Brake rotor temperature right/left and front/rear comparison questions
 

Just did a brake upgrade (master cylinder brace, DOT 4 fluid, stainless lines, slotted/drilled rotors, better pads) and I'm trying to evaluate how good a job I did and how much tuning is still needed.

Comparing how long the wheels spin freely isn't a very exact measurement. But even that coarse comparison makes me suspicious the brakes aren't balanced.

I picked up an infrared temperature gun (http://a.co/cDGoHAw) to take measurements before/after my drives to see how the brakes are performing. This morning I started my spreadsheet and initial graphs. Woot!

Assumptions I'm making:

• Rotor temperature is meaningful metric to measure brake function.
• The left/right rotors should be the same temperature. As in front left == front right, rear left == rear right, and therefore average left == average right.

Brake Questions:

1. Do those assumptions make sense?
2. Should the front rotors should be hotter than the rear rotors? (I'm assuming yes)
3. As a percentage or absolute temperature difference how unbalanced is acceptable between the left/right?
4. As a percentage or absolute temperature difference how unbalanced is acceptable between the front/rear?
5. How else do you determine your brake changes are working as expected? (Beyond simply checking that the car stops)

Thanks,
paul

Really tough to use temperature as a gauge on how well brakes are working. The number of variables can be huge and I have never heard of using temperatures to judge effectiveness.


The front will of course always run hotter than the rear. Don't know that there is a formula for how much is ok.


Both fronts and both rears should be roughly the same on left and right but again I have never heard of any calculation on what difference is ok.


Be interesting to see if any experts (real ones, not Ubersuber) weigh in on this one.

I would like to add that the e-diff and electronic brake force distribution functions in these cars is capable of creating differences between left and right side. I was having a tough time diagnosing one rear set of pads wearing faster than the other side, until i learned that the car will actuate a rear brake to force power to the side with grip, and if you run the same course repeatedly, this can add up.

I guess I'm not really looking to judge effectiveness and performance as much as I am looking for evidence of an issue. My overall assumption is that a consistent right/left temperature imbalance is a problem. Not really that a balanced temperature is evidence of good performance. The front/rear question is more curiosity than anything.

I'm taking my measurements from daily driving not track runs. So computer controlled brake application shouldn't be a big variable or should balance out with A->B and B->A driving over a few days. This is to get ready for track days coming up.

I want something better than a spin test to see if I'm being overly perfectionist about it. It's kind of fun to jump out of my car and take measurements every time I drive. Even if the data is ultimately worthless I'm still going to collect it for a while and see what it shows.

If your car pulls to one direction under braking, then there's an issue. If not, you're fine. You just did fluid, pads, and rotors, not exactly a huge change. If the pedal is a little squishy, bleed it again; if not, you're fine. No need to overthink this.

What are you trying to test? Brakes change bite with temperature. Do you have a biasing valve? Are you worried about street, track day, or racing. Each requires different characteristics.
That said, hard repetitive braking at a track will tell you how well you have done. Getting up to temp on the street is not easy or smart.
You could, I suppose, do the peddle dance and see witch wheel locks up first. Not sure what you would learn.

I'm trying to figure out two things really:

One - This is the first time I've touched brakes. Without anyone more experienced to verify my work I'm looking for any signs that something could be wonky before it becomes a real issue. As far as driving goes she stops fine. Doesn't pull driving or braking. Nothing seems wrong from the driver's seat. But what do I know?

Two - When I spin the front wheels the passenger side seems to have some brake drag and doesn't spin as long as the driver side. But that's hard to tell for sure. So I'm trying to see if this has any impact. So far today that rotor has been around 12% hotter than the driver side each time. Not a crazy amount but enough to convince me to clean and re-lubricate the guide pins to see if the caliper wasn't moving as free as it should.

I just put her back together, the wheel spins freer now (I think...), tomorrow I'll see if that translates to a temperature difference. Which may or may not be a meaningful metric. Probably putting way too much thought into it. But until convinced otherwise I'd like my front rotors to have similar temperatures.

Our cars have EBD Electronic brake force distribution, The brakes are applied at different pressures where needed depending on load in the vehicle or while turning.. Temps will always vary per wheel. Trying to find a problem via temperature would be a waste of time. Drag will be slight on the rear wheel because of the integrated drum parking brake system we have. Drum brakes have a slight drag to brake effectively, a very light drag on the front is fine. They are floating calipers so the position of the caliper may end up in a different position causing a scratching rotor sound. This is normal.If you hear a slight clunk in the brakes all that is is the calipers centering themselves to brake evenly against the rotor.

[ame="https://www.youtube.com/watch?v=UpP6WYKrtS4"]https://www.youtube.com/watch?v=UpP6WYKrtS4[/ame]

That's cool. Now I know. And now I'm done.

Ok, I'm a liar. Still taking measurements...

Before redoing the guide pins yesterday the front passenger rotor was averaging 12% hotter. Today after the redo the front rotors have been at worst 4%, and usually 2% different. I just warmed the car up, found a straight empty street, and did a series of 40->10 mph slow downs. I managed to get the rotors pretty warm and the fronts were exactly the same temperature.

Obviously the computer assist matters. And they won't generally be equal temperature. But at some point a consistent temp variance seems like a problem. At least worth looking at. I eliminated a 10% averaging daily difference. I'm convinced my wheel spins freer now and that they're both related. Maybe I'm still a deluded simpleton but I'm a happy one.

Brakes are heat dissipating devices. They convert kinetic energy into heat and then dissipate that to the atmosphere. There are water cooled brakes but not on road cars.

Brakes work best at very high temperatures because heat rejection reaches a maximum at very high temperatures. Racing brakes are run as hot as the materials available will allow for this reason.

Maximum effective brake temperatures are limited by pad material. Unfortunately, nobody has yet invented a brake pad material that is optimal across a very wide range of operating temperatures. Racing brakes at the pinnacle of Motorsport are based on carbon technology. These are unsuitable for road cars.

Braking effectiveness is measured by stopping distances. If you are not reducing your stopping distances your brakes have not been improved. Stopping distances are limited by the grip developed by your tires. That in turn is affected by weight transfer which is why rear brakes are smaller and generally cannot be run as hot as front brakes. If you could run rear brakes as hot as front brakes then total brake performance would improve.

The better upgrade route begins with tires. If you can fully activate ABS on best grip available then your brakes are sufficient. Any increase in potential braking force above ABS actuation is a waste of money. Disc brakes don't fade. Brake pads fade if the operating temperatures achieved exceed the temperature range for which the pads were designed. The next upgrade after grippier tires should be harder pads. Be aware that harder pads do not reach proper operating temperatures on the street. Therefore, generally speaking you need two sets of pads if you experience brake pad fade under some conditions. High performance brake pads will generally produce longer stopping distances unless fully heated up. Obviously you don't want those for street driving.

You also want the smallest and lightest brake discs that will produce the brake forces you require to lock up the tires. Anything larger than that is counter productive. Larger brake discs are less useful than harder pads if you're looking for shorter stopping distances and heat is a problem. Brakes are 100% unsprung weight.

Carbon ceramic brakes are a complete boondoggle invented by marketing guys, unless all you do is drive at racing speeds on a track. They are also a real pita to drive daily.

Almost as much misinformation gets bandied about concerning brakes as oil changes.

The BRZ stock brakes are exceptionally good. Harder pads for track work is all you really need unless you are running slicks.

Epic contradiction is epic.

Gforce: i'd agree on many bits, but you messed one with smallest & lightest disks. You are forgetting heat capacity that smaller disks lack and which is main reason for racing purposes switching to _B_ig Brake Kits. Smaller works only as far as brakes are not overheated with driving specifics intended. Once one goes for longer sessions, once one goes to higher speeds due eg. forced induction installment, heat load put in or accumulated per time grows. No sense from having very slight performance increase from lighter rotational unsprung weight, if you lost your brakes after 15min when planning to go for half an hour. For rest of session car with nonoverheated heavier brakes will run circles around car with faded brakes with boiling fluid, even though later one will still have it's (i doubt that >1%) better acceleration, but for much shorter time to not accelerate to speeds one is unable to bleed to level needed to take turn without going off track & crash.
Either one goes for larger heat capacity of BBK, or enhances cooling (via eg. airducts), or both. Otherwise claim that smallest/lightest is best will work only on daily driving & dragracing.

1) Who are you responding to?? The OP didn't ask anything about any of what you just said.

2) The irony of you calling out misinformation in your post full of misinformation is great.

3) There's two types of fade; pad fade and boiled fluid but both are caused by lack of thermal capacity in the braking system. Rotors that can absorb more heat and/or shed it faster will prevent both types of fade without resorting to higher boiling point fluid or pads that can take more heat.

4) Not all higher performance pads have longer stopping distances when cold, all the aftermarket pads I've run (Ferodo DS2500, Project mU Club Racers, G-Loc R10) have better initial bite and power when cold than stock pads. Do they get better when they're up to temperature, absolutely, but they're still noticeably better than stock even on the very first stop. The real downside to most track pads when cold is they're harder on rotors until they're up to operating temp.

5) The smallest disc that can trigger ABS point only works if you only care about stopping once before pulling over and letting them cool down. You should probably look at how you can get more thermal capacity AND less weight with a good BBK though.

6) Define "wide range of operating temperatures"... my current pads (G-Loc R10) are rated from 47*C to 801*C. I'd say that a 750*C operating range is pretty wide. My previous pads had a very similar range as well.

7) I wouldn't suggest running higher heat capable pads without an equally heat capable fluid, you'll easily boil the stock fluid on a track with better pads.