I'm reading through the IVA manual. It's all pretty sound (unlike the MSA rule book!). I'm only half way through it but few bits I don't get. Maybe someone can clarify them? I'm still only at the design stage of my build I'm just reading ahead to allow for things in my design.

Brakes need to be dual circuit and each circuit acting on one wheel on each side. Is this how pedal boxes are usually plumbed?

quote:

---

Brakes: On full power hydraulic braking system warning device must be fitted, operative, and visible or audible to the driver, including in darkness.

---

quote:

---

Brakes: 19.The hydraulic system must be fitted with a red warning lamp,
sensitive to line pressure and capable of signalling the failure of any
part of the hydraulic system as soon as the brake is applied and
remaining lit as long as the failure exists (with the ignition switched
on). As an alternative, the warning lamp must be sensitive to the
reservoir fluid level, providing the reservoir is directly connected to
supply the pressure side of the master cylinder when the piston is
in the “brakes off” position, so that a failure of either part of a split
system would result in a continuous draining of the reservoir fluid
when the control is released (see note 2 and 3)

---

Parking brake needs to be mechanical. That's so that any pressure leakage of the hydraulics doesn't let it off.

Pedal box with no servo is fine and the warning light just needs to be a level float in the reservoir just like all OEM cars. With the wiring for it goes to the handbrake switch so the light comes on when the handbrake is applied. Any drop in fluid has to light it up as well.

Hope that helps.
Steve

for IVA the brakes are usually spilt front/ rear, but can be configured as diagonal
you don't need a servo
its usual just to have a fluid sensor in the masters reservoir (or reservoirs if more than one)

don't know about parking brake thou.

Switch on the handbrake is a test just make sure its working. Failing that you need a button on the dash to test it.

IMO handbrake switch is much better than a dash mounted knob...

Brakes need to be dual circuit and each circuit acting on one wheel on each side. Is this how pedal boxes are usually plumbed?

Yes balance bar system 1 cylinder for front the other for rear is usually it
or a twin port master cylinder f/r
diagonal not normal on a kit

Brakes need to be dual circuit and each circuit acting on one wheel on each side. Is this how pedal boxes are usually plumbed?

Yes, most road cars used to be diagonally linked, now with modern ABS they are all independent but type approvals often dont comply with IVA.
If you plan on using a bias box, you will need to split front rear, if not you can do it diagonally but will need to choose MC carefully to ensure brake force is distributed correctly. (most systems apply a lot less to the rear)

Brakes: On full power hydraulic braking system warning device must be fitted, operative, and visible or audible to the driver, including in darkness.

No idea what this means!

Dont forget the Glossary in the IVA, its at the end and ofter gets missed.
Power Braking
A system that requires the use of stored energy to operate.

This is aimed at air braking systems on lorrys etc.
HOWEVER, another section still means a warning light is needed -
18.
Where a warning lamp is provided as the only means of checking the fluid level without opening the reservoir, it must be secure, operational, visible during daylight and darkness from the driving position, and fitted with a “test facility” that enables its operation to be checked from the driving position without opening the reservoir.


Brakes: 19.The hydraulic system must be fitted with a red warning lamp, sensitive to line pressure and capable of signalling the failure of any
part of the hydraulic system as soon as the brake is applied and remaining lit as long as the failure exists (with the ignition switched
on). As an alternative, the warning lamp must be sensitive to the reservoir fluid level, providing the reservoir is directly connected to
supply the pressure side of the master cylinder when the piston is in the “brakes off” position, so that a failure of either part of a split
system would result in a continuous draining of the reservoir fluid when the control is released (see note 2 and 3)

Or this!

You need to read the 2nd half of the paragraph to relate it to most situations. What its saying is you need a warning system to ensure brake pressure is maintained, but this can be simplified by using fluid reservoir level indicator, as if there was a failure, this would indicate it just as quickly as a pressure sensing system.

There's also a requirement to test the vacuum assistance. But the notes refer to the vaccum system "if fitted". So is braking assistance needed or not? I wanted to use a pedal box but I understand that they work without assistance.

Exactly as what is says, any assistance fitted needs to be tested, so if its not fitted, its not tested.

There doesn't seem to be anything about the parking brake not being allowed to be hydraulic. I though hydraulic was not allowed? Did I imagine that or have the rules changed?

In the main brake section (09A)

9. The ‘parking’ braking system must be capable of being operated using a control which is independent of the service brake, and once applied capable of being maintained in the ‘on’ position solely by mechanical means.

[Edited on 30-12-15 by loggyboy]

Thanks for all the help. So the balance bar in a pedal box usually balances the front and rear brakes? If so then that's good, saves on complex proportioning valves.

I'm still not certain about pedal boxes and power assistance. Pedal boxes appear to be installed to rally cars and the like but I'm seeing and hearing that there's no power assistance. Is this really true? Is it to get better feedback from the brakes? Or maybe the cylinders are sized to get more force on the brakes without power assistance?

So at some point I'm going to have to read up on brake system design to select the size of my master cylinders.

because the cars are so light no servo is required, which makes the brakes inherently simpler, and a better feel

Though from your info on the left, are you actually referring to a light kit, or a V8 MONSTER TRUCK STUMP PULLER APOCALYPSE THING?
If so servos may be good!

quote:

---

Originally posted by ReMan
Though from your info on the left, are you actually referring to a light kit, or a V8 MONSTER TRUCK STUMP PULLER APOCALYPSE THING?
If so servos may be good!

---

quote:

---

Originally posted by rcx718
Lol, I am building a mini rock crawler to use in 4x4 trials. But mine is going to be as light as possible, under 900 kg I hope.

---

quote:

---

Originally posted by WesBrooks
I had been wondering about the effect of going from standard wheels at 31"ish up to the now popular 35". People often talk about issues with gearing, but doesn't it also increase the leverage which the ground-tyre interface has on the disc-pad interface?

---

quote:

---

I am hoping to use the standard vacuum assistance system which has front/rear split curtsy of a pressure distribution valve, but I do have some concerns about brake balance after the re-body as the weight balance may have shifted a lot.

---

I should add that the load sensitive valves increase power to rear brakes when the car is loaded with weight at the rear.

But I've also read about valves change brake proportions under different circumstances. Maybe someone else can clarify what those are as I can't remember.

People discuss the effect on drive train, gearing, and speedo reading quite regularly on the forums but the effect on braking rarely gets mentioned. I calculate the braking torque to be about 87% of standard on my target of 33" wheels, or 82% at 35". Not an insignificant increase in required pedal force for the same braking torque. So with the same brake pedal pressure 29" (I was wrong earlier with 31" ) to 33" has a similar effect to increasing the mass of the vehicle from 1800kg to 2069kg!

I don't think the valve is load sensitive but I will have a closer look. I'll get it built up then do a shake down somewhere off road to test braking.

[Edited on 7/1/16 by WesBrooks]

At the risk of "should have paid more attention in physics class"

Do bigger wheels need bigger brakes **Other than to compensate for the extra mass and weight of the wheels themselves?

My simple mind says its the weight of the vehicle that is being stopped, not just the wheels so tis shoule be "small" as a % of vehicle mass?

I don't think you 'need' bigger brakes for bigger wheels, but you would need either larger disc diameter or greater pad clamping force to get the same brake feel as the smaller wheel setup - ie how quick the vehicle stops for a given amount of foot pressure.

Essentially you are just trying to convert forward motion (kinetic energy) into to heat and keep the disc temperature within their & the pads working temperature range. More kinetic energy can be from either higher speeds or more mass. You then have to deal with the increase in heat though bigger discs (larger surface area), vented discs, or ducting to force air over them.

Edit: As you say assuming the increase in weight for the larger wheels and tyres is negligable for the weight of the car. This weight will have an effect on the total weight and rotating mass so bigger wheels may have more of an effect than expected.


[Edited on 7/1/16 by WesBrooks]