DRUNKNORGY

I asked this question in the non scoob section but I think I should have asked it here. How strong are the scoobs brakes. Does anyone know ?

Ash

DRUNKNORGY

The reason I ask is I have seen a lot of posts stating that scoobs can out corner, out brake, etc, your average superbike by a comfortable margin. I have seen an article in Performance Bikes who tested the brakes on various bikes and the Kawasaki ZX6R Ninja can pull 1.18 g under braking in standard form. How does this compare. Anyone got any numbers ?

LG John

The brakes strength are surely irrelevant to this? Any car has strong enough brakes to lock the wheels (or engage the ABS) so if the driver brakes well (i.e. just before ABS becomes involved) then the brakes are doing all that they can to stop the car. Thereafter its mainly down to vehicle weight, tyre quality/tread, etc.

Dizzy

hate to dissagree but not soo... abs will only engage as you say when the wheels start to slip but this only really happens at lower speeds. oem scoob brakes are notoriously poor (I've got 2pot calipers but uprated disks now).
I wouldn't say a scoob could outbrake / outcourner a superbike anyway...
only the top cars can i.e. single seaters and good spec westi's / ca*****m's can, and then not by too much.

Dizzy

hate to dissagree but not soo... abs will only engage as you say when the wheels start to slip but this only really happens at lower speeds. oem scoob brakes are notoriously poor (I've got 2pot calipers but uprated disks now).
I wouldn't say a scoob could outbrake / outcourner a superbike anyway...
only the top cars can i.e. single seaters and good spec westi's / ca*****m's can, and then not by too much.

LG John

Lets assume for a moment that the abs was disconnected and the brakes (even the 2 pots) were working as normal non-assisted brakes. Surely if you jumped on them with all your might at 70mph they would lock........and you'd skid........and probably die!?

RT

Interesting points to note are:

1. that grip over the front of the car is determined by how much weight is over the front wheels.

2. weight transfer to the front is determined by the deceleration of the car. Taking ABS out of the picture, a "stab" from 60mph will always lock the wheels more easily than a "jab and squeeze".

The front of the car needs to be loaded up prior to the full amout of braking force being applied - this delays wheel lock. The harder you brake, the more weight tranfer to the front, leading to you being able to brake even harder etc. Its a loop.

Ultimately something has to give, it's usually tyre traction but could also be the car running out of braking ability. One can argue that front tyre traction is exceeded because the front wheels aren't loaded up enough, which is the result of insufficent weight transfer due to insufficient braking force available.

These are just my thoughts. Let me know if it makes any sense.

RT

Back to the original topic, I am surprised that a bike can pull 1.18g on the brakes. That is pretty high!

LG John

More to the point and 85kg rider would have to in the chest press position resist about 100kg of force acting on him (trying to throw him over the bars). Not many 85kg peeps can easily resist that kind of weight so surely something doesn't add up. BTW I realise these are bigtime ball park figures but I hope the illustrate my point

DRUNKNORGY

I haven't got anything to compare it against which is why I asked the question. The 600 Ninja Uses two-6 pot Tokico calipers with sintered pads (they are the same disks & calipers as the 900 Ninja but without the extra 30 kgs of mass). I assume that a stoppie is the only thing which is likely to limit this figure.
The back brake is just a single pot arrangement and is really just there to settle the back end on the entry to a corner.

DRUNKNORGY

The prone riding position of this type of bike means that any speed below 70mph isn't that comfortable as a lot of body weight is on the bars. We get used to it!. Obviously 100 kg of mass on you hands is a lot but its not on there for very long and the riders torso/legs are wrapped around the tank which helps to brace against it.

slippyr4

"...about 100kg of force..."

kg is not a unit of force.

On a bike, as you apply the front brake, you are creating a frictional force about the front axle. The momentum of the bike trys to counteract this friction and you do an "endo".

Optimum braking on a bike occurs at a situation where the braking moment (which is trying to send the rider over the bars) exactly equals the counter moment which is a result of the weight of rider and bike. Because the weigh of rider and bike is a limiting factor, this means that maximum braking effort is relatively small. It doesn't really matter what the "strength" of the brakes is, since once the front wheel locks, you're f**ked anyway.

The addition of the rear brakes on a bike makes the situation much more complicated, but doesn't much change the result.

A car has a similar physical setup. However, here, the limiting factor in the braking balance is the friction between the tires and the ground. The moment generated by the weight of the car is orders of magnitude greater. It wouldn't be very likely that you could tip the car over the front wheels.

So, to summarise, yes, from a given speed, assuming the brakes can cope, a car will outbrake a bike.

LG John

I'd rather just pull my parachute cord and let the bike do the talking with the offending obstruction

DRUNKNORGY

This still doesn't answer the original question.
Are there any numbers available for braking G's in a scoob ?
Less mass=less sheer stress=less effort ?.
A Flea can pull 20 G's on a hop and theres no mass there at all.
The bike tyres profile will flatten under extreme braking which increases its footprint substantially. The compounds on bike tyres are much softer than car tyres which increses grip also.
A 16 wheel articulated lorry has enough strength in its brakes to lock every wheel in an emergency but would not outbrake a car under any circumstance because there is too much mass.

Mick

iTrader: (1)

I'm sure I saw a bike mag test Bike vs 'non-standard' Scoob.

The decel 100 - 0 mph was 3.5 sec for Scoob and 4.5 for Bike if I remember rightly...

Someone must be able to do the math

Mick

GEJL

Accel = ( initial vel - final velocity ) / time

(if you assume constant acceleration).

Here final vel = 0, initial vel = 100 mph = 160 kmh = 160,000 metres per hour = 44.4meters/sec

So, a = 44.4m/s / 3.5 s = 12.6m/s/s

12.6m/s/s / 9.81 m/s/s (1g) = 1.3g

GEJL

..and check out the tyre tests in last months Evo. They were pulling well over 1g in the brake tests, IIRC.

Hoppy

Last year EVO tested a load of quick cars and the best car on the brakes was a 911 turbo with a 100-0 of 4.3 secs. I think the new shape WRX did 4.7 secs.

I did some tests on my UK00 car with APR 6-pots and did several 104-0 tests (corrected for speedo error) in under 3.3 secs. Best was 3.24. That's an average of 1.4g I think, probably peaking higher as the car shudders to a halt. The stop is ABS limited as it kicks in as soon as you hit the pedal. On standard brakes I couldn't get the ABS to trigger at anything over about 50mph.

If you feel like having a go at this, be very careful. Unless your brakes, pads, steering and suspension are in top shape you could find yourself in a ditch very quickly. Build up the speed slowly, and give the discs plenty of time to cool between runs or you'll prolly warp them. This kind of decelleration is positively violent and scary. You've been warned.

Happy stopping

Richard.

Andy.F

Ah but can you pull 1.2 G's acceleration from 0 - 30 mph My car gets from 0 - 30 quicker than it can do 30 - 0 better weight distribution going forwards

Hoppy

Andy, 1.2 accelleration is mental-fast. I know your car is mad, and infectious. Just look what you've done to the nice and mild Dr Banks

I once read that a Scoob was quicker to 30 than a McLaren F1. Maybe it's true

Regards,

Richard.