3 ms·

I believe the term "pumping the brakes" refers to applying and releasing pressure on the brakes. With ABS off, a tire that's locked up (not spinning) will stop

I believe the term "pumping the brakes" refers to applying and releasing pressure on the brakes. With ABS off, a tire that's locked up (not spinning) will stop in a significantly longer distance than one that's at the limit of grip (slipping with a slight under-rotation). Assuming you have exceeded the limit of grip of the tires with the initial brake bite and the tires have started to lock up, by releasing and reapplying pressure you allow the tire to spin up again to regain grip and then apply more brake to help stop the car. I assume this was to kinda emulate what ABS is meant to do (albeit much slower?) but I never knew this was a thing until recently. You do not need to pump the brakes if you can threshold brake, though I understand the fact that the vast majority of drivers on the road cannot do this and ABS is a life-saving fallback. Also to add to your comment about everyone taking some time to practice. I would also 100% recommend a good racing simulator if you or a friend you know has one. Specifically a setup that has a load cell braking pedal. Most entry-level sim pedals are potentiometers which measure the distance your foot travels as opposed to a load cell which measures the force applied on the pedal. This is how my younger self learned to threshold brake (among other things) and I was surprised at how it all transferred to the real world when I finally hit the track later in life.

cwillu 3y ago
Amusingly, a loadcell is in fact a very precise measurement of how far something has travelled in response to a load. More specifically, a resistor changes value very slightly as it is compressed or expanded. If you laminate a resistor to a strip of metal, you can use that change in resistance to measure the deflection, and then derive the force that drove that deflection. In principal you can get the same information with a lever attached to the same strip connected to a potentiometer; indeed, lever scales based on amplifying the deflection like that used to be universally used. Source: I was a loadcell technician in a previous life.
JohnBooty 3y ago
That's really cool and informational. Thanks for posting that. And yeah, pumping the brakes was essentially the "manual" version of ABS. Depressing and releasing as rapidly as possible.

cwillu 3y ago

Amusingly, a loadcell is in fact a very precise measurement of how far something has travelled in response to a load. More specifically, a resistor changes value very slightly as it is compressed or expanded. If you laminate a resistor to a strip of metal, you can use that change in resistance to measure the deflection, and then derive the force that drove that deflection. In principal you can get the same information with a lever attached to the same strip connected to a potentiometer; indeed, lever scales based on amplifying the deflection like that used to be universally used. Source: I was a loadcell technician in a previous life.

JohnBooty 3y ago

That's really cool and informational. Thanks for posting that. And yeah, pumping the brakes was essentially the "manual" version of ABS. Depressing and releasing as rapidly as possible.