Kart Wheels - An important part of kart setup

Let's talk about kart racing wheels! The kart wheel has gone from a two piece cast or even two piece nylon wheel (or so I'm told, I wasn't born when the Ny-Lite wheels were all the rage!) to a sophisticated machined aluminum or magnesium one piece wheel built for very specific classes and conditions. Wheels, which were once an afterthought on the kart, have become a very integral part of the kart's setup and handling.

So bottom line, why all the different types of wheels? It all comes down to stiffness. Some wheels are stiffer than others and this can be achieved through different materials, shapes or thickness. You can have two wheels of the same material that act completely different. A spun aluminum wheel that has been machined to a thin material will be softer and retain less heat than a cast aluminum wheel that is much thicker and stronger. The spun aluminum is great for low horsepower classes like Yamaha Sportsman and Rookie, the cast aluminum wheel is better for higher horsepower like the TaG class due to its stiffness. But one problem with the cast wheel is the thickness of the material tends to retain a lot of a heat. I have had the best luck using the cast aluminum wheels for rain tires and not for dry conditions.

Magnesium wheels have been around for decades but it's popularity has really sky rocketed with the introduction of the TaG classes. The magnesium wheels produce more grip because they are a strong (but brittle) material. Magnesium also sheds heat much better than aluminum, especially compared to the cast aluminum wheels. So in a sense you get the best of both worlds, a stiff wheel that doesn't retain heat which is perfect for classes with more horsepower and weight. Magnesium wheels increase side bite while not "binding" the kart up, especially over a long race.

There are different types of magnesium wheels as well. The "Low Volume" type wheels have a more filled out shape and take up more room inside the tire. More wheel, less air. The idea behind this is with less air volume you have less gas to expand as the tire heats up. This should translate into less heat and tire pressure gain over a run, meaning the kart should be more consistent. It's a great concept but like many things in racing if it translates to the stop watch is hard to say.

So why not run magnesium wheels in everything? In my experience the mag wheels are too stiff for the lower horsepower classes. If you are running a Cadet level class but something with decent horsepower like a Rotax Mini Max then the mag wheels can definitely help but for the Sportsman and Rookie Yamaha classes the mag wheels usually just have too much grip.

So what is a DSM wheel? DSM = Direct Spindle Mount, the bearings are pressed into the wheel and the need for a bolt in front wheel hub is not needed. DSM front wheels are available with 17mm and 5/8" wheel bearings. The DSM wheels are good for two reasons, they allow you to run the front of the kart very narrow since the hub doesn't stick out of the wheel and since a bolt in hub stiffens the wheel the DSM fronts are a pretty soft design. We typically run the spun aluminum DSM on the front of Yamaha Rookie and Sportsman karts for the two reasons mentioned.

Wheel Widths - Wheels are available in a variety of widths. Most of the time everyone in a given class runs pretty much the exact same widths. Spreading the tire out on a wider wheel will decrease the sidewall flex of the tire and remove grip from the tire since the sidewall can't roll over as easily. Running wider than average wheels is very common in 4 cycle classes and can benefit other classes with low horsepower that are looking for ways to free up a kart like the Yamaha Sportsman and Rookie.

Wheel Offsets - Some wheels are available in the exact same width but with different offsets, meaning the inside wheel half offset is either closer or further from the middle of the wheel (shallower or deeper wheel half). If the wheel is basically an even offset from the inside to the outside you have to slide the wheel hub further out on the axle to achieve the same track width as you would with a wheel that had a shallower inner offset. Since you had to slide the hub further out on the axle there is more axle exposed which effectively makes the axle softer. On most karts this can help free up the chassis since it's like running a softer axle.

This is how I would rate the different type of wheels -

Spun Aluminum - Softest, great for low horsepower classes like Kid Kart, Yamaha Sportsman and Rookie.

Cast Aluminum - Stiff, retains heat, great for very low grip conditions and rain. If you need tire temp this is a great option. Most popular rain tire option.

Magnesium - Stiff but due to material doesn't retain heat like aluminum wheels, great for high horsepower plus low and high grip conditions, can be too stiff for lower horsepower classes. Good for rain.

As with anything in racing, your mileage may vary. Chassis design, track conditions and class specifics can definitely make one wheel work better than another but this guide should help you better understand the how's and why's of wheels. I learn something new every time I go to the track, so test and tune, there's always more to find!

Mark Dismore Jr.

Thanks to Gary Lawson for his input