Apologies for going off topic here, but I'm curious about this. I've tested every car I've ever owned and all of the recent cars with all-round disc brakes have outperformed this statistic, but I've never been able to get agreement from other people (unless I demonstrate it to them in person).
I'm talking about optimal conditions here, wet roads would change things obviously but each of these cars was able to stop within it's own car length (around 15 feet) from 30mph, simply by stamping on the brake pedal with maximum force, triggering the ABS until the car stops:
2001 Nissan Primera SE
2003 BMW 325i Touring (E46)
2007 Peugeot 307 1.6 S
2011 Ford S-Max
I can't work out how any modern car, even in the wet, could need 45 feet to stop. In case it's not obvious, this is only considering mechanical stopping distance, human reaction time (or indeed computer reaction time which is the main topic here) would extend this distance, but the usual 45 feet from 30mph statistic doesn't include reaction time either.
I knew I'd get called out for not including sources. Those figures are from published sources, and do not include decision time. I'd imagine that these sources are for "average" roads and "average" cars
Car and Driver did a test with sports cars and profesional drivers and came up with 142 - 155 ft from 70mph, while my first reference quotes 245 ft (around 40% less, so extrapolating, their stopping distance from 35mph would be around 20 feet).
The average car on the road is not a sports car with performance tires and is not stopping on a clean, dry track. So I don't think it's a stretch to assume that an average car on average roads with tires optimized for tread life would be 40% worse than a $100K sports car with $400 tires that are optimized for grip rather than lifetime.
In addition, some cars such as the Nissan Leaf have a feature that locks the brakes at full power when there is a sudden control shift from accelerator to brakes, meaning that if you stomp on the brakes and then reduce pressure, the car will continue to brake at maximum power. This was done for two reasons: one, people hesitating in emergency situations, and two, people being taught to pump brakes, which increases braking distance in cars with ABS.
I learned about this feature when reading car forums for my car and finding threads from people who were rear-ended when they accidentally triggered this feature by slamming on the brakes when they didn't intend to come to a complete stop.
> In addition, some cars such as the Nissan Leaf have a feature that locks the brakes at full power when there is a sudden control shift from accelerator to brakes, meaning that if you stomp on the brakes and then reduce pressure, the car will continue to brake at maximum power.
Which is utterly stupid. Braking is the natural reflex, but not always the right one. I've been in more than one close call (think left turn on incoming traffic) where the correct response was not to floor the brake, but floor the gas.
> people being taught to pump brakes, which increases braking distance in cars with ABS.
Which is a mechanical turk version of what the ABS is doing under the hood.
> I'm talking about optimal conditions here, wet roads would change things obviously but each of these cars was able to stop within it's own car length (around 15 feet) from 30mph, simply by stamping on the brake pedal with maximum force, triggering the ABS until the car stops
How did you measure that? Because plugging these figures into a uniform acceleration calculator, 50km/h to 0 in 4.47m requires a deceleration of 2.2g but "Analysis of emergency braking of a vehicle"[0] experimentally measured very best case deceleration as barely scraping 1g (with ABS at 80km/h, significantly lower at lower speeds or without ABS).
Apologies for going off topic here, but I'm curious about this. I've tested every car I've ever owned and all of the recent cars with all-round disc brakes have outperformed this statistic, but I've never been able to get agreement from other people (unless I demonstrate it to them in person).
I'm talking about optimal conditions here, wet roads would change things obviously but each of these cars was able to stop within it's own car length (around 15 feet) from 30mph, simply by stamping on the brake pedal with maximum force, triggering the ABS until the car stops:
2001 Nissan Primera SE
2003 BMW 325i Touring (E46)
2007 Peugeot 307 1.6 S
2011 Ford S-Max
I can't work out how any modern car, even in the wet, could need 45 feet to stop. In case it's not obvious, this is only considering mechanical stopping distance, human reaction time (or indeed computer reaction time which is the main topic here) would extend this distance, but the usual 45 feet from 30mph statistic doesn't include reaction time either.