What is an appropriate stopping time and distance?

[slimyxylofone]

Every few weeks on one of my rides I'll perform a few emergency stops from various speeds.

Today I was testing how quickly I could stop from 100km/hr. I relaibly stopped in roughly 8 seconds and about 51m.

I measured the time by timing from my first application of the brakes and the distance by beginning to break at a certain landmark and then pacing out the distance in steps. Both measurements are obviously prone to my error.

I really noticed how the stopping speeds were really a sideways hyperbole (the first few seconds very little speed was scrubbed off). I can see how going 10km faster makes more of a difference to stopping time at 100km/h then at 20km/h.

Are there any data out on the internet about relative stopping distances etc to compare how I am doing?

It would be interesting to get others to perform this and post - get some comparasons between bikes and riders.

[Macktheknife]

You might want to try doing some carpark stopping practice, 8 secs @51 mtrs is a long way if you are in a hurry.
Maybe you could try hooking up with one of the mentors from the site to give you some tips.
http://www.kiwibiker.co.nz/forums/showgroups.php
you should find someone local there

[Transalper]

Actually I believed that about 50 meters to stop from 100km/hr is fairly average (and that does not count the reaction time you must include in real life emergencys). At 50km/hr the distance is more like 14meters.
One thing that you should note is that the car infront can almost always stop as quick if not quicker than a bike (not counting bikes with ABS). All a car has to do is jam on it's brakes and even if they lock all four wheels the average car will stop consistantly within the 50meters where as we have to really get practiced to be as consistant (This from my last defensive course).


ps... thought i'd google 'motorcycle stopping distance' and ....

This one is prehaps the one i'd take most notice off...www.rideforever.co.nz/ride_smart/control_braking.html (http://www.rideforever.co.nz/ride_smart/control_braking.html)
It says "Roughly speaking, in good conditions and without a passenger or heavy load, you can't expect a bike to stop in less than 12m from 50kph, 40m from 100kph and 50m from 110kph. Add to these a reaction time...."


This one (http://forums.about.com/n/pfx/forum.aspx?webtag=ab-motorcycles&nav=messages&lgnF=y&msg=22455.1) says modern Motorcycles that stop really well are capable of braking to a stop from 60 mph (97km/hr) in a distance of about 110 feet (33.5meters). He's got a nice new BMW with I asume ABS brakes in the picture.


The rest say the 50meter mark...
http://www.begin-motorcycling.co.uk/elc2.htm
http://www.survivalskills.clara.net/riding_skills_32.htm - that one says once you get to 100km/hr the 2 second following rule starts to hurt, needs to add another second kinda.

And now that's said that i must go and see myself just how far it takes me to stop the old Transalp (45 to 50meters i expect) by having a little practice again... then maybe check back in here.

[XP@]

In this thread there are some "very interesting" documents on stopping.

http://www.kiwibiker.co.nz/forums/showthread.php?t=12958

[Lil_Byte]

This one is prehaps the one i'd take most notice off...www.rideforever.co.nz/ride_smart/control_braking.html (http://www.rideforever.co.nz/ride_smart/control_braking.html)
It says "Roughly speaking, in good conditions and without a passenger or heavy load, you can't expect a bike to stop in less than 12m from 50kph, 40m from 100kph and 50m from 110kph. Add to these a reaction time...."

.

I have just read that article and noticed that they said in a nutshell never use your front brake unless stopped or in unison with your back brake. I usde to live on my back break (learnt on off road bikes a zillion years ago) and you nearly alway canned with excess front brake usage. When I migrated to road bikes I was told by the mechanics to live on my front brake for normal braking which is what I do and then balance them up in an emergency stop. So after all that what is the correct way of braking on a road bike

[Transalper]

lol, i read it as in a nut shell... always use both brakes and preferably with the bike upright rather than cornering.
I usually use both, but more of the front, even on the dirt.

[spudchucka]

Today I was testing how quickly I could stop from 100km/hr. I relaibly stopped in roughly 8 seconds and about 51m.

At 100kph your velocity is 27.77 metres per second.

In 8 seconds you would travel 222 metres at that velocity.

In a true emergency, taking into consideration the average perception-reaction times of between 1.5 to 2.5 seconds, your actual distance to stop could be considerably longer than 51 metres.

[Transalper]

And even that's if you're paying as much attention as you think you are.

[Ixion]

Mathematiclly invalid though.

You are only doing 100kph when you start braking. Not the whole time until you stop. I think you need to integrate the area under the deceleration curve, or something.

[Macktheknife]

Actually I believed that about 50 meters to stop from 100km/hr is fairly average (and that does not count the reaction time you must include in real life emergencys). At 50km/hr the distance is more like 14meters.
One thing that you should note is that the car infront can almost always stop as quick if not quicker than a bike (not counting bikes with ABS). All a car has to do is jam on it's brakes and even if they lock all four wheels the average car will stop consistantly within the 50meters where as we have to really get practiced to be as consistant (This from my last defensive course).


ps... thought i'd google 'motorcycle stopping distance' and ....

This one is prehaps the one i'd take most notice off...www.rideforever.co.nz/ride_smart/control_braking.html (http://www.rideforever.co.nz/ride_smart/control_braking.html)
It says "Roughly speaking, in good conditions and without a passenger or heavy load, you can't expect a bike to stop in less than 12m from 50kph, 40m from 100kph and 50m from 110kph. Add to these a reaction time...."


This one (http://forums.about.com/n/pfx/forum.aspx?webtag=ab-motorcycles&nav=messages&lgnF=y&msg=22455.1) says modern Motorcycles that stop really well are capable of braking to a stop from 60 mph (97km/hr) in a distance of about 110 feet (33.5meters). He's got a nice new BMW with I asume ABS brakes in the picture.


The rest say the 50meter mark...
http://www.begin-motorcycling.co.uk/elc2.htm
http://www.survivalskills.clara.net/riding_skills_32.htm - that one says once you get to 100km/hr the 2 second following rule starts to hurt, needs to add another second kinda.

And now that's said that i must go and see myself just how far it takes me to stop the old Transalp (45 to 50meters i expect) by having a little practice again... then maybe check back in here.

Have you actually tried this?
I have managed to stop easily within this distance from 50km, without emergency braking.
Seriously go and measure out a 12m length and mark it, you should be able to stop most bikes from 50K in less than that in my experience.

Read this, very interesting. http://www.fmq.qc.ca/pdf/amorce-freinage_eng.pdf

[slimyxylofone]

Thanks everyone for the replies! It'd be interesting to see how this pans out in for each rider; posting your stopping distances and times could provide some very interesting info in addition to the internet sites :)

[spudchucka]

Mathematiclly invalid though.

You are only doing 100kph when you start braking. Not the whole time until you stop. I think you need to integrate the area under the deceleration curve, or something.

He's saying he measured his emergency braking distance at 51 metres. I take that to mean that 51 metres is the distance from brakes applied to full stop, (this took 8 seconds to achieve).

Add to that another 1.5 - 2.5 seconds for perception / reaction time and he is looking at 91.83 metres - 120.425 metres to achieve full stop in an emergency situation at 100 kph.

1.5 - 2.5 seconds is the accepted range for perception - reaction time. This varies of course dependant on age, alertness, environment etc. Personally I think that most people who ride bikes will be at the lower end of the spectrum because they tend to be considerably more aware of their surroundings than the average bone headed car driver.

[eliot-ness]

[QUOTE] You can't expect a bike to stop in less than 12 mtrs from 50ks[Quote



A few figures here from road tests of 1970s superbikes.

Model Braking distance from 50km/hr


BMW R100RS 27'6" approx 8mtrs
Ducati 860GS 30'10" 9mtrs
Honda CB750F2 28'3" 8.5mtrs
Goldwing 29'
Kawasaki Z650 29'
Z100 27'
Laverda Jota 25'
MV 750s 29'
Norton Commando 28'
Suzuki GT750 3o'6"
GS750 25'6"
Trident 27'6"

All these figures were taken on dry seal. No reactiion time. An earlier road test, mid 1960s, of a BMW 600 gave a figure 22', (6.5mtrs) using the front, (2 leading shoe drum) brake only. Exceptional at a time when most bikes were doing around 30' from 50ks using both brakes, and would stack up well against modern disc brakes.

[slimyxylofone]

He's saying he measured his emergency braking distance at 51 metres. I take that to mean that 51 metres is the distance from brakes applied to full stop, (this took 8 seconds to achieve).

Add to that another 1.5 - 2.5 seconds for perception / reaction time and he is looking at 91.83 metres - 120.425 metres to achieve full stop in an emergency situation at 100 kph.

1.5 - 2.5 seconds is the accepted range for perception - reaction time. This varies of course dependant on age, alertness, environment etc. Personally I think that most people who ride bikes will be at the lower end of the spectrum because they tend to be considerably more aware of their surroundings than the average bone headed car driver.

Reaction times can be much lower/faster than 1.5sec. Typically someone, if paying attention, can react in about 400ms at fastest. Here's an excerpt from http://www.visualexpert.com/Resources/reactiontime.html (I'm not using this as my primary info source, but shows that I'm not talking out of my arse):

"Reaction times are greatly affected by whether the driver is alert to the need to brake. I've found it useful to divide alertness into three classes:

* Expected: the driver is alert and aware of the good possibility that braking will be necessary. This is the absolute best reaction time possible. The best estimate is 0.7 second. Of this, 0.5 is perception and 0.2 is movement, the time required to release the accelerator and to depress the brake pedal.

* Unexpected: the driver detects a common road signal such as a brake from the car ahead or from a traffic signal. Reaction time is somewhat slower, about 1.25 seconds. This is due to the increase in perception time to over a second with movement time still about 0.2 second.

* Surprise: the drive encounters a very unusual circumstance, such as a pedestrian or another car crossing the road in the near distance. There is extra time needed to interpret the event and to decide upon response. Reaction time depends to some extent on the distance to the obstacle and whether it is approaching from the side and is first seen in peripheral vision. The best estimate is 1.5 seconds for side incursions and perhaps a few tenths of a second faster for straight-ahead obstacles. Perception time is 1.2 seconds while movement time lengthens to 0.3 second."

[Macktheknife]

So slimy, have you taken my advice and measured out the distance and tried stopping? As you should be able to see from the above posts and links, 8 secs is a long time and 51mts is not short either.
What are you doing with this information?

[slimyxylofone]

So slimy, have you taken my advice and measured out the distance and tried stopping? As you should be able to see from the above posts and links, 8 secs is a long time and 51mts is not short either.
What are you doing with this information?

Well most of the above information shows that my stopping time and distance (which was timed in my head and paced out) is roughly average, not overly slow. That said, even if it is average, that means I have plenty of room for improvement.

As to whether I have actually done anything since my original post, no I haven't. I haven't even been on my bike. I'm in the middle of Uni exams which take precedence at this point.

I am planning to continue practicing with more accurate measurements this time (get someone to time me from them putting up a flag or something similar to include my reaction time; and try to get a hold of a walking tape measure).

Have you actually measured your stopping times, or were you just going off gut instincts that the times were slow? Maybe you can't stop as fast as you think?

I'll make an utmost attempt to post in this thread when I am able to get back on and go for another practice run. Two weeks and counting before I get to ride up to Auckland, pleanty of road for practice between Dunedin and Auckland!

[Macktheknife]

Slimy, PM sent in response to your questions. Good luck with your exams.

[Mental Trousers]

The only legal requirement for stopping distance I can find is:

Section 2.3 sub-section 6 (http://www.ltsa.govt.nz/rules/light-vehicle-brakes-2002.html#23): (b) is capable of stopping it within a distance of 7 m from a speed of 30 km/h

Can anyone who knows a little physics extrapolate that out to 100 km/h and that will give a maximum distance you should be stopping within.

[Ixion]

Back in the day, 30 yards from 30mph was reckoned the standard for good brakes.Memory (fickle, but) insists that Vincents could stop from 30mph in 22 yards.

[spudchucka]

The only legal requirement for stopping distance I can find is:

Section 2.3 sub-section 6 (http://www.ltsa.govt.nz/rules/light-vehicle-brakes-2002.html#23): (b) is capable of stopping it within a distance of 7 m from a speed of 30 km/h

Can anyone who knows a little physics extrapolate that out to 100 km/h and that will give a maximum distance you should be stopping within.

Could have a go at it but I don't have a scientific calculator at home. I'll try to remember to take this to work tonight and I'll post the results tomorrow.

[XP@]

Could have a go at it but I don't have a scientific calculator at home. I'll try to remember to take this to work tonight and I'll post the results tomorrow.

try Start -> Programs -> Accessories -> Calculator
then in the view menu select Scientific

[eliot-ness]

Back in the day, 30 yards from 30mph was reckoned the standard for good brakes.Memory (fickle, but) insists that Vincents could stop from 30mph in 22 yards.

I think you'll find that was feet, not yards. (see earlier post) although the Vincent figure would be a bit optimistic.

[Ixion]

Sorry. Yes, 30 foot it should be . Got carried away with all the switching of yards to metres. And lowish twenty something feet for the Vincent. It was very very good. Had twin front drums, never saw that again until the first Suzuki GT750. Vincents were only SLS though.

Part of the reason was the friction material. Bikes in those days weren't expected to be required to stop repeatedly from high speed, and there was less racing on the roads. So they used a softer material for the linings which gave better stopping at low speeds, at the expense of fade at high speeds.

[Ixion]

Yep. Found it. Vincent was 22.5 FEET from 30 mph (50kph). Copy of "The Motorcycle" road test here http://www.vincent-hrd.co.uk/story.html

Front brake only was 31 foot

22.5 foot is 6.75 metres
31 foot is a bit over 9 mtrs

Haven't come far in 60 years , have we?

[spudchucka]

try Start -> Programs -> Accessories -> Calculator
then in the view menu select Scientific

It doesn't have the functions I want. I've been too busy the last few nights, hopefully I'll get to look at it tonight.

[spudchucka]

Assuming that the vehicle, (a car) was under emergency braking and was fully locked up, to stop in 7 metres from a speed of 30kph the drag factor of the road would have to be only 0.5.

This is very low, most NZ roads are around 0.6 -0.65, some are as high as 0.7.

So a vehicle travelling at 100kph on the same surface, (drag factor of 0.5) would require 78.61 metres to stop under full lock up.

[Ixion]

I happened to be at werk this afternoon, with von Klunken and an empty car park. Large .

So I tried the experiment, Back up, accelerated to 50kph and hit the brakes hard - not quite hard enough to kick in the ABS but hard enough that one at least of the tyres was singing. Stopped and went back and measured the distance (started braking as I passed a mark)

Only paced out but I know pretty near exactly a one imperial yard pace Result was between 9 and 10 yards, about 8 to 9 metres.

Repeated , about a foot longer. Repeated again, this time hard enough for the ABS to engage, a couple of foot less . I imagine that in a real emergency adrenalin would knock a few foot off. I was probably releasing a foot or two earlier than necessary, even with ABS it is possible to lock a wheel and I didn't fancy a low speed spill.

So, the old 30 foot at 30 mph is pretty well right, and some of the figures discussed seem excessive.

EDIT. I think drums will always give better low speed braking distances than disks, it's a matter of the friction surface area. So we probably won't see figures to match the BMW or Vincent ones, but distances from higher speeds would be a different matter - at low speed the drum brake doesn't have time to get overly hot as it does from a high speed stop.

[Roj]

Some very interesting stuff in the various links posted, a lot of variation is possible, but the estimate of 50 or so metres from 100 kph from start of braking to complete stop is not unreasonable,

The "2 second rule" gives about 1 car length per 10kph, a car lenth being approx 4-4.5 metres, so at 100 kph you may be less than 50 metres from the vehicle in front, assuming that the vehicle in front starts stopping suddenly, taking 1.5 seconds to react would loose about 40 metres of distance, meaning the vehicle in front may be close to stopping, doesn't leave much room for error.

While watching the vehicle in front is very important, watching what is further ahead is just as important, its all about identifying hazards as quickly as possible, and always consider if you have to stop, the possibility of have to go beside the leading vehicle to give yourself more space, or in other words, "plan ahead and have an escape route"