'Performance' brake discs - qxman {p}
Can anyone with a automotive engineering background give a view on 'performance' brake discs and whether it is worth upgrading for the average motorist. I'm thinking of the discs that have grooves and/or holes in the discs.
Call my cynical but I can't see them improving braking performance by very much. I can appreciate that the discs might run cooler, but brake pads seem to be specified up to about 600 deg. C. so you would have to be seriously working your brakes to need this extra cooling. I can't see how they would reduce the stopping distance "by up to 40%" in normal, or even very fast, road driving.
I also wonder if the grooving/drilling weakens the disc and whether they also reduce the contact area?
'Performance' brake discs - blue_haddock
The drilled bits aid cooling and the grooves help stop the pads glazing over which can be more common whne using uprated pads. Yes it will brake better but for a proper upgrade your better off fitting bigger discs and calipers with matching pads.

For the average driver though i doubt theres any need to upgrade the braking system.
'Performance' brake discs - yorkiebar
90% of the "performance" brake discs with grooves and holes are for show not performance.

Even with old brake fluid in your system how many times have you ever suffered brake fade? I am heavily into rallying as a co driver and have rarely had it happen.

Ultimate (which is higher level than mine) performance brakes are a different thing though and may require such as grooves and holes , but for majority the brakes can be overcooled and actually perform worse not better with these upgrades.

Not recommended for majority.

If brake performance is down I always suggest , renew brake fluid and bleed properly, put in high quality brake pads and discs. Then see if you need more? very rarely will you.

Racer and boy in another order springs to mind as the main requirement for them!
'Performance' brake discs - Number_Cruncher
I was about to write something remarkably similar YB.

For ordinary motorists, keeping the original setup in tip-top condition is the appropriate thing to do - the performance of braking systems on modern cars is not problematic.

The stopping distance (from cold) is governed by tyre / road grip, and vehicle layout, and is virtually unaffected by what's within the wheel.

The only reason for upping the spec of brakes is to cope better with heat load (and for repeated rapid stops as per YB's motorsport examples). If you are running fully laden, with a laden trailer in the Alps, then it's a good idea - If you are going to work, carrying the odd flask and tupperware, then it's not really necessary.

The other thing you would have to do if you choose to fit these gimmicks is to notify your insurance company that you've changed the car's braking system.





'Performance' brake discs - qxman {p}
Thanks N_C. Rather confirms what I was thinking. I have driven a variety of modern cars, and even when 'pressing on' I have never found the brakes to be lacking on any of them. I reckon if you can lock the wheel up (or at least bring on the ABS system) then no amount of additional braking force will stop the car any quicker.
'Performance' brake discs - Number_Cruncher
>>then no amount of additional braking force will stop the car any quicker.

Quite. This is the vital point which many people simply don't understand.


The interesting thing is that from cold, there's no lack of power in a drum brake. The issue with drum brakes is that they partially rely on the friction developed by the brake to actually apply the brake (it's called self servo effect, or shoe factor). What this means is that when the brake heats up, not only do you lose braking force because the material is not performing as well, you also reduce the total force pushing the shoe into the drum - effectively it's a double whammy. Disc brakes aren't fitted because they give more power - they are fitted because they are more stable with respect to temperature.

Disc brakes aren't fitted because they give more power - This can be seen by the fact that even with the larger area in a caliper piston compared with a drum brake wheel cylinder, you still usually need a servo to build enough pressure to activate the disc brake. Servos weren't usually fitted to cars with drum brakes front and rear, because they simply weren't needed.


'Performance' brake discs - pleiades
Rolls Royce amongst others used to use a gearbox driven servo for their drum brakes and some other drum braked cars, Sunbeam-Talbot 90 for one, had two trailing shoe front brakes (Girling Hydrastatic), in the interests of brake grab and fade I believe, I presume they too must have had some sort of servo altho' the only Sunbeam I drove had exceedingly heavy brakes and not much stopping power!

My prewar Austin 7 had the footbrake pedal connected to a shaft across the car with the rear brakes connected by metal rods and the fronts by cables. The problem was that once the slight braking effect on the front wheels (single leading shoe only) took place the front axle and radius rods twisted slightly and reduced the distance between the front brakes and the crossshaft so they lost effect but you couldn't press any harder as the rods to the rear brakes prevented any further movement of the pedal, a common mod was to run the front cables through a Bowden tube, as on a bike, and arrange them to pull from the opposite direction so there was a servo effect of sorts - luckily not very high speeds were usually involved - happy days!
'Performance' brake discs - Number_Cruncher
>>had two trailing shoe front brakes

Yes, that would be a more stable system, although I can imagine without a servo, it would be both heavy and not especially powerful, as you had found.

For a trailing shoe, the servo effect is actually negative, and so, by losing this as the material friction reduces, the shoe will be pressed into the drum with more force. With a servo, I could imagine this system actually working quite well.

For most cars, a leading + trailing shoe drum brake on the rear axle is a good specification, allowing the simple incorporation of a strong handbrake. Many fitments of rear disc brakes are a nonsense.



'Performance' brake discs - John S
My Minor has twin leading shoe front brakes and one leading/one trailing at the rear. On the brake test it achieves 0.85 g - well above the MOT minimum. However on the road it definitely feels underbraked compared to my usual modern servo assisted car. Pedal force required is so much higher. It was my understanding that a key benefit of rear brakes with one leading/one trailing system to make sure the brakes worked well when reversing the car.

JS
'Performance' brake discs - Number_Cruncher
>>It was my understanding that a key benefit of rear brakes with one leading/one trailing system to make sure the brakes worked well when reversing the car.

Quite so.

Yes, there's quite a step change between a modern car and a Minor - however, most people who fit Marina disc brakes to a Minor find themselves fitting a remote servo very soon afterwards! (and also stripping the master cyclinder to remove the residual pressure valve which makes the disc brakes squeak and squeal during normal running)



'Performance' brake discs - tr7v8
The other thing you would have to do if you choose to fit these gimmicks
is to notify your insurance company that you've changed the car's braking system.

Why are so many threads on here finished with "oooh if you do that you have to inform your insurance co."
I've regularly changed pads & discs for EBC or their equivalents. I use EBC Greens because they produce far less evil brake dust than the rest & stop just as well if not better. I've used aftermarket discs because they've been cheaper than manufacturers OEM ones. The Rosinni ones for the Alfa were 2/3rds the price of Alfas & were grooved as well. Link here www.carparts-direct.co.uk/Performance_Brake_Discs....m
These parts are all Type 90 aproved which means they are TREATED as OEM you DO NOT need to inform your insurance Co.!
I agree mot genuine braking systems are OK, the Alfa wasn't fantastic neither is the Jag but the limiting factor is the tyre, with a lot of the muppets running on the cheapest they can find that's a bigger issue than brakes but that's another subject!
'Performance' brake discs - bathtub tom
>>the limiting factor is the tyre, with a lot of the muppets running on the cheapest they can find

I'm playing devil's advocate here:
If the tyres are for sale, then it follows they must have EU approval, and if they're approved, then they must be good enough for us muppets?

Edited by bathtub tom on 02/03/2008 at 12:25

'Performance' brake discs - L'escargot
If the tyres are for sale then it follows they must have EU approval and
if they're approved then they must be good enough for us muppets?


Aren't some tyres described as being only suitable for agricultural use, e.g. for use on agricultural trailers etc on farmland?
'Performance' brake discs - Number_Cruncher
>>Why are so many threads on here finished with "oooh if you do that you have to inform your insurance co."

It's a question of risk and consequence really. If a person fits performance enhancing parts without checking, and later finds out that their insurance is rendered in-valid, then they've probably lost a lot on money.

If on the other hand, they make the tiny investment in a phone call to their insurers, they can proceed with certainty, and with the authority of their insurers.

So, the advice to check with insurers is;

a) not costly or expensive advice to follow
b) always safe advice to give
c) allows people ceretainty and peace of mind

>>finished with "oooh if you do that...

I wasn't aware that my posts were so camp!


;-)

'Performance' brake discs - jc2
Tyres "for agricultural use" will be branded with that statement.
'Performance' brake discs - gordonbennet
Sound advice, NC.

Quick call to the NFU when i fitted winter tyres to the Hilux and went up one size to the 'grey size', resulted in 'no problem its in the file, thankyou' and peace of mind for me.

oooh you are awful, but i like you.
'Performance' brake discs - yorkiebar
Whilst I think tr7 has enough knowledge of cars and brakes to know what and why he has done by "upgrading" his brake pads, but.....

What a lot of people do not realise when they want to "upgrade" their brakes is how poor "competition" brake pads and discs are in normal use. In many cars, espeically town driving it will, without any doubt whatsoever make the brakes worse! The ONLY advantage of these pads is their higher resistance to heat and the consequent fade it brings.

Try driving a car with these brakes in in town and you will always wonder if the car will actually stop espeically in a sudden stop scenario.

They work much better at high temperatures; but much much worse at lower, normal temperatures. Thats a good reason why insurance companies want to know about changing brake systems from manufacturers standard to "roy bacer" standard!
'Performance' brake discs - tr7v8
Whilst I think tr7 has enough knowledge of cars and brakes to know what and
why he has done by "upgrading" his brake pads but.....

The whole point is that anything that is type 90 approved isn't an upgrade it's deemed a one for one replacement. Some competition stuff is E marked e.g. suitable for road use therefore would be an upgrade but their is a difference.
As for phoning the insurance Co. most of them would panic & say not covered or add a loading. If it's type 90 it's the same as using the motor factor pads or discs instead of the manufacturers. If you fit Mintex instead of Lockeed or Delphi you don't suddenly feel the pressing need to phone the insurers so why with this!
'Performance' brake discs - yorkiebar
agreed, changing pads is not an issue for the insurers, nor is changing discs. But changing disc type (from standard to drilled and/or grooved) could be deemed as such.

If it can affect the braking performance of the standard car (and it should because thats why they get changed) then the insurers have a clause that entitles them to be told.

The question is (imo) whether the change is for the better or worse? 90%+ of the time it is likely to make the brakes perform worse for normal driving conditions and as such may incur a financial penalty ( along with other factors such as car type, age of driver, use etc)
'Performance' brake discs - martint123
The insurance angle is also covered by perceived driver risk. I recall at least one insurer that includes as notifiable modifications "stripes".
I've had brake fade in Switzerland and it wasn't nice and not a lot of warning. I think modern, non-asbestos pads smoke a lot more than the old ones and the smell gives a warning.
'Performance' brake discs - Len Cooke
I come from a racing background racing formula 3 cars in the 80's. Yes I'm now an old foggie but have heaps of first hand experience. Depending on what car you drive and the driving style you have adopted, the discs themselves only make a small difference. Where you will notice the biggest difference is on the pads you use. What car do you drive?
'Performance' brake discs - diddy1234
A friend of mine has these performance brake pads on his VR4 and they really do work well.
No brake fade (under heavy braking on a race track) but .........

For normal road use there is little point (the brakes are never used that aggressively in normal driving).

Also the brake dust is a real pain as there is so much of it and its a pain to get off alloy wheels.
'Performance' brake discs - dxp55
I have had brake fade twice - first years ago in a Mk 11 Zodiac - belting down dual carrageway way to Island at top of M5 - managed a very fast circuit of said Island (so it seemed)- I then fitted VG95 linings but needed two feet on pedal so mate got me a vacuum servo off a truck - brakes were superb.
Second was being late for John Watson skid course at Silverstone - Gave my 84 Mazda 626 some beans round roads and fried front pads - Discs were so small I cured it for future by not driving very fast.
 

Ask Honest John

Value my car