Desired Rotor Temp

I’ve been using tempeture paint on my rotors and strips on the calipers to motor the components temps on track. I’m running a 2011 STI that’s largely in street trim, but only sees track time. The front brakes are 355mm rotor with AP Racing 9660 calipers. I previously ran ducting that only went into the wheel well and am currently running duting that funnels air all the way to the hub/rotor.

Regardless of the ducting I always see my rotor temperatures max out the temperature paint at >800 C. However, my calipers didn’t reach a high enough temperature to register on the caliper strips until the most recent track day. This weekend I was running a time attack event in 92 F weather. The outter face of both front calipers registered 300-331 F temperature on the strips.

My questions is, are my rotor temperatures acceptable? Since I’m maxing out the range of the paint, I get the feeling I need to do more to cool the rotors, however I’m about out of options. I run Ferodo DS1.11 pads and they have held up fine with the one exception prior to providing ducting all the way to the hub. Currently planning on switching to a Hawk DT70 pad next to mitigate heat issues during extended abuse. I’m likely over braking on track, cause well, I’m an amateur and have lots of room for improvement. So I’ll also keep trying to be better.

Any insight or perspective you can offer would be helpful. I attached a couple pictures for reference.

I think you need information such as the chart found on this page:

https://www.brakepartsinc.com/raybestos-racing-performance/technical-information.html

It describes the coefficient of friction for different brake pads at different rotor temperatures. You can see that many of their compounds are just fine up to 1100degF (~600 degC). But this is all pad dependent.

Here is that info for the Hawk DTC-70 Pad:

https://www.hawkperformance.com/dtc-70

They claim operation with rotor temps from 400-1600f (200-871c), with optimal being 800f - 1200f (426 - 648c)

Thanks for the reply. I probably worded my question poorly. The fact that rotor temp paints max out at 800 C implies to me that I should be keeping my rotors under that temperature threshold on most occasions. Is it realistic to be able to keep rotors below 800 C during track use assuming they are sized appropriately for the car?

My experience so far seems to indicate no. I consistently have more heat in my rotors than 800 C and will just purchase pads that can handle those temps as you point out with the pad performance charts. I’m just looking for a sanity check to make sure I’m not missing something. Otherwise, since my calipers are staying cool, and the fluid isn’t even close to the boiling point, I’m fine as long as the pads don’t fade/can handle the heat.

I’m just an amateur hobbiest, so I really appreciate getting a second opinion from all of you with vastly more experience than me.

The photo' may be misleading, but to me it looks like it's just about transitioned from the Brown to Yellow Green, so circa 580-ish and right where it should be? This is more in the area of the range I would expect, unless you've a very well built engine on full slicks.

It would also seem to support the caliper temp's.

This is a site I use - https://wiki.seloc.org/a/Brake_pads#DS1.11 - there's a lot of info' there.

I agree with Gord, I don't think that you are getting as much heat into the rotors as you think that you are. This is where IR Temp sensors provide much better information as you will be able to see what the thermal curve is on the rotors in use and the average temperature that they are running at. I do not use or trust the temp paint anymore.

If you're going bigger on ducting, be careful not to over cool the rotors, and be sure you're only blowing cold air in the rotor hat, not on the friction surface.

When you're getting the friction surface hot, the last thing you want to do is blast cold air at it. This causes thermal shock and you can crack all the way through a rotor.

Applying cool air to the vanes via the rotor hat helps disperse the cool air in a more controlled fashion, and the temperature gradient is less extreme.

And I'd use pads better suited to your use and temperature, specifically DTC-80 rather than 70 in the front. The 80 pad has more consistent friction over a bigger range and they put up with high rotor temps better as well.

Thank you all for the input. It’s possible the rotors are not getting as hot as I think although I did drive flat out till the pads glazed and gave up on me during my last event at Palmer. That was without the new ducting though. Thanks for looking out for me on the ducting Mike. It took me a while but I managed to find a setup that funnels the air into the rotor hat and not onto the face of the rotor. Thanks for the tip on DTC-80.

I’ll be mindful of not over cooling. That’s something I’ve been keeping in mind, but don’t really know how to verify other than temp stripes, paint, and feel on the track. It’s 2.5” ducting and based on last weekends event I think I’m not overdoing on the cooling so far.