The gearing ratios for the rx-8 are one unknown that we haven’t really discussed in much detail. There has been some talk and much speculation about the rx-8’s top speed, mileage, 0-60 times, ¼ mile times etc but they are *all* dependent on gearing.

Since the rx-8 was designed to seat 4 people and the gearing/diff ratios should take that into account and be much higher than the ratios on the last rx-7. What would everybody like to see the gearing ratios end up at?

I would propose the following aggressive and closely spaced gearing to give the best 0-60, ¼ mile, mileage and utility. Gears 1 thru 5 are aggressively geared and closely spaced. 6th gear is only overdrive gear and is spaced a bit apart from 5th . The .84 6th gear is mainly for fuel economy at highway/freeway speeds but will also lead to a very high top speed. Because of the renesis' wide power band and flat torque curve, the rx-8 will be very driveable (until we hear the dang buzzer). :D

Rear wheels = 225 45 18
Diff - 4.1
1st – 4.02
2nd – 2.46
3rd – 1.77
4th – 1.33
5th – 1.08
6th - 0.84

1st gear at 3500 rpm would be approx 16 mph.
2nd gear will hit 60 mph near the hp peak.
55 mph would be approx 2750 rpm in 6th gear.

Would there be any reason why the above gearing would not be practical? Below is also a chart which gives the speeds per rpm for each gear.

RPM 1 2 3 4 5 6
1000 4.6 7.5 10.4 13.8 17.0 21.9
1500 6.8 11.2 15.6 20.7 25.5 32.8
2000 9.1 14.9 20.7 27.6 34.0 43.7
2500 11.4 18.7 25.9 34.5 42.5 54.6
3000 13.7 22.4 31.1 41.4 51.0 65.6
3500 16.0 26.1 36.3 48.3 59.5 76.5
4000 18.3 29.8 41.5 55.2 68.0 87.4
4500 20.5 33.6 46.7 62.1 76.5 98.3
5000 22.8 37.3 51.9 69.0 85.0 109.3
5500 25.1 41.0 57.0 75.9 93.5 120.2
6000 27.4 44.8 62.2 82.8 102.0 131.1
6500 29.7 48.5 67.4 89.7 110.5 142.1
7000 32.0 52.2 72.6 96.6 119.0 153.0
7500 34.2 56.0 77.8 103.5 127.5 163.9
8000 36.5 59.7 83.0 110.4 136.0 ----
8500 38.8 63.4 88.2 117.3 144.5 ----
9000 41.1 67.2 93.3 124.2 153.0 ----

If the rx-8 were geared as such, the 0-60 times will *easily* be well less than 6 seconds and the 1/4 mile might be less than 14?


Brian

 

Oops, the tabs in the chart disappeared. I think the below chart will be easier to read:

RPM````````1`````````2`````````3 `````````4`````````5`````````6
1000``````4.6``````` 7.5``````` 10.4`````` 13.8`````` 17.0`````` 21.9
1500``````6.8``````` 11.2`````` 15.6`````` 20.7`````` 25.5`````` 32.8
2000``````9.1``````` 14.9`````` 20.7`````` 27.6`````` 34.0`````` 43.7
2500``````11.4`````` 18.7`````` 25.9`````` 34.5`````` 42.5`````` 54.6
3000``````13.7`````` 22.4`````` 31.1`````` 41.4`````` 51.0`````` 65.6
3500``````16.0`````` 26.1`````` 36.3`````` 48.3`````` 59.5`````` 76.5
4000``````18.3`````` 29.8`````` 41.5`````` 55.2`````` 68.0`````` 87.4
4500``````20.5`````` 33.6`````` 46.7`````` 62.1`````` 76.5`````` 98.3
5000``````22.8`````` 37.3`````` 51.9`````` 69.0`````` 85.0`````` 109.3
5500``````25.1`````` 41.0`````` 57.0`````` 75.9`````` 93.5`````` 120.2
6000``````27.4`````` 44.8`````` 62.2`````` 82.8`````` 102.0`````131.1
6500``````29.7`````` 48.5`````` 67.4`````` 89.7`````` 110.5`````142.1
7000``````32.0`````` 52.2`````` 72.6`````` 96.6`````` 119.0`````153.0
7500``````34.2`````` 56.0`````` 77.8`````` 103.5`````127.5`````163.9
8000``````36.5`````` 59.7`````` 83.0`````` 110.4`````136.0`````----
8500``````38.8`````` 63.4`````` 88.2`````` 117.3`````144.5`````----
9000``````41.1`````` 67.2`````` 93.3`````` 124.2`````153.0`````----


Brian

 

I'd rather see it a little shorter than that, but maybe that's just me. Perhaps 5-10 MPH lower in each gear at redline. I don't do a lot of high-speed cruising, but I do value quick acceleration.

 

Looks good,

I agree with Grimace to some extent, perhaps a little shorter... not as much as 10Mph though...

I do think that 6th should be a real long legged cruiser as suggested... I often cruise near 90-100Mph and when in germany I had the chance to cruise at 135+ for about 200 miles.... don't want to be ragging the engine at high speed cruising...

One thing though.... If you want to reach 60 in second, for 0-60 times... it must be 62 not 60 before the rev limit... because european tests are to 100Kph (62Mph).

 

Hi BlueAdept,

With the gearing that I suggested, 2nd gear would actually be going at 67.2 mph at the rev limit and 63.4 at the hp peak. I am hoping that the rx-8 will come out as aggressively geared from 1st thru 5th as my example (or even a little shorter).

The renesis is really different than anything out there though. Does anyone know any other production engine that comes close to (or beats?) 6000 rpm of greater than 90% torque?!?!?!

Brian

 

If the rx-8 6th gear was .84 as in the example, 135 mph would still be approx 1200 *below* the torque peak. The car would be *begging* you to at least take it 1200 more rpms to it's torque peak at 163 mph (or whatever the electronically limited top speed would be). :D

You wouldn't be ragging the engine and probably wouldn't even notice the revs were that high until you heard the buzzer. :D

Brian

 

Oh, absolutely,, I wasn't complaining about your numbers... but Grimace was suggesting lowering the ratios... I don't mind that, but 6th must be long legged...

As for the 0-62 thing... I don't think we are exactly sure where the redline will be...

 

Unfortunately, we will probably have to wait until at least January before we get more concrete info on many of the particulars.

Brian

 

Gear ratios OK to me. Perhaps a little taller, if anything.

 

I can't see taller myself... we're talking about a 6 speed box that can get to 60 in second.... even that's probably a sacrafice to get good 0-60 times.

 

Taller would be a mistake. You wouldn't get into the power band above 3500 RPM in first gear for 18-odd MPH. I'd favor shorter so that people get into the 4000 RPM powerband quickly. That way it feels more powerful. SHorter gearing takes advantage of the high-RPM, low-torque nature of the engine, while tall gearing would actually make the car feel sluggish.

 

Exactly... I agree they could all be a little shorter, except 6th which is just about right in my eyes,

 

I was playing around with CarTest (a car performance calculator) to see how different gearing might affect the acceleration of the RX-8. On my own, I came up with these values for gearing:

Final - 4.10
1st - 3.70
2nd - 2.65
3rd - 1.90
4th - 1.45
5th - 1.05
6th - 0.75

My ratios give the following results:

0-60: 5.35
1/4: 14.0 @ 102.0
Top Speed: 161 MPH in 121.6 seconds

The values suggested by Buger - His 1st and 2nd are shorter, while his 3rd, 4th, and 5th are taller:

Final - 4.10
1st - 4.02
2nd - 2.46
3rd - 1.77
4th - 1.33
5th - 1.08
6th - 0.84

Here are CarTest's results for Buger's ratios:

0-60: 5.40
1/4: 14.0 @ 101.4
Top Speed: 160 in 111.96 seconds.

This is only a computer simulation, so take it for what it is worth, but it appears that my slightly taller first two gears will actually help 0-60 and 1/4 acceleration, albeit ever so slightly. However, Buger's taller 3rd and 4th seem to greatly improve time to top speed. It seems that taller is better from this starting point. I'll play around with the numbers some more and see if I can improve on things.

Note that 6th gear has no effect on any of these tests, as top speed occurs at redline in 5th for both of our gear sets.

Other note: The simulations were based on a 2800 weight.

 

RedRotaryRocket

Good posts from you and the others. Why not use 2970 for the weight instead of 2800 like you've done. until we hear differently, we are better off using the last weight given by Mazda. if they better it by production, all the better but for now, let's see what the simulations come out with at the weight of 2970.
Just a suggestion.

 

Boowana,

Ask and you shall receive. :D Actually, the numbers using 2800 lbs are probably too optimistic, since the software assumes that the weight includes the driver.

I re-ran the simulation using a weight of 3170 (2970 + 200 lb driver). Here are the results:

My gear set:
0-60: 5.9
1/4: 14.6 @ 98.2
Top Speed: 160 in 140.03 seconds

Buger's gear set:
0-60: 6.0
1/4: 14.5 @ 98.3
Top Speed: 159 in 124.62 seconds

Howzzzat?

 

Interesting software....

I don't think it could be that hard to write somthing along those lines that did an "Auto optimisation"...

 

And the nissan guys just realized what power to weight ratio meant. I hope those new calculations are too conservative because I would love to easily be in the 13's with a few mods. That really shows how weight effects performance.

Have you plugged in stats from known cars and seen how they matched up?

I also just realized that none are 1:1 which one of them will have to be. In most sets it is fourth but your fifth is close @1.08 so try the scenario with it like that please?

 

The software actually comes with stats from many vehicles...generally it's within 2 or 3 tenths as far as 0-60 or 1/4 mile times are concerned. Plus or minus 2 or 3 tenths is still a pretty big spread, but it's not too bad for getting "in the ballpark"

 

Hi spdfrk,

I was aware that 4th was usually the 1:1 gear but before coming up with my original gear ratios, I found that the s2000 had the below gearing:

Final - 4.10
1st - 3.133
2nd - 2.045
3rd - 1.481
4th - 1.161
5th - 0.971
6th - 0.811

Oddly enough, the s2000 has no 1:1 gear. Honda geared the s2000 so that the gears are nicely spaced and it actually has 2 overdrive gears. Too bad the s2000 doesn't have a renesis torque curve.

Nice numbers RRR! I like that your 2nd thru 5th gears are a little shorter than mine. I think the only thing hurting your 0-60 time is the taller 1st gear.

I also think that your 6th gear is probably more in line with what Mazda has done in the past as rx-7s usually had their top gear rpms at around 2100 - 2200 at 55 mph.

That cartest software is pretty cool too. I downloaded the demo version and it puts out tons of graphs and info, even a mpg graph per gear! The demo version only lets you analyze the cars already in its database though. How about some revised gearing numbers:

Final - 4.10
1st - 4.10
2nd - 2.61
3rd - 1.84
4th - 1.39
5th - 1.06
6th - 0.75

I like your very short second gear but I made it just a *little* longer. I also made 1st gear shorter to maintain even spacing and because a sports car with seating for 4 adults should have ample torque in first gear. I slightly shortened gears 3 thru 5 and made 6th gear even longer as one of the goals of Mazda was that the car have much improved mileage. Could you try the below gearing numbers in Cartest?

Brian

 

Brian,

I ran your new numbers, but I made a change to your 5th gear...I made it 1.03 as that maximizes top speed.
Here's the results using your revised gearing (with 1.03 5th):

0-60: 5.80
1/4: 14.5 @ 98.0 MPH
Top Speed: 160.3 in 145.13 seconds

That's based on a test weight of 3170 lbs, so compare these numbers to the later set I generated...you've picked up 0.2 seconds to 60...pretty good!

Eric

 

It's DEFINATELY going to be 2940 lbs or LESS, so re-do those figures and lemme see those times again

 

yeah herc but ya gotta add the weight for the human ( or rotorhead) driving:p

 

Hrmm good point

How do they test cars in magazines and such?

 

Try it with 3115 lbs

That's so it accounts for ME in the car :P (175 lbs hehehe)

 

I just bought cartest2000 and have some good news. According to the help menu in the program:

"CAR CURB WEIGHT: Enter the curb weight of the car excluding the driver, passengers, or fuel. "

Furthermore, if you click "create car specific model parameters", you will see where you can specify the "weight of driver". :D

Unfortunately, I just got done with a long day at work and I'm going to sleep now. I will try entering the rx-8 hp curve values into the program tomorrow morning and see what the program will come up with for a curb weight of 2900 lbs.

Brian