very nice, definately in now

 

We have never tried the valve with ABS. Theoretically the ABS takes care of proportioning, but it might be interesting to try.

 

Could this valve help with my cars tendency to dive when I brake hard?

I have sport brakes up front, and the stock 1.8 brakes out back.


Can anyone explain how this thing routes into the brake system? Maybe a diagram?

 

Yes, I started this group buy mainly for people who want to upgrade the front brakes to the corrado rotors

 

I'm also curious about it's effects with ABS. I'm likely doing the Corrado rotor upgrade too. Want the rears to do more work. Does this work with ABS? Does it effect the ABS system negatively? It's a DD car that sees 5-10 track days a year.

At the track I haven't noticed ABS kicking in, I brake fairly conservatively. I'd only be worried about it's effect in panic (see: Impending Doom) situations.

 

I'm thinking you would better address brake dive with different springs and damping.

 

another answer for saml01, try pull up on the ebrake slightly when braking, it'll give you the same results as a proportioning valve, just with a little more danger

honestly from what I've experienced it does settle the rear end down a little, but not the front, and thats just a feeling. but as turbodog's dad said, springs and damping are the answer for brake dive.

 

Is there a guestimate on the shipping for me? Don't know what it would cost if shipped within the US. When would these be going out?

 

Which then creates the need for brake bias adjustment. My track car still doesn't have a portioning valve. But I want to address the bad pedal feel at the same time. I need to spend time researching master cyls...

 

Count me in on this.

I think this might get more interest if there was a link to this thread in the "group buys and member discounts" sub-forum. (?)

 

Count me in
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don't waste your time, there's a reason no one replaces the stock miata master cylinder, even when they race it. It's perfectly good. and what is this connection you keep making between shocks/springs and brakes? There may be a small connection, but no one has ever cared, shocks are springs are swapped out without doing anything to brakes, and vise versa.

 

The amount of braking force you can effectively use in the rear depends on the amount of traction available to the rear tires. The car's weight shifts forward under braking, thereby lightening the load over the rear and reducing traction. Softer front springs allow more dive and unload the rear more, so less line pressure is necessary to lock up the rears. Stiffer front springs don't allow as much dive, thereby keeping more weight towards the rear (and more traction) so you can increase braking force a bit without worrying about premature rear lockup. Ride height (center of gravity) also affects how much rear bias you can run, so multiple suspension parameters are at play here. Even with a stock car, the OEM valve (especially on the 90-93) is more conservatively front-biased than it needs to be.

@Saml01 The prop. valve won't do anything to significantly reduce dive. If anyone has cranked up the rear bias and noticed flatter braking from that alone, it's probably because they're not braking as hard as they could (safely) before, and are therefore not shifting as much weight forward (the force of which is acted against primarily by the springs). For an extreme example fire up Gran Turismo, and adjust a car's brake bias all the way to the rear. The car will stay flat up to a point, until you get on the brakes hard enough to make the rear end magically come around.

 

Lots of bad information here - sure you should be talking about seat covers on another forum? (kidding of course) So what scott said about spring rates and dive effecting brake bias. Maybe folks interested in qtr mile times have never cared about the relation of suspension changes to brakes, but road racers care plenty. These changes are what really create the need for the bias valve.

And master cylinder changes effect pedal feedback, clamp pressure curves, the ability for you to "feel" the threshold of brakes, etc. Spec miatas don't change the cylinder because they aren't allowed to. Some other miata race cars do. Tilton makes a pedal set for factory conversions for a reason. I'd prefer not to spend that kind of money and if the Mazda parts bin will do what I need it to for a price that is right.

Best,
matt

 

Relying on ABS for proportioning doesn't work as well as getting the proportioning right, and then letting the ABS do its thing on top of that. As you home in on the best balance, you can actually notice the reduction in frequency of ABS cycling events. This valve should work fine with ABS as long as it is upstream of the ABS control module, and unless the ABS also incorporates EBD. Then, you risk the EBD function and the proportioning valve fighting each other.

 

Sorry, late to the party here. But maybe I can add some value.

The metric flare to NPT adapters in this kit can't be found anywhere else. Trust me, I hunted everywhere. If someone does find another source, let me know. We're having them custom made. Anyhow, they're what make this kit a reversible bolt-in without resorting to non-reversible flaring.

curly's suggestion on where to mount the valve in the cockpit worked really well in the Targa car. I was able to adjust the proportioning in the middle of a stage. I've also been able to mount one in the recess intended for the parking brake handle on the Track Dog racer. However, neither location works on a car with an interior. It's just a matter of plumbing, though. Figure out where you want the valve, then figure out how to get the pipes to it.

If you want to install the valve in the cockpit but don't want to flare, we can help put together a kit that will do that and will also be reversible. Bending and supporting the lines (very important, that last one!) will be up to you though.

Now, ABS. With the 2001+ Sport brakes, Mazda lets the ABS do 100% of the proportioning. What looks like a proportioning valve in those cars is nothing more than a pass-through. In earlier cars, Mazda used a valve but gave a little more bias to the rears to start off with.
factory prop valve specs

I can see how an adjustable valve would help an ABS car, as it would allow you to get the basic balance right.

There's a bit of misinformation here about springs and brake bias. Brake dive is a result of weight transfer, not a cause. Stiffening the springs does not change the weight transfer significantly, and will not affect the ideal brake proportioning. Just think of a bicycle without suspension - despite the lack of dive, it still has weight transfer and can't put as much braking through the rear wheel.

Weight transfer is a function of the rate of deceleration (this can be related to traction available, and thus tire choice and weather), CG height, vehicle weight and wheelbase. That's it. Spring rate is not a factor.

Changing the ride height will drop the CG, though. So putting on stiffer springs that sit lower will decrease the weight transfer and move the ideal bias more towards the back.

 

Keith-

Curious where your info comes from on this. I respect your view of things, this conflicts with my personal experience, as well as the opinion of many of the people I have worked with that to Chassis set up for a living. Spring rate and compression valving effect wieght transfer and thus bias. Spring rate also effects mechnical grip which also effects wieght transfer.

When I have worked with brake and tire engineers on race car setup, spring rates are always a variable that is taken into consideration.

Matt

 

Grab some of the fundamental textbooks - Smith, Staniforth, Adams. It's common to get the cause and effects of weight transfer mixed up, and braking seems to be the least understood arena of all for many people.

Brake dive comes from the springs compressing under the transferred weight. Numerical example using nice round numbers: let's assume a Miata with 600 lb corner weights, 50/50 weight distribution and a wheel rate of 300 lbs/in. At rest, each spring is compressed 2".

Now, we hit the brakes hard enough to transfer 75% of the weight to the front wheels. Now we have 900 lbs on each front wheel and 300 on the rears. The nose drops by 1" (relative to the static height) and the rear rises.

Next, we increase the spring rates to 600 lbs but keep the ride height the same. At the same rate of deceleration, we'll have the same weight transfer - but the front springs will only compress an extra 1/2" and the rear will rise 1/2". Great, we've cut the dive in half. But the important thing - the amount of weight pressing those tires into the pavement - does not change.

Again, go back to that suspensionless bike. It's a simplified case of what's going on. Since the braking system is identical front and rear, you should be able to apply both brakes with the same amount of force, right? No, definitely not. But the bike has zero dive.

Spring choices can affect weight transfer in cornering by adjusting the roll stiffness. This won't affect the total weight transfer, but changing the roll stiffness will affect how that weight transfer is distributed between the front and rear of the car. That's why we can change the handling balance of a car by adjusting sway bars - the end with the higher roll stiffness will get a higher percentage of weight transfer, leading to lower grip levels.

But in the case of braking, you're not running different spring rates on the left and the right, so the weight transfer is equal on each side and thus rates aren't a factor.

Of course mechanical grip becomes a consideration. When you lose mechanical grip at both ends, you lose deceleration rate, which means less weight transfer. Which is why you want more rear brake in the rain. If you've got some other problem that's affecting your traction at one end - say, a front suspension that's on the bumpstops and is thus unable to keep contact with the road - then you need to solve that. A legitimate solution in that case would be to stiffen the front springs so they don't compress as much. The decrease in brake dive will avoid the boundary condition that's causing your traction loss.

 

huster is down for this ****. Who wants to let me borrow the flare maker?

 

You don't need to make any flares if you use the metric-NPT adapters.