I have an early 2004 with 135K miles on it.

The rear of the vehicle has always been lower than the front. (Of the RX-8s I've seen on the road, I've seen a few with this problem.) About a year after I got the car, I got the Racing Beat springs for the front only - the rear is still stock. This lowered the front a little without changing the ride characteristics. The car looked great and handled great for many years. People would often ask me what suspension set-up I had. I will tell them Racing Beat in the front and stock in the rear. "The rear is stock? Wow, that's low for stock." would be the normal reaction.

Slowly, the ride in rear got looser and looser and I found the car bottoming on the bump-stops fairly small bumps. Four months ago, I decided it was time to change shocks around the vehicle (the front was getting pretty loose as well.) I went with KYB Gas-A-Just mono-tubes. That helped for a couple months but now the rear is almost as bad as it was before. I'm looking for options. The performance of my front suspension is perfect. I would not change a thing. I would like to only fix the rear so here's what comes to my mind and you can give your comments (BTW, I do have about 70 pounds of stereo equipment in my trunk):

1. I could go with coil-overs and get exactly the height and feel that I want everywhere, but that would be a pricey option for a car with 135K miles on it. I also think the front is perfect the way it is and I doubt I could find coil-overs simply for the rear. (Also, this is my daily driver so I need non-race coil-overs.)

2. Could I upgrade to the newer RX-8 rear suspension? I know Mazda re-worked the rear suspension a couple years ago. Would it be plug-n-play? Buy the springs and shocks and slap them on. Are the mounts the same height and dimensions on the new RX-8 as my 2004?

3. Do my rear springs simply have fatigue? I could just slap on "new" factory springs designed for my model year and see what happens. That would probably be the most affordable solution, but I have this feeling that it will be just as bad as before. (The rear of my vehicle has been low from day one or almost day one.)

Looking for suggestions. I can provide pictures if they would help.

-Mr. Wigggles

 

Replace everything.... stop replacing just the rears...

 

^

"Four months ago, I decided it was time to change shocks around the vehicle (the front was getting pretty loose as well.)"

Anyone else...

 

Bilstein shocks... RB springs..

Don't buy KYB bullshit.

 

You have extra weight in the rear with a bias towards stiffer front aftermarket springs....

Surprised it handles decent at all....


Get a set of matching springs at least...

 

I thought about getting RB springs all the way around but it would (in theory) lower my rear even more by another 0.5" The sound system is only 70 lbs in my trunk (most of which is right behind the rear seat in a stealth install) That weight's equivalent to about the weight of 11 gallons of gas or a stick thin super model in my back seat. It's not a monster stereo system.

-Mr. Wigggles

 

You should have never bought just front springs...

 

It is not a completely crazy idea. Racing Beat sells the springs individually specifically for that purpose. I loved the way my car handled and drove for over 6 years and 100K miles with my current set-up.

-Mr. Wigggles

 

Your symptoms are kinda weird my friend. I would take your car to a Mazda import shop (preferably a shop that works on lots of Miatas or MX-5's). A dealer is fine too. I would go through the entire rear suspension. Having had this problem for a while the cause may have influenced the integrity of other components.

As far as the new suspension goes---don't bother. All the same. You could take an easy route and get a Jiffy Lube oil change and ask the wrench to give it a quick glance once over. Tip him $10 for spending a few minutes. Take a look in your trunk at the top of the rear shock towers and report back what you observe.

 

I have an issue with rear end sag as well; but can't tell if it's just because I have these ridiculous monstrosity speed bumps I have to climb over at the condo where I live at. I've been seriously considering switching to the S2 rear shocks because the spring perch is supposedly moved enough that on my S1 (mine is a 2004) that I'd get additional ride height in the rear without changing anything. I can't see any signs of uneven tire wear or anything else to suggest alignment is off in any way, so I'm not sure; however, I have about 55K miles and am on my original shocks, front and rear.

 

I've been thru this same quandry, and was about to get Bilsteins, and RB's, but the suspension feels very firm; it was just making a whump sound when hiting bumps.

So I realigned it once more, and found that the -1.9 camber I thought was in the back had changed to approx. -2.2 or so.

When I tried for -1.5 rear camber, the mechanic said he could only get it down to -1.65
on the right so we went with that on both rears.

It actually picked up the rear suspension by 1cm higher, the whump went away, and it feels smoother across bumps.

I see a lot of people (ricers) driving around with a rear splay on purpose, so you can eyeball the rear camber, and make sure the rear camber looks straighter than the front.

 

Sounds very familiar. I get the "whump" sound when I go over fairly minor bumps and if someone sits in the back it is much worse as you can imagine. Last time I had my alignment done, the tech at NTB said my car didn't have a camber adjustment for the rear even though the previous time I went to a different NTB the tech changed my camber from the stock -1.9 to about -1.1 on both sides. I wanted to get my suspension ironed out before I got my car realligned, but maybe the thing to do is go the other route. My camber is definitely negative on the rear (always has been); I just don't know how much.

-Mr. Wigggles

 

It sounds like a pretty good idea. It appears that the spring perch is about a half an inch higher for the S2 factory shocks. I am deducing that from the following. Koni only makes one set of adjustable shocks for all RX-8 model years. They have a disclaimer on Tire Rack if you use them in 2009+ RX-8's:

So I would have to think the opposite would be true. If you used stock S2 shocks in your S1 car, you should get 1/2" ride height raise or more. I'm going to look into this as well. It might be a good solution for me. My guess is that the dealer price is not going to be very good for stock shocks.

EDIT: Just checked with Rosenthal Mazda and S2 rear shocks are $395 a piece . I ordered the Bilsteins yesterday from Tire Rack I think I am going to keep those and go that route. (New springs for a 2004 are $79.95 a piece for your info.)

-Mr. Wigggles

 

Time to go somewhere else for alignments

 

The spec defines a range of ~1 degree in camber change over 1.9inch range of ride height for the rear suspensions.
since the tire ware and camber have little effect over ride height I see no reason in this height difference of 1.9inch rather than shock absorbers and springs ware.
dose drop from maximum spec height of 15.8 inch to 13 inch is because of shock absorbers and springs ware ?
Is there any other reason for this drop ?
If I replace to new OEM shock absorbers and springs, will the ride height be 15.8 inch ?
thanks,
Boris

 

My 07 GT was at 13.75 rear and 14.25 front from day one. I didn't want to chase the suspension, so I tracked what I had until I figured out the alignment I wanted; See Red's alignment above.

When the shocks are gone I'll put Bilsteins, but the car is firm and grips well on bumpy or smooth pavement.