DCT gear ratios in 4th and 5th - Kia Niro Forum
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post #1 of 6 (permalink) Old 03-14-2019, 03:05 PM Thread Starter
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DCT gear ratios in 4th and 5th

Does anyone know why 4th and 5th gear are functionally identical? In fact 5th gear is steeper then 4th gear (.96 vs .93) from what I've seen. It doesn't make sense to me to have the higher gear with a steeper ratio, nor for them to be so close together.

Thanks for any info.

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post #2 of 6 (permalink) Old 03-14-2019, 03:50 PM
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Originally Posted by KNEX2017 View Post
Does anyone know why 4th and 5th gear are functionally identical? In fact 5th gear is steeper then 4th gear (.96 vs .93) from what I've seen. It doesn't make sense to me to have the higher gear with a steeper ratio, nor for them to be so close together.

Thanks for any info.
My guess would be the fact that 4th and 5th are close in ratio and seemingly out of order is just a curiosity because the DCT uses two different final drive ratios, one for the even gears and another for the odd. This means that the effective difference between adjacent gears is not just a function of their respective ratios, you need to factor in the different final drives as well. According to the specs the Niro has final drives of 4.438 and 3.227 but it's not clear which is which.

I'm fairly confident that the Kia engineers did not put the gears in backwards.

Doing the math the one that doesn't make sense is 6th gear. If you assume even gears share one final drive and the odd ones the other, it makes the most sense if the odds use the 3.227 final and the evens the 4.438. If you make that choice you end up with this for the final drive ratios:

1st 12.48
2nd 9.83
3rd 4.42
4th 4.12
5th 3.08
6th 3.40 <---WTF?

My guess here is the DCT in the Niro is a modified version of the Hyundai 7 speed DCT with 6th gear removed. So 6th gear in the Niro is actually an "odd" gear. If you assume that you get this for the final drives:

1st 12.48
2nd 9.83
3rd 4.42
4th 4.12
5th 3.08
6th 2.47 <---Better.

Now, 3rd and 4th are still pretty close, but that's a different topic.

Jim
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post #3 of 6 (permalink) Old 03-14-2019, 06:07 PM Thread Starter
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Quote:
Originally Posted by jmurphEV View Post
My guess would be the fact that 4th and 5th are close in ratio and seemingly out of order is just a curiosity because the DCT uses two different final drive ratios, one for the even gears and another for the odd. This means that the effective difference between adjacent gears is not just a function of their respective ratios, you need to factor in the different final drives as well. According to the specs the Niro has final drives of 4.438 and 3.227 but it's not clear which is which.

...
Thanks, I didn't realize there were different final drive ratios in a DCT.

Do you happen to know engine redline?

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post #4 of 6 (permalink) Old 03-28-2019, 11:05 PM Thread Starter
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I found a service manual source online that gives 5th, 6th, and reverse the lower 3.227 final ratio, and 1-2-3-4 the higher final ratio.

Kia Niro : Specifications : DCT(Dual Clutch Transmission) System

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post #5 of 6 (permalink) Old 03-28-2019, 11:20 PM
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Originally Posted by KNEX2017 View Post
I found a service manual source online that gives 5th, 6th, and reverse the lower 3.227 final ratio, and 1-2-3-4 the higher final ratio.

Kia Niro : Specifications : DCT(Dual Clutch Transmission) System
Huh, that's a weird setup. Normally the whole point of a DCT is to have alternate gears on separate shafts so that the next gear can be engaged before the shift. Why would they bother just having the 2 highest gears coupled to a different output shaft?
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post #6 of 6 (permalink) Old 03-29-2019, 04:58 PM
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yes this is strange... I see the same thing for the ioniq so i assume it is not a typo...
more explanations would be nice and certainly very instructive
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