Not sure which gear to shift to

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sac1980
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#1
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Hello,

I have a peculiar question about a driving situation.
Suppose we are driving in 3rd gear with around 50 km/h in city. And you see a Red signal approaching. You start decelerating by braking a bit and then as you approach the signal and you are about to stop the car ( with say 15 KM/h) by pressing brake further. But suddenly you see the signal being changed to Green. In this case , which gear would be best to change to. 2nd or 1st. I had been in these situations and I couldnt decide which Gear to change to and I ended up selecting 1st and the car sometimes stalled completely or a bit .
Maybe the technique was not correct.

Any suggestions would be helpful.
Thanks.


- Sachin
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Mathlete18
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(Original post by sac1980)
Hello,

I have a peculiar question about a driving situation.
Suppose we are driving in 3rd gear with around 50 km/h in city. And you see a Red signal approaching. You start decelerating by braking a bit and then as you approach the signal and you are about to stop the car ( with say 15 KM/h) by pressing brake further. But suddenly you see the signal being changed to Green. In this case , which gear would be best to change to. 2nd or 1st. I had been in these situations and I couldnt decide which Gear to change to and I ended up selecting 1st and the car sometimes stalled completely or a bit .
Maybe the technique was not correct.

Any suggestions would be helpful.
Thanks.


- Sachin
At 15km/h you'd be better in second - personally, I think dropping into first should only really be done at a brisk walking speed or less
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sac1980
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(Original post by Mathlete18)
At 15km/h you'd be better in second - personally, I think dropping into first should only really be done at a brisk walking speed or less
Yes thats what we learned but then I guess I still got some some *push*. (which you normally get when there is a speed mismatch between actual speed and Gear) No idea why?
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Chichaldo
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If you're moving, go for second gear. Might struggle slightly but slowing greatly for incorrectly changing to 1st isn't better.
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Mathlete18
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(Original post by sac1980)
Yes thats what we learned but then I guess I still got some some *push*. (which you normally get when there is a speed mismatch between actual speed and Gear) No idea why?
Yeah, as far as I'm aware the 'push' you're experiencing is a result of your engine speed (the revs) not matching the speed you're actually going at for the gear you're trying to engage). So for example, suppose you're going a 30km/h in 3rd gear and you then disengage the clutch and slow down to 10km/h. Given the engine is disengaged it will continue spinning at roughly the same revs as it was before (slightly slower as it loses energy). But now when you change to 2nd gear and try to re-engage the clutch two things have changed: Firstly your speed is 1/3 what it was so in 3rd gear you would want the revs to be a third what they were. But because you're now in second gear (which has higher revs for the same speed as third) this will bring you somewhat closer to the right revs.

All that said and done, you can see why it's a difficult task to perfectly match the revs with the correct gear for your current speed. And when they aren't match the difference in revs either converts excess revs to inertial momentum and caused you to surge forward, or if there are not enough revs the car will stall.

Perfecting this balance, really comes with practice but in general I'd say stay in second and only get back into first at very low speeds. You can accelerate in first to a much higher speed than the speed at which you can get back down into first. Sorry for going off on one slightly! Haha Hope this helps
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sac1980
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(Original post by Chichaldo)
If you're moving, go for second gear. Might struggle slightly but slowing greatly for incorrectly changing to 1st isn't better.
Thanks for the suggestion. But in the process of doing so , all the passengers/family members get this sudden jerky motion , which I just hate it.
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sac1980
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(Original post by Mathlete18)
Yeah, as far as I'm aware the 'push' you're experiencing is a result of your engine speed (the revs) not matching the speed you're actually going at for the gear you're trying to engage). So for example, suppose you're going a 30km/h in 3rd gear and you then disengage the clutch and slow down to 10km/h. Given the engine is disengaged it will continue spinning at roughly the same revs as it was before (slightly slower as it loses energy). But now when you change to 2nd gear and try to re-engage the clutch two things have changed: Firstly your speed is 1/3 what it was so in 3rd gear you would want the revs to be a third what they were. But because you're now in second gear (which has higher revs for the same speed as third) this will bring you somewhat closer to the right revs.

All that said and done, you can see why it's a difficult task to perfectly match the revs with the correct gear for your current speed. And when they aren't match the difference in revs either converts excess revs to inertial momentum and caused you to surge forward, or if there are not enough revs the car will stall.

Perfecting this balance, really comes with practice but in general I'd say stay in second and only get back into first at very low speeds. You can accelerate in first to a much higher speed than the speed at which you can get back down into first. Sorry for going off on one slightly! Haha Hope this helps
Thanks Mathlete18. What you explained is what exactly happening. The Revs and Speed are not matching. One workaround I see to avoid this surge / jerk is when I am changed to 2nd gear , while accelerating , I would not release the clutch immediately , that will give me some time to match the revolutions with the speed and when I am bit more accelerated , can then safely release the clutch completely. I would try this next time to test if it works. Any other suggestions?

Mathlete18
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Mathlete18
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(Original post by sac1980)
Thanks Mathlete18. What you explained is what exactly happening. The Revs and Speed are not matching. One workaround I see to avoid this surge / jerk is when I am changed to 2nd gear , while accelerating , I would not release the clutch immediately , that will give me some time to match the revolutions with the speed and when I am bit more accelerated , can then safely release the clutch completely. I would try this next time to test if it works. Any other suggestions?

Mathlete18
Yes definitely, engaging the clutch slowly will definitely help as it will give the engine more time to adjust to the correct revs. One other thing I should have asked, is the surge/jerk a braking force or accelerating force?? If it's an accelerating force causing you to surge forward then you might still be going too fast for 2nd gear even and potentially it might be worth staying in third. This is possible if you are indeed going around 15km/h + but if you're going much less than this then 2nd is wiser And for walking speeds and under, first. That said, as long as the wheels are rolling staying in second is perfectly okay.
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sac1980
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(Original post by Mathlete18)
Yes definitely, engaging the clutch slowly will definitely help as it will give the engine more time to adjust to the correct revs. One other thing I should have asked, is the surge/jerk a braking force or accelerating force?? If it's an accelerating force causing you to surge forward then you might still be going too fast for 2nd gear even and potentially it might be worth staying in third. This is possible if you are indeed going around 15km/h + but if you're going much less than this then 2nd is wiser And for walking speeds and under, first. That said, as long as the wheels are rolling staying in second is perfectly okay.
It is the a braking force , in which you get this push (as if someone pushed you from behind). Which is a embarrassing moment. I would try the suggestions and get back. Thanks once again.
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Mathlete18
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(Original post by sac1980)
It is the a braking force , in which you get this push (as if someone pushed you from behind). Which is a embarrassing moment. I would try the suggestions and get back. Thanks once again.
You're very welcome, although if it feels like someone has pushed you from behind that would be an accelerating force...in which case, maybe try staying in third until your speed drops even more to say 10km/h...that should be much smoother. But yes, let me know how it goes then
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Chichaldo
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(Original post by sac1980)
Thanks for the suggestion. But in the process of doing so , all the passengers/family members get this sudden jerky motion , which I just hate it.
Perhaps it's your control of the clutch? If you rest the ball of your foot on the floor (if you don't already) it could give you more control/a slower release. That could be the source of the jerky motion
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sac1980
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(Original post by Chichaldo)
Perhaps it's your control of the clutch? If you rest the ball of your foot on the floor (if you don't already) it could give you more control/a slower release. That could be the source of the jerky motion
Thanks Chichaldo for the reply. You have a valid point. I say yes and no. I do rest the foot on the floor but I am not still (lets say smoothly ) able to control the clutch. I am working on it though.
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Chichaldo
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(Original post by sac1980)
Thanks Chichaldo for the reply. You have a valid point. I say yes and no. I do rest the foot on the floor but I am not still (lets say smoothly ) able to control the clutch. I am working on it though.
Yeah it'll come with time ~ all the best!
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