BasenjiGuy

Wow! I just got the car on Saturday and I've already done 750 miles, most of it back road twisties. The car is abolutely fantastic, the best combination of power and light, tossable handling that I have ever experienced.

My previous car was a E36 Series BMW 325is. When I set it up correctly for a corner, hit the apex, and powered out, the rear suspension seemed to take an initial set and not deflect/change its line as I powered out of the corner. When testing a late model Miata and also with my new RX-8 6Speed BASE ( no DSC - just me gettin' it done), it seems like the Mazda rear suspension has some passive toe change under load transfer/acceleration that feels like the rear end is stepping out/yawing a few more degrees than I am used to in the BMW.

Is this a feature of the Mazda "preloaded" multilink rear suspension, or is it the greater power of the RX-8, compared to my 189HP 325is, causing the rear end to squat as I lay on the Renesis ponies?

Or, are the stock RX-8 tires a little greasy once they get warmed up?

I never felt out of control, but I seemed to be hanging the tail out a lot more than my BMW would in the same conditions. I know from my previous '85 GSL-SE and from reading up on the design teams for the FD and RX-8 that the Mazda engineers like to hang out the tail, so maybe I just need to get used to this additional yaw as the car oversteers thru the corner. I definitely enjoyed, but I was a little concerned that the car could get away from me.

It seemed as if I would set up for the turn, enter at an initial yaw angle, and as I got on the power the car would hunker down and increase its yaw as I exited. Maybe I just haven't driven a car this powerful thru these kinds of turns. I was having a blast keeping the revs at a minimum of 6k and screaming up to 8k+ on the exit. Great fun.

Also, I've noticed that when entering medium G corners at highway speed that the car seems to tramline, or laterally step into the curve. Is this rear toe in, or something else?

I was doing most of this hooliganism NW of Greensboro, NC, up in the Pilot Mountain/Hanging Rock area. A lot of 2nd and 3rd gear tight turns...

Spin9k

After reading your whole post I went back and read the 1st line. Kind of sums it up, don't you think, your opinion that is? That's the difference and what you did not experience w/ur old car. So Happy Day! :D It will become normal fun soon enough.

Your other car's layout was similar, but still not exactly the same. Major differences are the low center of gravity, central body mass, 50/50 weight dist., and an flexible suspension setup that seem to give the car a 'dance' on the limit. I feel it as a subtle 'yaw back and forth' on fast sweeping turns.:D Tight slower turns are so awesome, the steering slip angle is negliable, it's like a slot car, who needs brakes!

Congrats and now you're done with breakin, and ready to spin9k, regularly!

neit_jnf

I saw on the Yamaguchi (spelling?) FD book that the rear suspension is set to provide some toe change under power while cornering. This suposedly provides better feedback and driver control. I don't know for sure if they implemented this in the RX-8 but I'll check the RX-8 book after work today and find out.

PhineasFellOff

I agree with BasenjiGuy. Under hard cornering, there's a little sway combined with a slight buckling. Is it a product of the multilink? Spink9k used the phrase "flexible suspension," which might be desirable in a road-going grandtourer to accommodate road variations, but I'm not so sure it's a desirable trait for highest-performance driving.

I know the RX8 sways a bit around turns, so I was thinking if custom springs/shocks and beefier sway bars would, in addition to causing less sway, take away the rear-end buckling. Can anyone with JIC coilovers or the Racing Beat suspension pieces or whatever else comment on this?

oryas

Again, I'm not saying it's a bad trait, just that it's pretty pronounced when powering out tight second and third gear turns.

Thinking about it more, and as the fellow a few posts above mentioned, the RX-8 is lower to the ground and has a faster yaw rate than my old 325is. The ride motions are going to feel somewhat different even though both cars are good handling well balanced machines. Another new thing for me is the huge rubber on the RX-8 compared to my old car's 205-60 15's... I'm going get a lot more grip and less sidewall flex from the RX-8's tires and thus the suspension will work more.

jonnyb

the 8 isnt much more powerful than your bimmer. how would you compare your 325 to the 8?

neit_jnf

From Yamaguchi's RX-7 Book:

1. Entry into a corner:
the driver applies the brakes. The front wheels toe-out, while at the rear, the kingpin offset's toe-in and trapezoidal effect's toe-out cancel each other, resulting in zero toe change.
During braking, the front end dives and the rear lifts slightly, accompanied by a shift of the center of gravity. As a result, more toe-out is added to the front while the rear aasume a toe-in attitude.
Assuming 0.75g braking force, the front suspension will have 0.25deg toe-out and the rear 0.34deg toe-in. The vehicle maintains a stable balance entering the corner.

2. driver completes heel-toe downshift and the front wheels gradually asume a steering angle. The driver reduces braking but engine braking is added. Now the front assumes a slight toe-in, rear toe-out.
As steering lock is incresed and lateral acceleration generated, toe-out is generated at the front and toe-in at the rear.
The vehicle rolls, with outside wheels in jounce and inside wheels in rebound. The suspension movements induce front toe-out and rear toe-in. If a 0.5g lateral acceleration is generated in this particular corner maneuver, the front assumes 0.12deg toe-out and the rear 0.17deg toe-in.
As the car passes the apex and begins to accelerate fully toward the exit, lateral acceleration increases and so do the front's toe-out and rear's toe-in values. As the center of gravity moves rearward, the rear's toe-in increases because of suspension squat. Toe out of 0.12deg front and toe-in of 0.19 deg rear are induced when the vehicle accelerates through the latter part of the corner.

3. at the end of the corner, the car straightens out and assumes its normal toe values.


Throughout the corner, the RX-7's trait remains very mild understeer, however, the driver's perception is that of stable neutral steering.
Traction may be momentarily lost if the rear wheels pass through rough or slippery spots, reducing lateral acceleration and regaining it when grip is restored. The RX-7's suspension is designed to prevent sudden changes in toe attitude, when these conditions are encountered.

neit_jnf

I can't find anything remotely as detailed as the above in Yamaguchi's RX-8 Book. All it says is that it's based on the RX-7's and Miata's suspensions but with slightly different link lenghts and overall geometry.

Snip:
In the new RX-8 suspension, the shock absorber/spring unit's axis crosses with that of the kingpin axis outside of the tire's centerline and aft of the virtual kingpin axis. The lower links are preloaded in tension, at slighly over 1.0g, resisting the shock absorber/spring unit's maximum vertical acceleration and sudden reversal that could cause wandering. Because of its relation with the virtual kingpin axis, which is in torsion, the shock absorber/spring unit's reactionary force generates a stabilizing toe-in moment.


ANYONE HERE UNDERSTAND THIS??

PhineasFellOff

neit_jnf,

Was all that really necessary?

neit_jnf

hahah maybe not, but maybe it helps to enlighten someone. I said I was going to look in the books so I did... I keep my word! :p

oryas

Both cars have delightful predictable enjoyable handling qualities. The 8 feels lighter and more tossable, the 3'er is softer and more comfortable on rougher roads. The 8 will change direction more quickly. The 3'er is less skittish feeling. The 8 feels more like a go kart.

You were saying the 8 isn't that much more powerful than my E36 325is - not true - the 8 has almost 50 more HP and weighs 200 pounds less than the 3. The 1994 E36 325is has 189HP and (I think) 184 ft/lbs of torque. Yeah, it makes more torque, and lower in the rev range than the 8, but the 8 feels much faster.

The 0-60 time for the 8 is usually tested at 5.9 sec. The 325is usually gets 7.2 to 7.4 seconds. That's a big difference.

RotaryZZ

I used to own a '95 325is with the factory sport package. I've to agree with most on the dynamics of the two cars. The 3 series will take a good set at the corner and that seems to be a bit more stable at high speed curve or corner. But the 8 is more dynamic and 'dance' a little at the rear end. I'm sure if you get used to this trait and learn how to take advantage of it, it'll be a great fun.

But one thing I personally prefer the 3 series (more so on the M3) over the 8 is the reaction of the suspension pieces. The suspension travel on the 8 feels a bit too long (slow?) and the rebound is not as tightly dampened as I would prefer. The bimmer just feel faster and especially the rebound set up is just about perfect. I'm planning to put in the MazdaSpeed pieces and hope that will provide better reaction feel to track driving.

Deslock

I found Yamaguchi's RX7 book (ISBN 4947659017, published in 1995) but not his RX8 book. Where do you get it?

Thanks!

neit_jnf

Ebay!

Ophitoxaemia

i had the same impression of the odd feeling of the rear in hard cornering. i think this car as progressive rate springs, which i attributed the bouncing sensation to, but then i wonder if i am not actually hitting the bump stops- i sure have bottomed the car hard driving fast on twisty, bumpy roads, and that gets really exciting really fast as it will jump around a lot and end up sideways.

on the flat surface of an autocross course, this sensation went away, and although i found it hard to find the right set for the drift, it didnt seems to bounce. ive autocrossed enough of the 3 series BMWs to be very impressed, my favorites are the E36, not only the M3 but the regular 325i is really fun to drive- you can hang it out with a great amount of confidence. just dont forget to turn off the TC on a bimmer!

james

Deslock

When I search Ebay for words like Yamaguchi and rotary, rx8, and rx-8 I get no hits (whether or not I look in just subjects or also include descriptions). Google also returns nothing for a Yamaguchi RX-8 book, only his RX-7 book.

neit_jnf

It took me a while to find it but keep looking eventually you'll find one.

Search for RX-8 Book or RX8 Book

Deslock

Cool! Does it have an ISDN?

neit_jnf

huh? I thought ISDN is a faster than dial-up but slower than everything else connection... Is there other meaning for this?

Deslock

I meant ISBN

neit_jnf

Still no clue... Serial number? I don't understand...

BasenjiGuy

The roads were pretty smooth, just kinky. If I had been bottoming, I think I would have felt some harsh impacts at the rear suspension. When it first happened I pulled off to make sure my tires were correctly inflated as the feeling was similar to that when the rears are underinflated and the sidewall is rolling over.

Again, I maintained this greater yaw once it set in, and I could add as much power as I wanted. Maybe the RX-8 is set up to hang the way out and keep it out. Or, I just am not used to a more powerful car being able to apply so much HP to the rear end.

HMMM, I wonder if the stock tires don't roll over on their sidewalls if you really load them up?

Deslock

On the back of books sold in stores, you'll see what looks like a UPC code. Above it will be a 10-12 digit number, usually with a few dashes breaking it up. For example, an RX-7 book by the same author:

http://search.barnesandnoble.com/boo...SBN=4947659017
http://www.amazon.com/exec/obidos/ASIN/4947659017

(the edition at Amazon is dated 1992 while the one at Barnes and Noble 1995, and they had different publishers)

PhineasFellOff

Basenji is right. It has nothing to do with bottoming out. It's almost as if the rear suspension isn't heavy-duty enough for great cornering loads, like maybe something in the structure of the links or mass or whatever.

neit_jnf

found it!

ISBN4-947659-02-5 P5000E