stevenrt

Worth noting is the torsional rigidity of the RX-8 - 30,000 NM/degree, 50% greater than the Ferrari 360 Modena and equal to a Porsche 911 (see end for reference).

Or, if you like, two and a half times that of a Lotus Elise.

In addition, the RX-8 has a moment of inertia that is as good as any of the above (the Ferrari with its longitudinal mid engine position is the standard, but the Rx-8 would better it I think since the transmission is in the center tunnel), and a center of gravity as good as any of the above (the 911 with its boxer engine is the standard, but the rotary has it matched I think) - the only road car in the world (except for the Boxster which has a flat 6 mounted in front of the rear axle, but it's a 2 seater and open top, therefore less practical and less rigid) with such a combination of lowest moment of inertia and lowest C of G.

The class leading chassis stiffness, low moment of inertia and low C of G are why the car handles so well - these three attributes are what all race cars are optimized for in terms of chassis design. No other road car in the world has a better balance (not 911, Ferrari, Pagani, Mclaren,...). This in a car that sits 4 comfortably and has a decent sized trunk.

Fuel economy should be compared with other performance cars such as a 911, which has the same nominal mileage 18/24. The RX-8 may not have the same outright straightline performance as the 911, but it has very strong performance, more enjoyable engine and far and away better handling.

I see this car as a latter day Citroen DS19 or (original) Lotus Elan - by virtue of the fact that each in its day was years ahead of the rest of the industry in terms of advancement of automotive design. Incidentally, how good was the original Elan? When asked in a recent issue of Classic & Sports Car, what sports car he would buy if limited to £10k ($15K), Gordon Murray (former F1 designer and designer of the Mclaren F1) replied 'Even if I had £100,000 ($150K) to spend it would be on an Elan. Still the best driver's sports car built'.

The only improvements I would ask for are Tucker headlights (they move as you turn a corner) and HUD (head up display) that includes thermal infrared nightvision - this stuff is available on other production cars so its not science fiction.

All in all, a remarkable car best suited for those who understand automotive design - not those who merely use styling (often confused with design) when determining their next car. People who buy it for its looks or novelty are the wrong type of customers, they would be better off with a 350Z since it looks better (IMHO - though I will still get the RX-8 which shows you my priorities) and has more power - these are the attributes the average layman goes for. Whether there are enough people in the world who know enough to appreciate truly great car design to meet RX-8 sales objectives once the novelty wears off, I don't know. It's a risky business overestimating the intelligence of the buying public.

I intend to buy the RX-8 and keep the sucker until the wheels fall off in about 25 years. This one is a keeper.

Steven


Torsional rigidity reference:
http://www.rx8.co.nz/Reviews/dompost.aspx and this figure confirmed by me using the well known torsional rigidity of the original rx-7 (http://www.rotorhead.ca/ref_1980.php and this figure confirmed by another source) and published figures for the improvements at each model change - and the fact the rx-8 is TWICE as torsionally rigid as the last RX-7.

ToRX-8orToZ

LOL!

nk_Rx8

In the RX8 book, it says that the targets for bending rigidity and torsional rigidity were the BMW 318i and the Lexus IS300. The RX8 is better than the 318i, but less than the IS300 in bending rigidity. And it says that it equals that of the 318i and IS300 in torsional rigidity. So after reading that, I don't know if the RX8 is considered a 'super' high torsional rigidity car compared to other cars as it's made out to be, or are most 'good' sports sedans pretty much close to the same measurements anyway. And that it is good marketing to compare a car to some big name cars like Ferrari and Porsche in some literature here and there to associate it other cars that people expect to be way better than others, even if many cars measure in that ballpark already.

stevenrt

The car with the highest torsional rigidity in the world is the Rolls-Royce Phantom at 40,500Nm/degree. Second is the VW Phaeton at 37,000Nm/degree. You may do some net research yourself to confirm the figure for the Ferrari 360 at 20,000 Nm/degree. The Lamborghini Gallardo is 23,000Nm/degree. The new Saab 9-3 is 20,000 NM/degree. A Golf is around 18,000 NM/degree.

As you see, there is a wide range in figures - not all cars are equally rigid, and the differences are significant. Weight and torsional rigidity are the two figures that are most revealing about the way a car will drive - laymen look at power and torque.

As I said in my reference, the figure of 30,000 Nm/degree was stated in one news article (presumably using figures supplied by Mazda) and then independently confirmed by me using the following methodology:

Original RX-7: 9153 Nm/degree
1st to 2nd gen improvement: ?
2nd to 3rd gen improvement: 30%
3 rd gen to RX-8 improvement: 2x

I couldn't find the figure for the improvement in torsional rigidity from gen 1 to gen 2. If there were no improvement, the RX-8 would still be 23,800 NM/degree. Assuming a 25% improvement (reasonable based on the 2nd gen to 3rd gen figure and also what typically occurs with other car makers) you get 30,000 Nm/degree, effectively confirming the news article.

Therefore, it is very likely the RX-8 does indeed have a super high torsional rigidity of 30,000 NM/degree, as good as a 911, better than a Ferrari 360, and up near the super stiff (and heavy) Phantom and Phaeton. A lighter car needs less stiffness since there are less bending torques due to the lighter weight - hence the Elise can get by with a relatively puny 12,000 NM/degree since it only weighed 700 kg (although the version coming to America will be 900 kg!).

Believe it or not, the mass produced 26K RX-8 outperforms supercars in such a critical area as torsional rigidity, not to mention moment of inertia and C of G.

steven

emailists

After tracking this car for 6 months, almost pre ordering for almost $1700 under MSRP,- then hestating (luckily) I finally saw it at the NY auto show. I liked the looks, 4 doors, etc, (I wanted a hatchback though) and was still unconvinced. It wasn't until I actually test drove one, that I said to myself, how could I not get this car? It was truly the driving experience that sold me on it, not the other qualities, (and there are many) and I belive the stiffness and 50/50 balance are responsible.

On another unrelated note, many would dissagree with me, but I like a car that is slightly underpowered. Instead of mostly never getting to use all the available power, I really enjoy pushing a car to it's limits, and letting my driving skills (or lack thereof) be the determining factor.

AFter taking some friends out in it last night, there were simply blown away, but when I mentioned a supercharger would be available, they said it would put the car in a whole other class - and I should defintiely get one installed.

And while I would love (and would buy) an ECU tuning that would give the car another 20-30 horses, I would never go the supercharger route. I really do love pushing the engine, and keeping it at high RPMS, to get the acceleration I want. MPG aside - I simply love this car, and would do very little to change it.

RodsterinFL

THis info is great for the forum!!!!!! People need to know this.

I really beleive the RX 8 is a product of superb design. It is obvious in every aspect. It is important to Mazda to succeed with this one. I do not see this to be the case with many other cars - design, that is.

Now lets really spin some heads

What are these figures for the G35, the 350 Z and the S2000?

ahhhhhh.

Ahas

<< THis info is great for the forum!!!!!! People need to know this.

I really beleive the RX 8 is a product of superb design. It is obvious in every aspect. It is important to Mazda to succeed with this one. I do not see this to be the case with many other cars - design, that is.>>

Very true. Producing the RX-8 is also a very bold and innovative move on the part of Mazda. Albeit the car may not yet be perfect, and confusion about power rating, etc., may be somewhat discouraging, there is a lot to be appreciated about Mazda's courageous initiative to bring this revolutionary car to market. I hope people remember that, as Mazda sorts out the minor problems that might occur in the process.

ChrisW

I'm a bit confused about these numbers. Mazda claim 30000Nm/degree torsional rigidity and also claim that this is the same as a BMW 3 series?

But, a new Mini has 24500Nm/degree:

http://www.autointell-news.com/europ...ant-06-biw.htm

which is claimed to be 50% more than a BMW 3 series:

http://www.mpt.org/motorweek/reviews/rt2137.shtml

That would imply the BMW is about 16000Nm/degree.

So is the 30000Nm/degree correct? Surely, it's going to be difficult to get such a high level of rigidity with the freestyle doors?

RodsterinFL

I have been looking in the RX 8 book at home. On one page it mentions that one aspect equals the BMW and inanother it exceeds it . Maybe that is why there is a confusion. Don't have the book at work.

babylou

Chassis stiffness is a good thing, a very good thing. However, just knowing the stiffness (Nm/degree) without knowing self induced loads is worthless. Twice the stiffness is great but if the loads are double the deflection is the same. Therefore, an obese VW Phaeton better be a hell of alot stiffer than a Ferrari 360.

droidekaus

Agreed. Completely silly. Beyond silly.

stevenrt

Is the LOL comment because comparison to a 911 is so ridiculous? I forgot, a Porsche NM/degree is worth more than a MAZDA NM/degree, so even though the RX-8 and the 911 have the same torsional rigidity, the Porsche is still stiffer, even though both are the same weight ...

And of course having the engine hanging behind the rear axle in a 911 gives you a lower polar moment of inertia than the RX-8 where the engine is well behind the front axle, because everyone knows the laws of physics are different for PORSCHE.

And since the Porsche develops so much more HP, any comparison is ridiculous right? Even though when you are going around a corner you are developing the same power whichever car you are in (you are limited by grip), and when you are travelling along the highway you are developing the same hp, it really is important to have all that peak hp potentially there, because THAT is what makes a sport car right? Even though Gordon Murray, who was a F1 designer and designed the Mclaren F1, believes the ~130 hp Lotus Elan is still the best sports car ever, a bunch of poorly educated cretins like you still know more about what makes a true sports car.

As for the comments regarding weight versus torsional rigidity, I already commented on this in my follow up post. Since the Rx-8 is the same weight as the 360 Modena, they exert the same chassis twisting loads under cornering, but the RX-8 suffers less hard point deflection because it has 50% higher torsional rigidity. Not to mention lower COG and lower moment of inertia. And dont forget the Modena is an Aluminum spaceframe - two things to remember

1) Aluminum burns if you crash
2) Spaceframes are inherently poorer in crashes than monocoques

Something tells me my comments are like throwing pearls before pigs. How about a thread talking about supercharging the RX-8 so it can spank the Z? Morons.

Red Devil

stevenrt, don't get too worked up...

I tried to make a similar argument comparing the RX-8 to the 911 months back before the car even hit the market. I didn't have nearly as technical an argument, I was simply comparing the two car's dimensions, proposed weights and supposed power. I even went as far as saying the Mazdaspeed version of the RX-8 would possibly be stiff competition in the straightline for a 911. Some entertained the thought, some quickly dismissed it.

Kev

I liked the "pearls before pigs" bit :D

Talking about rigidity, anyone ever pushed a SAAB turbo convertible round a bumpy corner???

The 911 a nice car and says "I've got money" a lot louder than an RX8. The RX8 has the benefit of the latest in design technology and is really the first in it's line.

Rigidity aside - they are very different cars. That said - pick another car like an RX8, go on. Anybody???

Ophitoxaemia

i recall the original rx7 had a very very high torsional rigidity, something like 4250lbs/degree. it sure felt that way. not sure my rx8 feels as rigid, but it is still very good.

james

klegg

First, thanks for your post, really good stuff

Second, I used the proper "pearls before swine" here before in a worked up moment, so I know how you feel.

take a deep breathe, do not let it get to you!!

Remember, many of us get it, even if we do not post!

zerobanger

yea, I want what he is smoking.

Q121825

Right on!

And those of us who do get it get a kleggspeed mod!