G4 / D2 8 Piston Brakes - The Diffinitive Review

[fr0st]

I think it has more to do with getting an even force across the entire pad. 'Stilhetto effect' doesn't really apply because the piston pressure is applied to the pad which is then applied to the rotor via the surface area of the pad, not the pistons. That was worded really poorly.... what I'm trying to say is any pressure applied to the pad from the pistons is spread over the surface of the pad acting on the rotor. Even pressure means even heat dispersion and less prone to frying brake pads.

Yep... thats it...

[dangerous_daveo]

Yeah, but 6 bigger pistons is going to have more surface area, which in turn would produce a more even spread of pressure. Im not knocking the idea of 8 tiny pistons, I just find it a bit strange. Like 6 pistons means less expencive rebuilds etc. 4 pistons less again.

[Roy]

Alcon made 16 piston calieprs that ran on 2l Super Tourers. Its more to do with the piston size, the differential size between leading and trailign pistons etc that all helps ensure even pad pressure and temps. It help stops glazing hot spots etc etc.

[kralster]

hows is the handling of the car affected by the new brake setup? I would say with having much bigger disc's and huge 8 piston calipers that there is going to be a lot more unsprung mass as well as gyroscopic force.

[tacker]

would not think there is much difference between them but the G4 would just be a little lighter as a package

[kralster]

but like i said, with the much bigger disc's there is going to be a lot of gyroscopic force that would in theory make the car run wide, and want to push.

[GTR1993]

Honestly if i had to guage it it would be 5/10 on the f**k all meter.

Rotational inertia has distance^2, there for having weight that is firther out is far worse. Looking at the disc sure its a bit firther out, and a bit heavier, but look at the tyre and rim, its huge compared to the disc in diameter and quite hefty.

so for arguments sake if you have 5 kg at 20 cm radius its 0.2 kg m^2

then we take 5 kg at 40 cm radius its 0.8 kg m^2, you can see a 4 times increase.

[sav man]

what are the adapters made out of? steel or aloy?

[djr81]

Honestly if i had to guage it it would be 5/10 on the f**k all meter.

Rotational inertia has distance^2, there for having weight that is firther out is far worse. Looking at the disc sure its a bit firther out, and a bit heavier, but look at the tyre and rim, its huge compared to the disc in diameter and quite hefty.

so for arguments sake if you have 5 kg at 20 cm radius its 0.2 kg m^2

then we take 5 kg at 40 cm radius its 0.8 kg m^2, you can see a 4 times increase.

Rotational inertia (Properly called the second moment of area - I) is measured in mm^4. As in Torque = I * alpha where alpha is angular acceleration measured in radians per second squared. This is the rotational equivalent of Newtons famous Force = mass * acceleration.

The only reference I have ever seen to the direct effect on steering was in reference to the Indy cars where some drivers noticed a change in steering effort due to a change in gyroscopic effect when they changed the material the rotor was made out of. This was at rather ridiculous speeds, however.

What a heavier rotor/caliper does do is add to the unsprung weight of the car which affects the ability of the suspension to keep the tyre on the road. This is something to be avoided if possible.

[tacker]

Does anyone have the weight of a standard 4 pot caliper and rotor, as i will weigh my 356mm G4 set to get a comparision.

I have some pics of the second set of pads as i think Roy noted he would like to see the wear of these but cant post any pic for some reason.

I also noted last night the the leading pistons in the G4 caliper is quite a bit larger than the 6 trailing ones.

If anyone can tell me how to post pics now i will bang them up for all to see

[Duncan]

Just wanted to mention in here that we are running the G4 brakes without any problems, including Targa Tasmania last month - their performance has been excellent.

There was an offset problem with the early kits which meant that the caliper was rubbing on the lower control arm ball joint, but anyone affected has been sent new brackets and hats which fixed the problem.

I've had no issues with the brackets or bolts at all.

[fr0st]

Strange question... but if anyone has the calipers off their car can they measure the diameter of the pistons for me?

[Duncan]

Mine are on atm....but I think the overall volume of the pistons will be similar to stock - which is one benefit of the calipers - you don't need to change the master cylinder.

As discussed above the biggest benefit of more pistons is spreading the force more evenly across the pad and to change leading/trailing pressures.

[260DET]

Yeah, but 6 bigger pistons is going to have more surface area, which in turn would produce a more even spread of pressure. Im not knocking the idea of 8 tiny pistons, I just find it a bit strange. Like 6 pistons means less expencive rebuilds etc. 4 pistons less again.

An 'even spread of pressure' would also depend on the rigidity of the calipers, the more the calipers flex the more uneven such pressure will be. No matter how many pistons the caliper has.

Those G4 calipers have a very open and long bridge which is unsupported, unlike eg Stoptech calipers. My bet is that those G4's flex quite a bit.

[Sayajin]

Okay...

So whats the final answer on these brakes?

This thread seems to lean more towards dont get them, as they are a waste.

The other G4 thread says nothing but praises about them however.

I need to know for sure as I was going to order these a few days ago for my high power GTR33.

Get them or pass and pay the extra for a name brand pair? As I said above, this is for a high powered GTR33.

-Sayajin

[Trust33]

from a bystanders veiw

they seem like a good calliper and rotor senario.

but their was the issue of:

-bracket bolts-(fixed with the help of a spring washer and nut.have you thought towards a loctite and split pin setup?)

-aftermarket pads-fixed by machining the top edge a 1mm or 2.

My R33

G4 brakes (356mm disk, G4 'street' pads): 130 degrees

Standard rear brakes (Nissan OEM pad) 280 degrees

Another R33

F40 Brembo brakes (340mm disk, Ferrodo 2500 or 3000 pads): 300 degrees

Standard rear brakes (pad unknown): 150 degrees

R34 GT-T

CSC brakes (343mm disk, Ferrodo 2500 or 3000 pads): 150 degrees

Standard rear brakes (pad unknown) 80 degrees

they obviously are up to the task.

Either way ducting,the best fluid and regular upkeep/brake and its assemblies seem to be the norm.

in conclusion:-

when they are compared to the other brakes,the temps are good.and given that they have had track and targa testing i can only see the plus's outweighing the negatives.price is also good.

if i were in your position i would lean towards them.just do the right thing and use the knowledge and experience that others have given you.

Craig.

[Duncan]

well...people who haven't used them or who spent 3 times as much to buy a "name" brand recommend against them.

People who have used them think they are excellent.

Ben had a strange problem with the brackets that no-one else has reported so it could just be a one off.

Fact is there are a lot of people in the world who don't beleive cheap can ever = good. Feel free to spend far more than you have to

[tacker]

i have them, and i have used them as their sole purpose as brakes for a track car. Car is good enough to run with porsche GT3, ferrari 599, 430 360, aston DB9, BMW M3 csl with AP brakes etc but cant catch them bloody Z06 corvettes they are seriously fast.

I have them so far no issues i am worried about. 3 sets of pads used with good wear pattern, been off and on many times and still bolt up perfectly. You will need to duct air to them as all brakes require if you are going to push the car to 100% of it performance

As far as i am concerned i would buy them again.

Edited June 11, 2007 by tacker

[Trust33]

well...people who haven't used them or who spent 3 times as much to buy a "name" brand recommend against them.

People who have used them think they are excellent.

Ben had a strange problem with the brackets that no-one else has reported so it could just be a one off.

Fact is there are a lot of people in the world who don't beleive cheap can ever = good. Feel free to spend far more than you have to

yeah.im sure that the name brand ones are better than the generic aftermarket equivelent.but not every1 has the cash to fork out.thats where these are good.

aside from the obvious problems.as i am sure every good brake manufacturer endless,harrop and the rest etc has had teething problems with.these are pretty good at an entry level point of veiw.

[T04GTR]

good write up. worth noting is using a bolt/nut would mean going down a size so it fits? or just a longer bolt with a nut aswell?

and it seems the fact the pedal is harder means theres less fluid area (force) being put to the pad compard to the standard one wich in turn will over heat the rears.

and the tru test is to get them red hot (literally) a few times and see if they crack