How fast can you stop. Have you tried?

[racefactory]

By CG I suppose you're meaning the centre of mass (or gravity as some errant folks like to put it). It is true that the CoM is important in relation to all of this - however, it has nothing to do with how much weight it puts on the rear wheel. It has everything to do with the vertical height of the CoM compared to the centre of your front wheel. If the CoM is higher, or a lot higher, than the centre of the wheel you will be, very, limited in how much braking force you can apply at the front tyre before making a somersault.

I meant CG rear weight bias. With the weigt further back i'm guessing it's an advantage under brakes right?

[Mikkel]

I meant CG rear weight bias.

So what does CG stand for?

[racefactory]

what's the formula for figuring out distance, given time? I think it's on this thread somewhere but can't find it!

If it's 145kmh lost in 3 seconds what's the distance and force?

Thanks!

don't worry- done it.

looks like the motogp bike was stopping at roughly 13.4ms^2 which is 1.37g!

[Jantar]

...looks like the motogp bike was stopping at roughly 13.4ms^2 which is 1.37g!

Correct. And at those speeds air resistance would play a reasonable part.

[Badjelly]

looks like the motogp bike was stopping at roughly 13.4ms^2 which is 1.37g!

Correct. And at those speeds air resistance would play a reasonable part.

Come on, how much then?

A post on this page has some numbers:

http://www.msgroup.org/forums/mtt/to...p?TOPIC_ID=955

The relevant bits...

This is a great link that compares a Hayabusa and a Kawi ZX-12r in a wind tunnel, here is some of their figures. The link has a graph and more details.
A lower figure means less drag, and the Hayabusa recorded a Cda of
3.37 ft2 (0.313 m2), about 8 percent less than the ZX-12R's figure of
3.67 ft2 (0.341 m2).

To achieve 187.5 mph, the Hayabusa needs 147.6 horsepower to
overcome drag alone; the 12R needs 161.3 horsepower for the
same speed. However, using the wind tunnel data, test weights,
our road-test dyno figures for horsepower and a rolling-resistance
figure, Cooper calculated that the ZX-12R would have a maximum
speed of 187.0 mph and the Hayabusa 187.7 mph. The effect of wind
can vary the result, usually decreasing speed unless it's a tailwind.
Sidewinds during a test can decrease top speed as a result of the higherdrag at yaw. This calculation doesn't include any ram-air effect, butessentially, the bikes have similar speed potential, although the Suzuki has the edge.

In order to measure the frontal area, we photographed the Hayabusa and
ZX-12R from the front, using a long lens to minimize parallax distortion,with a measuring stick beside each bike as a reference point. Later wescanned the photographs, enlarged them to an identical scale and close-cropped them. Using Adobe Photoshop, the pixels in the images wereadjusted to a scaled half-inch-square size and then counted, which gaveus an accurate measurement of the frontal area of each bike, confirmingour impressions. The ZX-12R has a frontal area of 6.09 ft2 (0.566 m2),physically larger than the Hayabusa, which is 6.01 ft2 (0.558 m2). Butthe advantage for the Suzuki is not just in frontal area. With figuresfor both drag and frontal area, it's possible to calculate the coefficientof drag, which is 0.603 for the 12R and 0.561 for the Hayabusa. The winner of this wind tunnel shootout is the Suzuki.

Unfortunately the link he refers to is broken.

[Badjelly]

And then there's this from Google book search (Motorcycle Dynamics,
by Vittore Cossalter):

http://tinyurl.com/ckp3w8

From p 75:

The value of the product CdA can vary from 0.18 m2 for speed record contenders that are completely faired to 0.7 m2 for motorcycles with no fairing and the rider in an erect position. A typical value for "super bike" motorcycles is 0.30 to 0.35 m2, while "Grand Prix" motorcycles reach 0.22 m2 or even smaller values. Touring and/or sporting motorcycles with a small front fairing have values around 0.4 to 0.5 m2. The change from an erect riding position to a prone riding position leads to a reduction in the value of the product CdA that varies from 5 to 20%, depending on the type of motorcycle and the rider's body structure.

On p 76 there's a chart of drag vs speed for various values of CdA. Taking CdA = 0.3 m2 ("super bike" motorcycles with rider prone) the drag at 200 km/h is ~ 600 N. If we assume a bike + rider weight of 250 kg (180 kg bike + 70 kg rider), the deceleration is 2.4 m/s2 = 0.25 G.

PS: the power required at the back wheel to push the bike along at 200 km/h against a drag force of 600 N is 33.3 kW. This sounds about right.

[gatch]

backtracking a little..

in the goldwing / cbr comparo, would the weight distribution/wheelbase of the goldwing work to its advantage too ? ie, the goldwing is longer and i imagine the weight closer to the ground then the cbr..

would it make a difference ?

[HenryDorsetCase]

nobody looks as if they will be taking my five hundy any time soon.

[Dean]

id think again henry ive put up the vid .check youtube gn 60kph stop in 2 meters . prepare 2 b amazed

[Mikkel]

Unfortunately the link he refers to is broken.

It doesn't sound like they used anything to simulate a rider on these bikes... Granted, on a busa or a zx12, it might not make too much difference since they have "comprehensive" fairings.

The reported Cds of 0.55-0.6 sounds plausible, considering that those two machines are about as close as we get to mass-produced streamliners.

A naked bike with a rider would be a very different kettle of fish I am sure.

[rastuscat]

id think again henry ive put up the vid .check youtube gn 60kph stop in 2 meters . prepare 2 b amazed

Please, I gotta see this, where is the link?

[Tank]

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

See the guys at the NSSS They meet Albany car-park between Farmers and Burger King Wednesday nights 7.30 pm.

Well worth while - nice people who can really help.

Then - I'd recommend English lessons.

[mikeey01]

The over-the-top brakes on sportsbikes are there to allow hard braking into each and every corner at very high speeds for hours on end, while maintaining consistent high performance and feel. For any imaginable single braking action such brakes are overkill and so are the ones on the GL1500 as well. After all, the GL1500 would have to be able to drive down a steep mountain pass without the brakes overheating and fading.
So, for a single braking action you shouldn't see too dramatic a difference.

The reason that trains take a long time to stop has more to do with the fact that it is steel-on-steel not rubber-on-tarmac that provides the friction that facilitate the stopping. Also, for some freight trains only the locomotive is braking, which makes a huge difference. But the steel-on-steel factor is also the reason why you only see fairly mild gradients on railroads - on the other hand, the fact that the steel wheels doesn't really deform during rotation is what makes railways so efficient.

Arr see I knew u clever fellas would explain that in a way I could get it! nice one now I sort of get it.
I was thinking about it after I asked that qustion "Does weight matter" and wondered if the transfer of those kilos onto front wheel of GL would allow a tad more stopping thingie.

[slofox]

http://www.kiwibiker.co.nz/forums/sh...ad.php?t=91326

Interesting how much faster you can stop in an emergency than when you "practice" emergency stopping.......

[rocketman1]

http://www.kiwibiker.co.nz/forums/sh...ad.php?t=91326

Interesting how much faster you can stop in an emergency than when you "practice" emergency stopping.......

I'm glad your practice saved you from an accident.
It is now something that I will continue to practice, I guess the only bikers that practice stopping hard are seasoned racers, not road riders, good to see it working