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Old 01-22-2018, 12:35 AM   #1  
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Default Wilwood Rear Calipers

I'm looking at switching out my rear stock NA6 calipers to Wilwood calipers. It's a track car, so I'll be able to drop a fair amount of unsprung weight and run larger pad area and fix the issue of pad taper on the rear. I'll move to a hydraulic handbrake so I'll be able to get rid of all the cable driver handbrake. I run endurance pads that are hard to source so I end up cutting down the pad to OEM shape which is an undertaking I'd prefer not to do again on my next set.

I've been looking at the Powerlite radial mount caliper (120-8724). I'm already running the Honda 11.44" rotor so I'll just need to machine up a billet bracket to mount it. This caliper has a 1.58" piston area, and is super light at only 2.26 lbs. There is a new DynaPro lightweight lug mount caliper but the piston areas are larger and they are over 1.5 lbs heavier. I did think about running vented discs on the rear, but with the pads I run I'm seeing excellent life out of the rotors plus I prioritise weight over everything else.

The piston area will push my bias slightly rearward but I think that will be fine given I'm already weighted rear on my balance bar. Hopefully it will bring it more equal without having to change the rear master cylinder.

Has anyone tried this yet?
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Old 01-22-2018, 07:20 AM   #2  
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Why not just use the V8Roadsters rear kit complete with the rotors? Then you can use the Wildwood $35 rotor ring replacements or the fancy directional rotors. Building brackets to modify something to fit a lesser rotor might be going the hard way.

Pictured also are some front ones from V8R because they are pretty.
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Wilwood Rear Calipers-80-image_49_jpeg_f52583f3213c4276ee4ca429dad9d71b9b438bbb.jpg   Wilwood Rear Calipers-80-image_50_jpeg_be9826e6e2e10dd29a8eedf75348d02679036c51-1.jpg   Wilwood Rear Calipers-80-image_50_jpeg_be9826e6e2e10dd29a8eedf75348d02679036c51.jpg   Wilwood Rear Calipers-80-image_49_jpeg_f52583f3213c4276ee4ca429dad9d71b9b438bbb-1.jpg  
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Old 01-22-2018, 07:45 AM   #3  
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Why not just use the V8Roadsters rear kit complete with the rotors? Then you can use the Wildwood $35 rotor ring replacements or the fancy directional rotors. Building brackets to modify something to fit a lesser rotor might be going the hard way.

Pictured also are some front ones from V8R because they are pretty.
They are heavy though! I could fit 11.75" vented rotors to the hats I have but they weigh lots more. I run them up front but this powerlite is both cheap and way lighter than any other caliper. As long as its better than oem I'm happy.

btw I spent 4 hours grinding the rear hubs to save a few ounces... time is free!
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Old 01-23-2018, 06:34 AM   #4  
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I am fairly certain this is the same caliper used in the FM LBBK. Given that, plenty of people have tried this caliper out but I would say the great majority of them have been autocrossers like myself.

I believe we had to take out a touch of rear bias once installed on our car. We have Wilwood BP20 pads all around with I believe a 3" piston area up front with NA8 rotors. Fairly close to stock with as you mention, a bit more rear bias. And not that it matters but we run a manual 11/16" master cylinder.

I know you are looking for road race feedback but your question seemed to be more about bias so HTH.
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Old 01-23-2018, 07:57 AM   #5  
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FM sells a kit to do exactly what you're describing, both hydraulic-only and with a bicycle-style cable-actuated parking brake.

https://www.flyinmiata.com/flyin-mia...e-upgrade.html

I have the kit on my car and am pretty happy with it. The parking brake is not terribly strong, but better than nothing. Paired with Dynapro front calipers, I did need to swap out the master cylinder for a 1" unit out of a 929 in order to get a good pedal feel, though. The early kits had some real problems with the ends pulling off the cables, FM changed it later on to use OEM NC cables instead which has fixed the problem.

With the old cable and a zip tie instead of the clevis bolt that I was missing at the time:


--Ian
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Old 01-23-2018, 09:04 AM   #6  
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So it is that caliper that FM use. I don't have any issues with rear bias change because I have dual masters with a balance bar. But then I'd prefer not to have to change the rear master cylinder as its a major hassle.

The little park brake FM sell isn't teally ideal for me as I still need to be able to use the handbrake for hairpins or autotests.

You've given me the confidence to order two calipers and see how they fit. I'll report back once they are on.
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Old 01-23-2018, 02:37 PM   #7  
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So it is that caliper that FM use. I don't have any issues with rear bias change because I have dual masters with a balance bar. But then I'd prefer not to have to change the rear master cylinder as its a major hassle.
The reason for the bigger master isn't the front/rear balance, it's because the fluid volume is different (larger, IIRC) in the Wilwoods, so the master to slave volume ratio is off. How this impacts dual masters I'm not sure.

--Ian
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Old 01-23-2018, 04:22 PM   #8  
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The reason for the bigger master isn't the front/rear balance, it's because the fluid volume is different (larger, IIRC) in the Wilwoods, so the master to slave volume ratio is off. How this impacts dual masters I'm not sure.

--Ian
Fluid volume change = force change

Someone correct me if I'm wrong, because I doubt that FM would shift brake balance this rearward...

It looks like piston area would be 30% larger on the powerlite. FM uses the 1" piston that has an area of 1.58" (on one side). Stock 1.8 rear brakes are a single 1.25" with a piston area of 1.225". To give some examples of popular combinations and their resulting brake balances (just due to piston diameter and rotor diameter, does not account for staggered pads, dual masters, prop valve, etc)
Stock 1.8 front/rear, 10" rotor front/rear: 72%
Wilwood dynapro front w/ 11.75" rotor, stock 1.8 caliper rear w/ 11" sport rotor: 72%
Wilwood dynapro front w/ 11.75" rotor, wilwood powerlite rear w/ 11" sport rotor: 67%
Same as above but with 10" rear: 69%

Plugging into my spreadsheet, the Dynapro 11.75"/Powerlite 11" setup would want a 0.625" front, 0.700" rear if used with a prop valve, or a 0.625" front, 0.75" rear without a prop valve. A 10" rear would stagger the rear master 1 smaller, so w/ prop valve would want 0.625"/0.625" and w/out would want 0.625"/0.7".

I don't have the stock prop valve modeled in my spreadsheet, only the Wilwood, so I'm not sure what the balance is actually like when going to the full big brake kit with stock master/prop valve. I'm surprised that FM recommends using similar front/rear rotor diameters for their LBBK.
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Old 01-23-2018, 05:00 PM   #9  
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I don't have the number on hand but the Powerlite adds slightly more bias than a stock Sport setup. IIRC a Powerlite on a 10" rotor is the same bias as a stock Sport 11" setup. Any master cylinder change is going to be for pedal feel, not to accomodate the caliper.
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Old 01-23-2018, 05:49 PM   #10  
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Actually after factoring prop valve, pad height, etc, a Dynapro 11.75" front and Powerlite 11" rear with a prop valve is pretty much spot on.

The graph below shows balance as grip increases. This assumes 0.625" masters front/rear, a 5.8:1 pedal ratio, centered bias bar, and Wilwood adjustable prop valve on setting 3 (3 away from all the way open, or closed, whichever end is closer to not effecting the pressure curve). The blue line is desired line pressure split, and the red is actual line pressure split. The data labels are placed every 0.1G from 0.4G to 1.1G, and the percentage corresponds to deviation from ideal, and when the red point is below blue, it's front biased. Label next to the red line corresponds to input force. Basically, this chart is saying at 1.1G balance is 2% front biased (slightly front biased is good, and is well within adjustment range to make it more front biased, or rear biased) and there's a 65 lbf input force. There's also plenty of prop valve adjustment to make this setup rear biased (just imagine a straight line before the knee). It starts raining or you're trail braking and max G is now 0.7G, so balance is now 5% and input force is 38 lbf. Since the front/rear masters are the same, this would represent a single master as well, the input force would just be skewed.

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Old 01-23-2018, 05:55 PM   #11  
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Quote:
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I don't have the number on hand but the Powerlite adds slightly more bias than a stock Sport setup. IIRC a Powerlite on a 10" rotor is the same bias as a stock Sport 11" setup. Any master cylinder change is going to be for pedal feel, not to accomodate the caliper.
I changed the master strictly on a pedal feel basis, not on a balance one. AFAIK, stock Mazda masters are all the same diameter for front and rear circuits, so I don't see how changing the master can change the balance anyway.

On paper, the difference in pad area (sorry, not fluid volume -- it was early and I wasn't thinking) between the stock NB1 rear cailpers and the Powerlite rears that FM sells doesn't appear to be all that big. In practice, swapping those calipers turned the pedal feel on my car from being decent to being absolute ****. I tried a ton of stuff to fix it, diagnostic bleeding the ABS, changing brake flex lines, replacing front calipers, and adding FM's master cylinder brace. I put 2 gallons of fluid through the car in bleeding it using every technique I could find. Finally I took it to TC Design (If you don't live around here, they're a well-known bay area race prep shop) and said "WTF? What's wrong with this?". They came back and said as far as they could see everything was working properly, but agreed that the pedal feel was crap and suggested a 1" master. I installed that and the problem went away.

So my experience is that if you want to use the standard Dynalite or Dynapro front calipers and Powerlite rears, you need a 1" master to make the pedal feel not suck. Or, presumably, an appropriately-sized dual master setup (no idea what diameters those would be)

--Ian
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Old 01-23-2018, 06:42 PM   #12  
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Pad area shouldn't really change bias. The surface force is less per sq unit but it's acting over a larger area. The larger pad helps it to wear less because temperatures are lower per area. It also smooths out any catching making it easier to progress to the limit of slip.

I run 0.625" front master and 0.7" rear master. I'm also running a slightly higher diameter of 11.44" on the rear which increases the bias a little too. I had it around the wrong way at the start of the thread but the Wilwood will further increase the rear bias not reduce it (larger area at the same PSI = larger force).

I have a spare 0.625" master which I'll install to bring it back towards center again. (or maybe I switch masters front / rear).
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Old 01-23-2018, 07:44 PM   #13  
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Pad area shouldn't really change bias.
Sorry, PISTON area, not pad area. I have no idea why I typed pad area. Clearly I wasn't thinking later, either!

--Ian
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Old 04-10-2018, 10:45 AM   #14  
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I made a bracket!... well half made one, but she bolts up nice and square. Just need to trim it up and cut some weight out of it.

These radial mount powerlite calipers are really nice. They are super low profile, nicely made and very light. Perfect for the rear wheel.

Now I need to order some shorter m10 studs and make a hydraulic handbrake.

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Old 04-10-2018, 10:48 AM   #15  
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Old 04-14-2018, 10:29 AM   #16  
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Now I need to order some shorter m10 studs and make a hydraulic handbrake.
Go titanium. We have the FM LBBK and it comes with stainless allen button head fasteners. After stripping one out, we went Ti on all 8.

It saved .225 lbs and only cost $100. But hey, it's unsprung and much stronger than stainless.
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Old 04-14-2018, 12:43 PM   #17  
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Go titanium. We have the FM LBBK and it comes with stainless allen button head fasteners. After stripping one out, we went Ti on all 8.

It saved .225 lbs and only cost $100. But hey, it's unsprung and much stronger than stainless.
Yeah, those button head phillips bolts strip really easily. After having to drill one out I now consider the bracket and the caliper to be permanently attached and just unbolt the whole assembly from the upright when I need to change rotors.

--Ian
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Old 04-16-2018, 04:29 AM   #18  
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Go titanium. We have the FM LBBK and it comes with stainless allen button head fasteners. After stripping one out, we went Ti on all 8.

It saved .225 lbs and only cost $100. But hey, it's unsprung and much stronger than stainless.
Ti stronger then stainless?

No.
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Old 04-16-2018, 08:55 AM   #19  
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We're forced to use a shitload of M8 stainless button heads at work and they're easily the worst fastener I've ever used for stripping out the allen. Stainless button heads suck in general but for some reason the M8s round the allen out easiest. Zinc-plated mild steel button heads are slightly better. Low head socket cap screws are even better. Almost none of them are rated higher than 8.8 though so you should use regular socket head cap screws if you don't need the clearance.
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Old 04-16-2018, 12:01 PM   #20  
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Ti stronger then stainless?

No.
Lolwut? He's comparing OTS button head screws, which means 18-8 or 316 and about 70ksi minimum yield stress. OTS "racing" button heads are 6Al-4V, which is at least 125ksi minimum.

Didn't realize precipitation-hardened, martensitic stainless button head screws were so common...
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