markhr

Brakeless people, what's your minimum stopping distance, approximately, from ~20mph if you had to stop in a hurry?

(assuming new tyres, fully aired up and dry, paved roads)

JackD

20MPH is about 9 meters per second. I'd be surprised if anyone at that speed could pull of a stop including reaction time which is under 9 meters or so.

markhr

I'd thought it would be longer than 1 car length (5-6m) but I don't have either a fixe (it's in pieces ) or fixie riding buddy to help test it.

zoltani

d = V2/(2g(f + G))
Where:
d = Braking Distance (ft)
g = Acceleration due to gravity (32.2 ft/sec2)
G = Roadway grade as a percentage; for 2% use 0.02
V = Initial vehicle speed (ft/sec)
f = Coefficient of friction between the tires and the roadway

markhr

thanks for that

I'm assuming a flat, well paved, dry road and 700x25c, 110psi slick tyres - anything else to take into consideration?

What is a reasonable assumption for coefficient of friction please?

clink83

The only real answer is: Not fast enough.

gmodo

what are these meters you speak of?

daybreak

meters, that is absolutely ridiculous.

uke

I only voted 1m because you didn't include options in inches. When you have a true zen connection with your fixie, you can stop at will.

Adam G.

No more than 5 feet.

MIN 

There are too many variables to make this remotely scientific. Even with brake, this sort of quantification is dubious at best because of reaction time, road conditions and whether or not skidding occurs.

iloveboston

is this in a controlled environment or live traffic? honestly i dont know. i dont skid to stop. in emergency situations gut reaction takes over and inevitably you try to find a way around rather than trying to stop infront of the situation ya know?

straws papers

if you are going 20mph it is impractical to skid stop. It will take too much strength at the drop of a hat and even if you can lock up your wheel you'll still go too far for it to be a practical method of avoiding a situation. I can tell you from personal experience that at 20mph when something happens you need to be able to either work around it or you're most likely going down.

straws papers

oh, also


stop saying fixie. you sound dumb. only journalists and market researchers say fixie

markhr

Fixie

https://www.cycles-for-heroes.com/

markhr

Now that I've trolled my own thread - anyone care to volunteer a reasonable assumption for CoF please? Also, as you can no doubt tell, I pulled 20mph out of my ......... so it might be a little un-realistic.

darksiderising

Depends on the pavement, tire, weight of rider/bike, strength of rider, etc. No way of just coming up with a general number.

Judge_Posner

the only right answer is "a dime"

spitfighter

Generally, around 1.5 for rubber on dry asphalt. Until you start skidding, at which point it drops to about half that.

Brvn

Dont you own a ****ing CRC bro?

Also judging from what I remember of physics, that formula totally will not work. You need to take into account things like forces and the static and kinetic friction of both the pavement and rubber. Its not a hard problem but I by no means feel like working it out. On second look, that equation may not be a horrible estimation.


RubberAsphalt (dry)-0.5 - 0.8 RubberAsphalt (wet)-0.25 - 0.75 RubberConcrete (dry)-0.6 - 0.85 RubberConcrete (wet)-0.45 - 0.75

markhr

cool - I'd guessed at 0.5 but wasn't sure

Anyhoo here goes with 0.75 CoF = a minimum of ~5.5m (so just over a car length excluding any added distance due to reaction time.)

https://www.roymech.co.uk/Useful_Tabl...o_of_frict.htm (0.6 ot 0.85 for rubber/concrete(dry))
https://en.wikipedia.org/wiki/Coefficient_of_friction

I'm guessing (No! Another one?) it would be safe to assume at least 2 car lengths to stop at that speed for an average reaction time.

straws papers

I think reaction time is the main thing here. Reaction time + the time it takes to actually get your wheel to completely stop is going to more than double the length of the stop

Sixty Fiver

Some answers can be found here...

The Art of Cycling

markhr

Just checked Effective Cycling by J. Forester and he puts braking deceleration in a very clear and simple way.

For front and rear brakes applied simultaneously, 0.66g decelarating force will cause a stoppie on a bicycle and above 0.5g is usual for strong braking. However, for rear brake only this is reduced to 0.3g or less, i.e., damn slow.

Sixty Fiver

I think that we all know that stopping with only a rear brake is far less effective than when one has a front brake at their disposal.

Experienced riders already know this.