I still stand by. Get some temp sensors. Do some testing. The thing to remember as well. As sometimes in heavy rain, more pressure can help shed more water. A mag will keep the higher pressure from over working.
The biggest reason I would run aluminum in rain. It tends to be chaos and the wheels are so much cheaper
I’m perplexed, as to the rational that the material’s heat retention capacity is why aluminum wheels work better than magnesium in cold conditions. The thermal transfer coefficient is higher for aluminum alloy (167 W/m^2K) than magnesium alloy (53W/m^2k). The higher the coefficient number the better the heat transfer, so it would seem that given every other parameter being the same between wheels the aluminum wheel would run cooler. Is there another reason why “aluminum wheels” perform better in cold weather or I’m all wet 
Could it be construction of the wheel?
As I said I found mag to work better. The peaks and valleys of the tire data showed for me. That I prefer mag in cold/rain. They maintained more heat on the straights. Where the aluminum lost almost all heat on straights
Aluminum wheels are softer as well.
Here’s an article from TKart discussing rim materials with Tony Kart’s R&D guy:
It’s basically universal that all major manufacturers use aluminum for wet. Take that for what it’s worth.
Honestly, some of the TKart stuff doesn’t seem to make sense to me. It might be the translation from Italian to English or the articles are written to simplify concepts.
It is interesting to note in the article that OTK claims that magnesium is a better conductor of heat, which is not the case (or at least that is what I understand).
Yes, one major reason for Aluminum in the wet is because it corrodes less than Mag. That alone should justify Al over Mag.
Think about where the tire heat is being generated and then think about where the heat paths are. I believe a more rational explanation might come through.
It seems that some of the information that comes out from the factory is BS or is not what the factory is saying or its’ being misinterpreted.
Signed,
Perplexed
I dont know much, but a couple things I have learned are:
Most of the time a racer doesn’t know WHY something works, just THAT it works. This might be one of those cases.
The theories in karting are rarely ever proven. Has anyone one back to back tested rain wheels? Probably. Was the test perfect? No. It would be almost impossible to accurately control the variables in a wet wheel test.
Lots of karting is monkey see monkey do. If the fast guy at your local track does it, usually half the field copies him. Same in the bigger picture. If OTK does it, then most other folks are gonna do it too.
I agree that this is the case with MANY things related to tuning a kart. Simply put, there are two ways to measure the effect and effectiveness of a given change:
) did the change produce?Beyond that, it’s not worth the time and effort to delve into the theory. Axles, wheels, seats, etc…all of these things have some level of voodoo associated with them. They DO make a difference, even if we don’t always know exactly why.
Or… (just playing Devil’s advocate here, so don’t yell at me) They may not actually make a difference to us and we pick the one that we are supposed to pick (the one someone told us to pick or the one the front guy runs) as to not be at a perceived disadvantage.
Definitely a lot of that going on as well! Personally I try and test/validate as much as I can, and I think the REALLY fast guys do the same.
Using correlation to solve karting problems is what most of us do, that includes me. Example is: If i put an H axle in my OTK then the kart will “free up” in grippy conditions.
I do believe that understanding the causation of a situation may lead to new concepts that could make the kart faster and may also help when track and kart circumstances can’t be solved using correlation.
I’m retired, so I’ve got some time to think “causation” and test, it keeps me busy. It’s all fun!
Not everyone is a engineer. You do not need to know how a phone works, just need to how to use it. Engineer create a lot of opinions and told you how to use it. Then you just need to figure out when and how to use it under correct conditions. Theory for sure will help you speed it the process, but not always required.
thanks for all the input. all in all, i’m trying to stack incremental gains, as this is the first year i really have the ability to focus on the mechanics of my kart, and actually test/practice. previous seasons, the kart stayed at the track, over an hour away, and it made maintenance and testing super inconvenient. if there is a benefit to the mags, however minimal, if i can add that gain to 3 or 4 other barely noticeable gains, i’ll get a NOTICEABLE gain. season is about to start, so i’ll find out fairly soon. thanks again.
I’ve tested them back to back… Test results were: I’m not good enough to make use of such a fine tune adjustment. 
Larry - I’m too far away from thermodynamics classes to feel confident, but here is a stab at answering your questions…
There are 4 types of heat transfer in this world (that I’m aware of anyway!) - conduction, convection, radiation, and phase change
When it comes to tires, I think everyone can agree that the primary source of getting a tire up to temperature while on-track is from the conduction at the high friction interface of tire/track (contact patch) as opposed to radiation (thanks sun), convection (tire is not a fluid or gas), or phase change (one would hope!)
As friction heats up the tire via contact patch friction, the tire heats up both the air inside the tire as well as the rim via conduction. We’ll leave out the convection going on inside the tire for simplicity.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. In the case of wheels, aluminum is higher than magnesium - so as the tire generates heat, an aluminum wheel will get hotter faster than a mag wheel
My head already hurts, but I’ll try this anyway - when an object is heated, it’s heat capacity determines how well it stores that heat. Aluminum has 2 things going for it vs. magnesium on this front - it has a higher heat capacity, and aluminum wheels weigh more and is a bigger “thermal mass”
So if we’re on a cold or wet track, the tire builds up heat very slowly because friction is a lot lower at contact patch. Thus, the air in the tire heats up slower and the wheel heats up slower. Aluminum helps, as it will both warm up faster and hold on to the heat better in these crappy conditions than magesium would. The “cool” part (hahaha - thermo dad joke) about this for us karters is that that aluminum wheel will also release its heat back into the tire better than magnesium… so in parts of the track where the tire isn’t generating much heat through friction (long straight), the aluminum wheel helps keep the tire itself hotter than a magnesium wheel would.
The inverse of this is why magnesium wheels are better on a hot day/track - they don’t build up or store heat well, so they stay cooler than an aluminum wheel. They don’t contribute to warming up the air inside the tire like an aluminum wheel does, enabling a higher starting pressure, which itself helps heat up the rubber faster.
There’s more to it all, but that’s the bulk of it. I think. Maybe.
Yeah, that. 
That’s how I understood it but my brain ain’t as gud so I don’t know all them fancy laws and rules of the dadgum universe.
That’s an explanation that my math-challenged-liberal-arts-masters-degree-brain can understand! Thanks! [hyphenate-all-the-things!]
Not to beat a dead horse but I took some time to research pertinent data for Aluminum and Magnesium as it relates to this discussion and found that that heat transfer characteristics are about the same for Al and Mg material.
Not sure of the exact alloy used for kart wheels so I assumed alloys. For the “Take Away” results, the assumption is the Al and Mg wheel geometry are the same, which is not the case.
The myth that Al retains heat better doesn’t seem quite right, as Al or Mg have about the same heat capacity and heat transfer capability. Al even has a 17% higher heat transfer capacity which should cool the tire more than Mg.
One could conclude from the data; That Al works in low grip conditions might be more due to the geometry/construction of the wheels and less about the material. So it’s a mystery to me. Maybe I made an error somewhere.
Interesting info from OFK.
I want to suggest that most of the heat dissipated from the tyre occurs by direct radiation/ convection from the tyre to the surrounding air which is scrubbing over the tyre surface.
The heat dissipated through the complex route of transfer to the rim and radiation from rim to atmosphere or conduction to chassis represents a small ( negligible??) proportion of the whole.
Do the rims get hot?. If so how hot?
Kart wheels are typically 6061 spun aluminum.
Spun aluminum wheels are only part of what’s out there. There are quite a few aluminum rims which are cast, basically anything aluminum from Europe is cast.
