Braking distance comparison of motorcycle to automobile - Yamaha FJR Forum : Yamaha FJR Owners Forums
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Old 12-12-2006, 09:20 PM   #1 (permalink)
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Default Braking distance comparison of motorcycle to automobile

Of course the comparison would vary widely due to actual vehicles used in the comparison but here is a link to a report.

http://www.uem-online.org/html2/tour...cker_pap02.pdf

For the impatient , scroll to page 11 and there is a grahic results bar chart.

A BMW K1200 LT can stop quicker(114ft) than an Oldsmobile Alero(141ft) from a speed of 62mph(100kph). BUT they also show that the majority of riders will use from 192ft up to 222ft!

Another study reports a 2004 FJR with ABS stopping at 151ft from a speed of 60mph. Many newer cars made today routinely stop at approximately 120ft.
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Old 12-12-2006, 09:29 PM   #2 (permalink)
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Here is the link for the FJR. A very interesting chart is on page 6.

http://www.msf-usa.org/imsc/proceedi...ngDistance.pdf
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Old 12-12-2006, 11:21 PM   #3 (permalink)
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Who? Vehicle. What? Speed of vehicle (miles per hour), Stopping distance (feet). When? 2000. Where? A closed course testing facility Why? To see how the speed of the vehicle is related to the distance it takes to stop the vehicle. How? The vehicle accelerates to the chosen speed. When it passes a specific point, the driver slams on the brakes. The distance from the point to the place where the vehicle stops is the stopping distance. Speed(mph)Distance(feet)2015303640695011060152 Bivariate Fit of Distance By Speed 050100150200Distance01020304050607080Speed-10-50510Residual01020304050607080Speed Linear Fit Distance = ?62.8 + 3.48 Speed Summary of Fit RSquare 0.984489RSquare Adj 0.979319Root Mean Square Error 7.974961Mean of Response 76.4Observations (or Sum Wgts) 5
Speed(mph)Distance(feet)2015303640695011060152
20 15
30 36
40 69
50 110
60 152
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Old 12-12-2006, 11:27 PM   #4 (permalink)
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Total stopping distance for a car is on the average twice that of the FJR!
http://www.highwayrobbery.net/redlig...HPReplica.html


Stopping Distance Chart


This is an exact copy of the CHP's chart, which was available on their website until May 2004. CHP public information staff said that they removed it from the site because "It didn't take into account ABS brakes." So far, they have not offered a replacement chart.


This chart is based upon very hard "panic" braking at 0.7 G, which is a decrease in your speed of 22 feet per second, each second (in engineering terms, 22 feet per second squared), while a comfortable stop is one with a deceleration rate less than half that. From FAQ #6 on the Links Page: "Olson and Rothery reported in 1972 that their research showed that drivers were "virtually" certain to stop if their required deceleration rate was less than 8 feet per second squared and virtually certain to continue if the deceleration rate required was in excess of 12 feet per second squared" [Determining Vehicle Change Intervals - A Proposed Recommended Practice," ITE, 1985]



Stopping Distances for Passenger Vehicles (chart)



Speed (Miles
Per Hour) Speed
(Feet Per Second) Perception + Reaction Distance "Brake Lag" Distance Effective Braking Distance Total Stopping Distance
15 22.0 33 0 11 44
20 29.3 44 0 19 63
25 36.6 55 0 30 85
30 44.0 66 0 43 109
40 58.6 88 0 76 164
50 73.3 110 0 119 229
55 80.6 121 0 144 265
60 88.0 132 0 171 303
http://www.highwayrobbery.net/redlig...HPReplica.html



Perception + Reaction Distance = Feet Traveled in 1.5 Seconds. The average driver's perception time is .75 seconds and the average reaction time is also .75 seconds.
"Brake Lag" Distance = Brake lag in a passenger vehicle is approximately .05 of a second. This figure is generally not taken into consideration in determining stopping distances.
Effective Braking Distance = Feet Traveled after brakes make contact with drums / rotors with good braking efficiency on good dry level pavement. Coefficient of Friction = .70 . Decelerating Rate = 22.5 feet per second average.
Total Stopping Distance = Perception + Reaction + Brake Lag + Effective Braking Distance.
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Old 12-13-2006, 12:13 AM   #5 (permalink)
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Quote:
Originally Posted by twister
Total stopping distance for a car is on the average twice that of the FJR!
Dude? Are you on drugs, or you just staying with Starcruiser at his parents' house?

Perhaps you're confusing your figures from your highly misengineered 2003 FJR. Either way, quoting statistics from an anti-red light cameras website followed by your own 'fuzzy' logic is as scientific as using Starcruiser for a political science dissertation.

I don't know about you, but when I run my finger down the 60-zero column in Motor Trend for average modern sedans, I see lots of 115s - 125s (feet). Even full-size SUVs (Suburban, Tahoe, Expedition) are reaching zero within 125 - 130 feet. Exotic sports cars with fat rubber are reaching zero in 90 feet.

Running a finger down the 60-zero MPH column in current motorcycle magazines yield 115s - 140s, ON THE BEST PERFORMING MOTORCYCLES.

Stopping a motorcycle may also require special skills not necessary in stopping a four-wheeled vehicle.


Now really, don't make me come in here again!




PS - Thanks Luke, for that paper. Very interesting. Nice to see some actual science on the subject.
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Old 12-13-2006, 01:19 AM   #6 (permalink)
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Quote:
Originally Posted by Liquidsilver
Now really, don't make me come in here again!
Uh oh, back under the bridge we go
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Old 12-13-2006, 08:56 AM   #7 (permalink)
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From a completely subjective evaluation the issue that is obvious to me is not the relative braking power available at each wheel but rather the ability for that braking / locking force to be transferred to the driving surface. The contact area between tyre and road on a motorcycle Vs a modern sedan are significantly different.

Without regrinding the data it's reasonable to suggest that there may also be more variability developed in the bike data due to the variations in the degree of adhesion with convex bike tyre cross sections and also bike weight transfer decell dynamics when compared to the "roller" effect of a car tyre and the 4 points of adhesion. The bike decell is so much more critical and dependent on operator input than a car - get it right with good tyres and road surface and the bike will stop quick but so will a car even with significantly more vehicle mass.

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Old 12-13-2006, 11:15 AM   #8 (permalink)
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Luke: excellent info

Twister: I see ZERO comparative data in any of your posts. What did I miss? I see nothing in that CHP study that has the slightest application to what we are discussing here. The verbage you add isn't clear either. It all seems to be a bunch of engineering hypotheses with no actual results or field tests. Can you put it in layman's terms and provide backup?

Bottom line, anyone who seriously believes the average bike can stop in half the distance of the average car will soon be inspecting the trunk lid of a car in your neighborhood at very close range and at uncomfortably high speed. Bad headache to immediately follow.
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Old 12-13-2006, 02:44 PM   #9 (permalink)
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Twister, the RedLightCam chart you linked includes total reaction time! If you look at the effective braking distance you will see that it is 171 ft. And most of the cars sold today do have better braking systems plus ABS. Look at actual braking test results from Motor Trend, Consumer Reports, etc. and you will see distances much shorter.

In the end, the first link I posted shows that the average riders braking distance sucks in comparison to the average drivers braking distance. Only after the riders were "schooled" and prepped for the test did their results approach that of the cars.

Yes, there are always exceptions but I see this as a HUGE safety issue. I normally allow a WIDE variation from the norm on posts and don't respond when IMHO they are way off base.

We all must recognize the facts or we will become trunk lid ornaments!



PS. I have a 2002 GMC 2500 series truck with 4-wheel ABS. We could do a test. Tailgate me and see if you can stop quicker than I can!
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Old 12-13-2006, 08:02 PM   #10 (permalink)
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So what to take from all this? Swerve. Practice "emergency" swerve. Train yourself to look for the open hole and not at the solid impact object. Get your body trained so that if you come into a real emergency you don't have to stop and think. Motorcycles have any 4 wheeler beat in manuverability but, apparantly, not in stopping. A few minutes in a blank lot every couple weeks increase your chances. At least that's what I've read, and if something is written is MUST be true!
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