How fast can you stop. Have you tried?

**Jantar** · 25th January 2009, 13:20

Originally Posted by youngbiker16

im being taught emergency braking by a mate he makes me speed as fast as i could (which aint that fast considering ive got a gn250 lol).and then visualize a little girl or boy ran infront of the road im getting there i gotta practise practise.my mate once raced in the isle of man and he made me do another excercise where i have to get my tyre nearly touching his like an mm away from his out in waipu.hes crazy whenever i dont do it right or i bump into him we have to do it again. im only on ma dam learners !!!!

For christ sake young man. DO NOT LEARN ANYTHING FROM YOUR MATE. You are learning to ride, not to race. Never ride that close to another bike unless you are on the race track and slipstreaming. On the road keep your distance.

Even on the track riding close behind another rider can be a risky manouver. Just ask K14 what happened when another rider touched his rear wheel. I know I have put another rider down at Ruapuna when his front wheel touched my rear. That is just dangerous, far too dangerous to be something you'd practice on the road.

Get yourself a mentor asap.

**R6_kid:Me** · 25th January 2009, 14:11

Funny how skidmark has shut the fuck up now that the maths and physics came out and got involved - hard to talk shit against cold hard facts... and to think that he could clock up 60,000km on ZXR250's alone. He's only owned one or two and they spent most of their lives time in pieces.

**marty** · 25th January 2009, 15:49

Originally Posted by trademe900

But it's not about brakes, it's about tyres and weight isn't it? Any properly maintained brakes can provide enough to skid the front wheel, so isn't it about how much of that force the tyre can take?

hmmm. you've never ridden a CX500 in the rain have you (or in the dry for that matter!)

**racefactory** · 25th January 2009, 16:23

Originally Posted by youngbiker16

im being taught emergency braking by a mate he makes me speed as fast as i could (which aint that fast considering ive got a gn250 lol).and then visualize a little girl or boy ran infront of the road im getting there i gotta practise practise.my mate once raced in the isle of man and he made me do another excercise where i have to get my tyre nearly touching his like an mm away from his out in waipu.hes crazy whenever i dont do it right or i bump into him we have to do it again. im only on ma dam learners !!!!

Just watch out for when your front wheel skids eh mate... Those Gn's got shit tyres if they are stock man.

**StatX** · 25th January 2009, 17:47

Not fast enough...

Managed to land my front wheel in the rear bumper of a toyota (or something small, bubbly and blue) a few days ago... Drum Brakes Front and Back + Speed + Split second of looking down = Cars stop and you have a sore groin for a week...Fun ++

I think my back breaks are glazed, the squeaking and the lack of resistance from them might indicate that...

**Ixion** · 25th January 2009, 18:19

Originally Posted by Jantar

Oh boy! Have you got a lot to learn. If any brake can lock up the front wheel, then why do manufacturers go to the expense of multi caliper, floating disks, etc? An old single leading edge drum would do just fine.

Repeatability. Drum bakes were fine for stopping quickly, once, from moderate speeds. But they fell off fast as speeds went up, and faster still if you wanted to stop several times hard in a short time. Heat build up.

Not really that much of an issue on the road (I try to seldom use my front brake at all), but definately so on the racetrack. And modern bikes are totally based around race bikes. Ergo , "the expense of multi caliper, floating disks", largely unjestified as it is.

**Jantar** · 25th January 2009, 18:47

Originally Posted by Ixion

Repeatability. Drum bakes were fine for stopping quickly, once, from moderate speeds. But they fell off fast as speeds went up, and faster still if you wanted to stop several times hard in a short time. Heat build up. .....

Exactly. From moderate speeds. However I have ridden many bikes that even with disk brakes wouldn't lock the front wheel until speeds were very low. Many dirt bikes were engineered so that that they wouldn't lock the front wheel at anything much more than walking pace (Jawa cocky anyone?).

**kiwi cowboy** · 25th January 2009, 19:34

skidmark were are ya DEFEND YA SELF if ya can NOT lmfao

**rocketman1** · 25th January 2009, 19:47

Originally Posted by BMWST?

you dont have to make 50 tyre shredding stops....all you have to do is make a few stops gradually increasing the force that you use on the (mostly) front brake...dont put it on hard at first increase the pressure as ou slow down.I am betting that you will decrease your stopping distance by lots....its really good practise!

I didnt measure on my last ride, but what I did do was stop hard from 100kmph about six times, interesting, I checked no one was behind and slapped the brakes on hard the harder as I was slowing.
The bike held the line very well, a good amount of G-force on the handle bars
To my surprise the bike scrubbed alot of speed off quickly in the first say 30m? but then when not going very fast it continued on for longer then I would thought.Maybe thats where I have to squeeze the brake a bit harder, almost felt like a bit of brake fade, very interesting, I would have thought I'd stopped quicker. What I did do was that I felt better at gauging the stopping distance, which is a benefit from all this carry on, I felt that as I was getting better and I repeated the exercise.I guess its the last few metres that count isnt it.
I will keep it going and yes will do some measurements.
Now I know the approx 40 meter stopping distance is benchmark to achieve, I will mark two marks on the road 40m apart, I guess if I can get under 40m from 100km/hr I am doing OK, Right

**Dean** · 25th January 2009, 21:15

Originally Posted by Jantar

For christ sake young man. DO NOT LEARN ANYTHING FROM YOUR MATE. You are learning to ride, not to race. Never ride that close to another bike unless you are on the race track and slipstreaming. On the road keep your distance.

Even on the track riding close behind another rider can be a risky manouver. Just ask K14 what happened when another rider touched his rear wheel. I know I have put another rider down at Ruapuna when his front wheel touched my rear. That is just dangerous, far too dangerous to be something you'd practice on the road.

Get yourself a mentor asap.

hi jantar yes i am thinking about getting a mentor i think my mate just wants me to be like him yano teach me the stuff he learnt when he was my age.im pretty sure he wants me to go on the track and eventually race,he told me he started riding on the road at the age of 14 and all this hard out skills he learnt and whatnot.it seems like he wants me to be the next rossi but i dont think i will be.any mentors round the northshore whangaparaoa in particular

**BMWST?** · 25th January 2009, 21:21

discs are bloody cheap to make too.Twin leading shoe drom brakes....sigh

**Ixion** · 25th January 2009, 21:26

Four leading shoe brakes. Sigh

**Mikkel** · 26th January 2009, 09:20

Originally Posted by trademe900

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?

It's a Jedi mind-trick - they're down with the force ya know.

Originally Posted by trademe900

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

Weight and forces are not considered if you're only discussing kinematics.

Originally Posted by trademe900

But it's not about brakes, it's about tyres and weight isn't it? Any properly maintained brakes can provide enough to skid the front wheel, so isn't it about how much of that force the tyre can take?

Well, the weakest link in the chain and all that. The most powerful brakes in the world wouldn't save you if they just came with an on/off switch (I guess they could if they had ABS...

). A poorly set up suspension system can dramatically increase your braking distance as well - braking only works when the wheels are touching the ground after all.
And feel and control are imperative in that regard.

Originally Posted by FzerozeroT

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

I notice that the data has been obtained using GPS. Do you know how well calibrated the unit is and how often the position is updated? Real world data - real world imperfections as well...
And also, how much does such a unit cost? I want one dammit!

At high speeds you'll be able to exceed 1g - airbraking is not restricted by the friction between tyres and tarmac. This is especially true for bikes since they are about as aerodynamical as a tree. Try and sit up at 200 km/h (don't let go of the handlebars btw.) and see how quickly your speed falls off - do it again at 50 km/h and notice the difference.

As for practicing emergency braking - all good, but do ease into it or you might repeat my embarrasing incident.

**Badjelly** · 26th January 2009, 09:34

Originally Posted by Mikkel

At high speeds you'll be able to exceed 1g - airbraking is not restricted by the friction between tyres and tarmac. This is especially true for bikes since they are about as aerodynamical as a tree. Try and sit up at 200 km/h (don't let go of the handlebars btw.) and see how quickly your speed falls off - do it again at 50 km/h and notice the difference.

That's a very good point that I hadn't considered. I don't have a bike that will do 200 km/h, so I can't do any tests on this. How much deceleration do you think is achievable by a rider sitting up at 200 km/h? As much as 0.3 g?

Oh, never mind, I'm sure I can calculate the answer. Let's see rhoa = 1.25 kg/m3, Cd = 0.8, A = ...