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The Ratios Thread
Topic Started: Jul 5 2010, 01:35 PM (10,866 Views)
Coche Blanco
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Gear ratios for US Swift/Metro 5-speed:
1st = 3.416 (3.583 1998+ 1.3L/4 cylinder)
2nd = 1.894
3rd = 1.280
4th = 0.914 (O/D)
5th = 0.757 (O/D)
Final drives:
79:18 = 4.389 (1995+ w/1.0L & Convertible)
78:19 = 4.105 (GT/GTi & 1989-1994 3 cylinder)
72:19 = 3.789 (1995+ w/1.3L & XFI)
74:21 = 3.524 (pre-1995 w/1.3L)

These are OEM numbers. Your car may or may not have had a transmission swap in its lifetime, so this will not be 100% accurate for everyone.

Tall vs. Short Gears:
A "taller" final drive is better for MPGs but hurts acceleration. i.e. putting a 3.79 in place of a 4.39.
A "shorter" final drive is good for acceleration but worse for MPGs. i.e. putting a 4.39 in place of a 4.10.


Tires General:

The non convertible Geo Metros from 1989 to 1994 all had 145/80-12 tires OEM. These tires diameter are 21.1 inches. I do not recommend you stay with the 12" rim, tires are more expensive/rare for that size. A popular replacement size is 155/80-12, so I will include that tire into the calculations too.

The 1995+ "Metros" all had 155/80-13 OEM. These tires diameter is 22.8 inches. I do recommend the 13" rims on ALL Geos, but I do not recommend the OEM size on them. I would run 175/70 (diameter=22.6 vs 22.8), they hurt MPGs a little but they make up for it in traction and ride comfort. I will not include OEM size in my calculations because they are so similar in size (OEM is 100.5% the size of the 175).

Convertibles had some weird tire size that was around the same diameter as the 145/80-12


Tires effect on gear ratio:

For all the examples we will use 5th gear, 0.757:1.

Below I am multiplying 5th gear by the final drive. That number is the amount of times the engine has to turn to rotate the tire once.

Final x 5th gear = engine revs:tire revs
A: 4.389 x 0.757 = 3.322:1
B: 4.105 x 0.757 = 3.107:1
C: 3.789 x 0.757 = 2.868:1
D: 3.524 x 0.757 = 2.668:1

Now I am multiplying the times required for the engine to run the tires once, by the amount of rotations it requires to go 1 mile. This will show me the number of times the engine has to turn to go one mile. The bold numbers are the RPMs @ 60mph in 5th gear.

175/70-13

A: 3.322 x 891 = 2960
B. 3.107 x 891 = 2768
C: 2.868 x 891 = 2555
D: 2.668 x 891 = 2377

Click the spoiler for other calculations.
Spoiler: click to toggle


Larger diameter tires essentially lower the gear ratio down and in doing so, lower the cruising RPMs and increases fuel economy.

How to DIY:
First, go to http://www.miata.net/garage/tirecalc.html
Enter into the first set of boxes your tire size.
Take the number that says "revs/mile" and call it (P)
Now multiply that number by A,B,C, or D (your final drive)
The number you get will be your 60mph RPMs.


Tire Size for Lower Ratio DIY:

*credit to KY Metro for helping my sore brain.
"I have the 4.10 and I want it to rev like the 3.79 ratio. " Divide it out:

4.10 / 3.79 = 1.08 (108%, or 8% 'longer legs' on the XFI). So you need an 8% taller tire. Since your tire is 21.1" tall, you need to go to 22.8". That just happens to be the standard height OEM for 95+Metros. Go to the Miata link above, punch in your starting tire on one side, and play around with the second tire. It does most of the work, as it has the diameter, revs/mile, %faster, etc.
Edited by Coche Blanco, Aug 15 2014, 09:30 AM.
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Good bye


Very good, keep going. :)
This will help us all make decisions about tires and gears, since 3.52s are rare and 3.79s are very available. What size 13s do we need to buy to equal 3.52s. I already have 3.79s and 175/70-13s on my 91.
Thanks
Andy
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bogs
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Duct tape heals all wounds

Good start on the thread CB .
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Coche Blanco
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I'm going to sleep. I'd like some good criticism on this when I wake up. But be nice, it is 4 a.m. here.
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Woodie
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Nicely done, this will be helpful indeed.

Here's your criticism, but it's minor quibbles and typos:

Up top, you should lose the 89-94 from this title - "Gear ratios for 1989-1994 US Swift/Metro 5-speed:"

Next paragraph, titled "Final drives", you should lose the wheel/tire size.

I was going to suggest four or five other names the car was sold as, but we are talking about North America, you probably chose best.

In the first sentence of "Tires General" you say "A popular replacement size is 144/80/12," you mean 155/80-12, simple typo.

Edited by Woodie, Jul 6 2010, 06:53 AM.
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Coche Blanco
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OH MY GOD!!!!!!! I nearly deleted the whole post...lmao

Thanks Woodie, that's what I needed. A fresh set of eyes. I've got to reword that last paragraph to make it a little easier to understand.
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mjspiess
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I think this fits in "The Ratio Thread" as well... I made this table for people who want to run different rims/tires, but would like speedo/odo stock or as close to stock as possible. Again, not all these tires exist or even fit the Metro, but in a perfect world would give you the closest OEM results. The combos in BOLD are dead on combos that will keep your speedo/odo reading correctly.

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Coche Blanco
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I'd like someone to tell me what's the max size tire you can run on a stock height Metro...
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KY Metro
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You could make this much simpler. I am not good at explanations, but I think the whole revs/mile thing is unnecessary.

Look at your example. You have a 4.10 and you want a 3.79, right? Divide it out:

4.10 / 3.79 = 1.08 (108%, or 8% 'longer legs' on the XFI). So you need an 8% taller tire.

since your tire is 21.1" tall, you need to go to 22.8". That just happens to be the standard height OEM for 95+Metros.

Look at the Rims n Tires Calculator.

Punch in your starting tire on one side, and play around with the second tire. It does most of the work, as it has the diameter, revs/mile, %faster, etc.
Edited by KY Metro, Jul 6 2010, 11:47 AM.
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KY Metro
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BTW, for the 95+ to get XFI gearing just from the tires, 4.39 / 3.79 = 1.16, or 116%. So you would need tires 16% over 22.8", which would be 26.4" diameter. Thats a tall tire.

The closest I can find in production is a 165/80 r15, which is 25.4", or 11.6% taller. Effectively lowers the ratio to 3.93.
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Coche Blanco
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I had gotten my mind wrapped around revs/mile for the RPM part of the question, and I forgot to "shift gears" and do it the easy way.
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Coche Blanco
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I see about 3 threads asking for information i've covered here. BUMP BUMP BUMP
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bogs
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Duct tape heals all wounds

I bookmarked this a while ago and use it quite frequently, thanks :thumb
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Murf 59
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One of the things to consider is the 3.52s are gonna be hard for a 3cly to pull. I think your gonna have to keep your foot in it really hard to get anywhere. I am not good with #s. I never have been. If you go to the tallest gears. Make sure you use a tire combo that will allow you to use this ratio. Neat thread CB.
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undgsx-R
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What happened to the original post? Its not much good now.
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