Explain brake upgrades to me, please

I wanted to read these and then explain them to you like I knew what
I was talking about. Then I realised that these articles were above me
so you're gonna have to read them yourself :-


http://stoptech.com/tech_info/wp_brakesystems_upgradeselections.shtml


http://stoptech.com/tech_info/wp_abs_bigbrakekits.shtml


I think the first article sums it up in a sentence. Ie , its not your brakes
that stop the car , its the tyres.

that and :-

Start Quote

"Why do I need a big brake upgrade?
Modern stock brake systems, for the most part, work well for a single 60-0 or 80-0 stop, and average daily street driving. The typical performance enthusiast will quickly push the stock brake system beyond its capabilities. Driving style and other performance modifications such as increased horsepower, tire and suspension upgrades quickly add up to overpowering stock brakes. A big brake kit will provide increased heat capacity, which means substantially more resistance to brake fade and caliper distortion with multiple stops from high speed. A firmer pedal due to stronger and stiffer components, as well as better modulation characteristics under threshold braking are also typical with a properly balanced brake upgrade. "

End Quote.



Notice that he doesn't speak of being able to stop better. Just that your
brakes will be more consistent and display better fade resistance.

If you find that your brakes are overcoming your tyres "too easily" , then
maybe its time to source better rubber.

cheers.

 

I (328 similar weight to a 360) run wider and sticker rubber then a stock 360 in the front, and since the front bears the load of the braking, should be able to out brake a 360 or at least be close to it....

...thats not remotely the case. Some part of the puzzle is a miss for me, and its not the pads or tires. Go figure. Well

 

http://ferrarichat.com/forum/showpost.php?p=135068784&postcount=147

 

those are the MOVIT MOVIT brakes from Madagascar , right ?

 

For the street, I think Tillman is correct. More than enough braking power already exists. Brake upgrades really address heat build up, not stopping power on a properly cooled system. On the track, repeated stops build up so much heat that the rotors and pads go beyond their operating ranges and the brake fluid boils. Larger rotors and pads handle more heat and result in lower operating temperatures, this in turn results in shorter stopping distances and less (or no) brake fade over the course of a run session.

 

Yup, what he said. If you can lock the wheels, and heat buildup is not an issue, the only thing you can improve is tires, and ease of getting just below lockup. Everything else is cosmetics. Bigger brakes do not stop a car quicker; they just deal with heat better.

Ken

 

Seems to me larger discs/calipers WILL stop a given car better. My 350Z Track model has Brembo brakes standard. They stop the car amazingly well, with little or no fade under hard use. The discs and calipers are oversized. My old 1995 300ZX TT had some sorry brakes, because they had less clamping power/brake torque.
Yes, the heat dissappation (sp.?) advantage or larger brake systems is without question, but more clamping force should equal shorter stopping distances....
Imagine my 350Z with 1/2 scale brakes. I could probably still lock up the tires, with some SERIOUS pedal pressure, but the stopping distances would be much longer, due to the time wasted stomping on the brake pedal trying to achieve (just short of) lockup. More powerful brakes should equal lower-effort, shorter stopping distances, with the added side benefit of better heat management.
I have a 1977 308 GTB that I plan on doing the Girodisc upgrade to soon.
I'm hoping they can develop a larger front system, because I have 17" wheels.

Does anybody find my logic "logical", or just plain crazy?

Greg

 

What is your definition of 'better'?

If the 'given car's' stock brakes are reasonably good (like the 3x8 stock brakes), they can lock the tires with reasonable pedal pressure & travel. Higher clamping force will not shorten the distance required for a single high speed stop as the tires are the limit in for both the stock & the larger brakes.


HYDRAULICS101:
In any hydraulic system, the pressure is uniform throughout the system. If the pedal is pressed giving n psi with a master cylinder piston of area m in^2 , and a caliper piston with area c in^2, then the total force on the caliper piston is n x c/m.

To move the caliper a given distance requires the piston to move a distance of c/m.

This implies the following:
LARGER CALIPERS = MORE PEDAL TRAVEL FOR A GIVEN CLAMPING FORCE -> EASIER CONTROL OF CLAMPING FORCE.

In fact, if you use brake calipers with larger piston area than stock with the stock master cylinder, it will actually take larger pedal travel to generate the same clamping force/in^2 of caliper piston(see below).

However, this extra travel means that you can better control the clamping force as you have more pedal range, therefore don't have to make such fine movement for a given change in force.

LARGER CALIPERS = MORE TOTAL CLAMPING FORCE for a given pedal force.

BOTTOM LINE: LARGER CALIPERS PROVIDE:

- Finer control due to more pedal travel for a given force change. Therefore easier to do threshold braking so as to retain steering control just short of locking the tires.

- Better heat dissipation due to increased size of rotors & calipers. -> Handle many consecutive high speed stops better.(ie: better fade resistance).

 

In many cases, unless you lower the car (ie lower center of gravity), larger brakes will not help much. The higher the CG, the greater the weight transfer from the rear to the front. Once the rears lock, control is lost.

If brakes are fading during track sessions, I'd duct them long before I'd opt for larger brakes. Some track fade is induced by novice drivers 'pointing and shooting' with a high horsepower car.

If brakes are fading on the street, I'd investigate to find out what is wrong with the brakes.

 

Another thing to remember is some of the brake kits use a spacer to move the stock caliper to use a larger diameter rotor. The brake equations are a function of radius and force generated by the pads. Rolling friction coeficient is larger(higher) than slidding coeficient so if the braking can be better modulated, the vehicle can have higher deceleration before wheel lockup.

Jeff Pintler
89 348tb, 86TR

 

Hi All & Auraraptor,

This is an interesting thread. Especially as I am pondering a suspension and brake upgrade on my beloved 328 at the moment.

Yes, ultimately, our brake components efforts add up to trying to stop the wheels turning and from there its the adhesion between tyres and the road that actually slows the car.

Here are some thoughts on why our 328 don't stop as well as a 360, even though you have wider and stickier tyres (and the 360 weighs only 20kg more)...

The weight distribution of the cars is different - maybe the 360 has more of a rearward weight distribution than the 328. Just by looking I reckon the 360's engine bay weight is more to the rear, with heavy components in the area that the 328 uses for a luggage bay. Under hard braking, each car's weight will bear down on the front more than when static, but this may be less so with the 360, meaning the rear tyres are able to contribute more. One way to improve weight distribution and thus braking is to increase the wheelbase, which on a 360 is ten inches longer than the 328.

Its very important that the rear tyres don't lock during braking - front lockup leads to understeer but that is stable because the rears are still providing decent grip laterally and are thus acting like a boat's rudder being held straight. Rear lockup is like a boat with no rudder - the tyres that are skidding can slide from side to side on the road as easily as they are sliding forwards. Why am I saying this? In the days of the 328 there were no fancy electronic stability systems etc that the 360 has, and so even on an ABS car I would expect the factory to fit a bias valve that distributes most of the hydraulic force toward the fronts. So on hard stops the front loads up to locking point or ABS-trigger point and you can't brake any harder, whilst the rears are still not being exploited to the full. I would expect on the 360 that any rear-protecting ABS/stability system is more able to exploit the rear brake ability of the car, simply through improved electronics & sensors.

The last thing is that the tyres will only grip the road if they are being held down against it, so if the 360's suspension design is better at keeping the tyres stuck to the road then its tyres can do their jobs better. This is one of the reasons that unsprung weight (the reduction of) is important to the performance of cars - a small mass will track the undulations of the road with less of a 'mind of its own' [inertia] than a large one.

After gathering a few bits of information about this topic, I'd say that the good points to look for in a brake upgrade for street driving [not racing] would be:

1) Ducting to apply cooling air to the rotors
2) Use of more up-to-date rotor/caliper material and design, meaning
a) lighter discs and calipers for reduction of unsprung mass
b) better built in heat capacity, cooling vanes and grooves for gas extraction
c) stiffer calipers for resistance to opening under extreme force & heat & so losing the ability to hold pads faces firmly against rotors.
d) floating rotors allow for even heat expansion without warping into cones and reducing pad contact with rotor, also floating rotors reduce the conduction of heat from rotor into bell/hat, so the rotors cool to the atmosphere rather than warming up the hub of the car.
3) Replace OEM rubber hoses with steel braided teflon ones (give more direct operation and better feel due to lower expansion under pressure)
4) Strive to keep brake caliper piston area as close as possible to stock (so that pedal travel is unaltered). The problem with bigger calipers is that they tend to have bigger pistons. If so, the well inside the caliper you are filling with fluid is bigger so to get the same piston movement, more fluid must go in and the brake pedal must travel further, no getting around it unless you are into changing the brake master cylinder or pedal/master cylinder ratio too.
5) Improved shock absorbers, better able to track the road surface.
6) Possibly an improved ABS setup, with a better/tunable ECU, so that rear brake bias/limit can be set at a sensible limit to make more use of the rears yet still without locking. This would probably be beyond the fairly handy amateur!
7) Use of titanium buttons between brake caliper pistons and pads to limit heat transfer from pad to caliper (and therefore fluid). Got this idea from the stoptech links above - very handy!
8) No need to go to bigger calipers/rotors for reasons given previously in this thread [although many quality aftermarket calipers are quite big these days].

Disclosure - I have worked on motorcycle brakes (my own) and followed about half of the the guidelines above [already had floating rotors]- I fitted rebuilt shocks (tuned to the weight of the bike plus me), braided hoses, different (progressive rate) springs and did a lot of study of braking practises (front/rear, bias provided only by my brain). I haven't applied this to any cars yet, yet on my motorbike the difference was like night and day.

I hope this helps someone!!

Best Regards,

Rich.

Edit: Auraraptor: I notice from your profile pic your 328 is ABS (as is mine) - whatever you do don't do anything the change the amount of brake torque applied per unit of brake fluid/pedal force if you consider any brake mods - you run the risk of confusing your ABS.

 

At times, I drive hard, both in the mountains and on the track. I have faded the brakes on pickup trucks and two prosches that i auto-xd heavily.

At Sears Point, I boiled the fluid and had to ease off. High speed autoxing gave me some serious pad fade, usually accompanied by "that smell".

I gave up on the trucks, i went to carbon kevlar and that helped.

On the first of the p cars, i installed disc brakes, from a 64 SC, on a stripped out 1956 speedster, (1300 pounds, 5.166 ring and pinion, close ratio box and 140 hp with a light flywheel and sticky tires). KICK ass and no fade Firmer pedal and better controllability,and easier to modulate.

On the second car, a 2060 pound 914, (same one that boiled earlier at sears point), I put BIG aluminum 911s calipers and cross drilled, vented 911 front discs. You will like this, On the rear, I installed the 914-6 Rear caliper with bigger pistons than the 914-4. These calipers are identical to the stock 308 rear caliper. I put spacers in the calipers and ran cross drilled 911 vented rotors, Bigger master cylinder, to offset the bigger fluid displacement in the calipers, add stainless lines, Hardie/Ferodo metalic pads with 8.5 inch rims and 225/50 pirelli p-7s and this little car could STOP - RIGHT NOW. Never was able to induce fade, but back to the point, the amazing thing was that the car was so easy to controll at the limit of braking.
I attribute a lot of this to the reduced pedal effort, the leverage, the thermal consistency of the bigger discs, of course, plastic suspension bushings, racing konis and stainless lines didn't hurt either (i ate a lot of top ramen during those years).
When i put current racing slicks on the car, it felt like i would stand it on its nose.

Having experienced both pad fade and fluid fade, I can heartily recommend that you change the fluid and go to a high performance pad.

I would agree with Lawrence that if you are experiencing fade with "street" driving that you take a good look at your system. Further, ducting might be a good first step before spending $$$ on bigger brakes. I would temper that with an observation that i haven't heard many reports of great results with ducting.

I would disagree with him on needing to lower the car to see much benefit from bigger brakes. Lowering the CG will reduce the weight transfer under braking, but braking can still be vastly improved with better brakes, particularly with respect to heat disipation and controll.

Verell's comment that braking controll is improved by fitting bigger calipers because it provides a proportionately longer pedal travel is accurate, but reducing the pedal pressure, (especially from the stock 308 effort), also adds to the controllability. I believe that going to larger diameter discs also reduces pedal efort because of the increased leverage that it provides.

Does anyone know if the stock 355 rotors have curved vanes.

Does anyone have experience with the QV London 355 brake kit for the 308??

curious,
chris

 

I changed my brakes and it made a dramatic difference. The stock brakes would fade and heat and warp after 5 or six high speed blasts. If the car was stock and not putting out more than double the stock HP I would more than likely leave the brakes alone. I have not had any issues of locking up the brakes. I have only done it once at roughly 15mph but I purposlely put my foot down extremly hard to see the difference from stock.

If you drive the car hard and track it occassionaly I would say go for it. It is a relatively inexpensive mod that yields dramatic results.

Saner sway bars make a huge differnce as well. I did both at the same time
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This is what my brakes looked like after 5 high speed stops. Obviously grossly inadequate.
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The big brake brembo kit available at Stillen.

Spacers were on the car when we bought it. Tristram Buckley would know since he put them on.

 

My car is just 'preABS', meaning I have everything for (wheels, hubs) but no ABS. After a long highway drive, I noticed under harder braking my car gets much more 'squirmish' then others I have driven without ABS. I wanted to simply go out and buy an upgraded brake system, but no one I know of offers it for our hub. (Some claim they do, but under further questioning reveal they didn't even know the hub changed between early and late model 328s.

I had (and still do) fancy the idea of buying a set of brakes from the 512TR and swapping them on, but I don't know anyone who will make me a set of caliper holders. I was thinking of getting a set of 512 calipers and floating hat/2 piece rotors, adding SS lines and a good street fluid. I am worried about that squirmishness now though.