is upshift more important than downshift?
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is upshift more important than downshift?
I'm talking about CVT (continuously variable transmission), not your typical manual or automatic.
Also, I'm not saying you can live without one or the other. I'm asking if being able to shift up CONTINUOUSLY is more important than able to shifting down CONTINUOUSLY in a CVT. This question is only relevant to a CVT.
What this question
means is do you think up shifting CONTINUOUSLY has more to do with car performance
and efficiency than down shifting CONTINUOUSLY?
Here's the situation to help you understand what I'm talking about:
Let's say there was a CVT A that can shift smoothly and efficiently (without any clutch or disengagement)
when the car need to up shift to a higher gear. But when the car need to shift down to a lower gear, the CVT A is no longer a CVT. It can only shift down in discrete gear ratios, and requires some sort of clutch (downshift only).
Now, compare this CVT A to a different kind of CVT B with the exact opposite trait: CVT B can shift continuously in the downward (downshift) direction, but when you want to shift to higher gears (it can only do it discretely, just like a conventional gearbox).
So, is CVT A more useful and beneficial than CVT B?
My guess is that CVT A will be a lot more benefical than CVT B because upshifting involves acceleration which takes the most power from the engine. CVT A will enable a car to accelerate smoothly and efficiently. CVT B isn't as useful because most of the time when we down shift, we want it fast. So being able to downshift in a continuous manner isn't too important.
Say we need to downshift to pass a truck on the highway, CVT A can just downshift discretely (suddenly) to a lower gear and then continuously upshift for a nice smooth acceleration. In the same situation, CVT B will downshift continously and then upshift discretely. But I don't see any advantage in downshifing continuously because most of the we downshift because we need more power, and we want it fast. So there isn't much advantage to a fast continuously shift and a discrete shift.
However, being able to shift up continuously have a key benefit in acceleration since it'll allow the best power/speed ratio in any instant.
So, I think CVT A wil be more useful than CVT B. What are you thought on this?
The only situation where downshifting continuously is beneficial would be:
crusing at a certain speed, but want to slow down to another speed. However, the slower speed will require less power. However, the rate of decrease of power demand is faster than the rate of decrease in rpm (which is related to power output decrease). This means at the original gear ratio, the new engine rpm (at the reduced vehicle speed) will not ouput enough power to maintain the speed, and this is dependent on the engine power curve. Then, being able to downshift continuously would be helpful since it can eliminate the clutch.
But most of the time, we downshift only when we need the extra power fast, like going up a hill or passing someone.
Therefore, I think CVT A is more beneficial than CVT B. Theoretically.
especially for urban driving.
Also, I'm not saying you can live without one or the other. I'm asking if being able to shift up CONTINUOUSLY is more important than able to shifting down CONTINUOUSLY in a CVT. This question is only relevant to a CVT.
What this question
means is do you think up shifting CONTINUOUSLY has more to do with car performance
and efficiency than down shifting CONTINUOUSLY?
Here's the situation to help you understand what I'm talking about:
Let's say there was a CVT A that can shift smoothly and efficiently (without any clutch or disengagement)
when the car need to up shift to a higher gear. But when the car need to shift down to a lower gear, the CVT A is no longer a CVT. It can only shift down in discrete gear ratios, and requires some sort of clutch (downshift only).
Now, compare this CVT A to a different kind of CVT B with the exact opposite trait: CVT B can shift continuously in the downward (downshift) direction, but when you want to shift to higher gears (it can only do it discretely, just like a conventional gearbox).
So, is CVT A more useful and beneficial than CVT B?
My guess is that CVT A will be a lot more benefical than CVT B because upshifting involves acceleration which takes the most power from the engine. CVT A will enable a car to accelerate smoothly and efficiently. CVT B isn't as useful because most of the time when we down shift, we want it fast. So being able to downshift in a continuous manner isn't too important.
Say we need to downshift to pass a truck on the highway, CVT A can just downshift discretely (suddenly) to a lower gear and then continuously upshift for a nice smooth acceleration. In the same situation, CVT B will downshift continously and then upshift discretely. But I don't see any advantage in downshifing continuously because most of the we downshift because we need more power, and we want it fast. So there isn't much advantage to a fast continuously shift and a discrete shift.
However, being able to shift up continuously have a key benefit in acceleration since it'll allow the best power/speed ratio in any instant.
So, I think CVT A wil be more useful than CVT B. What are you thought on this?
The only situation where downshifting continuously is beneficial would be:
crusing at a certain speed, but want to slow down to another speed. However, the slower speed will require less power. However, the rate of decrease of power demand is faster than the rate of decrease in rpm (which is related to power output decrease). This means at the original gear ratio, the new engine rpm (at the reduced vehicle speed) will not ouput enough power to maintain the speed, and this is dependent on the engine power curve. Then, being able to downshift continuously would be helpful since it can eliminate the clutch.
But most of the time, we downshift only when we need the extra power fast, like going up a hill or passing someone.
Therefore, I think CVT A is more beneficial than CVT B. Theoretically.
especially for urban driving.
Super Moderator
Joined: Apr 2004
Posts: 34,476
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You are thinking too much.
I have an Audi A4 with a CVT.
--In low throttle settings, it runs up to 1500-1800 or so and holds the rpm as the mph increases.
--At full throttle, it runs up to 5500 and holds as the mph increases.
There is a "manumatic" or whatever the heck they call it that will hold a "gear" and gives you 6 steps. You can "shift" up or down using that.
For other throttle settings, you can put your foot into it and hold it at just about any rpm and let the mph catch up.
If you are not in the wide-open mood, you can hold it at 4000, for example.
In "Sport" mode, it just runs the revs' up a little higher for each throttle "setting" than the "Drive" mode.
As far as downshifts, you can force a "downshift" using the manual feature.
Good for long downhills.
There is engine braking, esp at lower speed, and esp in "Sport" mode.
As far as downshifts for acceleration, it does the same thing at speed as when starting off--the more you toe it, the higher the revs go.
Not sure if this is what you were talking about.
Go drive one--it will all be clear.
I have an Audi A4 with a CVT.
--In low throttle settings, it runs up to 1500-1800 or so and holds the rpm as the mph increases.
--At full throttle, it runs up to 5500 and holds as the mph increases.
There is a "manumatic" or whatever the heck they call it that will hold a "gear" and gives you 6 steps. You can "shift" up or down using that.
For other throttle settings, you can put your foot into it and hold it at just about any rpm and let the mph catch up.
If you are not in the wide-open mood, you can hold it at 4000, for example.
In "Sport" mode, it just runs the revs' up a little higher for each throttle "setting" than the "Drive" mode.
As far as downshifts, you can force a "downshift" using the manual feature.
Good for long downhills.
There is engine braking, esp at lower speed, and esp in "Sport" mode.
As far as downshifts for acceleration, it does the same thing at speed as when starting off--the more you toe it, the higher the revs go.
Not sure if this is what you were talking about.
Go drive one--it will all be clear.
Senior User
Joined: Apr 2002
Posts: 333
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I don't see why anyone would make either a CVT with ONLY a manual upshift, or ONLY a manual downshift. There would be no benefit in that. How would you even make one? The whole concept of the CVT is to adjust appropriately to engine rpms no matter if your accelerating or decelerating. A quick downshift to a specific gear to shoot the rpms up to the maximum horsepower would be beneficial in certain situations, but like 85 said, they have settings that will downshift automatically depending on the throttle. Although the Audi is a higher end car, I am sure any CVT would come with some sort of quick manual downshift or a computer controlled downshift that would simply respond to the throttle.
I guess if I am understanding your question correctly, I would have to say the continuous upshift is more useful because there is little (if any) benefit in a CVT that can only continuously downshift. I mean, is there even a CVT that only either continuously upshifts or downshifts?
I guess if I am understanding your question correctly, I would have to say the continuous upshift is more useful because there is little (if any) benefit in a CVT that can only continuously downshift. I mean, is there even a CVT that only either continuously upshifts or downshifts?
Super Moderator
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Well, by definition the CVT continuously "upshifts" or "downshifts" depending on load, speed and throttle position.
The Audi's computer keeps track of what you are doing. Especially in "Sport" mode. If you are on wide open throttle, or off and on the throttle hard, it will keep the revs higher even when you let off. This list similar in effect to keeping a manual tranny in a lower gear when you are "powering" through uphill corners for example.
If you are driving like you're headed to an AARP meeting, and are in "Drive", it will keep the revs lower.
As I understand it, the CVT keeps the revs and the speed matched all the time, with some tweaks, and that is the C in CVT.
The Audi's computer keeps track of what you are doing. Especially in "Sport" mode. If you are on wide open throttle, or off and on the throttle hard, it will keep the revs higher even when you let off. This list similar in effect to keeping a manual tranny in a lower gear when you are "powering" through uphill corners for example.
If you are driving like you're headed to an AARP meeting, and are in "Drive", it will keep the revs lower.
As I understand it, the CVT keeps the revs and the speed matched all the time, with some tweaks, and that is the C in CVT.
Elder User
Joined: Aug 2003
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From: philly pa
Originally Posted by unclehan
But I don't see any advantage in downshifing continuously because most of the we downshift because we need more power, and we want it fast.[/font]
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