kit choice & Newton's nightmare

[aniken]

If you accelerate faster, then more force is being applied to move your vehicle, hence more force is required to stop it.

But the car doesn't weigh any more. Why would you need more force to stop it from any given speed?

You might have a problem with standard brakes if you typically accelerate fast in heavy traffic: more acceleration + same reaction time = reduced 'margin for error' = a need for more brake power to offset the reduction in your 'margin for error'. Or, you could just not drive fast in heavy traffic.

[Geeseman]

But the car doesn't weigh any more. Why would you need more force to stop it from any given speed?

You don't , as I said in the previous post. Both modded and non-modded cars are speed limited by the ECU. BUT, there are two factors to consider; firstly the modded car accelerates much faster, using much more force to do so (given that it has greater power and torque). To stop this faster accelerating car, you need a proportionate amount of force. This force is eliminated (in the form of a reduction in speed of a car) by dissipation of heat into the discs of the car's brakes(and the capacity of the brake calipers to provide the compression power to the discs). Obviously, to use standard brakes to dissipate so much extra force you will run into problems (fade, capacity to provide enough force resistance etc)

The second factor is that more powerful brakes will pull a vehicle up a lot quicker than standard brakes under identical acceleration for modified/unmofified vehicles.

[teebone]

But the car doesn't weigh any more. Why would you need more force to stop it from any given speed?

You don't , as I said in the previous post. Both modded and non-modded cars are speed limited by the ECU. BUT, there are two factors to consider; firstly the modded car accelerates much faster, using much more force to do so (given that it has greater power and torque). To stop this faster accelerating car, you need a proportionate amount of force. This force is eliminated (in the form of a reduction in speed of a car) by dissipation of heat into the discs of the car's brakes(and the capacity of the brake calipers to provide the compression power to the discs). Obviously, to use standard brakes to dissipate so much extra force you will run into problems (fade, capacity to provide enough force resistance etc)

The second factor is that more powerful brakes will pull a vehicle up a lot quicker than standard brakes under identical acceleration for modified/unmofified vehicles.

This has got me thinking about whether there are any implications for the Brake system performance and "legality" with respect to ADR 31.

Power and torque don't appear to be a consideration. Only vehicle mass (which I presume doesn't change much by adding a piggyback ecu?), the testing speed, deceleration rates and pedal effort - which is interesting.

APS and others don't appear to have made any reference to this in the past - only emissions & noise ADRs - so I'm assuming this interpretation is correct ?

[100%]

We'll that may be the case, but his car is probably far less dangerous than a modified T with 330 kw at the wheels and standard crappy brakes

So do you think stopping my car from 100km/h while accelerating at full throttle requires more force than is required to stop from 240km/h? At what acceleration/speed does the force required to stop exceed that required from 240km/h which the brakes are designed for?

Anyone into physics here?

Sorry to continue the hijack!

[geea]

Geea, I support you in the comments you have made. You have made educated choices in the modifications you have done and in my opinion made the best decisions for your T. Keep up the good work, I'm sure you get satisfaction doing it, much as I do. Not all people have the time or skills (nor the desire) to do the research to pick the better "stuff" mixing and matching so sometimes they have to take a stab in the dark, rely on someones advice and hope for the best ; but pay a HUGE premium for it also. You can look at it the other way also. Sometimes if its just a one off thing you want to do and your not that way inclined as a DIY person you are better off paying someone whatever it cost to do it and do what you do best to pay it off.

Geea.

[Dr Z]

We'll that may be the case, but his car is probably far less dangerous than a modified T with 330 kw at the wheels and standard crappy brakes

So do you think stopping my car from 100km/h while accelerating at full throttle requires more force than is required to stop from 240km/h? At what acceleration/speed does the force required to stop exceed that required from 240km/h which the brakes are designed for?

Anyone into physics here?

Sorry to continue the hijack!

I offered an intuitive explanation in the legality thread HERE, but since 100% wants a physics explanation..

As many of us may recall from our high school physics, the equation which relates the distance travelled to the quantities of acceleration and velocity is:

Distance = (1/2 x Initial Velocity ^ 2) / Acceleration

where in our case of wanting to stop a car from some initial velocity:

Distance = braking distance

Initial Velocity = initial velocity at which brakes are applied

Acceleration = deceleration required to bring car to a final velocity of 0

Note: The better the braking mechanism, the greater the deceleration (which was my point in the legality thread about 100% getting better brakes!)

This formula can be verified anywhere on the internet, like HERE for example (the example I used in the legality thread).

In addition, as I mentioned in the legality thread:

In terms of braking in a car:

* Thinking distance is directly proportional to speed

* Braking distance is directly proportional to the square of the speed

So:

Total stopping distance = reaction distance + braking distance

To highlight the dangers of initial velocity (speed) assuming reaction time on average is 1.5 seconds and deceleration is 10m/s^2, consider this:

At 60 km/hr:

Reaction distance = 60000m / 3600 seconds x 1.5 seconds = 25 metres

Braking distance = (1/2 * (60000/3600)^2)/10 = 13.9 metres

Total stopping distance = 38.9 metres

At 65 km/hr:

Reaction distance = 65000m / 3600 seconds x 1.5 seconds = 27.1 metres

Braking distance = (1/2 * (65000/3600)^2)/10 = 16.3 metres

Total stopping distance = 43.4 metres

Difference of 5 km/hr = 4.5 metres (43.4 - 38.9) which is a 12% increase in stopping distance! That is definitely enough of a difference to avoid or minimise damage to yourself or someone else!

..and what about at 240 km/hr?

Reaction distance = 240000m / 3600 seconds x 1.5 seconds = 100 metres

Braking distance = (1/2 * (240000/3600)^2)/10 = 222.2 metres

Total stopping distance = 322.2 metres

Hmm, that is nearly 1/3 of a kilometre stopping distance!

Is it relevant to braking distance what throttle was applied to get to 240km/hr? No!

Finally, how about the stopping distance for the fastest XR6T to date?...the APS Phase III run at Avalon clocked at 307 km/hr:

Reaction distance = 307000m / 3600 seconds x 1.5 seconds = 127.9 metres

Braking distance = (1/2 * (307000/3600)^2)/10 = 363.6 metres

Total stopping distance = 491.5 metres

Wow, that is nearly 1/2 of a kilometre stopping distance!

Conclusions:

1. The initial acceleration used to get a vehicle up to a certain velocity has ZERO effect on braking distance, though in the absence of higher anticipation in reaction times, it may significantly increase reaction distance, therefore total stopping distance.

2. Since initial velocity (speed at which brakes are applied) and deceleration capability (quality of braking power) are the only 2 variables that affect braking distance, then how much throttle is applied to get to that initial velocity is IRRELEVANT except for the purposes of reaction distance...which is why I advised 100% to get better brakes!

3. If FoMoCo rates standard brakes as sufficient braking power to stop a vehicle from 240km/hr then it is this initial velocity that matters irrespective of what throttle is applied to get there. In short, it is speed and NOT the acceleration to reach that speed which is the determinant for braking distance.

Anyone feeling tempted to quote Newton's Second Law relating to Force, Mass, Acceleration etc in an attempt to refute these conclusions is referred HERE to dust off some Physics 101 cobwebs.

Finally, just to get the thread back on track, I personally would definitely choose APS over any other modification supplier for their:

1. Legality compliance: which is also necessary for insurance duty of disclosure requirements so insurance companies cannot walk away from claims made on illegal cars.

2. Reputation reliability: since there are so many APS modified Ts out there going stronger than ever!

3. Component durability: where components are made from the best sourced materials and configured as a total package by qualified engineers.

4. Power consistency: given that the different Phase kits deliver high levels of power consistently, so power can be smoothly accessed at all throttle applications.

Brutebogart, or anyone else, no doubt there would be many volunteers who would happily test drive you in their APS Phase I, II or III modified cars so you can see what they are so thrilled about!

Safe and happy driving...Dr Z.

[Geeseman]

Thanks for the bible on physics there, DR Z, but you missed the point made in my previous posts.

The fact that a modified car accelerates much quicker than a standard T means that it gets to a level of speed at a much shorter time. This means, for example, it could take off at a set of lights and reach 100kmph in less than 1-2 seconds than a non-modified T. Of course, this means it also does it over a shorter distance, therefore meaning that in general the modified T is greater of far greater speeds than a non modified car over normal driving conditions (available distance in giving traffic situations).

Because of this greater speed capability, you would need more force to be applied to pull up the car in equally limiting distance conditions (ie citty traffic driving), which neccesitates the fitting of better brakes than the standard T has.

I've been in a car that can hit 100ks in under 5 seconds (probably closer to 4) and then had to hit the brakes hard to stop the car in a very short distance. It is without a doubt that the standard T's brakes could not cope with this situation, and that's exactly why I decided to change mine (although im still not happy with them given the increased ability of my car).

FoMoCo may say that the T's brakes can stop the car at 240's but over what distance. FAR greater than a car with better brakes is an obvious conclusion.

In regards to your final 4 points, it would be good to note that competing companies to APS also offer these sollutions. Point 1 may be a little difficult, but possible with companies like Chiptork

[TURBO4LT]

The problem I have with the standard brakes is that with the extra power I able to get to a higher speed between corners and because I get to the speed quicker the brakes have less time to cool down before they have to try and stop the tank again, so yes I think a brake upgrade is a good thing. The car wqas fine before to drive through kangaroo valley now it has a huge shudder after the first few corners.

[bcl]

Dr Z,

I understand that you are trying to assist people.

However, in my opinion there are a number of flaws in your arguments.

The formulas that you quote are quite well known.

I have no issue regarding you’re assertion (quoting from other references) that braking distance is related to reaction time and braking distance, which is obviously correct.

The main flaw in the arguments is the assumption that acceleration is constant.

To be specific:

Re your conclusion 1.

“The initial acceleration used to get a vehicle up to a certain velocity has ZERO effect on braking distance, though in the absence of higher anticipation in reaction times, it may significantly increase reaction distance, therefore total stopping distance.”

The rate of acceleration when you attempt to brake has a major impact on braking distance. The higher the power of the car the higher will be the RATE of acceleration, rather than acceleration being constant. During the reaction time (assuming it is constant) you will travel much further if you are undergoing increasing acceleration rather than constant acceleration. Constant acceleration is assumed in most calculations, largely for the sake of simplicity. In this case it is incorrect.

Conclusion 2.

Since initial velocity (speed at which brakes are applied) and deceleration capability (quality of braking power) are the only 2 variables that affect braking distance, then how much throttle is applied to get to that initial velocity is IRRELEVANT except for the purposes of reaction distance...which is why I advised 100% to get better brakes!

This conclusion assumes zero acceleration and therefore constant velocity, clearly not the case.

Dr Z, when you draw conclusions using an “air of authority”, I’d suggest you make sure you really understand your subject. If you want a demonstration of increasing acceleration and deceleration I would be only too happy to scare the hell out you.

Anyone feeling tempted to quote Newton's Second Law relating to Force, Mass, Acceleration etc in an attempt to refute these conclusions is referred HERE to dust off some Physics 101 cobwebs.

Did you actually read the reference that you quoted? It actually refers to the f=ma equation, (via “Work is the force times the distance, and since force is the mass times acceleration”) which IS Newtons 2nd law, and which is very relevant to braking. The higher the force generated by the vehicle, the higher will be the force required to stop the vehicle. The better the brakes, the greater the force that can be put on the vehicle in terms of deceleration to bring it to a stop.

Your unqualified recommendation of APS is remarkable, given that you don’t own a turbo, you have no previous turbo experience or experience with modified cars, nor have you ever dealt with that company before. How would possibly know about component durability, and the capability of the components to last over time. The guys running APS Phase 3 cars have no idea if their motors will last 2 years. In my case my motor was pulled apart, and block defects were found, that without rectification, would have caused problems down the track.

Please be careful about making comments in areas where you have no expertise or practical experience, as it is very easy to mislead people.

Brian

[Cobra]

"the Rate of Acceleration"

would someone explain it clearly to me

maybe I'm simple ..... but I thought there was a relationship between time and distance that could be explained by two things (I) the velocity at any point in time and (ii) the change in the velocity from a previous point in time (acceleration) ..... so .... isn't acceleration constant at any given time ?

the rate of acceleration is a really interesting concept but it is difficult to apply the to such a variable object as a car ....

to accelerate .... you use the pedal on the right

but

once you brake ..... you use the pedal in the middle .... the laws of physics come into play that relate to the velocity of the car at the time of the initial contact with the brake pedal

smoke and mirrors ... but maybe I'm too simple to understand this, but I do know that it I don't use the pedal on the right and the pedal in the middle at the same time when I'm doing 307km/hr .... and if I did (and lived), then maybe the double derivative of velocity may come into play ....

cause as soon as you take your hoof of the right pedal ... there is only an instant of constant acceleration .... and that is a fact