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post #1 of 4 (permalink) Old 09-14-02, 03:00 AM Thread Starter
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Focus ST170 Gearbox

While trawling through the specs for the Focus ST170 Getrag gearbox I noticed some funny numbers. Here are the specs ........

Gear Ratio Final Drive Effective Ratio
1st gear ratio 4.410 2.88 12.7
2nd gear ratio 2.670 2.88 7.7
3rd gear ratio 1.330 4.25 5.7
4th gear ratio 1.080 4.25 4.6
5th gear ratio 1.330 2.88 3.8
6th gear ratio 1.080 2.88 3.1

You will no doubt have noticed two things:

1. The ratios for 3/5 and 4/6 are the same.
2. There are TWO final drive ratios.

This merited a bit of further investigation on my part to find out how this had been achieved. The answer, for those who don't know, is that it uses a twin layshaft arrangement to create two effective final drive ratios. The actual box is a normal four speed manual but the additional layshaft contains (I am assuming) a reduction gear of 1.475:1 to alter the final drive ratio. The normal layshaft is direct and the physical final drive ratio is the 4.25:1.

Technically you would have to think that there is no reason this couldn't be an 8 speed box if the 1st and 2nd plane brought the normal layshaft into play as well. For those who remember the twin stick Mitsubishi Colt - this is a similar arrangement to that pseudo 8 speed box.

Using the current gear set if 1st and 2nd used the additional layshaft you would finish up with effective ratios of 18.742 (useful for climbing up the side of buildings) and 11.347.

The inherent advantages of this design over a conventional 6 speed box would presumably come from lower weight and less moving componrents along with a compact design for use in smaller vehicles. Be interesting to see how reliable it end up being.

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post #2 of 4 (permalink) Old 09-14-02, 04:59 AM
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Sounds like Ford really thought things out well.

The Peugeot 306 GTi6 is a six speed manual FWD and the gearbox hangs so far into the front wheel well that the turning circle for right hand turns is 13 odd metres, compared to 10 odd metres for the left! Not a problem if you're in a left hand drive country, but a right pain here in Australia.

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post #3 of 4 (permalink) Old 09-16-02, 05:42 AM
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RuseelW: I wonder how much power the 6 speed getrag could take? I heard that it's not a very stong box. Seems strange why the ST170 uses a 6 speeder while the top of the line Model RS uses a 5 speed box.

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post #4 of 4 (permalink) Old 09-16-02, 07:17 AM Thread Starter
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You are correct Cobra - the box is rated at only 389 Nm.
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