RX8ER

I was watching the video posted here called "TimeAttack" and I'm trying to figure out what gear the driver is in when he starts his lap. It looks like he is in 2nd gear until he hits around 107km@8500rpm and then shifts to third until around 149km@9500rpm and then shifts to 4th where he continues to 173km@7700rpm before he has to downshift. If this is true then this means that he still had two gears left to play with. So what is the top speed of this car?

I own a GrandPrix and it has some kind of a bullsh.t limiter that cuts out at 172km. It totally sucks when that happens. If the RX-8 can do 173km in 4th gear and still have two gears left then Waaaaa Hooooo!!!!!!. Not that I would ever drive it that fast, no really i wouldn't, well maybe once or maybe twice or maybe....

I can't wait to get my car.:D

Puppy1

ORIGINALLY POSTED BY Buger

Mazda did not gear the RX-8 for maximium acceleration. They spaced the gears so that top speed is in 5th and 6th is just taller for better fuel economy. The approx speeds @ redline for each of the gears are below:
1st gear ... 42
2nd gear ... 69
3rd gear ... 96
4th gear ... 132
5th gear ... 157 but drag limited at approx 155?
6th gear ... 186 but drag limited at approx 150?

RX8ER

So does that mean that the driver started his lap in 4th gear in the video?

Hercules

6th gear is for gas mileage, as it is in most cars. 5th gear is really the driving gear

RX8ER

Are those speeds in mph then? My original post was in km like the video was.

RX-7_16

wow i never thought of 6th gear as gas milage..its very true too..i just learned something

Hercules

It's also why all the BMW 3 series have only 5 speeds on their manual trannies. People complain about it but they don't know any better :p

Hercules

I said 3 series, not M models.

M3's gearing also makes use of 6th gear to be gas mileage gear

RX - 8

the Acura RSX type S has a 6th gear that is also used for saving gas

pmacwill

M5. *drool*

RXhusker

I suppose if the autobauhn went through Nebraska I could use a "real" 6th gear :D Since it doesn't I will take the better gas mileage. My first RX-7 was a 4 speed and you know what -- I never needed more than that -- it was plenty to beat my friends' 240Z and Porsche 914 :D

Given the top speed for 3rd gear is 96mph -- I doubt even 5th gear is much needed except for gas mileage.

bdclary

Gas mileage, eh? Than why (according to what Buger posted) does it take almost 3900 rpms to do 80mph? With one less gear, my 86 rx-7 only takes 3200 rpms (in fifth gear) to do 80.

Doesn't make any sense to me. With an extra gear, supposedly for mileage it should take me less rpms, right?

Brian

MikeW

The M3 top speed is achieved in 6th gear, 7K rpm, 175 mph
Those speed in gears for the Rx-8 look a little off.
1st 40mph@9000 (no tire slip)
2nd 66.56 @9K, again no tire slip
3rd 92 @ 9k (US gear, JDM 98mph)
4th 127@9k
5th 151@9k
6th 155@7800, probably drag(flat out) and electronically limited(for down hills & tail winds)

Okay to make the Rx-8 faster, the decision will be between 225/40 18 and 235/40 18's (wheel width is 8 inches wide)
The Rx-8 really doesn't need all the load carrying capacity of big 225/45 18's, with its 52/48 unladed weight distribution, going to 48/52 fully loaded, that is at most 1000 lbs on each tire(roughly) and 225/40 18 can carry about 1200 lbs.

So with 225/40 18, the Rx-8 (hopefully) will hit 160@8350 (roughly 245 hp)

Cihuuy

just wondering... if we change the ring a pinion for the 8 to a longer gear... can we increase the top speed then?? I mean 5-6th gear wont mean that much then if it only give 5km extra!?!

James

My BMW M5 also has a 6 gearbox.. But the 6th aint for low gas
milage.
:D

The picture is in KM/H not in Miles...

Buger

Hi RX8er,

You're correct in that the video starts with the RX-8 in 2nd gear. The speedometer in the video is in Kph which is more of a worldwide standard. Unfortunately, the US never switched to the metric system so we still think of everything in miles, gallons, etc. Note that there is some delay in the digital speedometer.

Assuming a conversion factor of 1.609, see the below approx speeds at 9000 redline again:

Mazda did not gear the RX-8 for maximium acceleration. They spaced the gears so that top speed is in 5th and 6th is just taller for better fuel economy. The approx speeds @ redline for each of the gears are below (mph/kph):
1st gear ... 42/67
2nd gear ... 69/111
3rd gear ... 96/154
4th gear ... 132/212
5th gear ... 157/253 but drag limited at approx 155/249? 6th gear ... 186/299 but drag limited at approx 150/241?

Of course the true frontal area of the RX-8 is not known yet so we will have to wait to see at what speed drag limits the top speed of the RX-8 (assuming there is no speed limiter).

6th gear can be slower than 5th if 6th gear is too tall to provide enough torque to overcome the resistance (mainly aerodynamic drag) at high speeds. Usually taller gearing allows a higher top speed **up to a point**. Further evidence that a taller gear does not *always* provide a higher top speed can be seen when the top speed of the Auto RX-8 is tested. The auto RX-8 4th gear (4.444 * .694 = 3.08:1) is actually geared taller than manual RX-8 6th gear (4.444 * .843 = 3.75:1) but the top speed will likely be about 15 - 20 mph less than the manual RX-8.

6th gear rpms @ 60 mph on the RX-8 may not be as low as your 86 RX-7 (or my 87 RX-7) but comparing apples and oranges does not always lead to meaningful conclusions. The auto RX-8 also has less gears than the manual RX-8 and also has a taller top gear that does 80 mph at around 3200 rpms.

Engineering is a field of compromise. You want the most power, the best fuel economy, the cleanest emissions etc, etc. If Mazda wanted to be conventional, they could have geared 6th gear for top speed and spaced the other 5 gears shorter for quicker acceleration at lower speeds. Mazda could have knocked off around 4/10 of a second in the 0-60 if they geared the RX-8 with something like the below speeds @ 9000 redline:

1st gear ... 37
2nd gear ... 62
3rd gear ... 86
4th gear ... 119
5th gear ... 140
6th gear ... 157 but drag limited at approx 155?

The 1/4 mile time would also be a bit quicker but then again 6th gear rpms @ 60 mph would be more like 3300 instead of 2900. Looking at how the RX-8 is geared from 1 - 6, we can safely say that "Mazda did not gear the RX-8 for maximium acceleration. They spaced the gears so that top speed is in 5th and 6th is just taller for better fuel economy".

Besides, rotors spinning at 967 rpms @ 60 mph (driveshaft spinning @ 2900 rpms) is not all that high is it? :D

Using first gear as an example, I have the total gearing @ 16.70944 (4.444 * 3.76). This means that the driveshaft rotates approx 16.71 times before the rear wheels rotate once. At 9000 rpms, the wheels rotate at approx 32317.06 times per hour.

The circumference of the 225/45R18 wheels/tires is approx 81.59" which leads to approx 776.52 revs/mile. 32317.06 / 776.52 = 41.6 mph which I rounded to 42 mph.

I assume you probably just punched some numbers into a speed/rpm calculator, yes MikeW? Which one was it? What did you calculate the circumference of the RX-8 wheels/tires to be and what was the revs per mile figure that you used? Also, I'm sure that you must be aware that tire slip or not in first and second gears has nothing to do with the speed at redline. (unless you believe the RX-8 will have so much torque that there will still be tire slip at 40mph and 66.56 mph?)

Brian

Buger

Below is a Cartest2000 graph of the drivewheel torque per gear assuming that the rev limit is 9500. You can see that 9500 rpms shifts should be done from 1st to 3rd gears for fastest acceleration. The 4th to 5th gear shift should be done at around 9310 rpms because 5th gear has more wheel torque after that.

You can also see how aerodynamic drag forces increase at higher speeds and how the greater wheel torque of 5th gear will lead to a slightly higher top speed than 6th gear.

unemployedpimp

so if the rx8 wasnt drag limited it would go 186 in 6th gear?
and if it can we like buy a chip or something?

DreamWarrior

You can't just get rid of the drag limit by chipping the car. The drag limit is because of the body design, the car is pushing through air, thus there is a drag. The faster you go, the harder it is to get the car moving faster, as the air is pushing harder and harder against you. The only way you are getting the car faster is to add more torque...MAYBE a chip will do that, but it sure as hell isn't going to add enough torque to get you up to 186.

unemployedpimp

ohhhh ok thanks, remeber people im just 14 i dont know as much as u guys so dont beat me up.

pelucidor

You could probably hit 186mph if you were in a vacuum (but you'd need to supply air to the engine and passengers)...

P00Man

lol

so mazda released the gearing of the RX-8....cant beleive i missed that!
________
Depakote Lawsuits

MWG

What if we change the rear end ratio so maybe we could get greater accleration and then lower the 6th gear to get better mile per gallon. Brian how high would the rear end have to be to, and I think the 6th gear be have to be lower I think, to give our RX-8 a higher top speed. Does any know if someone makes an ajustable rear end. I think they use them in F1 racing but don't know how they work. I could be wrong about the rear end does anyone else know.