03/01/2022
𝐇𝐮𝐛𝐬, 𝐒𝐭𝐮𝐝𝐬, & 𝐈𝐦𝐩𝐚𝐜𝐭 𝐖𝐫𝐞𝐧𝐜𝐡𝐞𝐬
𝘞𝘦'𝘷𝘦 𝘤𝘰𝘷𝘦𝘳𝘦𝘥 𝘵𝘩𝘪𝘴 𝘪𝘯 𝘵𝘩𝘦 𝘱𝘢𝘴𝘵, 𝘣𝘶𝘵 𝘐 𝘵𝘩𝘰𝘶𝘨𝘩𝘵 𝘪𝘵 𝘸𝘢𝘴 𝘦𝘹𝘵𝘳𝘦𝘮𝘦𝘭𝘺 𝘪𝘮𝘱𝘰𝘳𝘵𝘢𝘯𝘵 𝘵𝘰 𝘨𝘰 𝘰𝘷𝘦𝘳 𝘪𝘵 𝘢𝘨𝘢𝘪𝘯.
Over the years, the tendency in the pits has evolved from using hand held ratchets to high powered battery operated impact guns for tightening wheels. For obvious reasons, the battery operated impact gun has become the choice for most teams. The speed and ease of an impact gun allows for quicker changing of tires in the pits.
Like most things in life, battery operated impact guns come in a variety of sizes and are available in different speeds, voltages, sizes, and price ranges. As with most power tools: the higher the voltage, the stronger the tool. For example, a 10 volt impact gun will not supply as much torque as a 12 or 14 volt. But, bigger may not always be better for our specific application.
99.9% of domestic racing karts use ¼-28 wheel fasteners. Some have different configurations and mounting designs, but nearly all use a ¼-28 fastener. We did some quick research on the recommended maximum torque specifications for various ¼" fasteners. The highest torque spec that we could find for this fastener was 12 ft-lbs or 144 in-lbs. Then, we also did some research on the torque output for three of the battery operated impact guns commonly used by karters. See the chart below:
𝐈𝐦𝐩𝐚𝐜𝐭 𝐁𝐫𝐚𝐧𝐝-----𝐓𝐲𝐩𝐞-----𝐢𝐧-𝐥𝐛𝐬 𝐨𝐟 𝐓𝐨𝐫𝐪𝐮𝐞
𝘙𝘦𝘤𝘰𝘮𝘮𝘦𝘯𝘥𝘦𝘥 𝘞𝘩𝘦𝘦𝘭 𝘚𝘵𝘶𝘥 𝘛𝘰𝘳𝘲𝘶𝘦-----144
Bosch-----10.8V-----800 (555% overkill)
Makita-----12V-----1,110 (770% overkill)
Dewalt-----12V-----1,150 (798% overkill)
That makes it pretty clear. These impact guns are 500-800% over-powered for the application. This is why racers commonly deform hubs, strip nuts and break studs. A fastener rated for 144 in-lbs will simply not hold up to 800+ in-lbs!
Another component that compounds this problem is aftermarket “big” ¼-28 nuts which use ½” sockets. We’ve discovered that the thread pitch of these aftermarket nuts is slightly off; which requires excessive over-torqueing on the studs to tighten the nuts properly. We recommend using common ¼-28 nuts with a smooth fl**ge (PN 1115152).
The secret to tightening your lug nuts properly is control. A quick zip that allows the hammer to hit for just a split second on each nut is enough to secure the wheel. A good rule of thumb when tightening your wheels is to start each nut by hand, then tighten the nut by using the impact (to avoid cross-threading). The ratchet hammer should hit 6 to 10 times, no more. Do this one time for each wheel nut and stop. Don't keep going over the pattern again and again. If you're unsure about it the first time, get a socket and ratchet out and check it. Once you get used to it, it will become second nature, and you will never have a hub and/or stud problem.
