it's limit.
Thanks, yeah I know you got to change springs to change rates, I just wasn't sure how far you could go without revalving the damper.

It sucks that the options for fwd are so limited. After researching I decided I'd rather wait and shell out for ohlins or KW because for my application (turbo street fwd with occasional strip/track) I'd rather buy once.

But I found out they just don't make them for FWD. I guess I'm stuck with BC racing or similar.

If this car didn't have sentimental value and I wasn't so stubborn (and I didn't get such a great deal on it), I would seriously think about selling it and going to a better supported platform.

Oh well. BC Racing says you can go +-2kg for spring rate before needing a revalve so I think I'm going to go with 6k/7k FR to maintain stock ratio and see how I like it. After a deep forum dive I found another member that had that spring setup from Mueller for his fwd TT and he loved it. That gives me some room to fine tune it once I get some track time in. Also I've seen some feedback that digressive valving isn't great for the street and it's better to go with their BR series.

Thanks for the feedback.
 

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Any time. It's a very subjective topic, and didn't wanna sound like a broken record saying "iTs uP To YoU bEcAuSe aLl cArs aRe DifFeRenT"

I think a combination from 4.5Kg to 8.5Kg (min/max rates of your choosing) is a good entry level as far as spring rates go. They are not rock hard stiff, but not soft and floaty either.

Not a physics expert, but assuming "rate" stays the same regardless of material type (1lb of rice weighs the same as 1lb of steel ordeal). I think you will like the 6Kg/7Kg setup. I really enjoy mine at 8Kg/6Kg. It's stays planted on the ground, handles roads nicely and comfortably. If anything, that range is the perfect combination.
 
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