ilovepotatos

Excuse me. I'm not as smart as you guys are when it comes to cars, but I do know more than most. Why haven't made 7 speed manuals yet?

PatrickB

6-speed manuals are already reaching top acceleration and top speeds in 5th gear, with the 6th gear for highway cruising. With 7 you'd either be adding a wasteful cruising gear, or making the low-end shift-points even closer together. Obviously we don't want the former; the later is only justifiable from a performance point of view if it increases gearing enough to offset the increased shifting. From a drivability point of view, it also makes the car more cumbersome to drive in stop-and-go traffic. And all of this has to take into account the increased cost of a 7-speed.

ilovepotatos

Thanks Pat!

Hercules

This is also the reason that the 3 series BMW are only 5 speeds, there is really no reason for a tall 6th gear.

Buger

http://www.rx8forum.com/showthread.p...4964#post14964

has information on the top speed for 1st - 3rd gears on the rx-8. Usnig that information, we can see that the gearing will be:

1st gear... approx 18.778
2nd gear.. approx 10.783
3rd gear... approx 7.134

The latest information from several sources (including the mazdausa site) also has the torque peak as being 159@5500 rpm. While we always knew that the middle lobe of the torque curve was approx 159@5500 , Mazda may be understating the hp and torque at 8500 because most people will appreciate a torque peak at 5500 rpm over one at 7500 rpm.

Using the new parameters in Cartest2000...

hp:........... 250 @ 8500
torque:.... 159 @ 5500
redline:.... 9000 rpm
wheels: ... 225/45R18

Diff - 4.1
1st - 4.58
2nd - 2.63
3rd - 1.74
4th - 1.33
5th - 1.00
6th - 0.80

curb weight:........ 2950 lbs
driver weight:..... 165 lbs
drag coeff:.......... .31 (conservative estimate)
grnd clearance:... 4.9" (estimated)
launch rpm: ........ 1600 (optimum est by cartest using all data)

Below are the some of the results:

0-60: ........... 5.73 seconds
1/4: ............. 14.4 @ 98.99 MPH
Top Speed: .. 156 mph

Brian

Buger

Below is a simplified way to calculate rear wheel torque. Get the total gearing ratio and multiply by the engine torque then subtract drivetrain losses (approx 20%).

Rx-8
1st - 4.58 * 4.1 = 18.778 * 159 = 2985.7 * .8 = 2388.6 ft-lbs
2nd - 2.63 * 4.1 = 10.783 * 159 = 1714.5 * .8 = 1371.6 ft-lbs
3rd - 1.74 * 4.1 = 7.134 * 159 = 1134.3 * .8 = 907.2 ft-lbs
4th - 1.33 * 4.1 = 5.45 * 159 = 866.6 * .8 = 693.3 ft-lbs
5th - 1.00 * 4.1 = 4.10 * 159 = 651.9 * .81 = 528.0 ft-lbs
6th - 0.80 * 4.1 = 3.28 * 159 = 521.5 * .8 = 417.2 ft-lbs

While the 3rd gen rx-7 had much more engine torque than the rx-8 will, we can see that it barely had more wheel torque than the rx-8 is estimated to have.

1994 Rx-7 twin-turbo
1st - 3.483 * 4.1 = 14.28 * 216 = 3084.48 * .8 = 2467.2 ft-lbs
2nd - 2.015 * 4.1 = 8.26 * 216 = 1784.16 * .8 = 1427.3 ft-lbs
3rd - 1.391 * 4.1 = 5.70 * 216 = 1231.2 * .8 = 984.9 ft-lbs
4th - 1.000 * 4.1 = 4.10 * 216 = 885.6 * .81 = 717.3 ft-lbs
5th - 0.719 * 4.1 = 2.95 * 216 = 637.2 * .8 = 509.8 ft-lbs

Rear wheel torque for 1st and 2nd gear on the rx-8 is estimated to be only 3% and 4% less than the 3rd gen rx-7. The rx-8 will hit it's top speed in 5th gear so 6th gear can be geared specifically for higher EPA highway fuel economy.

Macabre

That may be a little misleading.. you should take speed into account, and plot the difference over a given MPH range (not a given gear ratio range). You need to account for the fact that you might be able to be in a lower gear in the RX-7 at the same speed or that the torque curve could favor one over the other despite the gearing difference. I don't know how that would pan out, I haven't done the math. You seem to have some time on your hands, though In other words, make the same speed/torque graph for the RX-7 as you did for the RX-8 and overlay them. How much grunt available in a given gear is less important to the consumer than how much grunt is available at a given speed, me thinks.

Buger

You are absolutely correct in that the 3rd gen rx-7 can stay in a lower gear through a higher speed range than the rx-8. The Rx-8 is geared approx 24% more but the redline is only approx 11% higher.

Of course the point wasn't to spend too much effort to analyze all of the performance differences between the 3rd gen rx-7 and the rx-8. I'm not trying to overstate the rx-8s case against the 3rd gen rx-7.

I believe the main concern that most people have is the relatively low torque peak of 159 ft-lbs. The point of the previous example was to illustrate that a car (which many of the readers here are familiar with) with 26% more engine torque does not necessarily have huge amounts of extra torque to the wheels.

There is no way the stock rx-8 can beat a stock 3rd gen rx-7 in a straight line because it is heavier, it still has less torque to the wheels and the rx-8 wheels/tires are bigger. For a practical 4-door sedan though, I would say it does a heck of a job trying though...

Brian

RX8-Rob

Hey guys,

As a current S2000 owner, I can add my impressions of the car. First off, the S2000 undergoes a gear reduction in the tranny before the final drive. In other words, at the end of the transmission, after the power has gone through the 6 speeds, and before it gets to the driveshaft, there is another reduction. Don't know the exact figure but I think it's around 10%.

The first time I rode in the car, after 5 minutes, my thoughts were "this car is geared too high". I still bought it, though, and I am still VERY unhappy with the gearing. It needs to be lower. The car is fine on a racetrack, but with all the power above 6k rpm, you come out of corners and stuff below the VTEC range. The aftermarket does make lower gears for the car (4.3, 4.44 and 4.77) so it can be fixed but I might just trade it in on an RX8.

The key reason why the RX8 will be a better street engine than the F20C is its powerband. It will be very linear, and have a lot of available torque in the mid range. Whereas I am always caught out in the S2000 at between 4-6k rpm (130lb/ft of torque here), the RX8 should have about 25lb/ft more in this range, and it will have a much more linear powerband.

Don't even get me started about the wimpy clutch or the weak rearend (Miata sized Torsen, not RX7 sized Torsen. )

Overall, I think that the Mazda will one-up the S2000 in terms of building a lightweight, hirevving sports car. I'm really looking forward to seeing the car at the Detroit Auto Show.

Anyways, just some food for thought.

Buger

Oddly enough, I can't find the article with the speeds at 9000 anymore. I think the thread above was moved to a different section so the link doesn't work anymore?

How about another torque curve with the latest specs? The torque peak was lowered at 7500 so that the peak is now at 5500?

torque peak: ... 159
rev limit: ..... 10000
engine band: ... 9300 (10000 - 700)
95% or > tq: ... 44.1% (4100/9300)
90% or > tq: ... 61.3% (9000-3300 = 5700, 5700/9300)
80% or > tq: ... 86.0% (10000-2000 = 8000, 8000/9300)

Realize that this is still all speculation and all of the rx-8 torque curves that have been posted here have been derived from the torque curve found on the Swiss Mazda media site (http://media.mazda.ch/dossiers/Wanke.../skizze-05.jpg). That curve was first posted on the rx-8 forum by stan11003.

1.3 liter

Buger, it's guys like you that I copied off of in math class in high school.

Niebla

Could you compare your RX-8 numbers to the ones for the new Nissan 350Z?

I know that the RX-8 is going to out handle the Nissan, but I would like to see how they will compare in 0-60 and 1/4.

BTW, I'm in top of the list at my dealer (I already put moneydown), so I'm not a "Nissan troll".

Right now I have two cars, an Audi TT (APR, Borla, eibachs, 18” etc... but not room for my 1 year old baby) and a BMW 330i that my wife drives. She does not like to drive the TT, so I need a "sporty car” with room for my baby. I think that for the price the RX-8 is what I need. If the car is a disappointment then I'll have to spend 10k more and get the 330i Performance package (.5 seconds faster) that will go on sale early next year.

If anybody wants to buy a very fast, very good looking TT around March.... please let me know.


Alfonso in Austin

TT will sell for around 22K

Hercules

Isn't a "good looking TT" an oxymoron :D

Just kiddin with ya

Niebla

Well.... this is a "better looking that normal" TT, the car has a sport suspension (lowered) and very nice 18" wheels.

To compensate with the cars "lossing the rear" problems that they had cornering at high speeds, I opted for getting pretty big tires in the back (even if the car is a not a rwd) so that will never be a problem.

The fronts are 225x40x18 (on 18x8'5) and the rears are 255x35x18 (on 18x10) RH Cup wheels. one more thing, the car is one of the first cars with the original "concept weight", so the car weight is only 2800 lbs, 4 months later the weight went up ...

If anybody interested I'll post some pics.

ilovepotatos

I'm not interested, but post the pics anyways. Show off for us. Make us envy you, and therefore bring yourself to a TIMELY end.
I'm just that bad.:D

wakeech

oh, i thought taht the reason for teh grip loss was aerodynamic, as the smooth sloping back would (does) create a lot of lift, hence the factory addition of the small spoiler... if you find this solution gives you better grip, hey cool, but wider tyres don't necessarily mean greater amounts of grip: it may even mean less. your car has some mass at any given time, yes?? that mass then needs a specific amount of normal force from the ground, and thus your tyres will get only as much normal force on the contact patches as the mass of your car causes (omitting downforce, 'cause nearly no street car produces any considerable amount of this... ya, i know about supercars, they don't count ), and thus only so much force will be applied to a specific area of rubber.
if you get wider tyres (ie. larger contact patch), you're then starting to spread that same amount of normal force over a larger area, then causing no net increase in grip, and decreasing the speed at which the rubber will heat (which, as i'm sure you know, is a major factor in tyre grip) up.

but again, if this solution worked for you, cool beans.

ilovepotatos

Wakeech, get on MSN.
Uhh.......I enjoy the RX-8....?

P00Man

first off, you people are sick......i love it blahAHA

Second off lol, the wider tires increase grip because they create a larger area that the car is on to have a grippable amount of friction. The friction between the road and the tires of your car (ie the road and the tires rubbing together) is what you feel as GRIP

ilovepotatos

I always get the last word. PizzaflavouredRX8

P00Man

god your sick, i love it blahAHAHA
________
Vaporizer Net

wakeech

welcome to the forum POOMan

well, what i was saying before was that this isn't necessarily true. the friction in this case is created (according to physical theory) by the ground pressing up on the tyre, which is exactly equal and opposite to the force of the vehicle presses on the ground (through the tyres). when you have a wider tyre, this force is distributed across a wider area, thus reducing it linearly as the area is increased. this linear decrease in force between the rubber and the ground creates then a similarly linear reduction in the "density" of the friction created by the tyres. what i mean is that the overall level of friction of the tyre is the same, but the specific amount of friction generated by some amount of area is reduced.

now, this can negatively affect grip as the level of adhesion a tyre has increases, to a point, with an increase in tempurature in the rubber of the tyre. the heat in the tyres comes from some some amount of rubber generating a specific amount of friction, translating the resistance to the lateral momentum of the car into heat (which heats the ground, the air, and the tyre). if the specific amount of friction an area of the tyre makes is reduced, the effective heating also is reduced, which will end up hurting grip (if the tempurature levels are below optimum).

sooooooo, long story short, more rubber means you need more force on them to get them to temp, and less rubber means it'll heat up higher, faster, and if there's not enough of it, blister.
in racing applications, where cars can use aerodynamically generated downforce, they can just add "weight" to their cars without adding "mass" allowing them to keep inertia low while heating really really big tyres to their optimum tempurature AND a whole lot of friction-producing "normal" force (force up from the ground), generating maximum grip.

ilovepotatos

Actually Wakeech, you're totally wrong. How can ground press up on something? Oh. Is it going to come up and smack it with a cane?
Is it the ground a pimp now?
Mr.SFU...disappointing.
What he's saying in the quote is, in actual fact. Blah blah blah blah blah. [Ben Stein Voice]
He discusses "linear reduction in the 'density' of the friction"
Well in actual fact there is no such thing as friction. Just a whole bunch of screwballs running around Surrey in a Toyota Echo.
Keech, what are you talking about. Tires don't run good at temp. You need COLD tires. Why do you think they have races in Northern China? Because they have Snow. People race as much as they can with cold tires. A common practise in F3000 is to get Liquid Nitrogen and pour it over the tires. Those babies are gonna last. And they give you a whole bunch of grip, because they become more denser than the concrete and they compact themselves onto it. They then thrust tiny particles of rubber into the concrete and create a line of force. Frozen tires ownZ j00.
And who says soooooooo anyway?
Keech, you really blew it this time.
TIMBER!

wakeech

okay potatoehead, that's enough...
ROFL... jesus, change your name to Sarcastro or something, seriously...
please, don't get mad at him, he's just an idiot...

ilovepotatos

I am just an idiot. But William Andrew, we've seen the pictures, drop the Chalupa.
And we all know the proper name for the so called FC is the FD:D

ilovepotatos

Don't anyone bother telling me I'm wrong. Cold tires own.
It says right here on my hand...wait a minute. It says up yours on it. Oh wrong hand. Right here, cold tires perform best. Go buy your Liquid Nitrogen today!