wildo

iTrader: (1)

Here's a screen shot of some recent data from Watkins Glen.
Key is to the left of the graph.
Black trace is front brake.
Red trace is rear brake.
Orange trace is longitudinal g's.

Todd TCE

Admittedly not a Miata expert I don't have data to prove the numbers I'm suggesting here but I've seen data off other cars and my experience says that psi figures are not normally as high as these. I could see your elevated 800-1000 under extreme braking perhaps but higher than that...? Hard to argue with the data graph however!

If those number are in fact correct your removing the booster would be very detrimental to the driving. You'd need to be able to push with roughly 90 lbs of leg pressure on a pedal (ratios taken into consideration) to get to 1000psi. That sounds easy enough but try it; put a corner scale angled up to the wall and secure yourself against something in a sitting position and push on it. 60-70 is doable but 90 is going to be a work out and I'm not sure I could do it fast enough to match the corner entry speed.

Taking some of that into consideration you'd certainly not want to increase the mc bore- you'd make it even worse. That dual mc and pedal set up could we be the answer for you but based on total area of the current bore you'll run some rather small cylinders too- ie. your combined area being roughly equal to what you like (1" or .875) will net you the same 'feel'. Pedal ratio not withstanding.

Moving to the 1" bore with the booster might help the pedal feel for now and at the same input (leg) pressure will lower the pressure at the caliper. But of course if your demands for torque are the same you'll push harder and boost the line pressure back up to where it was. As you know you're not making more or less brake torque relative to what your demand is, only changing how you get there.

At that pressure you may well need to consider moving to a more robust caliper to keep up with the pressure demands. You're certainly not going to get that out of a mid class caliper body. Moving to an FSL or more perhaps? With many successful MINI apps out there also running a very small mc I've had no negatives comments on that body under hard use. Doing a W4A or such...not sure you can do so on a small rotor.

SolarYellow510

If the caliper/pad/rotor system is losing efficiency for whatever reason (this one "might" be), then the driver will try to make up for it by pushing harder on the pedal to increase pressure.

Sure would be nice if there was a kitten-sized version of something you'd see on the line at the 24 Hours of Daytona.

Todd TCE

Maybe. Not sure how much that might have an impact. If the right pad is in use and all, then the flex is a byproduct. I think you'd find that there'd be no more pushing on the pedal to get the torque- it would be constant relative to piston area, pad and rotor math. But the flex would lead to a longer pedal to achieve that.

IHI

That flex is looking quite disturbing. Do the midilites have less flex?
I have heard of caliperflex before with Wilwood. If so, is it worth the upgrade? I do like the 4-wheel FM 11" kit...

Todd TCE

What's a midlite ?

IHI

Those:


they seem to be sold in europe only. They have dustseals.

http://www.rallydesign.co.uk/product...oducts_id=8317

Todd TCE

That's a radial mount Dyna Pro. This is the caliper used on the Miata and shown in the pictures/video. They've been here in the US for many years now. First appeared on some kits like the VW and quickly the MINI, Eclipse, WRX and others.

DYNA PRO

bbundy

That is a Radial mount Dyna Pro. You can get them with the dust seals and thermlock pistons or with the stainless pistons. I’m not using the ones with dust seals just the stainless pistons that come in the Mini Cooper race kit.

I was the first I think to install this caliper on a Miata Back in 2005. FWIW I have run Dyna Lite 11" kits and the Dyna Pro 11.75" kit. I never measured flex but the Dyna Pro kit was a substantial improvement in feel over the Dyna lite kit. Also the Corrado rotor Dyna lite kits were a total failure for me in terms of capacity or longevity. The 11.75 kit had substantially better thermal capacity and front pad and rotor life nearly doubled partially due to thicker pads to start with. The Dyna Pro has better Radial clearance than the Dyna Lite and made fitting 11.75" rotors in some of my 15” wheels possible where it wouldn’t work with Dyna Lites.

My brakes.

Front. 11.75” directional vane two piece rotors. Dyna Pro Calipers. (Off the shelf Mini Cooper 11.75” race Kit) now running Colman racing friction rings.

Rear 11.44” two piece rotors with the larger piston OEM sport brake calipers on relocation brackets. Rotors are again supplied by Colman racing but they are custom.

I am running a 1” master cylinder from a 929 with a late model NB booster and have a MC support brace.

I like Cobalt Friction XR2 pads on all four corners for the track.

I have never been in a Miata that has better feeling brakes and I drive this thing between 5 and 10 seconds under Spec Miata Lap records on most any track I have been to running down into GT car territory.

After seeing some of the data presented here I could possibly see bigger pistons with lower line pressures as a possible improvement and I have also thought about doing this to loose the booster all together. But honestly I can say I don’t have any complaints about brake performance at this point.

Bob

wildo

iTrader: (1)

Todd,

Yes, I have been considering all of the points you mentioned. The biggest problem is finding calipers that fit. I spent a good amount of time choosing calipers and designing brackets. Shortly before I pulled the trigger, I found bbundy's post concerning the Mini kit. I ended up ordering the MINI kit's brackets, the 3" DynaPro4 calipers, and using the aluminum hats I had. I hoped to find a staggered piston caliper that would fit under the 15" wheels I use, but it hasn't worked out. The only 6 piston caliper I know that could fit is the DynaPro6, however it is lug mount, not radial mount.

Thanks for your advice. What is your shop's website?

Bob,

What is your pad wear like? Even? Tapered at all?

Our brakes have several things in common. I kicked myself for not finding the MINI kit post you made back in 2004 or 2006 earlier. After spending a bunch of time looking for the right caliper & mount then designing my own, I couldn't believe that Wilwood had what is virtually an OTS solution for DIY types. I'm also pretty irritated that Wilwood couldn't make things easy. I asked them many, many times about the different radial mounts they have, but they were unable to give me any dimensions of their car-specific kits. I would have thought all that data is in a searchable database or spreadsheet, but apparently it is not. Anyway, thanks for posting what you have.

The 1" 929 m/c and '99+ sport non-abs booster I'm running were also taken from that long post on the other Miata forum.

My brakes are:
DynaPro 3 sq-in front calipers with
10.75" rotors and
Cobalt Friction XR2 pads.
Stock 1.8 rear calipers with
stock 1.8 rear rotors and
Cobalt Friction XR4 pads.

I just installed the 1" m/c and bigger booster, and haven't tracked the car with 'em yet.

With the stock m/c (7/8") and booster, the brakes pedal feel has been horrible.

The stopping power of the car is there, but the pedal is vague and sometimes inconsistent. I'm also getting radial and longitudinal pad taper, which are the two problems I was trying to solve by going with the Wilwoods in the first place!

Race weight of the car is 2380-pounds, and the naturally-aspirated engine makes 186hp. I also run significantly faster than SM records to the point where it doesn't make sense to use SM as a measuring stick.

I'm wondering if I'm running out of vacuum assist. The booster gets 14" of vacuum at startup & idle, then goes up to 22" as soon as I get on the throttle. When I hit the brakes, it seems that the vacuum drops to about 14" by about 1/2 the pedal stroke and stays there. At 1/2 strock, front line pressure is about =~600-700psi. Getting from 700 to 1,000 psi takes a good amount of extra pedal pressure.

New spacers have been cut to center to calipers exactly on the rotor. I now understand why Wilwood includes shims with all of their kits: manufacturing variances. Oddly enough, the caliper spacers on each side (driver/passenger) are different. In order to center the calipers on the rotors, the passenger side spacer needs to be about 0.0275" thicker. This is not a lot, but new Cobalt Friction pads are so fat that the pistons have to be completely retracted to fit, and even then, it is close.

I also took Hustler's advice and went with the reverse bleed.

At this point I've thrown everything I can at it. I may pick up a cheap vacuum canister and place it in-line. Everything should all be back together for a test-drive onto the trailer and thrashing at the track next weekend. I'm very much hoping to finish the season with more answers than questions. Got to have something to do in the off season.

The flex shown in the video is interesting, however I wasn't looking for it, just trying to solve the brake/pedal issue. I'll be psyched if the 1"m/c, big booster, and everything else solves my issues. That said, I'll be looking into upping caliper piston area F&R, going with an aftermarket pedal with dual m/cs, reducing overall line pressure (to reduce caliper flex). If all of that can be achieved and can result in a firm, reasonable-throw pedal, I'm in.

Cheers,

Will

Todd TCE

Fit within a 15" wheel is always an issue Will. I've done some drag kits of late and we are down to 11.5" to make them work. When you do a road racing deal you really have some limitations on rotor size. And honestly; I'd take rotor size and mass over caliper value any day. I'd rather have a larger rotor and a DynaLite then a real small rotor and an FSL. Rotor value is not to be overlooked; mass, leverage, cooling etc.

You're dealing with one of the most popular (and probably successful) medium class calipers I've ever seen. You can find some old AP parts off open wheel and sports racers maybe but they're all big bore and cumbersome in size.

I sold a couple of the MINI conversions in production form (yes thanks in part to Bobs help) and have not had any negative replies on them. The smaller DL class parts are simply not what you want for a road race car unless very light.

Speaking of weight...you want better braking? Take a weight out of the car. What's that mean to braking and flex? Less strain on the entire system. While I run DL parts pretty much all around they are on a 1500lb car and I have zero issues with them. I think you can make some improvements if you can cut some pounds here.

The DP6 is the only differential bore part in the medium caliper class. It's really a revised DL model with staggered bore. The staggered bore thing however won't make for much better braking, only better pad wear. A standard DP6 can be compared to a 1.625 bore DL, both are the same size with regard to area: 4.06 vs 4.1 so it's just a sub part. The DL and DP6 (and other DPLM parts other than NMDP- you got all that??!) are all .490 thick pads. Frankly for a road race car that's crap. Even .62 is marginal. But you're back to that fit issue again. Big pads take big calipers.

Not sure what I can do to help but you can reach me any time. HERE

bbundy

I get some longitudinal pad taper but never any radial taper. I flip the pads occasionally and the taper evens itself out as the pad wears through. I assumed some of this is caused because the pads are thicker and at full thickness there is a bit more of a mechanical force couple that gets generated from where the pad contacts the rotor and the longitudinal force gets reacted by contact between the caliper body and the backing plate. This force couple makes the leading edge of the pad tend to dig in. I also experienced the same behavior when I had Dynalites.

The vague pedal feeling your describing I am not feeling at all. The brakes feel spot on and right now. Pedal is solid so and doesn’t move much so heal toe throttle blips are consistant with varying levels of braking. Quite a bit of braking force can be generated with very little pedal force as well.

I assume you ment 11.75 and not 10.75 for the front.

I will say that putting on sport brake calipers in the rear made a fairly dramatic improvement. Even with my 11.44” rear rotors before going from the 1.25” piston stock rear calipers to the 1.375” piston stock Sport brake calipers I always had the Wilwood Bias valve set full rear. The larger piston rear calipers gave me some adjustment range to where I could just get it to the really sketchy point on rear bias and the whole braking system felt more responsive. If your running just the 9.88” stock 1.8 rear brakes with the smaller pistons there is no way you will get the bias right. I think minimum you need the 10.84” sport rear brakes with this setup, really any of the wilwood front kits available you need a minimum of the sport rears.

Bob

Todd TCE

Pad taper you describe is due to the "equal or square" bore aspect of the calipers, rather than them being differential bore. A differential bore caliper applies less bite to the lead area of the pad and more to the trailing. This counteracts the gaseous build up or boundary layer created by the friction and balances out wear.

There are no small size calipers in this class however that offer the split size. At one time years ago there were some split bore DL parts but it's too costly to produce them that way so only the larger parts and six pot are that way now.

Pad wear spacers are also a nice benefit to that pad swapping that Bob is doing- exactly what I'd have suggested too.

wildo

iTrader: (1)

Thanks Bob, good to know. FYI, I had some slight chunking on the inside corner, leading edge of the pads. Cobalt chamfered the latest set of pads for me, hopefully this will stop the chamfering (though I can't say that the previous chunking caused any obvious problems).

Also good to hear!

No, I am actually running 10.75" fronts. This is a custom setup which fits perfectly inside an Enkie RP-F1 15" wheel. As much as I like the weight of the RP-F1, I've picked up some Enkie PF-01 wheels and 949 6ULs, which would allow larger rotors. I'll likely bite the bullet and move to all 15x8 & 15x9 Enkies/949's for next season.

I picked up a set used sport brake calipers, brackets & rotoer and rebuilt the calipers. Tried them with the Wilwood front calipers &stock m/c and found that the pedal travel increased way too much, so I swapped 'em back.

10.75" front rotors and stock 9.9" rears are due to wheel fitment. My rain tires are on the Enkies, and I have a couple of sets of Enkies with other tires on 'em too, so I've been a bit reluctant to change over. I could see selling the Enkies and gettting a cheap set of wheels for rains. WIth these rotor sizes, the stock 1.8 calipers actually work well. Full brake pressure to the rear is too much, and threshold braking, not to mention trail-braking, can get pretty...exciting.

What wheels are you running that fit those rotors?

All that said, I haven't had issues with managing heat in the brakes. The car stops reasonably well, the pedal feel is just crap.

wildo

iTrader: (1)

I also swap the pads around to even out the wear...it definitely minimizes the taper. I've thought of pad spacers for a while, but never had any made. Closest I have are 0.5mm thick titanium backing plates from hardbrakes.com. Seems spacers would be a very good idea for stock floating single-piston calipers.

bbundy

The Light weight of RPF-1’s in a 15X7 may feel fantastic and make the car ride nice but my own testing back to back on the track showed

8” is faster than 7”
And later test showed
9” is faster than 8”

Even though the 9” were ~3 lbs a piece heavier than my Sprint Hart CPF 7”. I’m running 949 6UL’s now.

It wasn’t just a matter of more grip for which I do believe the wider wheel gave a little more. It was the improvement in the way the brake away was at the edge of traction. The limit becomes much less abrupt. The tire contact patch I believe stays more consistent at different cornering loads so the contact patch doesn’t snap to a different shape once you exceed the traction limit as much as it does with the narrower wheel. They also allow the peak tire performance to be with a few pounds less air so I believe it also increases the size and compliance of the contact patch to grip uneven surfaces.

Bob

wildo

iTrader: (1)

^^^ I agree with a lot of that, certainly with my car now that it has a bit of a built N/A motor. I stocked up on the Enkies for the car when it was a 1.6 ITA car, then with the new 1.8 ITA car (where max wheel width is 7"). I picked up a set of 15x8's and preferred the 7" (slightly faster lap times).

With 186 n/a hp and not having to worry about ITA legality anymore, wider wheels and wider still tires are certainly faster.

That said, if I ditch the Enkies all together it will be to go to bigger rotors, and when that happens, I'd like to find cheap 15x7 wheels for rain tires that fit over the larger rotors, which is why I asked about your wheels.

Thanks for the info!

bbundy

I got my old set of ATS comp lights in 15X8 for rain tires. Just mounted a new set of 225/45/15 Hoosier H20 Wets on them. The tires look like they have nearly an inch wider tread than the 225 Nitto's almost closer to my 275/35/15 A6's.

Bob

SolarYellow510

Was flippping through an old copy of Race Tech Magazine (March) today and found this. Looks kinda prototypey. Anyone going to SEMA to check it out?

SolarYellow510

Just noticed there appears to be pretty significant hysteresis in the proportioning valve function. On the initial release of pressure, the rear doesn't drop in proportion to the front drop, and by the time the fronts are down at 760-770, the rears are still up around 10-20 psi less. On the apply side of the chart, when the fronts are at 760-770, the rears are still down about 100 psi lower.

Wondering if this difference is consistent from stop to stop, or is it variable?