8 replies to this topic

[bmarshall1]

 I was reading a thread about pad compounds, weight transfer and such, and Saul had raised a very good point that wasn't addressed regarding proportioning valves and brake pressure.

 

Saul had mentioned 'knee' of the prop. valve chart.  I assume that he meant if one were to use very high brake pedal pressure, once past the apex of this curve, proportioning results would change.  Can anyone tell me what the change would be, ie: more or less brake power sent to the front/rear?  Or did I totally miss the intent of the post.

 

The reason I ask is that I run DTC 60/30 and have no problem with rear (or front) lock - meaning I may be leaving some time under braking on the table.  Some folks were saying to use the same pads front and rear, others said not to, and there seemed to be good arguments for both sides.

 

Having said all that, given my mediocre skills and based upon what I have read into the arguments.  If I were to use a less aggressive pad, I will be using more pressure to achieve the same stopping power and also using more large muscle groups.  This abundance of pressure may take me "over the curve" on the proportioning valve leading to ??

 

If I were to use a more aggressive compound, or even the same f/r compound, perhaps I could use more 'finesse' of foot and calf pressure, less pressure overall, and stay under the proportioning valve curve, leading to a difference of ?? vs. going past the curve.

 

I am most definitely overthinking this but now it is more of a point of curiosity regarding the prop. valve and what happens with excessive brake pressure.

[Steve Scheifler]

Some very good questions. I won’t attempt to answer your specific question about the prop valve but I will remark that there are probably five or more versions so to answer your question you might first confirm which you have (anyone buying a used race car beware that many were swapped for what people believed to be one with a better balance. No, that is not allowed by the rules.) If the other thread didn’t post a link to a post detailing the versions (as of that point) you can likely find it searching miata.net.

[bmarshall1]

Thanks Steve, good point about the version that I have.  My car is a 99 and I assume it is stock, but having bought the car used, there is no telling.

[SaulSpeedwell]

Just saw this.  Flyin' MIata does, or did, have the prop valve curves posted/published on their website.  As best I can tell, every SM that is being driven near the limit is "past the knee" on the prop valve curve.  As human brake controllers controlling 4 individually braked wheel ends with one pedal, our adaptive control subroutines are quickly trained to modulate based on the brake that locks the earliest.  My conclusion:  You only stop as fast as your most "overbraked" wheel allows you to.  Pay attention to the one that locks the soonest, because that means the other 3 aren't doing everything they can to help you get rear-end punted at the Runoffs

I certainly encourage any serious competitor to experiment with pad compounds to achieve the most reliable fast and consistent laptime.  What works for one driver won't work for another, etc. .... 

[Bench Racer]

bmarshall1

 

FlyinMiata proportioning valve info.

 

https://www.flyinmia...h/stock_bpv.php

 

Please not they suggest the 99-00 are similar to the 94-97.  Saul???

[bmarshall1]

Hmmmm - interesting info in the FM page.  If I read it correctly, once a certain brake pressure is achieved, past the knee, rear brake pressure drops off.

 

Now, how to utilize this info to choose brake pads, or just go out and drive w/ different compounds and see when lock-up happens vs. driving style.

 

And to Saul's point, likely we're only braking to the point our first wheel that locks up

[SaulSpeedwell]

"Ratiometric".  The rear line pressure becomes a lower "percentage" of the master cylinder pressure past the knee-point.  This was the bee's knees and cat's meow, and practically a Federal requirement in countries that pretend to overvalue a single life via the stroke of a Congressional intern's pen, before ABS and the parlor trick that is known as "Electronic Brakeforce Distribution".   I assure you that Middle North American American Covid Patient Zero Preston Pardus was not thinking about any of this when he somehow won the Runoffs - and every time I watch it, I'm still pretty sure he isn't going to win it.  Give the car what it wants.  If the car is locking the right rear every damn time, throw a stock pad on the outboard side(or flip it backwards), don't tell your brake pad supplier you did this, and figure it out before your next weekend showing off for the F1 scouts.  You are controlling 4 brakes with one lever.  The brakes suck, they are a wobbly imprecise rubber-mounted menagerie, and they act like an Asian Fingertrap when they are resisting 100+ ft-lbs of fake-205mm Continentals wearing a purple skirt that says "Hoosier".  You can sing symphonies to those single piston floating calipers and use magic grease, but they have a mind of their own.  But, they also have 4X+ the power of your $6000 engine, and they are your winghomosapiens in most of your passing.  They are worth paying attention to.

[LarryKing]

That's the kind of content you just can't get over at SMMD.

[bmarshall1]

I think Saul is channeling the ghost of Hunter S. Thompson...