Heat reflective paint/coating

[billet]

Anyone have a recommendation on a product to reflect heat on the inside of a aluminum wheel? Something simple for testing purpose and if it helps will move to something more permanent that won't chip and need re-coated all the time

[j-c-c]

This is not answering your question, but what are you trying to achieve?
I attended a Ron Sutton Suspension workshop a few years back, and one of the vendors/sponsors was a wheel manufacturer. One of the pitches they made for their line of wheels was their stiffness, and since most of the seminar centered around chassis/suspension control/rigidity, wheel stiffness dovetailed right into the discussion. Another vendor was for aftermarket brakes. I asked the wheel vendor, if they had any data/research on the effect of brake/rotor temps on an alum wheel less then an inch away, and how the alum wheel distorted on cornering with increasing temps. They at first gave me that tilted dog head stare, and then said it wasn't a problem, but had nothing to support the claim. I also addressed reflective/thermal heat coating treatments on the inner wheel, but got little interest in that potential solution. Or was this a 6 year old asking where babies come from type of question for you?

[billet]

New braking system then we've used in the past. When the car comes in the wheels, hubs, even lug nuts are super hot compared to any car I've ever dealt with. Having some slight issue with RR tire wear from heat, not sure it's from the brakes but just looking at maybe coating the inside of the wheel to reflect the extra heat these new brakes create. Just thinking about trying before we switch back to the brakes we have used in the past. Brake manufacture said these brakes run around 200 degree's hotter, wasn't aware of that before hand, funny they left that part out.

Also the tech guy inspected the car before after the races on the scales and looked at the RR tire, then after all that happened and back in the pit. He came over to get a tire sample (checking for tire doping) and said the tire wasn't cooked no where near as bad as it was when it came off the track. Not sure I'm buying that, but everything is so hot compared to what we always saw in the past it just got me to thinking.

[emsvitil]

Is it heat radiating from the rotor?

or

heat conduction thru the hub?

Don't think it could be convection from the rotor to wheel.........


If it's conduction, I think you'd want some sort of black paint for black-body radiation; then air ducting to the inside.

Air ducting would also be good if it happens to be convection.

[MadBill]

The stiffness (Young's modulus) for metals diminishes with temperature, so an aluminum wheel will become more flexible (As well as weaker) as its temperature increases.
A 'few' illustrations: https://www.google.ca/search?q=Young%27 ... 20&bih=974

As far as transferring brake heat to tires, it happens big time; that's why Formula 1 cars come in after the formation lap with their brakes (sometimes literally) on fire: They're trying to get/keep heat in the tires.

Also, rotors get plenty hot enough (1,000° F. or more in at times) to radiate a ton of heat (it varies with the fourth power of the absolute temperature), so black, which absorbs far more than lighter colours, is the wrong way to go.

You should determine if the new brakes are running hotter because of poor cooling or because they are dissipating more energy.

I've seen brake failure induced by poorly vented wheels...

I have on occasion developed brake cooling packages by thermocoupling the rotor and dragging the brakes while applying heavy throttle to maintain a steady 60 MPH until the rotor reached 900° F., then letting off the brake and continuing at 60 MPH, timing the interval for the rotor temp to drop to 500°. Shorter is better of course.

[billet]

Is it heat radiating from the rotor?

or

heat conduction thru the hub?

Don't think it could be convection from the rotor to wheel.........


If it's conduction, I think you'd want some sort of black paint for black-body radiation; then air ducting to the inside.

Air ducting would also be good if it happens to be convection.

It's a dirt Late model so running air ducts is somewhat a problem as they will get smashed from mud, not impossible but issues to overcome to try that. I'm not sure, just in 20+ years dealing with these cars (several series championships) I've just never seen the wheels and even lug nuts be so hot you can't even grab them. Sort of grasping at stuff and throwing ideas around, was just wondering if anyone used a product that was decent and actually reflected some heat. Finding info or actual % of reflection isn't easy on google as most of it seems to be on roofing reflective heat products. Only thing that is different, besides it's a new design car is the brakes which is the new recommended brakes by the chassis manufacture. This is the second car that I noticed it on and both the same new car design, I'm sure the other guy has the same brakes also but waiting on a call back to verify that.

This guy in particular has never been really hard on brakes as compared to some drivers I've dealt with over the years and some were brutal on them and even then I didn't see the heat in the wheels this guy is seeing.

Thanks for the replies so far.

[ijames]

I can't suggest any paints but some googling says that polished aluminum has a reflectivity of 85-90% in the visible and near infrared, so maybe just polish the wheels and make sure they are clean at the start of the night. Anodizing roughens the surface and cuts the reflectivity to maybe 50% as a starting guess.

[ProPower engines]

We send our sprint car front wheels to get coated with a coating similar to what is used on pistons to reflect heat back into the chamber.
It is like the coating the cup guys use on steel wheels to help keep the heat out of the bead area.
Depending on how many wheels you want to do will play a big factor on cost but the deal I got was $175 per wheel to coat the inside.
When your brakes are glowing red it does help keep the heat out of the tire
we run 10"' wheels with a 5" and 6"back space with 12" rotors so the heated brake components are well inside the wheel.

[Roundybout]

Do the rotors have directional venting vanes by chance? Possibly the direction the rotors turn have an influence on proper venting of heat. Are they undersized compared to the previous brakes? Driver complain of fade or anything? Things shouldn't be that hot as you describe short of a martinsville race.

[ProPower engines]

Yup 3/8 and 4/10 mile paved tracks.They get hotter then you may think with no place to vent them and cooling ducts get in the way of the tires between the body and chassis.

[MadBill]

I expect you re-balanced the brake proportioning after the upgrade? If not, the rears might not be doing their share.

[ProPower engines]

We run a single rotor and caliper in the rear. It has lots of cooling to it as it is in the open.
Yes the brake balance changes some what but the pads and rotors are replaced after about 4-5 race nights.
Performance friction Carbon metallic pads are used and their most aggressive pads are used on cast iron rotors up front while a 3/8" steel rotor is used in the rear. With the different coefficient's between the rotors it is challenging to find the right pad combo to get the balance right but the pads are much smaller in physical size then a street car would use but we only wear the pads till the heat line in the pad material for the best braking is then replaced some times before depending on the track run at

[Caprimaniac]

As Madbill said, check balance. As hotter at the rear, id suspect more of the car stopping happening here with new setup.

Is disc bolted berween wheel and hub? In that case i suspect most of the heat goes that route. Maybe a heat spacer? I currently run a floater afle, and rhe discs are mounted about 5'' away from wheel. Wheel still get hot after 5-10 laps on asphalt, curvy track- lots of hrd braking.

Radiatoon heat could be stoed by a heat shield between caliper and wheel?

[j-c-c]

"not sure it's from the brakes but just looking at maybe coating the inside of the wheel to reflect the extra heat these new brakes create. "
If balance stays the same, new brakes cannot create an extra 200F out of thin air without the tire offering equivalent more traction for that increase in braking temp. Additionally, the rotor is your primary source of radiant heat, the caliper is secondary. And Is pure nitrogen in use here?

[MadBill]

"not sure it's from the brakes but just looking at maybe coating the inside of the wheel to reflect the extra heat these new brakes create. "
If balance stays the same, new brakes cannot create an extra 200F out of thin air without the tire offering equivalent more traction for that increase in braking temp. Additionally, the rotor is your primary source of radiant heat, the caliper is secondary. And Is pure nitrogen in use here?

Well, actually they could. If for example the new rotors had less mass and/or poorer cooling vanes, the same energy input would drive higher temps.