I've been curious about this for a few years now.

What exactly are the differences in the suspension geometry of the RX8 compared to the FD that make everyone rave about the 8's handling?

Are the control arms mounted differently, longer, shorter etc?

Pics anyone?
Thanks.

 

I know nothing about anything and may be flamed for it,

AFAIK the FD handling is world class and everyone has always raved about it

The rx8 I've only heard people say its a "fun" car, in comparison with other sporty DDs

I'm not on these forums much so I'm probably wrong and people on here rave about the rx8 handling idk

 

The RX8 handling honestly, is okay. I know everyone raves about the RX8, but I've driven and owned both, and stuck with the RX7 at the end of the day.

You have to remember that the RX8 weighs more. Its taller than the 7, and its center of gravity is higher, and you do feel that in the fast corners. It does not feel as low and wide and planted as the 7 to me.

Has no turbochargers, so you really have to drive the hell out of it and keep the revs up there with the gearbox, to make it move along with urgency.

The 8 does have more electronic driver aid and soft, feel good, easy-to-drive stuff built into it, like stability control, etc, which give the illusion of it being better, or feeling nicer to drive. But turn all that off and push it with an FD, and the skilled driver would probably go quicker in the FD on the track. The RX8 seemed to soak up the roughness and have better ride quality though.

I'm not familiar with the RX8 geometry itself, but a LOT of race car development went into the RX7. Its suspension is as good or better than the equivalent Porsches of the same era, but cost far less. The RX8 was not developed to be as hardcore race as the 7. The RX8 had to appeal to a wider public, for sales. Therefore I'd expect some compromises, and not as race-orientated design as the RX7.

 

The only think I've ever heard is that the lower front a-arms are longer on the 8, and the rear suspension is a bit different configuration. The chassis itself is also significantly stiffer, which probably more or less evens out if you cage it.

 

good question! i've never seen a comparison of the actual geometries themselves, but that doesn't stop us from looking at other things.

the Rx8 also has a much longer wheelbase than the FD, the FD is right around 2400mm (like a classic Ferarri), the Rx8 is 2700mm its close to a foot longer. this makes it more stable. my base Rx8 was actually only 2950lbs with a full tank of gas, so its heavier than an FD, but not hugely.

the second thing is roll centers, the Rx8 manuals make a big deal about how the front and rear roll centers pivot around the roll axis, which is a refinement over the FD.

the front suspension looks a lot like the FD's, except that the arms are longer, and they all attach to the sub frame.

the rear has some detail refinements too, the subframe is stronger, with more mounting points, the arms are longer, the steering axis in the rear and the shock axis are different, there are a couple of preloaded bushings to improve response. they also removed the pillow ***** and replaced them with ball joints.

so the Rx8 is broadly similar to the FD, but with a bunch of detail refinements, as you'd expect.

the net result is that it rides better, its much much easier to drive fast (in fact the Rx8 lets you do monumentally stupid things behind the wheel, and it not only doesn't bite, but its still quick), but its still sharp, and very intuitive.

 

I've been curious about this for a few years now.

What exactly are the differences in the suspension geometry of the RX8 compared to the FD that make everyone rave about the 8's handling?

Are the control arms mounted differently, longer, shorter etc?

From what I observed driving both the substantive differences in the FD RX-7 and RX-8 handling are-

suspension-
RX-8 did away with the sliding bushings (and therefore pillowballs) that the FD had that affect toe based on loads transferred from the suspension arms to the bushings. Mazda says they did this to give it more pure handling- note it is also cheaper to produce.

Wheelbase-
RX-8 has a longer wheelbase which helps handling front/rear weight transfer is a function of center of mass and wheelbase. Longer wheelbase = less weight transfer to front in braking and less weight transfer to rear under accel.
Both of these are states of transition (seen clearly in the example of braking weight transfer to turn in cornering weight transfter).
The less weight transfer shifting around means the more stable the car is through transitions, which in turns means less time wasted waiting for the chassis to "settle" between maneuvers.

Center of mass-
Rx-8 moved the gas tank(s) way forward to under the rear seat and moved the engine back several inches. In addition they removed around 150Lbs of engine weight from the front end. More centralized mass means faster reaction to inputs related to rotation.

Lack of torque-
Want to make any car handle better in steady state? Remove the effects of throttle input. This DOES limit advanced use of throttle to affect weight transfers in transitional handling. You have to plan ahead and commit in the RX-8 where in the RX-7 you can improvise your line much more readily. It is a different experience.

Brakes-
Bigger is better it seems.

Advances in technology-
The RX-8 electric power steering rack reduces weight on the engine and also provides MUCH better feel. ABS has come a long way, we didn't get the updates to the RX-7 here.

Ergonomics-
FD is lacking shoulder bolster on the seats so you find yourself supporting your weight in cornering through leveraging the steering wheel which reduces your ability to input. Steering I already mentioned here, but its worth mentioning again.
A car that is easy to drive will be faster. This is what I have been working on for racing my FD lately. Mazda has been working on it a lot since they built the FD as well. My 2008 Mazda3 makes driving my FD feel like driving a truck, the RX-8 is the same way, but doesn't fall apart when you bring the driving up to 9/10ths or 10/10ths like the Mazda3.

My feeling is though the RX-8 is a superior chassis, the FD RX-7 is still a superior car. The RX-8 really did prove its not ALL about handling. I hope Mazda learned that lesson.

 

?? How did they lose that much weight? That's huge!

 

?? How did they lose that much weight? That's huge!

The question is how did Mazda let the FD RX-7s 13BREW get so heavy. Twin turbos and emissions.

Published engine weights

Sport Compact Car Feb 2002

"According to mazda, the Renisis weighs 332lbs, which is significantly less than the RX-7 engine, which weighs 450 lbs."

These weights are with full engine attached accessories, flywheel, etc to maximize the weight savings of the Renisis from lack of PS pump, air and AC comp bracket as well as plastic UIM, and lighter flywheel.


More published engine weights from 279 page book "RX-7, the New Mazda RX-7 and Mazda Rotary Engine Sports Cars" By Jack Yamaguchi 1985


1965 production Cosmo L10A (alum. sidehousings)--- 225 lbs (pg 261)

1968 production Cosmo 10A (alum. sidehousings)--- 224 lbs (pg 262)

1968 production R100 10A (cast iron side housings)--- 268 lbs (pg 262)

1971 production JDM RX-3 10A--- 282 lbs (pg 264)

1967 production R130 13A--- 301 lbs (pg 264)

1977 production USA 12A --- 321 lbs (pg 244)

1977 12A sports kit (over the counter P-Port)--- 242 lbs (pg 244)

1977 12A MFR (factory P-port)--- 224 lbs (pg 244)

1977 production 13B--- 330 lbs (pg 244)

1977 13B MFR (factory p-port)--- 233 lbs (pg 244)

1978 production RX-7 12A--- 348 lbs (pg 267)

1983 production RX7 12AT (turbo)--- 356 lbs (pg 270)

1986 production RX-7 13B DEI--- 337 lbs (pg 47)

1987 production RX-7 13BT--- 377 lbs (pg 52)

 

450-332 = 118 lbs lighter which is still a lot. The turbos aren't really all that heavy; they feel like maybe 15 lbs or so. Of course there is also the cast iron piece between the turbos and the housing, which I've never removed. Having trouble "seeing" that whole weight difference.

 

heres a part explosion i found on all data, cant really get much out of it but maybe it will help.

front


rear

 

Front (Standard Suspension)


Front (Sport Suspension)


Rear (Standard Suspension)


Rear (Sport Suspension)

 

Some more info on the Rx-8 front suspension...

 

and the rear suspension...

 

So in short:

1. Stiff(er) sub-frames
2. Longer suspension arms/optimized geometry
3. Better shock lever ratios
4. redesigned bushings with less deflection

OK, now somebody break out the CAD program and build us a couple sub-frames that will adapt the RX8 suspension to the FD :-)

Just goes to show how bad *** a car Mazda could build if they'd lose the 4-door weight, and add a little power.

 

my 2004 Rx8 base is 2950lbs, which is not that much more when you consider it grew 9 more airbags, two seats and the car is a foot longer... and my FC convertible is 3000lbs on the nose!

i drove an FD back to back with the 8 the other day, and the FD does feel like a truck, the NVH is much much better on the 8, the FD made the 8 feel really flat power wise.

i think if we were doing quarter miles, its actually very close, but in the 8 the turbo never spools up, so it doesn't feel like much.

 

i drove an FD back to back with the 8 the other day, and i was surprised at how much better the NVH is on the Rx8, the FD is rough!

 

I was always impressed with the way the Rx-8 drives and handles.


If I was going to make a dedicated track car I would choose an 8 over the 7, and install an REW. Plus they are cheaper now.

 

The Fd turbos are freaking anchors and a lot heavier than 15lbs. Don't forget to include all the turbo related accessories, IC, piping, pre cat, exhaust manifold ect. FYI the new bigger 16x should be lighter than even the Renesis because of the aluminum side plates. An All Aluminum 13b short block only weighs 110lbs. I'm guessing 130lbs for the 16x shortblock.

 

Well at least we know that the future Rx7 will have an even more superior suspension.

 

Yup, now imagine it as a more compact, spartan 2650 lb. 2-seater with the 280 hp it was supposed to have. That would have been a nice 2003 RX7.

 

that's the rumor for the new car, half a GTR in weight, and 300-350hp.

 

The shame is, they could have built the car I just described in 2003, not 2017... and it's looking more like 2800/300.

 

I'm sure Mazda wanted to but wasn't allowed. Ford was barley persuaded to let them build the 4 seat Rx8 (which had to be more practical) let alone another profitless, slow selling 2 seat sports car. The engineers silently built the Rx8 prototype behind closed doors on a stretched miata platform. When the engineers gave the head guy at Ford a ride in the prototype, he was excited by the way the car handled and performed. He green lit the production after that. I'm really excited because now after 30yrs, Mazda can FINALLY do what THEY want as long as their other skyactive vehicles sell well (which they are).

 

2800 lbs with 300hp sounds pretty darn good. Maybe there will be a little extra power in a 2nd model year or Mazdaspeed edition. I know lighter is better but if it's too light, it's bound to be small. It needs to be bigger than the current Miata and 3rd gen FD.

 

Why does it need to be bigger than the FD, and how many Mazdaspeed models have ever had more power?