Concerns autocrossing powdercoated RPF1s?

I found a decent deal on a set of RPF1s that are wider and lighter than my current set. I plan to use them as my autocross wheel/tire setup, so sticky tires and some sudden force application should be expected. Seller says he was told they've been powder coated. No more info on the subject.

The internet says that powdercoating forged aluminum wheels is somewhere between the worst thing imaginable, and totally harmless depending on tons of factors. The RPF1s are manufactured with a fancy casting/forming process though. Anybody have concerns? Anybody done it? Am I asking for trouble autocrossing with (probably) powdercoated RPF1s?

It's a very questionable practice for sure, and the heat treatment stage of powder coating definitely has the capability to weaken the wheels (depending on temperature and time, which doesn't have much effect on the powder coating process but can make a big difference to the wheels). I'd look elsewhere.

So is the thought that baking on the powder coat ruins the heat treatment of the alloy?

I'm far from an expert, but I don't think the powder coating process is anywhere near the heat of the manufacturing process.

Someone with real metallurgical knowledge will be along shortly I'm sure

Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

HappyAndy wrote: I'm far from an expert, but I don't think the powder coating process is anywhere near the heat of the manufacturing process.

That's the thing, It Depends. It is possible to powder coat wheels with a heat treatment process that won't weaken the wheel in any way. But that's not how powder coating is always done, and you don't know how Some Dude did it.

Appleseed wrote: Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

I think it's because the wheel acts as a heatsink and mostly doesn't get anywhere near as hot as the friction surface of the rotor. It's true that the hub face probably does see extremely high sustained temps though.

Appleseed wrote: Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

So, I guess that leads to the question of how warm wheels actually get from braking? If a wheel is powdercoated at 400F-ish for 30 minutes, how does that compare to aggressive stopping where heat might be higher, but is probably more concentrated, and for less time?

You are starting with a wheel that has questionnable longevity in Auto-x to begin with. And from what I understand of their forming process, they use some plastic deformation to provide some strength. And there is a huge difference between exposing the wheel to some radiated heat from the brakes and cooking the entire wheel.

Personnaly, I wouldn't risk it.

STM317 wrote:

Appleseed wrote: Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

So, I guess that leads to the question of how warm wheels actually get from braking? If a wheel is powdercoated at 400F-ish for 30 minutes, how does that compare to aggressive stopping where heat might be higher, but is probably more concentrated, and for less time?

I've felt wheels get hot enough that bumping against them when checking lug nut torque was immediately painful. Probably in the 140* range. And this was on the street without super sticky tires.

fanfoy wrote: You are starting with a wheel that has questionnable longevity in Auto-x to begin with.

I understand there's not a ton of material there (hence the low weight), but this is the first I've heard about RPF1s having questionable longevity in auto-x. Any more info?

I think it'd be fine. Wheels are powdercoated from the factory. And while autocross is aggressive, wheels are subjected to higher loads on track days, or high speed interstate runs, or while hauling the entire clan 1,000 miles over potholed highways. Inspect your wheels regularly (a friend recently cracked his 949s) but I'd go ahead and use them.

**** And just out of curiosity, how hot do you think a wheel gets on a track day repeatedly stopping a 3,000 lb car so hard the rotors glow orange?

I'm seeing powdercoat cure temps around 400F. I'm seeing aluminum annealing temps around 650 or more depending on the alloy; https://www.tinmantech.com/education/articles/aluminum-alloys-annealing.php This concern seems overblown but I bet some smarty metal guy will weigh in soon.

I wish I could find a nice of RFP1's set for my SX4 but I don't want to pay that much for wheels for this car. I only do that when I own a junky Mustang, apparently...

rslifkin wrote:

STM317 wrote:

Appleseed wrote: Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

So, I guess that leads to the question of how warm wheels actually get from braking? If a wheel is powdercoated at 400F-ish for 30 minutes, how does that compare to aggressive stopping where heat might be higher, but is probably more concentrated, and for less time?

I've felt wheels get hot enough that bumping against them when checking lug nut torque was immediately painful. Probably in the 140* range. And this was on the street without super sticky tires.

Most powder coating processes are hot enough that bumping against a wheel that temperature would cause 1st or 2nd degree burns. The rotors are that hot, sure, but the temperature drops pretty quickly as you get away from them. 400F would make the grease in the bearings and the rubber in the ball joint boots burst into flames.

The fact that they're used wheels (which the present seller THINKS are powdercoated, suggesting they are 2x used) is a lot more relevant to a possible failure than the powder coating.

Somebody point out a wheel that has failed because of powder coating? (Not hitting stuff, including driving to/from an event?)

My totally uninformed GUT feeling about powdercoating weakening wheels is ROFL.

Talking about glowing rotors is like talking about aluminum heads facing the intense heat of combustion. Aluminum dissipates heat very quickly, and aluminum wheels have a very effective air cooling system via the spokes. HOWEVER, this is VERY different from baking a part in an oven where it has no ability for the material to shed that the heat.

The aluminum wheels are probably brought to the final temper at something like 325 or 350 degrees. If your powder coating temperature is too close to this, let alone in excees of, you risk 'over-aging' the aluminum. This can significantly reduce the strength and fatigue life of the part.

Note that many powder coatings are cured in the 300-425 degree range, although there are also powder coatings available which cure at 250 or less. For me personally, the long-term risk/reward equation doesn't favor thin spoke aluminum wheels that have been baked at an unknown temperature.

Alternatively, if you still wanted to take a look at them, you could try to see if you can discern whether they were actually powder coated or just painted. Powder coating should be more chip and scratch resistant. So if they look perfect still, it may (depending on prior usage) be an indication they were powder coated. However, if they have any chips, you may be able to look at the coating thickness and see if there are any signs of primer underneath. Powder coating is thicker and wouldn't typically have primer under it.

I'm trying to find the article, but a now defunct Import Tuning mag actually ran an article on a certain set of popular wheels that were failing fairly often due to powder coating. So yes, failures can happen when aluminum wheels are powder coated.

Only one way to know for certain, just do it and let us know how it goes.

GameboyRMH wrote:

Appleseed wrote: Blazing hot rotors from nuclear hot brakes baking the hub portion of the wheel don't seem to be a concern, why should powder coating at a much lower, uniform temperature be one?

I think it's because the wheel acts as a heatsink and mostly doesn't get anywhere near as hot as the friction surface of the rotor. It's true that the hub face probably does see extremely high sustained temps though.

I don't think the hub is getting that hot, as you'd be cooking the grease out of the bearings just as fast.

STM317 wrote:

fanfoy wrote: You are starting with a wheel that has questionnable longevity in Auto-x to begin with.

I understand there's not a ton of material there (hence the low weight), but this is the first I've heard about RPF1s having questionable longevity in auto-x. Any more info?

A few local guys have had RPF1s crack. To be fair, they are on high powered, AWD, slick/RE-71R shod Subaru's and Mitsu's.

YMMV

I've read the big deal is sandblasting to clean them before powdercoating by creating tons of little stress points vs powdercoating.

But who knows. Not me.

http://www.miataturbo.net/wheels-tires-78/sandblasted-6ul-failure-need-replacements-75325/page2/#post1059618

These are the go-to wheel for the group I race with (PRO3). High spring rates, offs, jumping FIA curbing, and heavy braking are the norm. Last race weekend I had to do one of those 10 minute front brake jobs. The rubber on the front calipers all turned to dust in my fingers, so I know it gets plenty hot. Last race was an hour long enduro, it was 102 out when it started. Just a data point for you.

Jcamper PRO3 #101

I don't auto-x it but I run a set of forged center Volks on my Mazda5 that I stripped the original anodized finish from and powdercoated two years and 64,000 miles ago. I have had them off checking brakes and for any damage and they are (or appear) fine. My guess is that the ones that have been damaged have seen some other catastrophic event that was forgotten or overlooked while it was easier to point to it being a sandblasted powdercoated forged wheel based on Internet lore.

I can speak to this issue on Kosei K1 racing. I powdered them after a sand blast and managed to bend or crack 5 of them over a 2 year period. Heat cycling alloys can be an issue.

I'd be leery of the heat effects of powder coating an aluminum wheel. Another consideration is that powder coating would make detecting cracks harder than a paint or anodized finish. I've powder coated aluminum, but nothing structural.

I recall a thread on an s2000 forum about stock wheels cracking after being powder coated. I think it was an autocross car too.