PV1
Site Moderator
Posts: 2992
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Panic Braking

Wed May 11, 2016 5:28 am

I figure it's about time we make a dedicated thread for this.

I definitely gave the panic braking system a workout this morning. Travelling downhill around 35-40 MPH, a deer jumps out right in front of me :shock: :o . As soon as I noticed him on the side of the road, I dropped into B mode (natural habit at this point to keep my hand on the shifter when going downhill, especially on the particular hill I was on), then when he kept coming out onto the road I stood on the brake pedal. Within 30-40 feet, I was stopped. I MISSED HIM!! :mrgreen: . I was amazed that the i-MiEV stopped so quickly, especially on a wet road while going downhill.

Of course, since my tires did squeal shortly before stopping, this must have scared the deer as the front of my car is peppered with dark spots that weren't there before ;) . I wish I had a dashcam or CaniOn running, so I could see just how quickly I stopped.

The (rhetorical) questions I have are:

1. Which tires skidded?
2. How did I manage to not have someone behind me for once?
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

sandange
Posts: 907
Joined: Thu Jul 05, 2012 2:21 am
Location: Quebec, Canada
Contact: Website

Re: Panic Braking

Wed May 11, 2016 7:33 am

Glad to hear you had no injury or damage.
We have a lot of deer up here , - one neighbor had a run in with one in her Fiat 500 ICE and had almost $ 6,000 worth of damage
The Miev always impresses me how quickly it can stop .
Which also makes me worry about having someone close in behind in situations like that.
Tesla Model 3 SR+, 2019
Previous EVs
Puey Bluey 2014 Miev
200,000 km , 124.000 miles.
Blackie - 2012 ES Miev 2 years - 67,000 km / (41,630 miles)
http://thecordstead.blogspot.ca/

PV1
Site Moderator
Posts: 2992
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Re: Panic Braking

Wed May 11, 2016 8:08 am

Thanks.

That's always my concern, which is made worse because I'm one of about a dozen people in my town that actually drives the speed limit. So, I almost always have someone 3 feet off my tail. That, coupled with the lousy reaction time of many of the drivers I see every day, I was very lucky that there wasn't anyone behind me this morning.
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

wmcbrine
Posts: 386
Joined: Wed Apr 29, 2015 10:26 am
Location: Laurel, MD
Contact: Website

Re: Panic Braking

Wed May 11, 2016 8:25 am

I've done it once, when I realized I was about to pass a stopped school bus with its sign out. Oh, the embarrassment of that squeal. I didn't quite stop short of the rear of the bus, either. Luckily I didn't get a ticket.

PV1
Site Moderator
Posts: 2992
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Re: Panic Braking

Thu May 12, 2016 10:07 am

I looked on my way to work this morning. Apparently, my back left tire skidded and left a 10 foot long skid mark on the road. Based on how the timing felt during the incident, I brought the car to a full stop within 30 feet from 35 MPH. I'm not sure how long it took to stop, but the tire started squealing about halfway between hitting the brakes and stopping, but the deceleration would mean that the first half of travel time covered a longer distance than the second half.

Impressive :mrgreen: .
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

Don
Site Moderator
Posts: 2882
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Panic Braking

Thu May 12, 2016 4:31 pm

I've always wondered how ABS with our rear drum bakes would work. Don't think it worked all that well on the compact pick-ups that had it either. *Theoretically* you can't lock up a wheel for 10 feet, but your experience proved otherwise. The road must not have been all that wet if you could see the skid mark the next day

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

PV1
Site Moderator
Posts: 2992
Joined: Fri Apr 27, 2012 4:22 pm
Location: Pittsburgh, PA
Contact: Website

Re: Panic Braking

Thu May 12, 2016 5:31 pm

Road was a bit more than damp, but it's not a smooth blacktop road. It's tar and chip.

Theoretically, ABS prevents the wheels from locking, but there is a point where the system can't overcome the brake pressure. Plus, once a tire breaks traction, it can't provide anywhere near the friction it had when rolling. The thing with drum brakes is that once the pads touch the drum, they roll slightly and increase their pressure on the drum. That, combined with tire traction loss and how hard I was standing on the brake pedal, the ABS likely couldn't back the hydraulic pressure off enough to allow the wheel to spin.
:idea: :idea: :idea: :!: :!:

Dropbox maintenance in progress. If any of my links aren't working after November 17, please PM me and let me know which one isn't working.

Thanks.

JoeS
Site Moderator
Posts: 3762
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: Panic Braking

Fri May 13, 2016 7:46 am

IIRC, our i-MiEV's braking system has a rate detector: slam on the brake pedal rapidly and the deceleration is maximized and simply amazing! Sure, the ABS judders, but the car stops - just ask the deer that's still alive or the monster pickup that ran a stop sign coming in from my left. Not often that it's needed in my case, but the car's stopping power is the best I've ever driven. I didn't think that drum vs. disk brakes have much difference in responsiveness to the ABS pulsing.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Don
Site Moderator
Posts: 2882
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Panic Braking

Fri May 13, 2016 8:24 am

JoeS wrote:I didn't think that drum vs. disk brakes have much difference in responsiveness to the ABS pulsing.
Evidently, there must be a difference. I'm not aware of cars employing disc brakes which actually lock up the wheels vs pulsing them. As I mentioned, this isn't that unusual on older compact pick-ups which had the disc/drum combination

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

jray3
Posts: 1658
Joined: Tue Dec 06, 2011 1:05 am
Location: Tacoma area, WA
Contact: Website

Re: Panic Braking

Fri May 13, 2016 12:54 pm

Don wrote:
JoeS wrote:I didn't think that drum vs. disk brakes have much difference in responsiveness to the ABS pulsing.
Evidently, there must be a difference. I'm not aware of cars employing disc brakes which actually lock up the wheels vs pulsing them.
Don


Indeed, I thought that ABS and drums were a tough combination because of the self-amplifying effect of drum brakes that still make them preferable for trucks, but also slow down the reaction time due to wider clearances between the brake shoe and the drum lining and slop in the linkage.

Most of my rear wheel skidding has been due to heavy regen on off-camber turns rather than braking. I'd bet that I've locked up one rear wheel for almost 10 feet several times coming down wet and winding hills. :twisted:
2012 i-SE "MR BEAN" 105,400 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

Return to “Suspension - Handling”