pd_day

iTrader: (6)

I have new tires, new brake pads, new fluid new rotors. The stopping power is very good compare to all my other cars. But I want more.

Right now, if I slam on the brakes, the rear tires will lock up. So the best method is to modulate the brakes so that the rear would be on the edge of locking rite?

So to fix this problem, would upgrading the suspension help me? I mean, if I have stiffer springs up front, that would prevent the rear from lifting and would allow them to be planted on the ground right?

Please shine some light upon me.

Thanks

Drakk0r

Get the widest, stickiest tires you get get to fit on your wheels. Or get 8 or 9 inch wheels and get 245-255 rear, and 245 front.

Wankel7

Not to sure about your question but I saw the coolest thing on Speedvision. They (Unsure of company) was testing a new braking system on a 4 door VW. It had special sensors in the tires and brake sensors. They brought this car 60-0 in 98' !

Of course the best and more expensive option for you would be a big brake kit.
http://www.rx7.com/cgi-local/2catalog.cgi?cat=1&part=1

James

1FastT2

iTrader: (1)

Big brake conversion! www.k2rd.com

Im getting this as soon as my engines done.

SpeedRacer

As the saying goes, brakes don't stop your car, tires do. Wider, stickier tires will help. And yes, stiffer suspension will help a lot too. There is less pitching when under heavy breaking which transfers more weight to the front tires to help slow the car.

Cheers!

I don't think you can stop any faster with the existing hardware you have.

However there is one modifcation you may be able to make it it dpends on what happens to your car when you slam on the brakes.

Does the card dive to the front hard? because if that does happen then that could be the reason why you rear is locking up before the right... ideally the fronts should lock up sooner then the rear under full brake.

Feel free to correct me if i'm wrong...

Because during a race if you are full on the brakes the last thing you want is the rears to lock up which will create instability when you make a corner with the brakes trailing.

So try looking at your front suspension to see if they are worn (ie shocks are shot etc...)

pd_day

iTrader: (6)

I don't think I need a big brake kit if I can lock up the tires.

Tires will lock up even when I use my A008R tires (R compound) heated up.

Probably need new suspension then.

Samps

you can lock up the tires on a pedal bike; that does not mean it has a great braking system. a big brake kit will shorten your stopping distance alomost indeffinitely. the more sweeping area of the brakes the better. locking up the tires is only good for; well, wrecking...

pd_day

iTrader: (6)

More sweeping area = higher friction
Good brake pads = higher friction

Why can you stop faster on a big brake system?

Samps

the amount of surface area that the brake pad has in contact with the rotor will effect your stopping power. if your brake pad was the size of a quarter, it would take an hour to stop from 60; but if your brake pad was the size of a frisby, completely covering the rotor you would stop like a champ (although the brakes would heat up and melt the rotors) so increasing the amount of contact area between the pad and rotor will increase your stopping power. I am no expert but I'm sure someone else can maybe dig a lil deeper into this.

pd_day

iTrader: (6)

Hmm...maybe...don't know how this could be different from having pads with high co-efficient of friction. Maybe better modulation? But this is not my question.

My question is, when I brake, the rear locks up, how can I remedy it? Maybe due to too much forward pitch?

maxpesce

Ideally ALL FOUR wheels should lock up at the same time under HARD Braking next best is for the FRONT to Lock first - You have too much rear brake Bias - A Front BIG Brake kit may help, but costs $$$ - Try using a HIGHER FRICTON pad on the front (like Hawk HP+ w/ HPS rear) or installing a proportioning valve. It may also be that your Master Cylinder is going bad and not providing full line pressure to the front brake circuit. Most cars are set up w/ lots of FRONT bias from the factory - in a panic its better to slide off the road straight ahead with the fronts locked than spinning around with the rears locked

go_speed_go

Suspension will help preventing the rear from locking up a little.

A popular road race mod is a brake biasing system. It allows you to somewhat regulate how much pressure goes to the front and back. With something like this, if the back's are locking up too soon, you can bias pressure more towards the front until they all lock up at the same time.

Edit: The proper term is a 'brake proportioning valve'.
One writeup can be found here:
http://www.rx7turboturbo.com/robrobi...rake_valve.htm

No7Yet

You're close, but you've gotten confused on some points.

A car will only stop as quickly as its tires will allow it to. The tires are the only thing holding the road, and when their friction limit is exceeded, you'll lock 'em up. Threshold breaking is the technique of holding the tires right at that limit, but unless you increase that limit, you'll never stop any faster. With that said, keep in mind that the lighter a car is, the less intertia it has, and therefore a tire's friction will have more of an effect upon it.

You are (mostly) right about swept area and heat dissipation, though. Bigger rotors can dissipate more heat, and therefore will help keep the brake fluid from boiling. But if he's not having fading problems, that's not much of an issue. Oh, and swept area is (see above) only as good as the tires will let it be.

To answer the original question, the best way to stop faster is to learn to brake better. Threshold braking is your friend. Locking your wheels up is a very bad thing to do, and will increase your stopping distances. Your fronts should definitely lock up before your rears, however. That's a mechanical problem that you need to look into. My guess is that your rears are unloading too much when you brake, due to a weak suspension. Lower your CofG (springs) and increase damping stiffness (shocks) and you'll be golden

Gurus, feel free to correct me (You probably will, won't you Chris? :p)

Brandon

maxpesce

Actually FOR A GIVEN FRICTION COMPOUND the AREA of the pads is only 1/3 of the equation, the braking force also depends on the PRESSURE of the pad on the Disk and the RADIUS of the disk. LARGER PADS actually run COOLER because they need Lower Friction to produce the same stopping force. MY 66 E-type had VERY STRONG brakes but the circular pads were only about 2.5" in diameter. They had a HIGH FRICTON fairly soft organic compound that only lasted 5-6,000 miles on the street though .

speedjw

How to brake better.

Threshold braking is the art of maintaining maximum braking. This is great in a straight line, not so good in a corner. (unless you like looking at oncoming traffic)

But, that said, thats not what were looking at here. We are looking at what will help you decrease your braking distance in a straight line. First find yourself the lightest wheels you can. Moment of inertia is huge, it takes a significant amount of force just to slow the spinning of the tire/wheel/brake rotor/hub..., nevermind the momentum of the car. More tire to the ground will also help. Brake feel is also key, a firmer pedal will allow you to modulate brake pressure with more accuracy (the human foot senses pressure far better than displacement). So, in race cars, we install a larger bore master cylinder.

2nd gen RX-7's have too much rear brake bias, you can counteract this using a brake proportioning valve, as mentioned before. A stiffer suspension may also help by stopping weight transfer from the rear, but be careful, go to far and the suspension will not be able to cope with the small irregularities in the road surface. Also, unless your car experiences rediculous amounts of dive, its probably not the problem.

If you are experiencing brake fade, maybe a bigger brake rotor is necessary to dissipate the heat generated by braking. But, that is not what you described.

So,

1) reduce the rotating unsprung mass
2) install brake proportioning valve
3) look into larger master cylinder to increase pedal effort
4) maybe buy "The Brake Handbook" and learn how to design brakes all on your own.

Sorry about bouncing around so much, not much of a writer.

SpeedRacer

Nevermind...speedjw covered everything I said, and did it MUCH better than I could have.

MaxRX7

with practice.

you need to find a place where you can do some runs and practice your braking technique.

You need to pump the brakes, but you need to know how to pump them for optimum performance.

The tires have maximum grip right before the brakes lock up.

You'll get the feeling just like when you where learning to drive with a manual tranny. There is a "G"-spot....

kamisama12

i didn't see anyone post that you should also engine brake that helps a lot. just downshift when braking into the gear above (keep doing it till you reach first ) and it should help a lot. oh yeah go to an empty parking first and learn this cause it will feel strange so do it when no one else is around

pd_day

iTrader: (6)

Hmm, I personally don't do much engine braking. Engines are made to accelerate and not brake, it will wear the engine faster.

I always slam both the clutch and brake pedal when I brake.
Moreover, locking rear brakes while engine braking = stall

Engine brake = engine break (well, at a faster rate) = $$$
Regular brake = replace pads = cheap

tesla042

Actually, I posted a thread on this maybe 8 months ago.. There was a good bit of debate.. A few said it may not be good, many people said that it really doesn't hurt at all, and a few even said it may be GOOD for the engine, as it somehow...like...gives a different force on the apex seals..or something.. I really have no idea what they said..heh

Ok..I'm a bit confused... Let's say that the stock braking system can lock up your tires up to 60 mph. A big-brake system would be able to do the same thing. Wouldn't threshold braking produce exactly the same results in both case, since both are capable of holding the tires right before their limit? Sure, the big-brake system can do more, and for longer, but ignore that for a sec, as any more will lock it up.

I'm not saying that big-brake systems aren't better.. I'm sure that at higher speeds, they could more easily reach the threshold.. And the whole heat dissipation business.. But, if the stock is capable of doing the same thing, I don't see how big-brakes are necessary at all.

-Tesla

maxpesce

CORRECT if your brakes are already strong enough to lock up all your tires then stronger brakes are NOT going to reduce braking distance - you need better tires and / or suspension.

pd_day

iTrader: (6)

My point exactly

pd_day

iTrader: (6)

Better suspension it is.

How will spring rates affect braking?
Do I want stiffer front and softer back or do I want both front and back stiffen up?

Thanks

Mark S

iTrader: (1)

Bigger brakes almost always = shorter stopping distances because they're easier to modulate. If the brake system isn't working as hard, it is much easier to maintain the car at threshold.

To answer the original question, it sounds like you have a brake bias problem (mentioned above)

One solution is to run good pads up front, and shtty ones on the rear. I run Porterfields front and autozone rears and it seems to work pretty well.

Also, a blown rear strut could cause lockup as well. If the tire bounces under braking because of poor strut performance, it could cause the rears to lock as you describe.