motorcycle weight vs. stopping distance

[Alsterbator]

come on truck drivers... does an empty truck stop as fast as a loaded one?

A Tractor Trailer is a whole nother topic... Anything involving a trailer is a different discussion altogether.

 

[BA BUSA]

A Tractor Trailer is a whole nother topic... Anything involving a trailer is a different discussion altogether.

Where did he mention anything about a trailer ???

 

[Alsterbator]

Where did he mention anything about a trailer ???

I figured that where he was going with it...

Not directed at any one person here:

What I am hearing is basically that if you add say 50lbs to a bike (remaining within the GVWR), that bike now takes longer to stop because of the brakes not being able to transfer the extra energy/heat???

If that were the case than DHSMV and DOT needs to hammer down on manufactures of all braking components. The brakes on your bike, car, p/u are more than capable of handling the added weight without it affecting the overall stopping distance.

It takes more brake pressure to slow down added weight, however with the added weight shift forward the increases in applied brake pressure can be increased resulting in more traction or bite on the road which compensates for the added distance... They cancel each other out.

 

[Mr Bogus]

I would have to say that stopping distance is directly related to tire loading... so there is not a "true" answer that covers all bikes.. I can change the stopping distance of any bike by changing tires and tire pressures along with tire compounds... adding or removing weight may or may not affect the stopping distance depending on the tires.. I could probably show a bike that stops faster on a given set of tires with more weight on the bike and visa versa.. You are going to need ABS to prove much to most however (has been proven to shorten the stopping distance on almost everything ever used on)

All this relates to the truck comment too 18 tires on the ground can stop hard enough to pitch you through a windshield..

 

[twotonevert]

I like Pie!

 

[BA BUSA]

Does increasing a motorcycle's weight increase the stopping distance for a given speed during a maximum braking event.

A. true

B. false

"Maximum Braking"

This is the point where the tires are loosing traction and start to skid...then you modulate the brakes to keep the wheels from locking. Sure if you add more weight you will increase traction, BUT...the bike will take a longer distance to stop!!!!!

 

[HT_USMC]

I figured that where he was going with it...

Not directed at any one person here:

What I am hearing is basically that if you add say 50lbs to a bike (remaining within the GVWR), that bike now takes longer to stop because of the brakes not being able to transfer the extra energy/heat???

If that were the case than DHSMV and DOT needs to hammer down on manufactures of all braking components. The brakes on your bike, car, p/u are more than capable of handling the added weight without it affecting the overall stopping distance.

It takes more brake pressure to slow down added weight, however with the added weight shift forward the increases in applied brake pressure can be increased resulting in more traction or bite on the road which compensates for the added distance... They cancel each other out.

My only reservation with that is whether they truly cancel each other out. I don't believe it's one to one relationship between traction and braking, but I could be wrong. I haven't done, and probably won't do, the math considering there are so many variables and forces at play with a braking event. I already have a day job.



I will say; Physics class taught about mass and what it meant to velocity, inertia, and kinetic vs potential energy - maybe I misunderstood. Though, personal experience has also taught me to brake earlier when I have a heavier load in the truck than normal. Perhaps motorcycles are different but that too doesn't seem to "feel" that way.

 

[KokomoBusa]

Hey Alsterbater...

 

[Alsterbator]

"Maximum Braking"

This is the point where the tires are loosing traction and start to skid...then you modulate the brakes to keep the wheels from locking. Sure if you add more weight you will increase traction, BUT...the bike will take a longer distance to stop!!!!!

I have ridden through courses that encourage to achieve "Maximum Braking"... In a class of 11:
When asked who felt they achieved "Max Braking" everyone raised there hand (including me). They followed that with this question: When you were nearing your stop 2-3mph (approx) did anyone feel their front tire slide? I kept my hand raised along with one other rider... Most feel like they achieved max braking when infact they did not.

I myself have measured my own stopping distances using multiple variables (added weight, tires, brake pads, passenger, stock ride height, lowered, etc..) with two constants (Me as the rider and the bike I was using).

I was able to stop in the shortest distance I safely could consistently with in 3-4ft each time. The stopping distance for the given speeds loaded were inline with my unloaded distances.

 

[KokomoBusa]

I have ridden through courses that encourage to achieve "Maximum Braking"... In a class of 11:
When asked who felt they achieved "Max Braking" everyone raised there hand (including me). They followed that with this question: When you were nearing your stop 2-3mph (approx) did anyone feel their front tire slide? I kept my hand raised along with one other rider... Most feel like they achieved max braking when infact they did not.

I myself have measured my own stopping distances using multiple variables (added weight, tires, brake pads, passenger, stock ride height, lowered, etc..) with two constants (Me as the rider and the bike I was using).

I was able to stop in the shortest distance I safely could consistently with in 3-4ft each time. The stopping distance for the given speeds loaded were inline with my unloaded distances.

??? you're so cool that the laws of physics don't apply!!! Grats....oh, and i'm selling a box of inertia for all that's interested.

 

[jellyrug]

Physics and applied math tell us there will be no difference in stopping time, comparing a heavy bike to a light bike, if WEIGHT WAS THE ONLY FACTOR.

In theory, we have two vectors, the vertical is down (weight of bike) and the horizontal is the stopping vector (weight of bike x coefficient of friction).

So, provided the coefficient of friction is a constant (rubber on pavement) there will be no difference.

In practice, it comes down to how the rider applies the brakes and how the suspension reacts when applying brakes. The suspension will change the kinetic energy vector, which without braking is horizontal and angle it towards down vertical, this can make a very big difference in stopping distance.

Hope that helps.

 

[Alsterbator]

My only reservation with that is whether they truly cancel each other out. I don't believe it's one to one relationship between traction and braking, but I could be wrong. I haven't done, and probably won't do, the math considering there are so many variables and forces at play with a braking event. I already have a day job.



I will say; Physics class taught about mass and what it meant to velocity, inertia, and kinetic vs potential energy - maybe I misunderstood. Though, personal experience has also taught me to brake earlier when I have a heavier load in the truck than normal. Perhaps motorcycles are different but that too doesn't seem to "feel" that way.

As a direct question I stand by my posts... In general though there are far too many variables to simply give a Yes or No answer.

 

[Alsterbator]

Hey Alsterbater...

 

[Alsterbator]

Physics and applied math tell us there will be no difference in stopping time, comparing a heavy bike to a light bike, if WEIGHT WAS THE ONLY FACTOR.

In theory, we have two vectors, the vertical is down (weight of bike) and the horizontal is the stopping vector (weight of bike x coefficient of friction).

So, provided the coefficient of friction is a constant (rubber on pavement) there will be no difference.

In practice, it comes down to how the rider applies the brakes and how the suspension reacts when applying brakes. The suspension will change the kinetic energy vector, which without braking is horizontal and angle it towards down vertical, this can make a very big difference in stopping distance.

Hope that helps.

 

[KokomoBusa]

Physics and applied math tell us there will be no difference in stopping time, comparing a heavy bike to a light bike, if WEIGHT WAS THE ONLY FACTOR.

In theory, we have two vectors, the vertical is down (weight of bike) and the horizontal is the stopping vector (weight of bike x coefficient of friction).

So, provided the coefficient of friction is a constant (rubber on pavement) there will be no difference.

In practice, it comes down to how the rider applies the brakes and how the suspension reacts when applying brakes. The suspension will change the kinetic energy vector, which without braking is horizontal and angle it towards down vertical, this can make a very big difference in stopping distance.

Hope that helps.

you should study harder...."weight of the bike" changes!!!!!!!!!

 

[KokomoBusa]

It's adorable how some folks take a semester or two in physics then secretly possess the ability to create their own laws. speed=constant....brake force=constant....mass=not constant......basic and i do mean BASIC newtonian physics is the only thing you need to look at....MO' shat is harder to stop than LESS shat.

 

[Mr Bogus]

here ya go, stolen directly from the physics forum... :

it's an issue of momentum and friction force.

friction force is proportional to the "normal" force, F_n ,, the component of all resulting forces acting on an object that is "normal" or perpendicular to the surface. often the normal force is simply the weight of the object.

there are, in classical mechanics, two constants of proportionality. 1. the coefficient of static friction, k_s , which governs the maximum force (parallel to the surface) needed to dislodge the object from sticking to the surface and skidding. 2. the coefficient of kinetic friction, k_k , which governs the force of friction when the object is skidding. these coefficients of friction are dependent mostly on the materials of the two surfaces rubbing together. (so there is some coefficients of static and kinetic friction for rubber against road.) usually the coefficient of static friction is greater than the coefficient of kinetic friction. (it takes more push to get your refridgerator to start sliding than what you need to keep it sliding.)

assuming that the brakes are applied to the maximum degree so that slippage between rubber and road (or skidding) does not occur, that's where the maximum braking can occur.

the bracking force is

F_b = k_s F_n

the normal force is the weight which is proportional to the mass.

F_n = m g

where g is the acceleration of gravity. so the braking force is

F_b = k_s m g

and that braking force is proportional to the deceleration a of the vehicle

F_b = k_s m g = m a

so the deceleration due to braking is

a = k_s g

independent of the mass of the vehicle. the increased mass increases the braking force, but it also increases the momentum by the same factor. if the vehicle was on a slippery surface, k_s would be less and the vehicle would decelerate more slowly. if the vehicle was on the moon, g would be less and the vehicle would decelerate more slowly. also if the vehicle is pulling a trailer which does not have braking on its wheels, that increased mass from the trailer and load contributes to the momentum, but not to the braking force because only the pulling vehicle weight is pushing down on its wheels (that have brakes), so it decelerates more slowly.

if you know the velocity when the brakes are applied, the braking distance is:

d = v t - \frac{1}{2} a t^2

and since the final velocity is zero

0 = v - a t

then you can calculate the braking time

t = v/a

and

d = v (v/a) - \frac{1}{2} a (v/a)^2 = \frac{v^2}{2 a} = \frac{v^2}{2 k_s g}

 

[KokomoBusa]

here ya go, stolen directly from the physics forum... :

 

[Mr Bogus]

yea I do not understand it either but it sure looked impressive

 

[KokomoBusa]

yea I do not understand it either but it sure looked impressive

dang....i thought you were S-M-R-T smrt for a second