How fast can you stop. Have you tried?

[racefactory]

V=at +Vinitial
d=integral of v.t
d=at^2/2 +Vinitial*t
Vinital = Vkmh /3.6
t = Vinitial / G where G = 9.8m/s/s for '1G'
a = -G

Thus
d=-G(Vinitial/G)^2/2 + Vinitial*Vinitial/G
simplified:
d=-G(V^2/G^2)/2 + V^2/G
d=-V^2/2G + V^2/G
d=V^2/2G

finalise for real numbers
d=(Vkmh/3.6)^2 /(2*9.8G)
d=Vkmh^2/12.96 / (19.6 G)
d=Vkmh^2/254G where G=1 is now 1G

60kmh^2 / (254 *1G) = 14.2m
60kmh@0.9G=14.2 / 0.9G = 15.8m
.....
Assumes no reaction time, no progressive braking blah blah blah which would increase the distance.

That's cool. Where does weight come in here though? Surely weight has a big effect.

[racefactory]

so basicaly skid mark can out brake a f1 car and motogp bike?

Yeah, it looks like skidmark with his ZXR and dunlop GPR100's can out brake michael schumacher in the Shell Ferrari. the Fiat yamaha of course doesn't even make the equation here...

[Rodney007]

yeah well hes pretty talented young boy..
he was damn serious about it too..

[FzerozeroT]

Rocketman, this will be relevant to your interests.

My fastest logged lap at Puke on my SV1000S (1:07.934)

285.6 Metres from 233kph to 44kph with a maximum decelleration of -1.03 Gs coming into the hairpin. Thats the point where forks are fully compressed and it's a choice between washout and stoppie, SV has a high centre of gravity

A 600 getting a 1 minute lap can get 1.3 Gs into the hairpin (pilot climbing back onto the pillion seat)

SV wheelies at 0.83 Gs, an R1 manages 0.95 before it lifts. Both of these are in 'regular' position, climbing on the tank improves the figure

[Jantar]

Hey that's interesting... but are you sure you don't mean that 'friction coefficient' of 1?

Reason I say that is because any light bike with good tyres can pull 1g of force in cornering on the skid pad test. I suspect braking would yield far more force right?

F1 car can pull just over 5g in braking force. From watchin both motogp and f1 i'm guessing a motogp bike can surely pull about 2.5g on the brakes?

interesting.

No, I mean G force where 1 G = 9.81 m/s/s. Coefficient of friction is a factor that varies according to the tyre compound and the road surface. It is most obvious when, as you say, you are cornering. That is because the forces are all balanced and working through the Center of Gravity and the contact point of the tyres. Under braking the forces are unbalanced, and instead of working through the contact point the forward vector is some distance away and above. (This is why it is possible for bikes to perform stoppies.)

F1 cars can decellerate at almost 5 G, but then look at the contact area compared with a bike and also consider that their lower CoG puts the forward vector much closer to the multiple contact points.

That's cool. Where does weight come in here though? Surely weight has a big effect.

Weight does have an effect on the maximum force that will be exerted on the tyres, but has no effect on the calculations of stopping distance vs G force. A 1 G stop from 60 kmh will take the same distance for 100 kg as for 1000 kg. Galileo proved this concept some 520 years ago.

[Jantar]

Rocketman, this will be relevant to your interests.

My fastest logged lap at Puke on my SV1000S (1:07.934)

285.6 Metres from 233kph to 44kph with a maximum decelleration of -1.03 Gs coming into the hairpin. Thats the point where forks are fully compressed and it's a choice between washout and stoppie, SV has a high centre of gravity

A 600 getting a 1 minute lap can get 1.3 Gs into the hairpin (pilot climbing back onto the pillion seat)

SV wheelies at 0.83 Gs, an R1 manages 0.95 before it lifts. Both of these are in 'regular' position, climbing on the tank improves the figure

Thanks for that data Fzerozero. That confirms what we have been saying. You figures of 233 down to 44 in 285.6 m works out to an average decelleration of -0.73 G. There will be peaks and troughs and your maximum of -1.03G is around what I would expect, but the average is lower than I would expect.

It just goest to show that average decelleration of -9 G just isn't possible.

[GaZBur]

....I suspect not. I have reminded myself to practice again next time Im out.
The more you practice the better you must become
Any others out there that have tried out this tyre wearing past-time

Yes I have but to be honest didn't measure distances. Good topic question, more passing is done in racing under brakes than cornering but more bragging is done about corner speed. When you practice think of other things than just distance. Type of surface and temp and condition. You will be amazed at the difference in braking ability of a warm tyre compared to a cold one, different compounds and tread etc etc. Do you use back or just front.(that old arguement again) When practicing be careful and ease into it - I have found locking up the front can result in a very fast dumping and trip for x-rays.
I don't know the "officialy sanctioned technique" is but I like this technique, slam on both brakes reasonably hard then immediately ease the back and harden the front until the front just starts skuffing. This use of the back brake seems to drop the centre of gravity, reduce the weight transferance loading on the front and reduces the tendancy for the back end to try overtake the front while increasing the bite on the front tyre. Thats what I find best from seat of the pants but willing to try other styles if some else got good advice.
Stoppies are showy but not good for slowing you down, and I am crap at them so will dis them anyway.
I also have stopped from 60kph in under 2 metres. Made a fecking mess of the car I stopped against though.

[WuZards-Eugene]

It is a proven fact that one can stop in a miraculous 2 meters, from 60 kmh. I for one have the ability to come to a complete stop from 100 kmh in 2 meters, which I am pretty sure many others have successfully done.

Mark should get this on video, as I have not seen much footage of bike and rider, vs solid concrete wall, and I do not have the balls/stupidity to practice that particular feat. Sort of being like a suicide bomber instructor. "Ok everyone, Im only going to show you this once"

[racefactory]

Thanks for that data Fzerozero. That confirms what we have been saying. You figures of 233 down to 44 in 285.6 m works out to an average decelleration of -0.73 G. There will be peaks and troughs and your maximum of -1.03G is around what I would expect, but the average is lower than I would expect.

It just goest to show that average decelleration of -9 G just isn't possible.

interesting data Fzerozero. Thanks.

Assuming the surface stays the same.... Is the only reason that the maximum force figure of 1.03 can't be held constant for the braking because at high speeds even though you may be using all of your front tyre force, the air resistance is slowing you down on top of that?

Is the average lower than expected partially because at the end he may have been turning and braking at the same time into the bend? Fzerozero- that 44kph is including turn in whilst still on brakes right?

If so we can probably say that 0.8 is a good figure for working out rough braking distances for road machines eh?

In this case using 254@1g= 203.2@0.8g

100kmh^2 /203.2 = 49.26m ----motorway stopping distance.

55kmh^2 /203.2= 14.8m -----suburbian speeds.

Wet grip assuming 75% of dry grip (what most people seem to agree on)

100kmh^2 /152.4 = 65.6m ----motorway stopping distance.

55kmh^2 /152.4 =19.8m -----suburbian speeds.

Seems about right eh? Maybe the suburbian speeds would have slightly poorer figures because of no help from air resistance?

[Jantar]

Fucking interesting data Fzerozero. Thanks.

Assuming the surface stays the same.... Is the only reason that the maximum force figure of 1.03 can't be held constant for the braking because at high speeds even though you may be using all of your front tyre force, the air resistance is slowing you down on top of that?

Its more likely that the maximum figure is achieved late in the braking rather than early. As the weight transfers forward and the tyres load up the braking effect will be maximised. If the rear wheel starts to lose contact (start of a stoppie) then it will fall off again.

You are right about air resistance, that aids in decelleration, and is more effective at higher speeds.

[McDuck]

so basicaly skid mark can out brake a f1 car and motogp bike?

Well he is never really moving is he?

[SARGE]

Mark, my mechanics is rusty, but 2 mtrs from 60kph would require over 6g deceleration. T'ain't physically possible dude. Not without a rack and pinion down the road.

or a tailhook...

[SARGE]

Not only that - the poor fella quotes people out of context and makes himself look like a right idiot.

He also crashes barbeques uninvited......

bwhahahaha..

lonely boy

[FzerozeroT]

The horizontal scale on that is distance so if you try to translate that into forces per second on the bike it is (parabolic/hyperbolic/logarithmic?), I'll post it vs time when I get home, the first patch is loading the front wheel, at 200+ you do cover a bit of ground before getting max braking, then once you do hit max decelleration you start to judge how far short of the corner you are going to stop and ease it off again to make sure that you keep decent speed up to the corner, the margin for error on any given corner for perfect speed is the width of the track, how fast do cover 8 metres? I probably have some laps where I got better braking there but the rest of the lap didn't stack up to be faster.

[Badjelly]

F1 car can pull just over 5g in braking force. From watchin both motogp and f1 i'm guessing a motogp bike can surely pull about 2.5g on the brakes?

F1 cars have wings that generate downforce. That's why they can achieve lateral accelerations much larger than 1 g and that's why an F1 car is 20 s a lap faster round a track than a MotoGP bike.

Without wings you're limited to something in the vicinity of 1 g. But I'm not sure what "in the vicinity of" means exactly; there are some interesting numbers on other posts on this thread. A MotoGP bike pulling 2.5 g? No. I might believe 1.3 g.

When doing calculations, a conversion factor I find useful is 1 g = 9.8 m/s/s = 35 km/h/s. So from 0 to 100 km/h (or vice versa) at 1 g would take 100/35 = 2.9 s. Assuming constant acceleration during that 2.9 s, your average speed is 50 km/h = 13.9 m/s so you would travel 40 m. Some modern cars can brake from 100 km/h in 35 m, so that's a bit more than 1 g.

Last year watching the Taupo A1GP on TV, they showed the instrument readout on a car braking at the end of the main straight. By my reckoning that car dropped from 270 km/h to 70 km/h in 2 s. So that's 100 km/h/s, or 2.9 g. Changing your speed by 100 km/h in a second--bloody hell!