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Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

Posts: 2519
Reg: 11-2004

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Monday, November 28, 2005 - 12:04 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Manny, fair point. The weight transfer due to forward body roll will give more traction to the fronts under braking, though less to the rears - the car still weighs the same after all. Unlike acceleration however, where a drag car usually has no drive to the front wheels, the rear brakes on a 32 can still contribute and I would suspect there would be no real trade off if set up properly.

It would be fairer to compare the 32 under brakes to a 4wd under acceleration than to a rwd car.

Similarly a car with some body roll can take advantage of the weight transfer to the outside wheels for better cornering, but it does so at the cost of losing weight on the inside wheels.

Which raises the point that a large factor in the 32's cornering ability may be more due to the 4ws than to the active suspension.

Back to braking however, the forward body roll of a softer car probably also lowers the cars centre of gravity which has been shown to improve braking distance.

It's all pretty interesting stuff actually :-)

About heat dump though, I am thinking that the small amount of extra metal isn't really going to take much more heat away from the pads, and also isn't going to dissipate a lot more heat out into the atmosphere.

My experience with new OEM pads (OK, they were only run in briefly before hitting the track) doing major fade on the 4th lap - just about like glass, serious paddock excursion, wouldn't have been improved much by bigger rotors and callipers. Possibly an extra lap or two before the same result.

Yet the cheap Lucas pads kept stopping (though felt a bit soggy) doing 30 minute sessions (which is about 15 laps).

The day the Hawk street/sport pads let me down, Gazza lent me a set of worn DS2500's. Heck, it was like night and day. I had used DS2500s previously, but then they wore out, I embarked on testing various other brands in the quest for real life information. Going back to them, was a revelation, as I had been getting used to driving with pads that failed or went soggy, and these pads just kept on stopping the car with power and confidence, lap after lap.

So I still put my money on pads being the best upgrade in most situations. :-)
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

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Monday, November 28, 2005 - 12:12 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Now to contradict myself a bit. :-)

Jeff, my thinking is that the 4 pot brakes would probably have an advantage in being able to spread the power more evenly over the pad surface, and hold it flatter to the rotor. Torsional forces at work on the pads usually means they wear at a slight angle so they aren't being made full use of.

Depending on the piston ratio compared to the master cylinder, they might also give more power to the brakes at higher speed where there is less chance of the ABS measuring stick coming into play.

A race specialist mate of mine commented that the car seemed to slow down more as it slowed down, ie increasing rate of decelleration.

Bigger brakes may well change that, or it might be a measure of how I use them, even though I think I am slamming them hard, I am probably squeezing them a bit which would also cause this affect. This was just from visual observation, probably a g-force meter would be the best way to really find out.
David Vaughan
DieHard
ACT
Soarer GT-L (4.0 V8) Lexus is300 (3.0 VVT-i 6)

Posts: 828
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Monday, November 28, 2005 - 01:15 pm, by:  David Vaughan (Davidv) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Without going through it comprehensively, there are a couple of interesting points here.

Firstly, weight transfer reduces total cornering [braking] force, not increases it. Secondly, harder springs increase weight transfer while softer ones reduce it. You can not make a parallel with drag cars because they would really like to run on two wheels, the front ones being something to stop the front end from digging into the tarmac. Your selection of a 4WD drive car as a comparison is more appropriate.

The disadvantage of roll for cornering [braking] is geometry change in the suspension, which is likely to have a bigger impact on total grip than does the stiffening which the Active uses. When you hit the brakes your wheels try to turn their toes out and lift their outer edges off the road; not good stuff for adhesion.

I have no argument that a bit more steel in the discs is probably less important than better pads. However, I made the point that even within a single stop, F1 carbon-ceramic discs will perform better from racing speed. In my last post I also mentioned the important assumption that ABS is able to be fully driven. Your conjecture about four-pot brakes falls into the same class. The general issue affecting all three of these statements is the fact that energy (to be dissipated as heat in the brakes and tyres) rises with the square of the speed. An ABS-supported braking system which can break tyre traction at 90km/h may not be able to do so at 180km/h when the heat dump through the braking system will initially dominate the brakes. The energy needing to be dissipated from 180km/h to 90km/h is three times that needing to be dumped from 90km/h to zero so, as your race mate says, the car will indeed slow more as it slows (provided your brakes are not fading out of sight). This is also the reason that braking distances do not rise linearly with speed but (again) go up with the square of speed.

Hope this clarifies a few things. Perhaps I should have drawn more attention to my comment about street speed vs racing speed above. Manny's issue of repeated use has similar importance.

Peter's "weakest link" post summarises the most important part of the analysis, although you also need a context for deciding what is weak
Jeff Harper
Trader
NSW
UZZ32 Active V8

Posts: 690
Reg: 07-2005

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Sunday, December 04, 2005 - 06:49 pm, by:  Jeff Harper (Jeffh) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Please explain why this BMW stopped in a shorter distance with only a brake upgrade.

http://eurotuner.com/howto/82958/

Test Numbers
Stock Brakes:
Trial 1: 138 ft.
Trial 2: 137 ft.
Trial 3: 131 ft.
Average: 135.3 ft.

Modified Brakes:
Trial 1: 125 ft.
Trail 2: 127 ft.
Trial 3: 126 ft.
Average: 126 ft.
David Vaughan
DieHard
ACT
Soarer GT-L (4.0 V8) Lexus is300 (3.0 VVT-i 6)

Posts: 874
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Sunday, December 04, 2005 - 07:19 pm, by:  David Vaughan (Davidv) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I already did.


Let me tell you a comparable story:
Car 1: Subaru Impreza with 16" wheels, 205/60 tyres.
Car 2: Citroen Xantia with 15" wheels (and slightly smaller brakes), 205/60 tyres, carrying an extra 150Kg and most of that over the nose so the rear brakes are less effective.

Test: A string of stop tests from 80Km/h

Result: Citroen consistently stops two metres inside the Subie from 80Km/h. Why?

Answer: Superior quality tyres.


You need good brakes. You need good tyres. Neither can magically exceed the limitations of the other, and your current combination is optimised by a good quality ABS.
Graham Dollisson
TryHard
QLD
GT-TL

Posts: 500
Reg: 07-2005

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Sunday, December 04, 2005 - 07:29 pm, by:  Graham Dollisson (Alloyvee) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

It's too bad they didn't go a bit further and try some different good aftermarket pads on the Beemer's standard brake set up as well!!
Jeff Harper
Trader
NSW
UZZ32 Active V8

Posts: 691
Reg: 07-2005

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Sunday, December 04, 2005 - 10:35 pm, by:  Jeff Harper (Jeffh) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Um, David you didn't...

1/ Same car.

2/ Same tyres.

3/ Only brakes changed.
Dan McColl
TryHard
Victoria
UZZ-32 V8 Soarer #138

Posts: 464
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Monday, December 05, 2005 - 02:34 am, by:  Dan McColl (Hoon) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

There is still a lot of variables that need to be taken into account.

Perhaps the larger volume of fluid that now needs to be moved allows the ABS to operate more smoothly. Maybe it gives the driver a slightly better pedal feel.

Maybe the tyres weren't the major limiting factor with the original brakes. They also changed the brake fluid for higher quality stuff, Maybe the old fluid was gassing off with the temperature, Maybe the old pads were fading with the heat, A 5 series BM is not a light car.
After re-reading the article this was probably not the case as the distance decreased after a couple of runs, indicating that fade was probably an issue.

Or in this case, maybe the pads needed a bit of heat to work at their most effective, thus not being completely effective for the first few meters.

Maybe the road was warmer later in the afternoon after the brake change and thus the road was actually a bit stickier.

Unless all these variables can be controlled it's not exactly a comparison.

Ultimately the braking distance will be the result of the limiting factor.

If the brakes are fading before you stop or mechanically unable to reach the traction threshold of the tyre then this is the factor.

Most likely though, unless you are using wide sticky racing tyres, you're tyres will be the limiting factor in the stopping equation, and no matter how much money or effort you throw at the brakes, if they are not the limiting factor then you won't stop any quicker.

You would probably find if they put race tyres on the BM they would knock another 20m off the stopping distance.

Bigger brakes will help with repeatability, as there is more meat to absorb and radiate the heat, but will not often help with a once off stop.
Jeff Harper
Trader
NSW
UZZ32 Active V8

Posts: 693
Reg: 07-2005

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Monday, December 05, 2005 - 07:25 am, by:  Jeff Harper (Jeffh) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I don't care it did it, the distance is shorter with only a brake upgrade.

I'm being told that it won't. I require proof otherwise, not supposition.

The figures do not agree with any of you.

Test Numbers
Stock Brakes:
Trial 1: 138 ft.
Trial 2: 137 ft.
Trial 3: 131 ft.
Average: 135.3 ft.

Modified Brakes:
Trial 1: 125 ft.
Trail 2: 127 ft.
Trial 3: 126 ft.
Average: 126 ft.

I have shown (well this article has) that a brake upgrade will shorten stopping distance, even on the 1st application.

Please show me a test that disproves this.

There was a lot on this subject, I only chose this article.

If needs be I will contact the brake manufacturers themselves to show that improved brakes will stop shorter, even on 1st application.
David Vaughan
DieHard
ACT
Soarer GT-L (4.0 V8) Lexus is300 (3.0 VVT-i 6)

Posts: 876
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Monday, December 05, 2005 - 09:08 am, by:  David Vaughan (Davidv) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Jeff, you appear to be wilfully misreading all that we have written.

Repeating what I wrote under the thread "Celsior 4 pots" since you responded as if you did not want to read it there:

quote:

So, the previous brakes could not drive the ABS to its limit. Big deal. We said better brakes will not help if your tyres are the limiting factor (read the posts) and we remain correct.


Reiterating what I said above

quote:

You need good brakes. You need good tyres. Neither can magically exceed the limitations of the other, and your current combination is optimised by a good quality ABS



Now go back over every post we have made in response to you on this topic.
We first responded to your apparent position that tyres made little difference and ABS made things worse, both demonstrated to be wrong positions.
Now you seem to have taken it that we are saying that brakes are irrelevant. None of us ever did. We have consistently and repeatedly said that braking relies on a series of factors and that (here I go saying it yet again) you can not exceed the final capability of the weakest component.

Unlike a simple chain analogy, you can make improvements with diminishing returns (hence wasted money) in one of the components, but improving the weakest component first will give more "headroom" to improve others.

That is why F1 brakes are so good - all the components have been optimised, not just one of them, except that ABS is now banned (happened a few years ago).

Incidentally, in the test to which you point, they changed the brake pads as well as the rotors. There is therefore zero evidence presented in the article that the larger rotors made any difference in the braking system. Alternatively, perhaps the new pads may actually have been worse and the four piston calipers made all the difference. You do not know, although Peter's comments on pads are relevant.

Tyre quality is the simplest and best upgrade for braking with benefits in handling as well. Pads are recommended next, because standard pads are optimised for quietness and feel with acceptable braking. If you may be in a position where you will get brake fade or you can not drive the ABS on hard from high speed having already improved the pads, then upgrade the brakes and calipers.
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

Posts: 2605
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Monday, December 05, 2005 - 11:57 am, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

My take on that test would be that it again hilights the importance of brake pad choice.

In the first test, just changing the temperature of the stock pads resulted in saving 7 feet.

They then only gained another 6 feet (on average) by throwing $$$$$$$$$ at the braking system - including better brake pads.

My bet is that they could have achieved similar results just by changing the pads. Note too, that they went to a Ferodo front pad. While I haven't done brake distance tests, I am sure that those of us that have used Ferodo pads on the track will agree that they are simply awesome. They bite, they stop the car fast time and time again, and then they ask "is that all you got big boy?"!
David Vaughan
DieHard
ACT
Soarer GT-L (4.0 V8) Lexus is300 (3.0 VVT-i 6)

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Monday, December 05, 2005 - 12:43 pm, by:  David Vaughan (Davidv) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I will soon find out what the TRD Black Pads are like. I am also getting slotted discs (still TT size) at the front to replace my previous TT upgrade. At that point the pressure will be well and truly back on the tyres.
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

Posts: 2606
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Monday, December 05, 2005 - 01:15 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

David, slotted rotors = cheese graters :-)

If you get ABS to come on, see if you can notice how fast it comes on with the old and new pads.
David Vaughan
DieHard
ACT
Soarer GT-L (4.0 V8) Lexus is300 (3.0 VVT-i 6)

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Monday, December 05, 2005 - 02:22 pm, by:  David Vaughan (Davidv) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

So I'll always have fresh clean cheese
From reading the TRD web site I suspect the Black Pads get their extra grip through softness (higher wear rate including more brake dust) so the experiment may not last long, especially given they are no longer sold for pre-Z4 Soarers. The Red is their higher performance semi-track pad but I am more likely to go to one already recommended here than start testing a new series. Using the Blacks is opportunistic, picked up from Shom.

A comparison will be difficult given I will have to bed in the new pads before hitting them, and I ought to test both pads on the same rotor but I will see what I can do.
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

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Monday, December 05, 2005 - 02:27 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Save your old pads, then do a test once the new ones are run in :-)
Jeff Harper
Trader
NSW
UZZ32 Active V8

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Monday, December 05, 2005 - 09:04 pm, by:  Jeff Harper (Jeffh) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I did not discount tyres, you presumed I did.


I have only been asking questions and drawing layman's conclusions to what was written by the experts.

So, we are agreed.

The best way to stop your car in a shorter distance, even the initial application, is to

1/ Improve your pads.

2/ Improve your tyres.

3/ Fit Maltech brake lines.

4/ Improve the efficiency of your brake system by getting bigger rotors and more "bite" in your calipers.

5/ On some vehicles a master cylinder brace is beneficial as the fire wall moves under load.

Whew!

OK, so I can now happily continue to sell the UCF21 series, light weight alloy calipers.

We are not agreed on ABS, but I don't give a damn, as I would never drive a NON ABS car "in anger" again. I love ABS, and wish I had had it 36 years ago!
Gary Morriss
TryHard
SA
2.5 TT

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Monday, December 05, 2005 - 09:24 pm, by:  Gary Morriss (Gaza) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

So Jeff
to get those calipers

1: I need bigger rotors

2: The calipers need to be ground down to fit.

3: My rims have to be wide enough!

4: I would need another set of brake lines ?
is there any thing else that i would need to consider?

cheers
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

Posts: 2611
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Monday, December 05, 2005 - 09:30 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Yeah, that all sounds good to me Jeff :-)

I think the ABS in Soarers is pretty good too. It doesn't come on excessively or way too early, and appears to only lock the wheel needing traction (but I could be wrong on that).

When braking hard into a left hand dip, I am pretty sure that only the LH front wheel got the ABS treatment. It impressed my mate also, who then told me that some cars would apply ABS to either both fronts or worse, all 4 wheels under those conditions.

With a good ABS setup, theoretically you would be able to get just about 100% brake efficiency, almost impossible to get without ABS as human reaction times to adjust brake pressure and keep it just on the verge of losing traction would be almost unachievable.

Perhaps like everything, it varies from car to car and model to model.
Peter Nitschke
JunkFilterer
South Australia
GT4.0 V8

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Monday, December 05, 2005 - 09:31 pm, by:  Peter Nitschke (Pen) Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Gary, probably new brake pads :-)

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