RotaryZZ

Well, I guess the next thing I'm going to do is to put in the Mazdaspeed suspension pieces and see if that help with stablizing the back end under hard braking.

Ophitoxaemia

with the spring and strut out, you can do as simple a test as tape a laser pointer to the hub and move the suspension through the travel to see which way the toe changes.

under braking load, the suspensions i am familiar with generally exhibit toe out due to bushing deflection. a small amount of bushing deflection can have a large effect on the total toe. i would imagine the mazda engineers are well aware of exactly how much deflection there is, as well as the overall contribution to handling feel. as the rubber ages, it will change, or if you use race tires it might head into uncharted territory.

my experience is hard trail braking will get the front suspension on the bump stocks and then the front goes away.

all this said, my rx8 is the most stable, precise car i have driven in anger.

james

GeorgeH

iTrader: (2)

Another good reason for stiffer springs on the track, assuming the loss in travel (assuming lowering springs) is more than compensated for by the increase in spring rate.

Ophitoxaemia

this is the big reason i ordered a set of RB springs, they are supposed to be 20% stiffer, 1/2" shorter but you cut down the bump stops a little.

modern cars generally are tuned with the bump stops as a useful transition, but i find the stock springs are so soft the bump stops are a bit jarring.

now i am starting to think- what effect would touching the bump stops in front have on the stability of the rear of the car? maybe that could be causing the wagging as the weight transfers quickly back and forth from front to rear as the front suspension bounces on the bump stops.

james

AlexJ

We raced at the Glen a couple of weeks ago and did not notice any of the problems you described on either of the cars. In fact I cannot say enough good things about the braking characteristics of this car. Our cars are setup with Carbotech XP9 in the front and XP8 in the rear, Braided steel lines and AP550 fluid. We have not experienced any faid or unpredictible behavior at all in a 40 minute race.

As for the bus stop at the Glen we are going into that braking zone at about 8000 in 5th gear, hitting the brakes at the 300 ft marker and slowing the car just enough to get the car in 3rd, you are going through the bus stop at about 8000 in 3rd gear and hitting 4th right at the second apex.

As for alignment I dont know what your setup is but we are running full neg. camber in the front about 1.6 deg. and 2.0 deg. neg in the rear. Caster is set to stock spec. set the front toe to just slightly out 1/16 to 3/32 with nothing in the rear.

Are you turning in while you are braking? Try to complete as much braking as you can in a straight line. What tires are you running, I assume stock? Also what type of lap times does a street RX-8 run at the Glen?
Alex

GeorgeH

iTrader: (2)

Excellent data point, thank you.

2 degrees of camber in the rear - I seem to remember hearing that negative camber has the same effect as toe-in, adding stability.

Or, perhaps it is the tires. Alex, I assume you are racing on something other than stock tires?

RotaryZZ

Alex,

>As for the bus stop at the Glen we are going into that braking zone at >about 8000 in 5th gear, hitting the brakes at the 300 ft marker and slowing >the car just enough to get the car in 3rd, you are going through the bus >stop at about 8000 in 3rd gear and hitting 4th right at the second apex.
I didn't up shift to fifth on the back straight. I stay in fourth and I've glanced at the speedometer as it approaching the braking zone and it was about 115mph+. I have no problem when I squeeze on the brake hard at the 300' marker. But when I try to push it deeper in the 100' - 200' marker, the back end start fishtailing!

>As for alignment I dont know what your setup is but we are running full >neg. camber
I ran my 8 in bone stock setup with the OEM RE040 tires. The only changes I made for the track is to put in the Mazdaspeed brake pads all around.
I'm afraid the setup you have would be too much for street driving!

>Are you turning in while you are braking?
At first I thought that was the case. So on subsequent laps when I try to see if the fishtailing will go away by holding on to the steering dead straight and finishing my braking before the right turn. But the car would just fishtailing crazy as it was in the previous laps! So I know its the car itself.
After that the only thing I can do is to ease up on the braking and tried to squeeze on the brake at around the 300'+ marker to stablize the back end.

Again, I have experienced nothing like this before in my last car, the E36 325is. I've used the Porterfield track pads and I can brake deep in between the 100' and 200' marker without any drama at the back end. And I haven't changed any suspension on that car either!

>Also what type of lap times does a street RX-8 run at the Glen?
I don't know. Its a DE with the PCA so its not a timed event. You are not even supposed to have any timer in your car.

Pete

Gord96BRG

Excuse me if I'm mistaken, but I don't think I saw in any of your posts that you've checked your alignment or had the alignment set. If that's the case, you shouldn't presume that the alignment out of the factory is any good! Mazda's tolerances are very sloppy, and you could easily have a bit of rear toe-out from the factory. Before worrying about camber/toe curves and changing any parts, start with the basics and get your car on an alignment rack!! (again, apologies if I missed that you've already done this)

Regards,
Gordon

red_rx8_red_int

Yep Gordon, you hit another one squarely on its head. This car however performance based it is, is made for the masses, and is street tuned, which means a lot of tolerance when it comes to alignment.

RotaryZZ

>you shouldn't presume that the alignment out of the factory is any good!

So are you saying that the alignment out from the factory may be out of the specification already?? But I feel my car tracking real straight and everything else seems fine until on that hard braking situation on the track! If that's really the case, that would be really sloppy on Mazda's behalf. Where's the quality control and pre-delivery inspection go?!

In that case, I may need to go back to the dealer and have them check/re-do the alignment on my car! Do you think its covered under the warranty??

Pete

PUR NRG

If you're tracking your car I'd recommend going to a dedicated alignment shop. I don't trust dealers to do a good job. Do a search on "alignment" and you'll see a post I made about my car's alignment as it came from the dealer. It was way off.
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GeorgeH

iTrader: (2)

And this is where the toe and camber curves come in. The sloppy factory/dealer settings are fine for just driving around, but when you start pushing the envelope of the car, you need a precision alignment, to specs that either push the envelope of the factory reccomended settings, or go outside of them.

RotaryZZ

Anyone would recommend a good Mazda shop/mechanic or a good alignment shop for the job? Btw, I live in the tri-state area (NY/NJ/CT).

Gord96BRG

Not exactly. I'm saying that the tolerances (+/-) permitted in the factory specifications permit wide variations in settings, and could easily be the cause of your handling problems. It's entirely possible to have a car with positive camber on one side, negative camber on the other, toe in on one wheel, toe out on the other, and still be within factory specs.

As I mentioned, the tolerances are huge - your car could well be within specs, so as far as Mazda is concerned - no problem.

Like PUR NRG says - do NOT try to get a dealer to do a performance alignment. They will just look at the factory specs, check your car, say "Yup, it's in range", and you still have a sloppy handling car. Find a shop that does performance alignments (check for recommendations with local sports car clubs, SCCA chapters, etc), figure out beforehand exactly what alignment specs you want, make sure they hit the numbers exactly (and the same side to side), and - this is important - make sure you either sit in the car while they do the alignment or that they ballast the drivers seat with the equivalent to your weight. If the tech doesn't believe it will make a difference, bet him a case of beer, then have him set the car up on the alignment rack, measure it, then you get in and have him measure it again. You'll find that the right rear camber, for example, will increase noticeably (IIRC, ~0.3 to 0.5 degrees?) from your weight in the car. Have the car aligned with it loaded as you typically drive it!!

I had an alignment done in May, and saw the before (ie factory) numbers and after. Both sets were within factory spec ranges, but my after alignment handling is much improved (much less understeer, better turn-in, from more front camber).

Regards,
Gordon

RotaryZZ

Btw, what's the factory spec. for the 8??

PUR NRG

Once again, do a search. There's a lot of info out there if you bother to look for it.
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cortc

Get the MS suspension and flywheel and do it again...

RotaryZZ

For whose who care to know, I've talked with Ground Control about my situation with hard braking on the track. They told me the problem is basically caused by insufficient rebound on the shock. When the car is under hard braking, the nose dive down and the rear will got lifted up. If the rebound is stiff enough, it'll hold the rear down and hence will give the rear tire the enough traction to stay planted. So, in a nut shell, the car will need a stiffer suspension setup :-)

cortc

Mazdaspeed....

Gord96BRG

I suppose that could be a factor, but... did you bother to mention to them that you've never had the alignment checked, and that you have no idea what your alignment settings are? I'm sure GC would love to sell you new springs and shocks, but why don't you at least try the inexpensive and easy solutions first?

Again - if you're having stability problems like you described while braking exclusively in a straight line, that is NOT normal for the RX-8. You really, really need to get your alignment properly set.

Regards,
Gordon

RotaryZZ

I've been thinking if the alignment is out of spec, wouldn't it show up already while the car is not under braking? I should have felt something weird going on while turning, making lane changes, straight line cruising.......etc, right?!
Anyway, I'll mostly likely re-align the car after putting in the new suspension pieces. Now, the question is what suspension pieces to get? MazdaSpeed, RacingBeat or wait for something from GC??

PUR NRG

Gord96BRG, you can lead a horse to water...

Reminds me of a study done on frogs. Scientist puts a frog on a table, makes a loud noise and measures how far the frog jumps. Amputates one of the frog's front legs, makes another loud noise and measures how far the frog jumps. Repeats the process until the frog has no legs. Scientist makes a loud noise and the frog just sits there. Conclusion? The fewer legs a frog has, the more deaf it is.

RotaryZZ, the question is are you actually going to listen to the advice you asked for or are you going to ignore it? If you're going to ignore it then there's no point to answering your questions.
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Infant Prilosec

RotaryZZ

Yes, I'll have the shop to check on the alignment, especially the toe settings on the rear. Btw, does anyone have the factory spec for our car?

PUR NRG

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GeorgeH

iTrader: (2)

Look at all settings - camber affects stability to. Negative camber will give the car better straight line stability, and it just so happens that both the front and rear suspensions are designed to add negative camber as they compress, which means that as they extend (like the rear under braking), they add positive camber.

And remember, it may not be enough for the car to "be within spec." Most alignment techs, if the alignment settings are somewhere within the tolerance range on all settings, won't bother to change anything. But you want to make sure toe is equal on both sides, pushing more on the toe-in side of things, especially on the rear. Likewise, rear camber should be the same both sides within .1 or .2 degrees, with as much negative camber allowed by the factory specs. Given that you track the car you probably want more negative camber than the factory specifies (I would). Do a search and see what you can learn. Look in the racing forum as well as the suspension forum.

And tell the tech what you do with the car - make sure he knows that you routinely brake from 130 (or whatever it is) and that's why you want a precision alignment.