Track Rotor Temperatures

Magpie · Postby **Magpie** » Mon May 25, 2015 7:59 pm

At the MX5 Club Day today did some data collection on the temps of the rotors. Used Racetech Thermal Paint and Temp strips.

Green to white at 430c
Orange to Yellow at 560c
Red to white at 630c

The temp stickers are single use and will show a max temp above 204c

DSCN2631 by Eipeip, on Flickr

After the first session, the decision was made to sit out the next so that Jason could back the rear calipers off a bit... The rear calipers had just been rebuild after an issue.

Front Right. Winmax W5's, Trackspeed 1.5" ducts and temp was just getting to 430c.

DSCN2636 by Eipeip, on Flickr

Front left. Similar to Front right

DSCN2637 by Eipeip, on Flickr

Rear Left - In excess of 630c. This is outside the recommended temperature for Winmax W3's. The disc is also polished an no real pad material deposited onto the disc.

DSCN2638 by Eipeip, on Flickr

Right Rear - In excess of 560c with the red starting to lighten in colour.

DSCN2639 by Eipeip, on Flickr

The temp stickers did not show a temp above 204, however it was a bit dark to check them after the National run, so when the light gets better I will have a look.

Jason from Automotive Plus will be using the paint on their shop NB on the weekend so that we can get a baseline to see if the rear temps are normal.

What this does show is the rears are getting used which is a surprise to me because I think the rears do nothing. The higher temps at the rear will be because of the rears being a solid rotor and no ducting, however it is outside the range of the pads temp and they will possibly fail.

Once the baseline is known a plan will be made to address the rear brake temps. Options are limited as to be road registered a hand brake is required.

madjak · Postby **madjak** » Mon May 25, 2015 8:53 pm

Great info Magpie... I need to get some of that paint!

I know my rear rotors are working because I'm wearing them down quickly and if I dial my biasing to the back any further I get a rear wiggle under brakes. Also you can see the temp colouring the metal.

For reference my rears are the solid rotor 11.44" Wilwoods with stock NA6 caliper. My fronts also get hot as I have no ducting but they aren't wearing quite as quick because they are vented I think. Brake ducting is something I'll sort out next.

Magpie · Postby **Magpie** » Wed May 27, 2015 8:43 am

Thanks madjak. Will look into the data and see what the weight transfer is doing under braking. The rear temps are suprising as when you take weight transfer into account the rears should do less work. Using the info from a previous spin, it that there was 760kg of weight on the front or 27% more than normal, therefore the rear was 27% lighter, Therefore the rears are not working as hard as the fronts and the temps should not be so far apart. Yes the fronts are vented and have more mass so can better managed the heat. The rears are smaller in mass, not vented, different pad type but doing less work.

Even if I sort the brakes out the slowest part of the car is still the driver

The wear you are experiencing madjak could be because of the heat not use. Is there pad material being transfered to your rear discs? Photos of my rears show the lack of pad material transfer, the rotors had just been machined, brakes beded in according to Winmax procedure.

manga_blue · Postby **manga_blue** » Wed May 27, 2015 2:25 pm

I'm not sure what'svgoing on with yours but I'm getting about 1,000 laps out of a set of HP+ rears and I don't pussy around with the car. It's a standard NA8 brake setup except for DBA rotors front and chinese cheapies rear. A Willwood bias adjuster is kept screwed up so that the rears are just short of locking.

plohl · Postby **plohl** » Wed May 27, 2015 3:06 pm

Forgot to take the hand brake off? :lol:

Pretty interesting results mark.

Magpie · Postby **Magpie** » Wed May 27, 2015 3:58 pm

Plohl thought that, but when I put the paint on the rotors they rotated freely, plus Jason backed them off at the track after the first session. I'm not home till Thursday night so I will check how free the rear wheels are when I pick the car up from the airport. At the track I use wheel chocks not the handbrake.

manga_blue I agree with your post, some thing is not right and it is not as if I really push the car either.

Hellmun · Postby **Hellmun** » Wed May 27, 2015 9:16 pm

I used to lose 2 temp strips off the front and none on the rear. I'd routinely see post-session temps without cool-down of 500+ front but barely 280C rear. That was stock brakes, XP12's all around and 90kw aspirated. I bet the rears are dragging after use.

madjak · Postby **madjak** » Thu May 28, 2015 1:01 am

I was using DS3000 pads and in one season chewed them down to the backing plates. I also went through the front dba rotors. The car stopped brilliantly with the little na6 rotors but I think the heat destroyed them not wear. At night on the track you could see the rotors glowing.

I'd be interested to know if ducting would extend their life. Now I have much bigger rotors 11.75" and larger pad area braking has slightly improved but I also think temps are way cooler. I'm also now using DS1.11 pads which have a flat friction coef but is lower than the Ds3000. I must say these DS1.11 are brilliant for the events I'm doing. Have a look at their friction to temp curve. They work just as well cold as 600 deg.

I wonder if anyone over here has thermal paint as I'd be very interested to see what my rears are doing. They dont see the same cooling as the fronts and have way less metal volume. I wouldnt be suprised if they are getting hotter than the fronts.

Magpie · Postby **Magpie** » Thu May 28, 2015 7:33 am

Hellmun I'm thinking the same, that is they are dragging after the event. However when the rear was jacked up to back them off they were spinning freely and still very hot.

My understanding of the rear brake operation is that it self adjusts as the pads wear but needs the occasional manual adjustment. This may also cause drag on the rears, however the rear calipers were just rebuilt so there should be no issue with this.

Madjak you can always buy the paint http://www.racerindustries.com.au/afawc ... r-Kit.html

A good article on the rear brake http://fastcraft.biz/blog/wp-content/uploads/2014/01/Parking-brake-operation.pdf

If you don't want to read the article it finishes off with:

I'd like to take a minute to thank Lance for his valuable information re the parking brake. I had a problem with my parking brake and after reading over my Miata
shop manual many times, I could not resolve the problem.

Thanks to Lance and his informative piece on the proper operation of the E brake I was able to correct the problem. The key to the problem was releasing the parking brake cable fully to allow the actuating levers to fully release, and then, adjusting the allen screws in until the pads just touch and backing off 1/3 of a turn. The last step is to readjust the parking brake cable to the proper number of clicks and lastly verifying that the brakes do not drag when released. Thanks again Lance.

PS
Nowhere in the shop manual does it say anything about returning the levers to the fully released position before making the allen screw adjustments. Someone
had messed with this problem before me and apparently didn't realise that there were manual adjusters. I had one new caliper with no adustment made, or it was backed off fully because of the intermittent overclocking of the lever and the resulting brake drag on that wheel.

Magpie · Postby **Magpie** » Sun May 31, 2015 9:51 am

Well the problem could have been found, brake system not releasing all of its pressure.

In between Jason working on Danny's car the brake issue was again discussed and after a thought by Jason I decided to have a look at the data. It is only small but it is there. My pressure sensor only looks at system wide pressure not front rear pressures.

This was on the way to Jap Nats. Brake pressure is normally 209 (green), however it went up to 223 for no reason.

Brakes by Eipeip, on Flickr

This is from QR, again the brakes did not fully release. Down main straight, release, after turn 1 not fully, just before turn 2 released, after not, dipper hard brake, even more pressure left in the system, small touch for 4, but still pressure left, down the small straight into 6 hard brake and heaps left in the system. Time to go back through the previous data and see how long it has been there for.

Brakes QR by Eipeip, on Flickr

Well, had a look at the data from Eastern Creek. I had an issue with the logger and only got stuff from the first session. Issue now fixed by the way. Rear pads and calipers have been replaced/refurbished since Eastern Creek, but the issue is still the same, a retaining of pressure in the brake system

Brakes EC by Eipeip, on Flickr

manga_blue · Postby **manga_blue** » Sun May 31, 2015 12:54 pm

Typically a brake booster fault. Do you still have one? Otherwise it's occasionally a master cylinder fault.

Magpie · Postby **Magpie** » Sun May 31, 2015 1:45 pm

Yep still have the booster. It was Jason that suggested the master holding pressure hence the log check.

Going to Plus on Monday for a post track service, a few other things and the master.

Thanks for the feedback everybody, makes being part of the forum worth it.