Race brake setup for FD
 

I've been pondering a change to a racing brake setup.

Reasons:
- better control
- better adjustment than can be obtained with a proportioning valve

brakes front and rear
front: wilwood setup with 12.75 inch rotors
rear: 99 RZ brakes

There is no ABS, as at least in my experience the OEM ABS in the FD doesn't work very well.

And I still cannot get enough rear brake bias.

While googling this topic I came across this:

Comp Brake RX7 Dual M/C

Anyone here heard of this or have thoughts about it?

Other comments on brake setup also welcome.

This FD is autox only and does not get driven on the street

I have a Racing Brake BBK setup on my car. Are you referring to that or just using 'racing brake' generically? :)
With the Racing Brake bbk, the front calipers pistons are sized to move a bit of bias to the rear. Coupled with the larger diameter rear rotor, the change in bias is noticeable and welcome. Check the original thread for more details.

If using the term generically, then you should probably be able to adjust a ton of rear brake bite with the 12.75" f and the larger ~12.9" rear rotor setup of the 99 coupled with an accurate proportioning valve.

I can't comment on the kit you linked to but it seems to remove the vacuum assist making it totally manual. I would think that would take some getting used to and may slow down your ability to quickly transition from brake to throttle and down shifting.

Edit: maybe they figured out the lack of assist with the Pedal Ratio?

Generically, not the brand. :)

You would think so, but that is not the case. The Proportioning valve is set to send nearly as much pressure as possible to the rear brakes, and the inside front wheel still locks up when trail braking.

Not a big bad tire smoking locking, just some smoke as the wheel is lightly loaded, but even so, it is not turning (verified by an observer)

Fully manual would be fine. It doesn't appear that the kit has done anything to help with pedal ratio.

The stock FD pedal ratio is about 4.12 (as per Howard Coleman), and this kit claims 5:1. No idea from the kit description how they may have accomplished that.

What sort of rear bias are you looking for, and what front calipers do you currently use?

The pivot point in the add-on box would be the reason for the additional ratio. Stock pedal ratio is in the workshop manual, unless your foot contacted the upper part of the pedal pad, still flummoxed how they arrived at that number! Seems to be 70mm from the pivot to the pushrod and 300mm to the centre of the pedal by my measure.

Diyman is running the Revolutionesque modified stock pedal with dual masters, be interesting to see how that's working out for him.

Enough rear bias to eliminate lockup of the inside front wheel on sharp turns. It doesn't take much to lock up that tire.

Wilwood 6 pot calipers in front.

If the inside front is becoming lightly loaded and prone to lock-up on trail braking in my opinion you are dealing with a chassis limitation or chassis set-up issue and not a braking issue.

I get it that in a street class Miata you are limited to jacking around with brake bias to tame the stock spring, heavy front swaybar and short wheelbase chassis; but you have options in SSM.

You can set-up the brake bias to slow the car the quickest and set-up the chassis to rotate off the gas the quickest without as much compromise.

If the chassis rotates well as you release the brake and turn in you will not have to trail brake so hard. On a well set-up chassis the amount of trail braking required is just that tiny bit of rolling off the brake pedal as you turn in vs jumping off the brake pedal and onto the gas.

If that is the rotation you already have and are worried about a puff of tire smoke for an instant that doesnt show in tire wear- I would say, dont worry about the lock-up.

What do I suggest doing to the FD chassis?
If possible widen the front track (track, not width) so it is stock ratio or even a bit wider in front than the rear track and eliminate any understeer bias that could lead to the need for excessive trail braking. This could be decreasing front/rear tire or rim stagger, decreasing front swaybar (may have to increase front spring rate to keep off front bumpstops), or increase rear spring rate or swaybar.

Set the car up to be fairly loose off the gas, yet hook well on throttle with some rear toe and be stable at high speed with the aero package.

JDM street tire FD (200utqg) typically run 16k front springs, 18k rear springs, square wheel/tire/offset, either stock swaybars or both f/r minor upgraded rates and a big GT wing to keep it pointed straight at speed. OFC you will need more spring rate for the hoosiers, but you see by the rear bias how they set the chassis up to rotate off the gas.

SSM FD I think you are kind of limited to 315/30-18 on 18x12 +30 and cutting the headlight bucket or doing a full front suspension redesign like Mike Kojima did for Rocket Buggy front fenders to get more track with a lower offset wheel

Rear its tempting to do the 335/30-18 on 18x13 +20 which is going to be hard to balance the chassis around. You could do a bunch of work (trailing arms and lower shock mount relocation and maybe get it to 18x13 +30 which would get you back to the stock track width ratio f/r.

Lets hope one of the fast SSM guys comments, because they make it all work somehow.

Oh, and weight. You should be able to get FD 200lbs under min weight and then put the ballast just behind the center of the car so you dont go over the max allowed rear weight bias.

This will both help rotation and help traction on throttle which is a rare combo in F/R chassis.

Lots of time and effort in this reply Blue TII, much appreciated.

Previously the lockups didn't require turning, as the front was heavily biased. The RZ rear brakes made a big difference.

Yes, those lockups are minimal, definitely not any flatspotting. I guess I was getting tired of being told the inside front was locking up. If it was serious, I would see the tire smoke, which I do not.

[quote[What do I suggest doing to the FD chassis?
If possible widen the front track (track, not width) so it is stock ratio or even a bit wider in front than the rear track and eliminate any understeer bias that could lead to the need for excessive trail braking. This could be decreasing front/rear tire or rim stagger, decreasing front swaybar (may have to increase front spring rate to keep off front bumpstops), or increase rear spring rate or swaybar.[/quote]

The track is a bit wider due to wheel hub clearance issues on the brake setup. Hadn't considered that it would help handling.

Got wing, springs and shocks. High downforce dual element wing.

Springs are 1100 lb (~20k) in the rear, 1200 lb (~21k) in front. This may seem high, but getting to that point was a progression (I have a few springs) and the car really likes to turn quickly.

Shocks are Koni 2812 rebuilt for those rates.

Front Sway is a TriPoint with the 120lb bar. No rear sway bar.

At one point the inside rear tire would not stay planted in corners. That is when the rear sway bar came off, and I don't miss it.
Rear springs were increased 100 lb to help compensate for that.

The the inside front was lifting, so the sway bar softened and spring rate in the front increased 100 lb.

I have 18x12 +20 in the rear with 335/30-18.

There is also a set of the same wheels I picked up, and I intend to see if I can make them fit on the front for some 315/30-18.

Thanks again for this Blue TII, much to ponder here.

Just haven't gotten to that yet, what with the motor sucking in a piece of iron that chunked off the turbo manifold. Fortunately all that broke from that event was a rotor and apex seal.

Quite remarkably, no other damage.

As for the weight. I have a hard time seeing how I can get this car to 2300 lbs in SSM, too much stuff has to be retained.

There are a couple of heavy-ish items.

The splitter is rather heaver. It is alumacore, kevlar and carbon fiber. Probably 15 lbs or so I think.

The differential brace is probably 10 lbs, but not taking that off.

Exhaust is fairly lightweight, custom Stainless setup. 15 lbs lighter than what I took off.

The car is about 2660 lbs last time I weighed it a few months ago.

I probably have the most rear-biased set up you can find, with StopTech fronts with the 30/36 pistons designed to match the OE rears, but with the RB rear kit that's larger diameter rotor than the RZ. Sakebomb's rear may be a little bigger still. My calculation was 65/35.

Are you also running the same pad compound F/R? I run PFC08 fronts, so I can't... I usually pair with Hawk DTC60 rears.

Front is EBC yellow.

Rear is Hawk+.

I have a set of Hawk DTC60 for the rear, but haven't used them. The Hawk+ seems to work well enough, and they are quite dusty.
From what I have read, the DTC60 has good initial bite, but is even dustier than than the Hawk+

DTCs are great pads. Try the 60s on and see how you like it. I would consider the EBC Yellows similar to HP+, so if you want more rear bias, try the 60s on in the rear with the yellows up front. I run 60s in front and 30s in rear (stock calipers/300HP/255 tires/ducted front calipers). I find that a little front biased and just got 60s for the rear. Just keep in mind that DTCs are track pads and require a lot of heat. I ran mine on the street and almost couldn't stop at a light. They also dust and eat rotors, but it's worth it.

https://cimg7.ibsrv.net/gimg/www.rx7...f1386df07a.png
https://cimg9.ibsrv.net/gimg/www.rx7...67df6a3713.jpg

Sounds like you have a really good set-up already and the racers commenting on your inside front locking momentarily might not realize how much grip and how narrow the FD is. You are barely on 3 wheels and not impossible to get o to 2 wheels.

As far as weight, it gets really expensive and takes a lot of work at your stage.
One would ofc start at the ends to have the most effect on polar moment. Dry CF front and rear bumpers, Ti muffler/ piping with the cannister at cat position.
Use "16.1 O" parts modification with 1lb weight loss liberally, but honestly.
Also, any part that can be swapped has the allowance of unlimited fastner use, so use Ti, Alum and plastic where appropriate.
Subframe can be substituted for engine mounting. Put a 13B-RE in and build lighter subframe incorporatimg RE mounts.
Likewise all suspension and brakes can be substituted or modded for less weight.
All interior or parts that can be modded for comfort and convenience can be lighter (CF is a good starting point as is leaving out metal fastners).
Drivetrain is unlimited, trans, driveline, diff, axles can all be lighter (two speed trans, cf shaft, alum case diff, gun drilled rear axles.)
Wheels- think of using GT350 CF rear wheels for f/r (requires 19" tires).
Strip paint and repaint White (laugh, but realize its a documented 15lb difference on White production ND Miatas vs any other colorND).

If you havent already check out the Red FD that was featured by Larry Chen and is "onesixtwo" on this forum.

Ohyeah, engine accessories.
I found my jdm Black aftermarket alternator was 1lb lighter than stock, probably lighter units than that available. Oem lower, upper intake manifold with TB and Greddy elbow is 20lbs. Projay 4150 LIM and 4 barrel TB with Airaid CF boost hat is probably less than 10Lbs.
Oil coolers, electric PS pump, coils, IC, etc can be moved to rear/middle of car (remember you are at min weight and moving weight around at this point).

agreed

Yes, it does, as if this car wasn't already expensive enough.

One would ofc start at the ends to have the most effect on polar moment. Dry CF front and rear bumpers, Ti muffler/ piping with the canister at cat position.

In short, I have no plans to take this car to nationals, but do attend national tour, and will try pro solo next year (derailed from that this year)

If I think I have gotten the most of the car I can, I am usually happy with that.

All of these mods do add up to weight loss, but not as fast as the money adds up.

All interior or parts that can be modded for comfort and convenience can be lighter (CF is a good starting point as is leaving out metal fastners).

Now this is one I am curious about. For instance, I could change the door panels. Is that allowed? From the rules I don't see how so, but perhaps I have missed something.

CF diff would save what, maybe 4 lbs? True, it is rotational wait, but with the small diameter of a drive shaft I don't think it would help much for response, just the weight.

I am going from a sprung 6 puck clutch back to an unsprung. Also have a flywheel that is 9.8 lbs, while the previous was 14 lbs. That rotational weight matters.
It is also an SFI approved flywheel.

CF Wheels? I don't have that kind of 'budget' ;)

If you havent already check out the Red FD that was featured by Larry Chen and is "onesixtwo" on this forum.

Thanks, I will check that out.

Still planning on electric PS. Just haven't done it yet. Not that much weight savings, if any, but does let me move weight around, and make more room in the engine bay.

Just give me $2,00,000 and two years and we can see if all my crazy ideas could make a faster SSM FD than what you aleady have.

Lots a good ideas, but my 'budget' doesn't extend quite that far.

I tried electric power steering and it sucked. stock has a lot of feedback

I run a pedal box with split masters for the front/rear brakes and a bias bar like the kit that you posted. I do track driving with DTC-60's. I personally really like the manual brake setup. Gives you a lot more feel of what is going on with the brakes, and the brake pedal is a lot more solid, which allows you to modulate brake pressure more easily. Never had ABS on the car and haven't had a problem. Right foot is all the ABS you need.

For brake pads, keep in mind that you probably won't be putting that much heat into them during an Auto-X, so shoot for a compound with high friction at lower temperatures.

I run a manual steering rack (stock rack with the P/S stuff removed). That allows for the best feedback from road --> hands. It does require slightly more steering effort in the paddock, but as long as your scrub radius isn't all jacked up it is fine in my experience.

Just my $0.02

there are basically 5 ways to do power steering.

1. the stock stuff, it fits, and it works.
2. the Mazda 3/MrS way, these have the hydraulic rack, but the P/S pump is electric, could be mounted anywhere, you would need to fab up lines, and figure out the controller.
3. Rx8, Electric, big fat motor as part of the steering rack. control unit is very simple, hookup is easy.
4. Hyundai way, they have a normal manual rack, and the electric motor is in the steering column. nice for a race car because the rack is just a normal part, and all the expensive stuff is in a place that doesn't get damaged. the con is that you need to find a place to put an electric motor under the dash
5. the 2016+ Mx5 has a normal column, and the rack has a motor growing out of it, its almost like it has a sport for LHD and RHD steering, and the motor goes in the one that isn't used by people. pic enclosed.
https://cimg2.ibsrv.net/gimg/www.rx7...17971fc05d.png