Hey Mike something just seems so wrong with that statement. If that were true than a vehicle traveling at 60kmh weighing 1000 pounds would stop in the same distance if you added another 500 pounds to it. Is that true?
What stops faster "Car VS bike" - debate
- Thread starter mike.from.canmore
- Start date
Hey Mike something just seems so wrong with that statement. If that were true than a vehicle traveling at 60kmh weighing 1000 pounds would stop in the same distance if you added another 500 pounds to it. Is that true?
Glad you brought this up..
short answer = YES!
Of course - as with anything else there are a few minimum conditions that must be met first,
the braking system on that 1000 lb car must provide adequate stopping force to still be capable of locking the wheels with the full 1500 lbs of weight at that speed (lets say 60 mph).
Also, the tires can't be bicycle tires - they must aslo be able to handle the 1500 lbs under extreme braking without overheating
as long as these basic minimums are met - then yes - stopping distances would be the same (all things being equal). Some minor variences would of course occur depending where you added that weight - and certainly if that 500 lbs of weight was added as water! (bad).
without going too deep into details... I do have a very simple example that should help to make sense of it all.
Picture a 1000 lbs car and it stops from 60 in 100 ft (example data of course).
A. now, if you add a 250 lb trailer with a 250 lb payload (500 lbs of additional weight) balanced to have a 0 lb tongue weight - the 1000 lb car now of course unquestionably will take much longer to stop
B. instead of a free rolling trailer trailer - add 500lbs to the car - but add the weight at or near the already existing center of gravity (perhaps 2/3 large passengers - don't just add 500 lbs on the roof - that would significantly change the COG. Now you have a 1500 lb car - and yes it will stop as quickly or as short as the 1000 lb car. all things being equal.
in example A - significant inertia was added, but nothing was done to increase the traction. - longer stopping distances is the result
in example B - significant inertia was added, but traction was also increased by the same amount - more weight on the wheels.
This very concept is one of the permitting factors behind why an F1 car can decelerate at up to 5g when traveling at full speed. - but can hardly exceed 1.5 Gs of deceleration when going slower (no downforce).
http://en.wikipedia.org/wiki/Formula_One_car
http://en.wikipedia.org/wiki/G-force#Typical_examples_of_g-force
A question that I thought of regarding braking, Mike's post previous to this triggered the thought:
Is traction on a tire linear within the normal operating range of the tire?
For example, if you doubled the weight on the tire does traction also double? My gut says that unless tire deformation becomes a big issue, then yes it should be prettty close to linear. I imagine that in reality there will be some effects on the tire that cause the tire's grip to be slightly behind the increase in load (caused by tread squirm, heating effects, small deformation of the tire,) and that at a certain point there will be massive deformation and the tire will let go.
I don't actually know that this is true so I would like to know what the reality would be.
On a separate note: someone commented to the effect "who cares about the physics, all that matter is the results." To a large extent that is true, but sometimes knowing why something happens can help us deal with situations we hadn't expected, and some people are just curious.
..Tom
Is traction on a tire linear within the normal operating range of the tire?
For example, if you doubled the weight on the tire does traction also double? My gut says that unless tire deformation becomes a big issue, then yes it should be prettty close to linear. I imagine that in reality there will be some effects on the tire that cause the tire's grip to be slightly behind the increase in load (caused by tread squirm, heating effects, small deformation of the tire,) and that at a certain point there will be massive deformation and the tire will let go.
I don't actually know that this is true so I would like to know what the reality would be.
On a separate note: someone commented to the effect "who cares about the physics, all that matter is the results." To a large extent that is true, but sometimes knowing why something happens can help us deal with situations we hadn't expected, and some people are just curious.
..Tom
my gut feeling is the same. perhaps as weight increases, traction might actually increase initially at a greater rate - until an optimum balance of weight & temperature is reached, and then beyond that point - adding more weight would cause traction to increase at a lesser rate.
just a guess.
but i agree, unless massive deformation occurs - I expect a fairly linear relationship of weight VS traction.
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No it's not. Grip doesn't increase as quickly as increased load on a tire. That's why even load distribution is always prefered.
If true, then that implies that as a bike gets closer to doing a stoppie (putting all the weight on the front tire), the total amount of traction would decrease a certain amount. That implies that the longer the wheelbase (less weight shift to the front wheel) and lower the center of gravity (less weight shift to the front wheel), the shorter the stopping distance. Of course this assumes everything else is equal.
..Tom
Thanks Mike, So all things being equal (the car and the bikes ability to reach their respective maximum braking force given their individual weight doesn't exceed the traction capability of their tires or the friction capabilities of their respective braking systems) wouldn't this question basically boil down to traction, and then ultimately tire compound?
Does it work the same for boats vs jet skis?
If not what's different?
If so, which stops faster?
If not what's different?
If so, which stops faster?
Correct, in theory AND practice.
Close.
A bike is at maximum braking capability just before the front wheel locks and starts to skid.
A bike that tends to stoppie (ie short wheelbase) will flip over way before the front tire locks. The bike does not have a chance to reach maximum braking capability.
That implies that the longer the wheelbase (less weight shift to the front wheel) and lower the center of gravity (less weight shift to the front wheel), the shorter the stopping distance.
A long wheel base, low center of gravity, and a sticky sticky front tire are the key factors for motorcycle stopping distance.
Keep in mind a skidding front tire indicates the front end of the machine is about to tuck. ABS says a lot for safety in terms of emergency motorcycle stopping distances.
*gSTP*
Mike this thread is an eye opener. My riding style will change as a result.
Before reading I really believed that following Sue too closely in her 5000 lb. BMW X5 SUV is not a problem because I'm on a 600 lb. (with me on it) GSXR600 super sport so I'll stop in half the distance.
BWM X5 SUV Braking, 60-0 mph, ft 119.
GSX-R600 ’01 Braking, 60-0 mph, ft 117.6
Great Sue has dropped her cell phone and slams the brakes when she tries to pick it up. At that point I need trigger finger stoppie control like JohnnyP636 to stand a chance.
Whats worse is if I'm on a 250cc Suzuki GZ250 I'm not going to make it.
Suzuki GZ250 Braking, 60-0 mph, ft 123.8.
Thank you for bringing up this topic.
Before reading I really believed that following Sue too closely in her 5000 lb. BMW X5 SUV is not a problem because I'm on a 600 lb. (with me on it) GSXR600 super sport so I'll stop in half the distance.
BWM X5 SUV Braking, 60-0 mph, ft 119.
GSX-R600 ’01 Braking, 60-0 mph, ft 117.6
Great Sue has dropped her cell phone and slams the brakes when she tries to pick it up. At that point I need trigger finger stoppie control like JohnnyP636 to stand a chance.
Whats worse is if I'm on a 250cc Suzuki GZ250 I'm not going to make it.
Suzuki GZ250 Braking, 60-0 mph, ft 123.8.
Thank you for bringing up this topic.
Correction;
Thank you as well.
half way through this thread, I was beginning to loose faith that anyone would come around... But then luckily a few fact based posts brought us all back on track.
I too used to think a light bike would stop way faster than a heavy car/SUV.. People have such a difficult time admitting when they are wrong, some of them go through life refusing to accept logic.
All I wanted to convey is simply that - a bike DOES NOT stop way faster than a car. They are actually quite close.
Next - is that even though we think we are superstar riders - most of us are really just average riders (tough pill to swallow). And the average car driver in front of us can probably stop quicker - so be aware of that when following anything
ride safe everyone.
sadly the poll results indicate that we, collectively, have no idea what we are talking about.
You've brought a lot to this thread. I gave up on it before even trying (just look at the poll results, people were clueless from the start) but now it's turned around which is pretty impressive considering it's the internets.
It bears repeating; "a bike DOES NOT stop way faster than a car. They are actually quite close."
RedDogDarren
Well-known member
A bike stops faster than the car when they hit head on. I've tried it once just to prove it.
This is like Beavis vs Butthead. People citing wikipedia, .com pages, and other things that would fail you in university.
I took physics 3 years ago at Western but don't remember ****; I do vaguely have an idea of how to calculate the stopping power and time blah blah. HOWEVER I believe if we had a mechanical engineer who actually did some calculations we'd come to an end. Seeing as how this thread was mostly filled with "I THINK...." or "LOOK AT WIKI" I'd say we don't have any engineers...period.
Oh well, this is almost as stupid as people not eating sushi because Japan nuked itself accidently; all sushi comes from Japan AMIRITE?!?!?!
EDIT: I got a better question: is ABS necessary? I did a 24 hour endurance race in an M3 with 4 others with ABS DISABLED (TS or whatever the hell BMW called it was still on, though only on level 3 or something rather than max). We all agreed we were more comfortable without ABS because we all drove cars that our parents owned without ABS back in the day. I'm instinctually inclined to pump the brakes if I feel a lock up; I do the same on a bike. And in case anyone is interested we finished 2nd in class out of 4.
I took physics 3 years ago at Western but don't remember ****; I do vaguely have an idea of how to calculate the stopping power and time blah blah. HOWEVER I believe if we had a mechanical engineer who actually did some calculations we'd come to an end. Seeing as how this thread was mostly filled with "I THINK...." or "LOOK AT WIKI" I'd say we don't have any engineers...period.
Oh well, this is almost as stupid as people not eating sushi because Japan nuked itself accidently; all sushi comes from Japan AMIRITE?!?!?!
EDIT: I got a better question: is ABS necessary? I did a 24 hour endurance race in an M3 with 4 others with ABS DISABLED (TS or whatever the hell BMW called it was still on, though only on level 3 or something rather than max). We all agreed we were more comfortable without ABS because we all drove cars that our parents owned without ABS back in the day. I'm instinctually inclined to pump the brakes if I feel a lock up; I do the same on a bike. And in case anyone is interested we finished 2nd in class out of 4.
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Here is the calculator...just so you don't have to read through the posts: http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=4673
Here's some common stopping distances for bikes, notice that the supersports aren't in the top 10: http://www.mcnews.com/mcn/technical/200801perfindex.pdf
As far as your question goes on pavement I stomp the brakes in the cage, and squeeze, stomp and lean back on the bike - the brakes just won't lock up. We're talking panic stops here and not controlled decelerations, or racing. Do you actually ever panic stop in a race?
