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Discussion Starter #1
Hello.

I have been spending a fair while trying to work this one out.

When you upgrade the brakes from the STD brembo items up to the AP 6 pots or the tar ox 10 pots, with huge rotors and massively powerful calipers. how come the wheels dont just lock up when you stand on them ?

I have std brakes and the abs kicks in when you brake really hard even if it is a progressive braking pressure rather than a stamp.

There is no extra rubber on the road as some people keep std wheels but put the big brakes on.
Having been out in cars with AP 6 pots on the difference is eye poppingly noticeable not just a little bit.

So with all that extra force stopping the wheels why do they not just lock up and engage the abs ?

any light shed on this would be most appreciated...

/Steve
 

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If I'm not mistaken, making the brakes larger in size doesn't increase stopping power. You can exert just as much force in a smaller kit. (check the WRC brakes)

Where you benefit from a larger kit is heat dissipation.

Not certain, so all usuall disclaimers :confused:

CemK
 

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Interesting.

Larger diameter brake rotors will increase the mechanical leverage and therefore braking torque the brake sytem can generate.

Larger diameter rotors will also give you a larger area for heat dissipation.

So thats more mechanical power and a better ability to shrug off heat.

Brake systems work by converting kinetic energy into heat energy. :)

Hum.

However... If you factor in other things that exist in the real world, such as size, shape and composition of tyre contact patch and the suspension systems ability to keep tyre on road, you will probably get to a point where brakes are not the weakest link, thus fitting ever larger ones won't offer quite the gains they should, hence Diminishing returns.

I would also argue that larger brake systems tend to allow the user greater control of retardation, being that the system will tend to have more torque in reserve in general use, so (in my expirience) you should be able to use more brake power whilst retaining control (not locking up).

(Note) This is just a summary of how I understand it, and I am happy to be corrected if i am wrong. :)

Cheers,

Moray
 

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Discussion Starter #4
I sort of follow but I still don't understand the basic layman fact that when Peter E goes onto his brakes I get the urge to fly straight through the windscreen, this urge is only suppressed by the seatbelt.

Wheras in my car with STD brakes and DS2500 pads the brakes don't have anywhere near the stopping power and attempts to slow the car as quickly result in the ABS kicking in.

In my mathematical gymnastics I have worked out that bigger stopping power should equal the tyre stopping spinning completely and thus the ABS working even harder. This is clearly not the case.

Peters car ( sorry to use you Peter but I have no other point of reference I went in your car before and after the brake mods.) has the same wheels/suspension on it as it had originally and a similar tyre. So with no difference in the geometry or any other factor the braking distance comes down significantly.

Fair enough that you'd expect less fade because of the increased surface areas etc.. but I am talking about raw stopping power.

sorry to waffle
Steve
 

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In answer to your post, I would refer the honourable gentleman to the penultimate paragraph in my original reply. ;) :)

"I would also argue that larger brake systems tend to allow the user greater control of retardation, being that the system will tend to have more torque in reserve in general use, so (in my expirience) you should be able to use more brake power whilst retaining control (not locking up).
"
 

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Steve,

I think I can sum up the reason in two words, crap tyres!

I know that the wear ratings, etc. on our tyres are similar but that doesn't give any insight into the tread composition, grip characteristics, etc. of the two brands. I have only had the ABS come in a few times on track although I can get in to work in the wet on the road. As in most things in this life and this I believe is certainly true when it comes to tyres, you get what you pay for. :)

BS SO3s rock, don't let anybody tell you different cos they aren't right!

Peter.
 

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Bigger brakes(larger diameter disc & increased pad surface area) create more leverage on the tyre/wheel, hence more braking power with the same amount of pressure.

Think about it this way.... is it easier to stop a rotating bicycle wheel from the hub/ceter of the wheel or from the tyre? It will take far more work to slow it down from the center as there is more torsonal force.
 

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Dan,

Pleased you agree. As I'm about to get some Michelin Pilot Sport Cups, did you test those by any chance?

Steve,

Sorry to digress, hope you don't mind.

Peter.
 

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Bigger brakes can exert more power.

Bigger brakes let you control the power more accurately (in my expirience).

Braking technique makes a big difference too. If you slam on the brakes you will not stop as quickly as you would had you fed them in progressively to allow weight transfer to load up the front suspension before applying full braking force.

Tyres/suspension etc all affect ultimate grip envelope available for braking, acceleration and cornering.

So, your mate can probably throw you at the windscreen because of a combination of some or all of the following factors:

Bigger more powerful brakes

Better tyres

Better suspension

Better braking technique

Possible difference in drive/passenger perception of braking forces.


Regards,

Moray
 

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Discussion Starter #11
Peter,

I did have good tyres on when I was experimenting, I was referring to the tyres you were using before and after being the same...

I have not mentioned mine because they are an unknown.

Infact I have not locked them up accidently at all with the wierd tyres I am currently using, but then I cannot apply anywhere near the braking force that is there in your car.

It may just be an "oh shit factor" where I will not try them as hard as you use yours after experiencing fade a few times now.

Moraymackenzie. Cheers. Still not sure about that though because the point at which a tyre loses grip on the road should be the same given conditions etc. ..

I think I have it straight in my head now though.
I think that because I have had a few heart stopping moments where nothing happens when you apply the brakes I am less willing to go into corners hard. The big AP's would reduce that fear as there is not as much chance of them fading over time and they appear to stop the car faster due to a higher commitment level. This combined with the fade resistance provided by the big rotors and pads means overall, and for a more sustained period, you have efficient braking.

So going on that would it be the same stopping distance for a stock car and an ap equipped car from 100-0 if both cars had the rotors and pads at their optimum operating temp with the same tyres/suspension etc..? for just one run... I know the AP's would stop the car the same time after time which is the whole point in upgrading them. It isn't that the std brakes slow the car less it is that they cannot dissipate the heat quickly enough.

/Steve
 

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Steve,

Your first post mentioned that your ABS kicks in, that was where I was coming from. If your tyres have less grip, ignoring all the other issues, I will be able to brake harder before the ABS kicks in. Given the size of GT-R tyres, you need a hell of a braking force to actually lock the wheels up. Bigger brakes will stop the car quicker than stock brakes and will continue to do under gruelling situations.

Peter.
 

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putting the "which" tyre issue to one side...

and learning all the time...

was thinking about this after the day at Brands. My standard brakes never felt up to it (understandably) at the end of the two straights. The ride with Peter showed me what an upgrade can do, but raises the same question as Steve. I found that, what I felt to be, braking hard couldnt come close to the stopping power Peter had.

As I understand what has been said - the road contact with the "right" tyre is sufficient to avoid locking up and not engage the ABS with upgraded kit.

Makes sense...
 

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Discussion Starter #14
I was getting the ABS happening at Kemble 2

But the car wasn't slowing anywhere nearly as much as yours does even without the ABS.

The thing was I was comparing two different things, I had experience of ABS happening which I don't doubt for a second was due to kneejerk reaction driving as it was my second venture onto anything other than a road.

But when you took me out in your car before and after the AP upgrade I couldn't believe the percieved difference.

I agree that when you are in the passenger seat things seem to happen harder and faster than when you are driving yourself.

I wonder if anyone has actually tested the stopping distances.
Is it just the fact that the big brakes don't fade as readily enabling you to repeatedly use max braking.

Dino,
Do you know if it is possible to get bigger disks for the std Brembo calipers ? Thus moving the point of contact out and addind efficiency. this could be a cheap and interesting alternative to the best part of 1500 quids worth of solution.

I was wondering if Porsche disks fit, as I have a mate who can get these fairly cheaply.
 

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Almost without fail, everybody who I take out on track, mentions the brakes. Some mention the car's performance, some my driving, some nothing else but the brakes are nearly always commented upon. The AP kit with the right tyres is why I guess, with a little bit if driver application too perhaps. :)
 

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SteveC said:
I was getting the ABS happening at Kemble 2

But the car wasn't slowing anywhere nearly as much as yours does even without the ABS.
Steve,

What tyres did you have on then?
 

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Discussion Starter #17
I can't remember I think they were bridgestones on the front... Thinking about it they were a mismatched set of tyres on there when I got her, so that could explain it, Back end locks up because the tyres ane not as good as the fronts or vice versa.

when I changed the tyres for a set all round the Torque split guage settled down and stopped going mad like it did before.

proof that mismatched tyres on a 4wd are not good..

/Steve
 

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PeterE said:
Dan,

Pleased you agree. As I'm about to get some Michelin Pilot Sport Cups, did you test those by any chance?

We've only tested the SO3's, Pilot Sports, and the new Pilot Exalto's... Yokohama AVS Sports are currently in evaluation.

Dry weather was as good for the Pilot Sport as it was for the SO3, although with more defelection in the sidewalls the turn-in was not quite as good as an SO3.

Aquaplane was almost non-existent in the wet and we bottled out before it all turned messy. This was for SO3's and Pilot Sports.

The Exaltos again lost further precision on Turn-in compared to both others, but generally seemed to offer less tyre thrum into the cabin at speed on even the most broken surfaces. Havent tested aquaplane yet though.

Wear rates, Pilot sports are king, believe it or not they feel softer on the "prod" test over the SO3's but are lasing longer on our test car...

Heres the proper end (the decent tyres) of our tyre store :D Lots of nice tyres to toy with :D



Cheers,

Dan
 

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SteveC...yes of course there are many to choose from and very popular if you are not at the track every week-end. Some of the more popular are Project µ and coupled with decent pads, braided hoses and fluid you are on to a pretty good improvement.

http://www.project-mu.co.jp/e/product.html





And the brackets to position the calipers:

 

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I've just switched to so3's and gotta say very happy with them, brakes seem to work well with them aswell.
 
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