Why run aluminum over magnesium rims with rain tires?

[Michael Taksa]

Please enlighten me. Does it have to do with heat dissipation?
Thank You.

[scot smith]

Corrosion i think.

[Derek Hastings]

For us budget racers, it may be a cost thing. I got a used set of aluminum rims cheap in order to keep my rain tires mounted and ready to go all the time.

[Michael Taksa]

Ok, I knew about those two points, but I now have a magnesium set that is pretty much corroded and my rains are mounted on it. So mainly I was asking this question to know if I now need to buy another aluminum set for rains or just run the mag wheels already have.

[Jim Howe]

I was under the impression that aluminum wheels got hotter quicker under racing conditions as opposed to the magnesium wheels, which took longer to absor the heat.

Under dry conditions, you want the mag wheels as they take longer to absorb and store the heat generated by the grip of the tires. This allows you to keep the chassis freer at first although eventually even mag wheels store the heat and you get too much grip.

In the wet, you want as much grip as possible since the moisture cools the tires off. Thus, it is better to run the aluminum wheels which retain the heat more at first and allow the tires to stay "grippier" (if that is a real word).

Now, maybe an engineer out there can tell us the real reason but that is how it was explained to me.

[Michael Taksa]

OK, so if it is heat dissipation, how much difference there is? I know you can't meaure it, but is it really noticable?

[Justin Martin]

Now I am no engineer, and Jim seems to make some valid points....

However I really doubt it has anything to do with heat dissipation...

quite frankly I am not sure Aluminum vs Mag would feel much different at all due to "heat" in the wheels. Now I do believe the different materials may naturally give a different feel, however the 140-200 degrees I dont believe would be enough to greatly change any characteristics. Now keep in mind, I highly doubt the rims get that hot, keep in mind the tires get up to those temps, the air would be slightly lower than the tire, and the rim even more so, due to their resistance in the change of heat.

Therefore truthfully, I think that most people run aluminum wheels on rain tires as they are much cheaper, for a set you rarely use. The second big reason I would imagine is the abuse, in the rain there is usually many more "off track" and rubbing going on with other karts, of course due to slippery conditions. This being said, aluminum wheels are cheaper

[Nathan Adair]

There's a number of factors that differentiate aluminum vs. magnesium wheels. Cost, weight, heat management, elasticity (flex), and corrosion are the main points.

Cost: Aluminum is generally cheaper than magnesium. As said before, why spend a lot on a set of wheels that you might only use a couple of times a season if at all. This is likely the biggest determining factor for 95% of karters when it comes to rain wheel choice.

Weight: Magnesium is about two-thirds the weight of aluminum. In the rain, there is less to be gained from light weight wheels than in the dry.

Heat management: The magnesium has a lower specific heat which allows it to absorb energy (heat) easier. This allows the wheel to act as a heat sink to keep from cooking tires in dry conditions. Think of the wheel as a thermostat/radiator for your tires. The aluminum wheels don't absorb the heat out of the tire as easily which helps keep the temperature in the tire which is needed in the wet. Side note: besides minimizing the pressure gain through reduced volume, low volume wheels have greater surface area which enhances the cooling effect.

Elasticity: Aluminum is almost twice as stiff as magnesium which creates more grip.

Corrosion: Magnesium is more reactive than aluminum, therefore it corrodes easier.

Keep in mind these are generalizations and it's hard to site specifics without looking at specific alloys.

[Chris Livengood]

The main problem with any of this is that I haven't seen a true set of mags on a kart in years. Birel made a set maybe 12 years ago that were notorious for burning, since then they have all been alloys. Out of curiosity I have tried to burn more than one busted up wheel and I couldn't get a decent magnesium fire going with any brand of semi-modern mag wheel. I used more than ample heat.

Also, there is a lot of shaky science going on around here.
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[Justin Martin]

+1. a pure magnesium wheel is very hard to ignite.... However some small shavings/chips will get her going good!

Trust me, Ive set an Airline wheel on fire... 30 pounds of pure magnesium!

[Adrian Baran]

[Jimmy McNeil]

[Britt Robinson]

[quote="Jimmy McNeil"]

[Dan Haynes]

I used to work at a steel mill that disposed of magnesium. We have to dump it in the loader bucket and hoe it onto the feed belt very slowly, into the Rotary Hearth Furnace. The RHF operator was always yelling to slow down cause the temps were spiking. We had to be very careful to clean the bucket completely. There were more than a few instances where pieces were missed and later garbage would be taken to the dumpster and these pieces would get wet from other material in the bucket or from rain. A few times the fire department was called in and they would get their water hoses out . We would eventually just flip the dumpster over to smother it. But the most effective way was to bury it with dirt or dust.
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