Teach me Oppo

"505 - morphine not found" (morphine500) 08/07/2015 at 08:59 • Filed to: Miata

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There’s this H2H video doing the rounds comparing the MX-5 to the BRZ. It’s been to the FP, and it’s seriously worth a look, if you haven’t already. But there are info in there that have surprised me tremendously, and now I need some input from this great pot of knowledge, that is Oppo.

It’s turns out, that the Miata has a 1:1 6th gear, so there’s no overdrive, even though most cars have at least one, if not two overdrive ratios, AFAIK. That said, the diff is relatively long at 2,866:1 but still: I don’t think I ever heard about such a setup. Are there other drivelines out there like this?

Funktheduck > 505 - morphine not found 08/07/2015 at 09:03

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No idea. But that video made me want a ND even more. The gf is still not on board.

Nonster > 505 - morphine not found 08/07/2015 at 09:06

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huh, didn’t know that about the new Miata. I don’t know of any other transmissions like that. I imagine that first gear is pretty deep

m2m, apex detective > 505 - morphine not found 08/07/2015 at 09:10

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Not sure it’s got a 1:1 6th, but the previous-generation Clio R.S. topped out at 215 kph due to hitting the limiter. Way too buzzy for fast Autobahn travel.

Couldn’t instantly find numbers on Google, though, so it’s but a guess.

505 - morphine not found > Nonster 08/07/2015 at 09:15

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1st: 5,087 !!! Here’s the brochure: http://www.longlivetheroadster.com/pdf/2016_MX5_G…

505 - morphine not found > m2m, apex detective 08/07/2015 at 09:20

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That’s an excellent suggestion, but i have no idea how to check. Will do later...

Nonster > 505 - morphine not found 08/07/2015 at 09:41

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Holy hell that seems crazy for a Miata or any regular car, but that makes sense if 6th is 1:1. I had a heavy duty 4 speed gear box in my old Jeep CJ-7 where 4th was 1:1 but 1st was an unsynchronized 6.32:1!

Snuze: Needs another Swede > 505 - morphine not found 08/07/2015 at 09:57

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I like weird gear setups. My old Dodge Ram had a 6 speed with a granny 1st - 5.38:1. 2nd thru 6th were like a normal 5 speed, about a 3.21:1 2nd gear, 5th was 1:1 and 6th was like a .78 overdrive. It also had 4.10 rears, and a 2.42:1 low range xfer case. Needless today, I normally started in 6th.

On the flip side, the Cruze Eco w/ manual has a 6 speed with triple overdrives. And the C5 and c6 corvettes, 4th and 5th gen Camaros, Vipers, and anything else using the Tremec T-56 has 2 overdrives.

SnapUndersteer, Italian Spiderman > 505 - morphine not found 08/07/2015 at 10:15

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Yes, there are many other drivelines like that

Textured Soy Protein > 505 - morphine not found 08/07/2015 at 11:03

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Your actual drive ratio is the gear ratio multiplied by the final drive ratio. So “oh whoa this is such a short 6th gear, it’s not even overdrive” is cancelled out by the very, very tall final drive ratio.

These are the combinations* of top gears and final drives in Miatas over the years:

NA & NB 5-speed: 0.814 5th x 4.3 final = 3.5
NB 6-speed (’04-’05): 0.843 6th x 4.1 final = 3.46
NC 6-speed (’06-’08): 0.832 6th x 4.1 final = 3.41
NA & NB 1.8 5-speed LSD; NC 5-speed: 0.814 5th x 4.1 final = 3.34
NB (’99-’03) 1.8 6-speed: 0.843 6th x 3.909 final = 3.3
NC 6-speed (’09-’15): 0.79 6th x 4.1 final = 3.24
NB 1.8 6-speed (Australia): 0.843 6th x 3.636 final = 3.07

Sooo....if you look at the ND’s 1:1 6th gear and much-taller-than-other-Miatas 2.866 final drive, that means the actual top gear ratio is 2.866, which is still taller than any other previous Miata.

* Mazda liked to mix-n-match different gear ratios and final drive ratios for different markets. This is the US market plus the Australian NB 1.8 6-speed which is the only version that had the 3.636 final drive, but I’m sure I missed some others.

505 - morphine not found > Textured Soy Protein 08/07/2015 at 14:16

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Hm, that’s interesting. But if you go all out anal on this, you will also have to factor in the wheel size. I’m not ready to do the math, but considering this isn’t more powerful, yet is quicker than an NC, I would wager there’s some play with that as well. Or no?

505 - morphine not found > SnapUndersteer, Italian Spiderman 08/07/2015 at 14:17

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Would you care naming a few? Honestly curious, and gear & final drive rations aren’t the easiest info out there to find on a hit and miss basis....

505 - morphine not found > Nonster 08/07/2015 at 14:23

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Most all 4speed boxes i know have 4th as 1:1 (except old 3+OD boxes in trucks), and when 5speed gearboxes came around, a lot of them kept 4th as 1:1 and made 5th an overdrive. I would say a lot of ‘boxes are still thus, even a lot of the 6speeds still have 4th as direct, and the next two are both overdrive. Even the 6speed auto in the same miata is thus, just has a completely different final drive....

SnapUndersteer, Italian Spiderman > 505 - morphine not found 08/07/2015 at 15:34

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ZF S5D

Textured Soy Protein > 505 - morphine not found 08/07/2015 at 15:58

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Yes, tire diameter does factor into the true drive ratio. But I’ve only posted the numbers for the top gears. These have less to do with acceleration and more to with highway cruising RPMs. The lower these numbers are, the lower the revs on the highway.

Since the gap between the ND’s top gear drive ratio to any other Miata is so big, those other cars would need to have way taller tires than the ND to make up the difference. Miatas aren’t exactly known for their large wheels.

505 - morphine not found > SnapUndersteer, Italian Spiderman 08/07/2015 at 17:34

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Well, I don’t mean no disrespect, but that’s one single example, even though built in quite a few bimmers. And also it’s a 5speed, and the final drive rations are shorter in all applications... but nevertheless, that’s one example of this style of driveline, thanks!

505 - morphine not found > Textured Soy Protein 08/07/2015 at 17:42

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OK, I get your point, and it’s an interesting one too - it seems even though a 1:1 top gear would imply a hectic highspeed drive, the tall final drive means the ND might be the best motorway cruiser of the lot. Seems they set huge store by the torque advantage the Skyactive engine offers over previous incarnations....

Anyway, this is quite unusual a driveline, I would say, one where they decided to go their own way instead of playing like the rest do. It still seems to work though, shame I most likely don’t drive one at least until next spring. However, this off-the-beaten-path thinking is exactly why I love Mazda!

Textured Soy Protein > 505 - morphine not found 08/07/2015 at 18:47

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The best way to think of it, to me, is that when you combine the transmission gears with the final drive ratios, the resulting ratios end up being pretty normal in the scheme of things.

If I were to guess, this could be a weight saving strategy. By having really short gears in the transmission, the gears can be physically smaller, which makes for a smaller, lighter transmission without necessarily using any exotic materials. The tall final drive ratio balances things out while not really having a larger differential—it’d just be a different ring & pinion gear.

505 - morphine not found > Textured Soy Protein 08/07/2015 at 19:24

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Another thing is the closeness of ratios they get this way. Just as, if not more important.

Textured Soy Protein > 505 - morphine not found 08/07/2015 at 20:42

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Final drive doesn’t really determine ratio closeness. You can accomplish that just the same by messing with gear ratios.

Motor Trend posted this comparison of the NC & ND speeds in each gear. They’re very similar (with the ND being a bit quicker) but not as different as you might expect with such different final drive ratios.