Lug Nut Torque of 100 FT/LBS – Why? Because Racecar
Joking aside, I would like to share about proper wheel setup and lug nut torque for track days. I know it must seem trivial, but I have seen my share of accidents on the race track due to ignorance of basic safety measures. Don’t let that that happen to you!
I will admit I have had a wheel or two fly off during “spirited” driving sessions. It’s embarrassing to say the least and life threatening at the extreme end of the spectrum.
Most OEM wheel studs are designed to take torque specifications which meet the DOT safety standards for street use. In high performance applications our wheel studs and hubs share the burden of nearly ALL of the vehicles extreme gravitational forces (WAY beyond DOT guidelines).
80 ft./lbs. (give or take) is about standard for OEM lug nut torque specs. Usually, if a vehicle is heavier, or extreme stress is placed on the hubs, the specification might be higher. This is assuming that we are dealing with your run of the mill sport sedan, hatch or coupe. This is well below what I would consider “safe” in a track day situation. It is very common for drivers to torque to around 100 ft./lbs. on track days, and then re-torque after each heat/qualifier (20ft/lbs over OEM spec…give or take).
This scenario creates a whole new problem that is often overlooked: The stress of the additional torque on the OEM wheel studs (especially when combined with hard cornering).
Massive amounts of heat are transferred from the hubs and brakes into the wheels studs (physics 101). When a driver ends a heat/lap series and re-torques the lug nuts, the studs themselves are super-heated. This is a perfect recipe for failure. When the studs are subjected to this kind of stress, it is very common for them to begin to elongate (especially when subjected to the extra torquing sessions we talked about earlier). Eventually, the threads are beaten into a “soft state” and can no longer hold even OEM torque specs – much less race day torque specs.
End result? Well anyone who has been to enough amateur track days has seen some poor soul’s wheels fly off on a long straight or in a hard corner. It happens…it doesn’t have to.
I propose the following. Next to tires, a helmet and a proper safety harness for the driver, the single biggest safety feature you can add to your track day vehicle is a set of high quality, high-tensile wheel studs (and maybe a few driving classes).
ARP Long Wheel Studs
ARP extended wheel studs are rated to 200,000 PSI. Combine those with a decent set of open-ended lug nuts, and you may just save your car (and your neck).
The set pictured just happens to be for Subaru applications. Who would have guessed? They are tapered and extended to ease wheel removal/replacement and eliminate cross threading of the lugs (much like an NPT thread). This particular set can be had for around $150 (street price) and is enough to do all four corners of the car.
This is not, by any means, a review or advertisement for ARP fasteners, but they have an unparalleled reputation in the motorsports world. It’s hard to go wrong with these guys.
Install is usually pretty straightforward. Knock the old studs out and put the new ones in. In some cases however, the ABS sensor ring may need to be drilled, to accommodate the larger stud head. Another option is to grind some radius off the back of the stud head, but I recommend against this… unless you know what you are doing.
It’s highly recommended that you seat the new studs fully. I would also recommend that you do not use Locktite or any other thread locking agent on the stud backs until they are fully seated.
A good way to seat them is with a spare open-ended lug nut and a socket behind it. You basically apply torque against the hub to press in the stud splines.
…anyone who has been to enough amateur track days has seen some poor soul’s wheels fly off…
After they are seated, some attention needs to be taken to “break them in”. The studs themselves aren’t going to stretch (that is the point of these after all), but the splines might need a few re-torquing attempts to fully seat and settle. This can be done by simply torquing your lug nuts to around 100ft./lbs. with the wheels on the studs/hubs and going for a drive.
As standard practice dictates, drive the car for 50 to 100 miles, then re-torque the lugs. This will need to be done a few times until the studs fully seat.
It’s always a good idea to check torque and wear on the lug and stud threads. Another important thing to take note of… avoid using impact tools on your lug nuts! I know, this is commonplace in dealerships and tire shops, mostly because of speed and general ease of removal and installation.
For the life of me I can’t understand why this practice is acceptable. This goes double when you have aluminum or specially keyed lugs, ALWAYS remove and re-install with hand tools, using the most linear force possible.
When re-installing lugs always finger tighten in a star pattern to properly center the wheel (doing so with the vehicle weight off the wheels). Most decent wheels have hub-centric rings to aid in this as well (if not, invest a few dollars in a set). Once your wheel is centered use a high quality torque wrench to finish installation to proper spec (with vehicle weight on the wheels). Remember to always tighten with the torque wrench in a star pattern as well.
What about wheel spacers?
Another pet-peeve of mine is wheel spacers. These are often used with the false understanding that they will “widen” the track of the vehicle and improve handling. Nothing could be further from the truth. Spacers ruin alignment geometry and put massive, un-due stress on your hubs and wheel bearings (and create an improper roll center….double that on lowered cars). I could write a few pages on this subject to illustrate this point, but let’s take it for face value and say wheel spacers = bad… wider wheels with proper offset = good.
Before this simple article turns into a rant on this author’s personal opinions and gripes, let’s cut it short and save those discussions for the future.
I hope this information helps keep people safe. It is by no means a manifesto or gospel on the intricacies of linear and sheer forces on a motor vehicle’s drive-train, but it’s a great place to start.
All of us weekend warriors should gain an extra boost of confidence and safety by thinking these topics through and implementing some strategies to keep our tortured wheels on our cars. At the end of the day, it can’t hurt and could possibly save you a lot of pain and suffering (and embarrassment) on the track.
I have a list of OEM torque specs (lug nut torque chart), if anyone wants some further details. With decent lugs and studs you should be able to go 20 or more ft./lbs. over OEM specifications.
Please don’t hesitate to ask question and second opinions – That’s what the comments section is for. Plus, you can always contact me. The end result will be knowledge. Knowledge is power.
Keep it safe fellow drivers.