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What stops quicker, performance bike or economy car

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What stops quicker, performance bike or economy car

Old 12-30-08, 09:35 AM
  #1  
mustang1
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What stops quicker, performance bike or economy car

Assuming rider is not fat, the bike and car are both doing 50mph (assumption, they were going downhill and are now on the flats). Now they slam on the brakes... who stops first?

Further assumption, bike brakes are in good working order, good pads, DA brakes. Car has stock brakes that work correctly.
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Old 12-30-08, 09:43 AM
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I want to say the car, because they aren't worried about going over the bars. Even though the car is a lot heavier they have a lot more braking power. When a person is strapped into a stable vehicle they can really slam on the brakes, on a bike braking to your fullest potential is a very risky move.
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Old 12-30-08, 09:47 AM
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2008 Volkswagen R32 does 60-0 in 111 ft. Someone do the math, I'm tired.
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Old 12-30-08, 09:51 AM
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Most cars can stop within 120 feet from 60 to 0 mph. A bike can't come close to that.
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Old 12-30-08, 09:55 AM
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Good question. If you got your ass way back off the saddle, MTB style, that would change a lot.
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Old 12-30-08, 10:06 AM
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Since a car weighs so much more than a bike, the normal force acting on the car from the road is much greater resulting in a greater frictional force. This will make it so a car can slow down while a bike would skid out.
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Old 12-30-08, 10:12 AM
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the r32 is not a economy car its a performance car,a rabbit would be,besides vw's are junk!!!. does the economy car get abs, if so the car would stop quicker, could never balance your weight on bike to stop in 100 feet without locking up front or rear wheel
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Old 12-30-08, 11:53 AM
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Car
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Old 12-30-08, 11:56 AM
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I have "abs" because of all the situps I do.

But the car will stop quicker, assuming the bike has to stay upright.
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Old 12-30-08, 12:01 PM
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Definitely the car. Even some economy sedans are stopping in the 110- to 120-foot range from 60 mph nowadays. On a bicycle? The only way to stop that quick is to slam into a stationary object. (Maybe the back of the car.)
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Old 12-30-08, 12:08 PM
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Originally Posted by tchap27 View Post
Since a car weighs so much more than a bike, the normal force acting on the car from the road is much greater resulting in a greater frictional force. This will make it so a car can slow down while a bike would skid out.

But all that weight results in momentum that has to be slowed. So the added weight doesn't make the car stop faster. (if it did a Semi would outbreak a Porsche).


The reason the car will stop faster is the size of the contact patch as a function of weight.


Bike has about 2" of contact patch and a combined weight of say 200lbs.

Economy car example has a contact patch of at least 120". Assuming a total weight of 3,000lbs, the car has 15 times the weight, but 60 times the braking surface.

Thus with a similar tire compound and therefore an equal coefficient of friction per inch of contact patch, the car is going to stop faster.
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Old 12-30-08, 12:12 PM
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Originally Posted by merlinextraligh View Post
But all that weight results in momentum that has to be slowed. So the added weight doesn't make the car stop faster. (if it did a Semi would outbreak a Porsche).
Bingo.

Interstingly enough, even an economy car will probably out corner (the best bikes top out about 0.75-0.8 G's laterally) and out brake a really fast sports bike. 2 wheels and a high center of gravity does not work in our favor.
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Old 12-30-08, 12:21 PM
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And how much would the bike be helped if it was using disk brakes?
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Old 12-30-08, 12:24 PM
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Originally Posted by Cdy291 View Post
And how much would the bike be helped if it was using disk brakes?
not much, when the limiting factor is the traction of the tires to the ground.
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Old 12-30-08, 12:46 PM
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disc brakes really only help with modulation of braking. You can lock up your wheels with calipers, cantilevers, v-brakes, or disks. If you can lock them up, you've got enough braking power.
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Old 12-30-08, 12:51 PM
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I guess the road bike would be helped the most if it didn't have a rigid frame. If you had a suspension fork you would be as likely to throw yourself over.
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Old 12-30-08, 01:07 PM
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The car CAN stop faster, but how often does the driver of a car use full braking power? Especially if there is a cyclist behind them (That last part may depend on the mentality of the region). On the other hand, drafting that fast you want a Semi, bus, or not carrying rocks dump truck, and they stop slower.
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Old 12-30-08, 01:22 PM
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Originally Posted by fix View Post
Good question. If you got your ass way back off the saddle, MTB style, that would change a lot.
Or if you were riding a MTB, for that matter.

Road bikes are probably the worst stopping vehicles on the road.
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Old 12-30-08, 01:59 PM
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Originally Posted by tchap27 View Post
Since a car weighs so much more than a bike, the normal force acting on the car from the road is much greater resulting in a greater frictional force. This will make it so a car can slow down while a bike would skid out.
It's actually friction-to-weight ratio that matters. The problem is that the vertical-loading on any square-inch of contact area is so much higher on the bike than a car (100psi vs 32psi). A 200lb bike+rider has 2 sq.in contact @100psi while a 3200lb car @32psi has 100 sq.in. While total friction goes up with vertical-loading, the friction-coefficient goes down. The car will have a higher friction-coefficient because it's not loading its contact-patch as high as the bike. I.E. forcing twice the weight onto the same surface-are does increase total friction, it doesn't double it.



An MTB with strong cantilevers or V-brakes and fat slicks at low-pressure can come close to a car's maximum-braking force. ABS on modern cars actually increase braking-distance as it can't really modulate at the limit as well as a skilled driver. But it does allow steering control while braking under adverse conditions like rain & snow.

Last edited by DannoXYZ; 12-30-08 at 02:02 PM.
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Old 12-30-08, 02:37 PM
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Old 12-30-08, 02:39 PM
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good science trumps bad science.
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Old 12-30-08, 09:34 PM
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Originally Posted by Fat Boy View Post
Bingo.

an economy car will probably out brake a really fast sports bike.
Wrong
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Old 12-30-08, 11:30 PM
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umm..try it out and let us know how much road rash you manage to garner when you squeeze the brake to death.
i would *guess* surmise that, given a non suicidal cyclist and a really lead footed driver..the car wins.
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Old 12-30-08, 11:32 PM
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Originally Posted by merlinextraligh View Post
The reason the car will stop faster is the size of the contact patch as a function of weight.


Bike has about 2" of contact patch and a combined weight of say 200lbs.

Economy car example has a contact patch of at least 120". Assuming a total weight of 3,000lbs, the car has 15 times the weight, but 60 times the braking surface.

Thus with a similar tire compound and therefore an equal coefficient of friction per inch of contact patch, the car is going to stop faster.
Wouldn't the size of the contact patch not have any bearing on stopping power? I thought the frictional force was the same regardless of contact patch. Am I wrong or did I actually learn something in the physics classes I took?
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Old 12-30-08, 11:39 PM
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Originally Posted by JaRow View Post
Wouldn't the size of the contact patch not have any bearing on stopping power? I thought the frictional force was the same regardless of contact patch. Am I wrong or did I actually learn something in the physics classes I took?
The coefficient of friction might be the same, but not the force of friction.
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