Brake Upgrade question

[RS2000]

I've read of forum members installing high performance pads in the front, while using a 'lesser' performance rear pad. What about the following setup on a track NB8A:

Upgrade front calipers & rotors to NB8B, while retaining factory NB8A rears, & using high performance pads all round. Thoughts? Anyone tried it?

Cheers

[Magpie]

It is all about weight transfer. The reason for a lesser pad in the rear is that under heavy braking the rear jacks up and hence does not need as much braking torque. However you could just as easy use a proportioning valve to balance the braking forces instead of pad/rotor size at the rear.

The larger rotors allow for better temperature management as well as a larger surface area for the pads to bite on. This in itself would be a good reason to go to the NB8B setup. Plus depending on your intended use NB8B rotors can be picked up cheaply (OEM, RDA) and pads like A1RM's or Wimnax W3's are a good pad for daily drive and light track work.

What is the final use of your car?

[RS2000]

Hi Magpie, it is a track only NB8A.

I bought a set of NB8B front calipers & rotors from a forum member, but am yet to find a set of 8B rears - hence the question.
There is a couple of complete F & R sets available on the forum, & I may have to buy the extra front sets if my idea is not feasable to try.

Cheers

[Magpie]

I have 2 complete sets of NB8B calipers If using on the track I would suggest that greasing the sliders be done after every few track days as well as a yearly rebuild. I have had issues with the NB8B rears not fully releasing and causing drag and excess heat! If it is track only then you could remove the rear parking brake circuit, this makes rebuilding cheaper and reduces the possible sources of sticking from the rears.

Rear brake operation http://www.miata.net/garage/ebrake/index.html or http://fastcraft.biz/blog/?p=725

But I'm starting to digress...

I would say if track only try the mix of NB8B/NB8A and possibly install a proportioning valve to allow for adjustment of front/rear bias. Do you have brake ducts on the front?

[Dan]

It is all about weight transfer. The reason for a lesser pad in the rear is that under heavy braking the rear jacks up and hence does not need as much braking torque. However you could just as easy use a proportioning valve to balance the braking forces instead of pad/rotor size at the rear.

Temperature range is something to consider as well, since rears won't ever get as hot as fronts (so you won't need the upper range) and as you mentioned you don't need as much torque lesser pads might still be a good choice to get them in the optimum temperature range quicker.

[RS2000]

Thanks for replies & info.
When I bought the car, I had issues with one side of rears not fully releasing. It turned out that with hand brake released, there was still tension on the lever at the caliper on one side only - fixed by proper adjustment of cable at caliper lever, followed by hex adjusters at caliper, then handbrake lever adjust.
Magpie - no brake ducting.

Out of interest, anyone know the reason for Mazda increasing the rear disc dia. on NB2 ?
NB1 - F 255mm, R 251mm
NB2 - F 270mm, R 276mm (larger than front!)

Cheers

[Nevyn72]

Out of interest, anyone know the reason for Mazda increasing the rear disc dia. on NB2 ?
NB1 - F 255mm, R 251mm
NB2 - F 270mm, R 276mm (larger than front!)

NB2 -> Front = ventilated, Rear = Solid

With the larger calipers on the front, this was the biggest each end to fit inside the 16" rims.

[madjak]

In my car with stock brakes, I couldn't get enough rear. I think for a track car getting the rear working is required for the best brakes. This generally requires the SE calipers (larger piston) or offset caliper with a larger rotor.

I don't know the NB brakes on the track but can you get the rears to lock with no proportioning valve?

In my NA6 with race pads all around and stock brakes I think my rears were only about 50% loaded. With my wilwood setup, a fully open proportioning valve will mean my rears are locking first. One and a half turns is where I run at and I can see the temp in the colour of the rear rotors.

I can tell you the brakes work a lot better when the rears are doing something.

[RS2000]

NB2 -> Front = ventilated, Rear = Solid

Same for all MX5's from NA to ND.

Maybe a lot of cars have the rear rotor larger in dia. than fronts, but I've never owned one in 40 years. As far as I know, the NB2 is the only factory MX5 like this, & I am interested to know why.

Cheers

[RS2000]

In my car with stock brakes, I couldn't get enough rear. I think for a track car getting the rear working is required for the best brakes. This generally requires the SE calipers (larger piston) or offset caliper with a larger rotor.

I can tell you the brakes work a lot better when the rears are doing something.

Makes sense madjak - so going larger on front only could be going backwards.
Cheers

[Magpie]

RS2000 as yours is track only you have a lot more scope to make changes than myself whose car is still road registered. Madjak has put a lot of effort into his brake setup and I have always found his advice useful.

I do not see anything wrong with your planned setup. The rear rotor whilst be smaller can still be mad effective by a combination of manual proportioning valve and pad choice compound. Maybe trial the same compound as the front as a test and use the manual valve to adjust bias. If you can't get enough bias increase the pad compound in the rear. I would suggest Winmax W5's all-round and possibly Winmax 6.5's front and 5 in the rears.

I use W5 front and W3 in the rear and since the rebuilding of the rear calipers and NB8B proportioning valve my rear braking is a lot better, not perfect but getting there. Whilst I'm tempted to go manual proportioning valve I plan on testing a set of 10kg springs on the front (6 kg rear) to slow down the weight transfer. This will also have the benefit of reducing some of the oversteer and if required I can re-install my larger adjustable rear sway to balance out the larger front springs. If this does not work then a test with W6.5 on the front and W5 on the rear soon and if this does not sort out the rear then the manual proportioning valve.

I'm also lucky as I can data log the front/rear brake pressures and see the pressures, once I start to log all 4 wheel speeds I will then be able to see which wheel is looking and at what pressures. Further I can also calculate the weight transfer and see if the suspension changes are having the desired effects.

Let us know how your testing goes as you never know what you will find down the path less traveled.

[madjak]

For a track car, you need all corners working well. Having the rear be effective gives you that extra half car length or takes a little bit of load off the front.

With my stock Na6 brakes and race pads, I had no problems pushing past the limits of Advan A050 Softs with the front brakes, however I could never get the rears to lock up even with an open proportioning valve. So I needed to push bias back to get the rears more effective, either by changing the caliper to a larger surface area, or larger rotors. In my case, going to the larger front 11.75" rotors with Wilwood calipers and the much larger 11.44" rotor on the rear pushed that bias back. The first time I applied the brakes with the Wilwood setup and I felt the rear squirm I knew I had the balance much closer. I find in the wet I have to close the proportioning valve a little for stability, but in the dry I can open it up to max if I'm feeling keen and on the ball. You can see/hear in this video the back locking into the hairpin and squirming into the chicane.

The NB brakes I assume have the same issue as the NA6 just with larger rotors all ends. Mazda designed the cars for safety so the brake bias is always well to the front at stock settings. I think to really work the rear brakes you either need a larger rear rotor, a larger caliper or if you can, install a brake biasing bar with dual masters so you can actually get a decent balance rather than trial and error. If you can't get the rears close to lock up then you haven't got enough bias to the rear.

And for those that say that rears do nothing in an MX5, you are wrong. They can contribute nearly 50% of the braking force especially if you have rear aero. Also if the rears are working well you can run the same pads as the front since they are getting just as hot. If you run less rear pad, the rear doesn't brake as hard and doesn't get as hot... bit of a catch 22.

Rick

[Nevyn72]

NB2 -> Front = ventilated, Rear = Solid

Same for all MX5's from NA to ND.

Maybe a lot of cars have the rear rotor larger in dia. than fronts, but I've never owned one in 40 years. As far as I know, the NB2 is the only factory MX5 like this, & I am interested to know why.

Cheers

As I said, it was to do with what they could fit inside the factory 16" rims (NB2 went to a 16" rim compared to the 15" rims found on the NB1, a lot of 15" rims don't fit over the NB2 brakes)

They could get away with a smaller disc rotor on the front (required because of the larger caliper) because it is thicker and ventilated.

[Dweezle]

But the stock mx5 15" rims do fit over 8B Brakes.
So there must be other reasons mazda went with a larger rear Rotor?

Sent from my SM-N9005 using Tapatalk

[RS2000]

Thanks Magpie & madjak. Enjoyed the video too.
Plenty to think about there, & got me searching thru' posts on brake upgrades & proportioning valves.
Magpie - you say you use a NB8B PV, but many posts say the NB8B doesn't have one - due to abs & the computer control of proportioning ???

I presume the female/female socket shown in this kit
https://www.flyinmiata.com/complete-adj ... g-kit.html
is for joining the front pipes after removing the factory PV ?

Cheers