hsitko

iTrader: (1)

So. First off, i love this car for many reasons. There are a lot of fast cars in the world. For the ones that i have driven, which is a lot as i work in the automotive industry, the fd really shines in terms of handling. According to Mazda, the rx7 holds .95 lateral "g's" on a skid pad. So my first question is, does it make any sense at all to modify this car's suspension?

My second question is. When deciding to modify the suspension there are a lot of things to take into account. If you lower the car you will lower the center of gravity for the vehicle. Sure but then you change all of the suspension's angles while the car is resting on the ground. This effectively changes the roll center of the car. This can make a pretty big difference in how the car handles. So they make coil overs where you can adjust the height of the springs and you can adjust the portion that attaches to the control arm. This way you can retain the factory roll center. That being said, doesn't that make strut and spring combo's absolutely pointless for this car if you lower it from the stock ride height?

The next topic that i want to touch on is corner balancing. If you decide that the roll center is not that important what about corner balancing? There are small adjustments that companies like koni or billstein have put on their struts. Things like adjustable perches. But even still you cant really get too finite of an adjustment out of something like that when they are not infinitely adjustable. So here again this points us in the direction of coil overs.

What suspensions are you fd owners out there running? What ones don't you like? Which ones are the best for the price, and why? I'm really interested in the JIC FLTA2's. Inverted mono-tube, adjustable bases, helper springs. The only thing i dont know is if they are hydraulic or gas. I prefer hydraulic.

--Hank

RE-Amemiya

Answers will be very different based on what kind of driving you are going to be doing.

Autocross, drift, Time Attack/Road Course???

Have you reached the limit of your car already, and do you really need an upgrade?

Just some thoughts to think about. I'd say the average person doesn't need to upgrade anything.

Black91n/a

Just to clear something up, the ONLY way to regain the stock roll center location using the adjustments on the coilovers is to raise the ride height up to the stock location. The coilovers don't change the suspension geometry, position or anything other than through ride height. On a double a-arm suspension like the FD's, this isn't that big of a deal, and other concerns like ground clearance and tire clearance are bigger worries.

Yes there is a point to changing the suspension, even if it's just maintenance. There's plenty of bushings, pillow *****, shocks and so on that are wear items. Replacing them, even just with new stock items will make the car feel and handle better.

Corner balancing is important, and no you can't do it with the different spring perch heights on Konis, etc. The adjustment is far too coarse. Doing a proper corner balancing allows you to have equal handling turning in bothe directions, so you don't oversteer one way and understeer the other. For purely street use just setting the ride heights to be exactly the same side to side will get you fairly close and is good enough.

All dampers (shocks, struts) work hydraulically, even if they are "gas" shocks, that just means they're gas pressurised, which all shocks are to some degree. Generally it's used to differentiate monotubes and twin tubes, with the mono's being the "gas" (they operate at higher pressures) and the twin tubes being "hydraulic".

What suspension's right for you is a very personal thing and depends on the intended use, the road/track conditions, wheels and tires, power, your tolerance for a bad ride and many others.

hsitko

iTrader: (1)

Black9, thank you for a very informative post. I thought that the roll center was only related to the control arm angles. I thought that it only really effected steering input. Things like bump steer etc. I know that the center of gravity changes when lowering the car no matter what.
I had never thought about the reasoning behind corner balancing. That is a really good point and made my brain feel really good to read. It totally makes sense that you might induce under/over steer depending on how much weight was applied to each wheel. I guess that there are a lot of options as far as which suspension to get. I suppose that my main concern is getting something that is very versatile. I intend to drive my car on the street as often as possible. I think that getting as much seat time as possible is an important thing. But should i take it to a lapping day or an autocross i would like the dampers to be as versatile as possible. Alignment may need to be tweaked a little depending on the situation but thats ok. I have access to alignment devices, and know how to use them. As far as spring rates i'm ok with something kind of stiff. In my ae86 right now i have it set up with 6kg/mm front and rear. Its only intolerable on the street with the struts at their hardest setting and its a light car. So, i am kind of starting to lean towards the tein monoflex or the jic flta2's. Are there any recommendations that you can make on a good affordable competition for these two setups?

Black91n/a

Yes, roll center is directly linked to control arm angles, and since the control arms are fixed to the body and to the spindle, the angles are determined by the ride height. The coilovers don't move the suspension pickup points, so the only way to change the roll center with coilovers is to go up or down. You can fix it by moving the pickup points, but this is beyond what most people can or are willing to do.

Most of the time when lowering a car the roll center drops faster/further than the center of gravity (increased roll couple), meaning the car wants to roll more for a given cornering load. This means you need to be even stiffer to compensate. That's why it's a bad thing to have the roll center drop when lowering the car.

Bumpsteer is a funtion of the relative angles of the control arms and the steering linkage. The factory sets it up to be best around the stock height, so when lowering it often gets worse. Again, the only way to fix it is to move a pivot points.

As for autox and track days, each requires a somewhat different setup to be great. In autox you basically want an unstable car that oversteers a fair bit at low speeds, this translates into it being unstable at higher speeds, which is bad at the track, where more high speed stability is a good thing. One way to get the best of both worlds is to have an adjustable rear sway bar, or use a reasonably small one and disconnect it for the track. That way you can have low speed oversteer for autox and high speed stability at the track with minimal changes. You don't even need to remove it, just disconnect one side.

For both street and track the standard reccomendation is Tein Flex. I've got them in my FC and my dad uses them in his turbo Miata, as does about half the club we autox with. They're a very good deal, are usually on the soft side as far as the competition goes, which is good for comfort, but they're still plenty stiff for track use. They're durable, have good valving, can be revalved and serviced in the US, are inexpensive, perform well and aren't too uncomfortable. Definetely a good combination. I'm very happy with mine.

zonblitz

iTrader: (9)

I have the JIC Magic FLT-A2's and I love them!

I also have the JIC Carbon strut braces front and rear, Racing Beat front and rear sway bars and Fighters Garage Trailing arms and toe links.

I can say that my car handles amazingly. In my personal opinion if you get the JIC's you will NOT be disappointed!

2MCHPWR

iTrader: (2)

the MONO flex for the FD isn't sold in the US yet.

7racer

Howard Coleman has a shock dyno and has some good recommendations for suspension settings for the FD

here is one of his quotes:
https://www.rx7club.com/forum/showpo...4&postcount=19

7racer

and another one:
https://www.rx7club.com/forum/showpo...2&postcount=10

7racer

here is that thread:
https://www.rx7club.com/forum/showth...ight=25+inches

7racer

and another:
https://www.rx7club.com/forum/showpo...1&postcount=10

7racer

ok done searching

https://www.rx7club.com/forum/showth...ight=25+inches