Sputnik

For those of you who claim that the contact patch is merely "reshaped" on a wider tire, answer this:

If changing the tire patch so that it is wider is the only thing that makes handling better, then how come braking and launching also improves with wider tires?

Explain that.

---jps

BryanH

They were. Purchased at the same time in staggered sizes, otherwise identical.

Tread pattern? What tread pattern? :D
http://home.earthlink.net/~bryan64/p...v700safter.jpg

ilovepotatos

Oh Bryan! By the way, I was biking home from work (Whoo hoo! Pizza Hut! Actually I'm not working much anymore, but thats beside the point)
I was biking along past the Bank of Montreal, and I hear this loud and unsettling fart. Now I think I've crapped my pants, but it was someone driving a black MR2 to the bank, very similar to yours! That guy had the worst aftermarket exhaust I've heard, (well 2nd worst, theres a guy at my school who took a Firefly Turbo and put a huge kit on his car, took it from 110 hp @ 3000 rpm to 110 hp @ 6000 rpm
:D
Anyhow, I think this must make you sad, to see a fellow MR2 owner (who was a girl by the way) go and take a quality set of wheels, and Crapify it...and who goes to Bank of Montreal anyways? That persons got their head on backwards.

BryanH

Meh... rice happens.

ilovepotatos

Wow! I've got almost as many posts As Bryandog!

Buger

Ok everyone, here are the final rx-8 torque curves...

zoom44

so why does it appear to go up to 220 after your max torque point?

Buger

Final production gearing ratios for Japan (US to be same?)...

Diff - 4.444
1st - 3.760 * 4.444 = 16.7094
2nd - 2.269 * 4.444 = 10.0834
3rd - 1.539 * 4.444 = 6.83932
4th - 1.187 * 4.444 = 5.27503
5th - 1.000 * 4.444 = 4.44400
6th - 0.843 * 4.444 = 3.74629

Not quite as aggressive as the one article that mentioned speeds at redline for the first three gears but the gears are better spaced.

If the curb weight is 2920, Cartest estimates the below:

0-60......... - 5.99 sec
1/4 mile.... - 14.49 sec @ 100.68 mph
Top speed - 158 mph (if not speed limited)

Brian

Fëakhelek

Nice. Where does this graph come from?

Buger

That would be a good question to ask Mazda. I did not come up with these torque curves. It appears that the torque curve actually peaks at around 6000 rpm but perhaps Mazda marketing felt like a 5500 torque peak would "sound" better?

confucious

Buger,

Using your formula from a few pages back (3.760*4.444*159*.8), I get 2125 ft/lbs of wheel torque in 1st gear.

How does this compare with like g35 or 350z or s2000? I don't really know where to go to look up the numbers.

Buger

Hi Confucious,

Off the top of my head, the rx-8 will have more torque than the s2000 and less than the 350z and g35. This is expected as the 350z and the g35 are both several hundred pounds heavier .

Torque is good because it can accelerate a vehicle. But 300 ft-lbs wouldn't mean much if the car weighed 6000 pounds. What is a meaningful way of measuring what we are talking about?

I am at work now but I can graph something that really matters tomorrow morning when I'm home. A graph of accelerative G-forces throughout the rev range will take weight, gearing, powerband, etc into account and show you how the torque is really applied...

Brian

revhappy

RX8

Diff - 4.444
1st - 3.760 * 4.444 = 16.7094 *159 *.8 = 2125/2920 = .736
2nd - 2.269 * 4.444 = 10.0834 *159 *.8 = 1283/2920 = .439
3rd - 1.539 * 4.444 = 6.83932 *159 *.8 = 870/2920 = .298
4th - 1.187 * 4.444 = 5.27503 *159 *.8 = 671/2920 = .230
5th - 1.000 * 4.444 = 4.44400 *159 *.8 = 565/2920 = .194
6th - 0.843 * 4.444 = 3.74629 *159 *.8 = 477/2920 = .163

S2000

Diff- 4.11

Gear Ratios

1st 3.13 *4.11 = 12.8643 * 153 * .8 = 1575/2790 = .564
2nd 2.05 *4.11 = 8.4255 * 153 * .8 = 1031/2790 = .370
3rd 1.48 *4.11 = 6.0828 * 153 * .8 = 745/2790 = .267
4th 1.16 *4.11 = 4.7676 * 153 * .8 = 584/2790 = .209
5th .97 *4.11 = 3.9867 * 153 * .8 = 488/2790 = .175
6th .81 *4.11 = 3.3291 * 153* .8 = 407/2790 = .146


The RX8 looks pretty good compared to the S2000 and is consistent with Buger's analysis using Cartest a few days back. Can anyone do an analysis of the EVO and STI?

Zio

remember torque in that curve is in newton meters which would have a lower ft-lbs torque.. im guessing 159 ft-lbs = 216 newton meters?

RedRX

Buger -- did you use the curb weight of 2920 in your calcs? I ask becuase if the car weighs in at 2920, actual race weight with driver and fuel will probably top 3120 lbs. And that may even be optimistic, since I've been hearing curb weight estimates in the 3K lb range.

Unfortunately, I don't see the RX8 breaking 100 mph in the 1/4, although I think it will be close. I suppose we'll know definitively within the next few months.

Even worse, I live in Colorado. Realistically, the RX-8 will be a high 15 second car up here, which is why I, maybe more than most people, desire a turbocharged RX-8.

Buger

Hi Zio,

We are aware of the differences in the units used. Us Yankees always seem to need to look at things in our own way so we use hp and ft-lbs.

Brian

Buger

Many people have posted about the "lack of engine torque" that the rx-8 has. Indeed, many people who don't know any better will automatically think that their car will easily "beat" the rx-8 *simply* because they have more engine torque. Engine torque is just one of many factors though.

I previously mentioned that a graph of accelerative G-forces throughout the rev range will take weight, gearing, powerband, etc into account and show you how the torque is really applied...

Let's do a quick comparison of the Infiniti G35 5spd Auto and the Mazda RX-8 6-spd. I believe both will be priced around 27,000 US (G35 for this comparison is probably a little higher priced). I know that the g35 6 speed is a better performance comparison with the RX-8 but we will save that for later since I'm trying to illustrate how more torque doesn't always mean better acceleration here.

The specs for the G35 are taken from http://www.infinitihelp.com/Infiniti...fications.htm.

G35
Price : Approx little more than 27,000 US
HP: ... 260 hp
Torque: 260 ft/lbs
weight: 3,336 Base (I used the lighter weight - G35 w/leather was listed as 33 lbs heavier for some reason)
Gearing: Diff - 3.357
........ 1st - 3.54
........ 2nd - 2.264
........ 3rd - 1.471
........ 4th - 1.000
........ 5th - 0.834
Wheels/Tires: P215/55R17 (Sport-Tuned suspension version)

RX-8 (Hi-Performance)
Price : Approx little less than 27,000 US
HP: ... 247 hp
Torque: 159 ft/lbs
weight: 2,920 (We've seen estimates under 2900 but 2920 is a reasonable estimate)
Gearing: Diff - 4.444
........ 1st - 3.76
........ 2nd - 2.269
........ 3rd - 1.645 <-- note that US has diff 3rd gear ratio than Japan
........ 4th - 1.187
........ 5th - 0.843
Wheels/Tires: P225/45R18

Just by glancing at the hp and torque specs, one might think that the G35 must be a lot faster. Taking the 400+ lbs of weight difference into account changes things. What about the gearing and tire size? Cars will accelerate based on their torque curves. Here's a comparison of the G35 and the RX-8 in first gear:

Buger

Note that I used the production rx-8 torque curve. Cartest estimated the G35 curve based on the peak hp/tq figures.

You can see above that the 159 ft-lb rx-8 is estimated to have better acceleration than the 260 ft-lb g35 for the entire powerband in first gear.

260 ft-lbs of engine torque does not always accelerate faster than 159 ft-lbs of engine torque.

Brian

zoom44

help me out here buger i'm tired. this means the rx8 pulls harder correct?
edit oops you alredy answered my question

Buger

Hi zoom44,

Yes. The g-forces are what you feel when you get pushed back in your seat. The harder you are pushed back, the more g-force you are feeling.

zoom44

i know what g's are bug's i'm tired and the graphs are kind of fuzzy from my view. i need more caffeine. thanks for the posts though. keep knocking it into peoples head and between you and rich maybe they'll all get it eventualy

ZoomZoomH

iTrader: (1)

hey where can I find that cartest software???

I sure can use it to tune my cars in Gran Turismo 2 :D

from the gearing numbers, looks like the low final gear ratio in the RX-8 (frigging 4.444!!!) is what makes the car pulls so strong

infinitepat

I havent used caartest in forever, but I do remeber it could make graphs of speed VS time. I always found those most usefull when bench racing. The g-forces in each gear are cool, but it only tells the tale of the tape in one gear. SO the RX8 will beat the g35 in first, what happens after that shift into second, or third.

What happens when the two cars meet on the road, and the mazda driver nails it from a lower rpm in 3rd rather than downshifting to 2nd? If the G35 leaves the line first, will the rx8 catch up? Is the rx8 going to be one of these engines that feels totaly slugish when it gets heat soaked a lil, like after sitting at a red light for a few minutes? Or is its performance going to be more depoendant on air temps than the g35? which car is going to be easier to launch? These are all things that cartest cant tell you, and will make a big difference in how this rotory is respected.

So in conclusion, if you wouldnt mind posting a speed vs. time graph, I think that will be more helpfull.

Buger

Hi ZoomZoomH,

I originally found it by doing a google or yahoo search on cartest. I got the cartest2000 demo and paid 20 bucks or something to unlock the features that let me customize and add new cars to the database.

Brian

Rx4FUN

Buger-

Can you rerun your numbers through cartest with the 1.645 third gear that is on the North American 6-speed. I believe the numbers you previously posted used the Japanese 1.539 third gear.

How does this effect 0-60 times? I'm guessing that Mazda made this gear change for the US market since we're so hell-bent on 0-60 times.

Thanks,
Robert