Rim type characteristics and rear rim sizes

#1

Hey everyone, wondering if someone can school me some different use cases for rims and around the rear rim size usage. look for “rule of thumb” type stuff.

  • When to use aluminum rims?
  • When to use Magnesium rims?
  • Why use 180mm over 210mm rims (and vice versa)?
  • Why stretch smaller tires on 210mm rims? does this improve/change any characteristics of the kart/tire?

From speaking to some people this is what I’ve gathered, they general recommend running magnesium because it maintains heat better and you should use them 99% of the time, alternative being when it rains you switch to aluminum, but no real reason why. unsure about why people sometimes use smaller (control tires) on 210mm rims, some say larger contact patch, some say it gives you more turn-in bit…

Anyways looking to hear from the experts on these topics.

#2

I can answer why switch to aluminum when it rains, magnesium is FAR more susceptible to corrosion than Aluminum, and it hates water. Keep em dry.

#3

The other reason, I think, is that aluminum transmits heat pretty darn well. It’s sometimes used instead of copper for heat sinks. Anyways, when its really raining cats and dogs, aluminum rims heat up the tire very well.

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#4

Lots of good wheel discussion here: Are MXC wheels worth the money?

Otherwise, as Dom said, aluminum wheels will heat the tire up more and are cheaper to replace in the event of damage, so they are the preferred material for rain conditions.

All other dry conditions, magnesium wheels are likely to be a better choice. Wider or narrower wheels with the same width tire will change the amount of sidewall flex in the tire during cornering. This can be positive or negative depending on what you’re trying to achieve.

#5

@tjkoyen

What typically would you see when stretching the sidewalls? I’ve been looking for side bit from the rear.

#6

Stretching the sidewall is going to reduce the tire flex, lowering the limit before the tire starts to slip. I’ve found it to reduce sidebite and allow the rear to slide a little bit more. I haven’t stretched any tire like that for probably 15 years. Seems to be a valid tuning option for some chassis, more of the American-made 206 chassis specifically.

If you’re looking for sidebite, narrowing the rear, raising the seat, or raising the rear ride height can all help.

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#8

Hi George.

When it is very cold or in the rain. As the others have said, helps the tire heat up more quickly.

Most normal racing conditions. Please note there are different types of magnesium wheels with a lot of different variables – spoke v. solid, different offsets to name a few. These will have a big impact on the handling characteristics of your kart.

If you are 206 racing, you can use aluminum to the point in which you need to free the kart because of rubber build up and track temp. I have never 206 raced so this is my assumption based on what I know about 2 cycle racing.

I assume by this question that you are 206 racing. Use 210mm to free the kart. If you are looking for side bit stay with 180mm wheels. TJ rationale explains it.

Here is an explanation I put together called Kart Wheels Explained on some of the different wheel designs, coatings, and construction methods used and the impact they have on performance.

In the interest of full disclosure, I am the east coast importer for AMV wheels. I try to be objective in this overview. It was compiled from all the information that I have received from AMV SpA.

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#9

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I dont have experience with stretching tyres but do have some positive results from running aluminum front wheels with my shifter kart. During dry summer days at about +20´C.

When got into shifter karting I had tyre temps somewhere at 45´C at front and rears were running 90-100´C. For my lack for experience didnt find enough ways to adjust the kart so the temps would be even on four corners. One solution that worked was fitting these aluminum front wheels - they brought up temps 10 to 15´C . Didnt feel any stiffness differences. Grip just got better as tyre heated more and didnt cold rip to pieces

Bright alu wheel Righetti Ridolfi

Black mag wheel made by Douglas

Alu wheel felt really heavy so compared it to mag wheel on scale. Results : 504gr vs 381gr

I dont know how wheel weight affects go karts handling

One curiosity from Drag Racing world is that wheel weight didnt have any affect on quarter mile times. Confirmed that fact several times when I was in the sport. Nor running 17" or 18" wheels. Diameter difference between the tyres was about 40 - 50mm. Time and top speed were always the same. My 18" wheels were twice the weight of 17" - sure felt like that

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#10

What was confusing me (and still is a bit) is around stretching tyres on rims and the availability (at least from OTK) on only 210mm mag rims. if your using a 7.1(180mm) tyre, wouldnt that be consider streching on a 210mm rim? or is stretching generally the 6-6.5in tyre being put on a 210rim?

#11

Stretching would usually be putting a 6.0 inch tire on a 210mm rim. I wouldn’t put a 7.1 inch tire on a 180mm rim, as the 180mm are generally for 6.0 inch tires that you would use in 206 and rain tires. I am surprised that its that difficult to find 180mm rims, as they are usually not hard to find, but I don’t drive an OTK.