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navenarf OP t1_ja7xhqj wrote

Reply to comment by Atmosphere-Terrible in ELI5: What is the fastest way to stop a car with a manual gearbox ? by navenarf

I am trying to figure out if a car (say running at 100km/h on asphalt pavement) would stop faster 1. slaming on the brake, or, 2. slaming on the brake plus rev match downshift, say if you can execute it at 100% accuracy. Basically I am trying to approach this question from the matter of physics rather than real life situation. Hope that helps clarify.

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Mental_Cut8290 t1_ja7zix7 wrote

From a physics standpoint, you can only brake with 100% of your tires' grip. If your brakes are capable of locking up the wheels (or triggering ABS) then you already have more than enough braking power. Engine braking won't help unless your brakes are weak.

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tjn182 t1_ja851xr wrote

Your brakes and ABS slow you down at the maximum amount without your tires losing friction with the pavement (sliding / slipping). When you are already at the maximum braking-power:friction ratio and you dump more stopping force by downshifting, you will have more stopping force than friction and you will start to slide, taking you longer to slow down.

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Atmosphere-Terrible t1_ja7y10c wrote

Got it! Ok in an ideal and I am talking textbook scenario probably, but it would be so marginal that hitting the breaks would be the most efficient.

Because what you are suggesting is:

You are in 5th or 6th gear at 100km/h you start hitting the breaks and you simultaneously shift to 3rd, or something? It might be more efficient, dunno.

I tried, I am not a physicist.

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