Gear Ratios - FMVperformance.com : The site for all your Ford Mazda and Volvo needs
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post #1 of 24 (permalink) Old 09-24-2003, 04:34 PM Thread Starter
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Gear Ratios

I'm trying to understand gear ratios of a gear box. So I get something like this...

Ratios (:1) (Overall in parenthesis)

Manual
1st: 3.153 (13.031)
2nd: 1.842 (7.613)
3rd: 1.258 (5.199)
4th: 0.947 (3.914)
5th: 0.733 (3.029)
Reverse: 3.002
Final Drive: 4.133

Automatic
1st: 3.801 (14.109)
2nd: 2.131 (7.910)
3rd: 1.364 (5.063)
4th: 0.935 (3.471)
5th: 0.685 (2.543)
Reverse: 2.970
Final Drive: 3.712

And I'm not too sure what to make of it. Any help?

(those are the ratios of the 6s btw)


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post #2 of 24 (permalink) Old 09-24-2003, 07:56 PM
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Gear Ratios

Hmm... I can't quite explain it. I forgot

Check www.howstuffworks.com <- Great site!!!

Maybe they'll have an explanation.

If they do, please post it. I'd like to refresh my memory.
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post #3 of 24 (permalink) Old 09-24-2003, 08:06 PM
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Gear Ratios

It has to do with how much tq can be put to the road.
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post #4 of 24 (permalink) Old 09-24-2003, 09:19 PM Thread Starter
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Gear Ratios

I'll check that out later.

I'm just trying to figure it out, because I suppose it's pretty important. We all look at Torque and HP and engine size to gauge performance, but over look gear ratios, so I figured maybe they could just say a little more about the car if I understood them.

Simple mechanics... heh... and I want to be a physicist.

I can kind of understand it from what I know. I think that in 1st gear for every 3.1 rotations of the imput (engine) there is one rotation of the output (Wheels). So in 5th gear, for every .7 revs of the engine there is 1 rotation of the wheel, making it possible for higher revs and faster rotation...

So does that mean higher speed is more easily achieved with the automatic, having .6? And then if we look at the 4 speed auto and in 4th gear it's at .72, which is almost as much as the manual in 5th gear.

Or maybe I'm just off base with my logic.


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post #5 of 24 (permalink) Old 09-25-2003, 09:35 AM
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Gear Ratios

According to the #s it could, but any AT will sap MUCH more pwr from the engine than a regular MT.

If you can drive a 5spd, stick to it (pun intended ). You'll have a little more fun, control and pay a cheaper price.
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post #6 of 24 (permalink) Old 09-25-2003, 10:33 AM
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Gear Ratios

That has nothing to do with gear ratio though, that's because it goes through a torque converter.
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post #7 of 24 (permalink) Old 09-25-2003, 10:51 AM
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Gear Ratios

True. Was just pointing out one little think about ATs and MTs.

Oh yeah - they're EXPENSIVE to fix too!
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post #8 of 24 (permalink) Old 09-25-2003, 11:14 AM
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Gear Ratios

Yeah I know. Had to get a auto trans rebuild in my old civic. Cost was more than what I owned on my car.
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post #9 of 24 (permalink) Old 09-25-2003, 09:19 PM Thread Starter
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Gear Ratios

Okay, I think I've got the gear ratios worked out.

I think I also figured out why more gears are better: The ratios are closer together, so when you downshift you don't lose as much RPM and thus can accelerate faster. Is that correct?

I also learned a lot about Automatic Transmission, and have a new respect for it. It's so sophisticated, an absolute work of art. It has a great implementation of planetary gear systems. I suppose its sophistication is the reason it's so expensive to replace.

Also learned a little about the torque converter. I don't know if you guys are just exaggerating the power loss, but it didn't seem like the Torque Converter was such an impedement to the car. I even read that in certain cases at lower RPMs, the Torque Converter can provide some extra torque.

I have another question though, and this one I think more people might have some insight on. What's the ideal Torque/Horsepower configuration?

I see some cars with this:

200hp @ 5000 RPM
150 ft lb @ 3000 RPM

or maybe

[email protected] RPM
200hp @5000 RPM

If I want to be a speed racer, do I want a peak torque at a higher RPM, or do I want lower? How about HP?

If I want to be quick at casual driving, do Iwant a peak torque at a lower RPM?


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post #10 of 24 (permalink) Old 09-25-2003, 11:06 PM
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Gear Ratios

Take the RX-8. It was estimated to 250 horsepower and 125lbs-ft of Torque, which means that you will accelerate and feel it but you will be more likely to reach high speeds in lower time than a Protege for example.

The horsepower is used to move the car over a distance. The torque is the force that the wheels puts on the ground to get the car moved. So if you have like a big pickup, which will be like:

250 horsepower @ 4,500
300 torque @ 3,000

Then your pickup will be amazingly powerful with loaded charges and will be able to reach high speeds with a huge load.

-Frank

Founder, President & Webmaster

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