Thread-in Vs. Press-in Studs
A recent discussion that has come up is the offering of "press-in" studs as a cure to broken studs. Some common facts and misconceptions about press-in studs.
- Alloy steel does not increase in yield or tensile strength when pressed in or threaded in. Although there are engineering improvements that can be made with a design, a M12 piece of hardware will have the same strength irregardless of configuration. If you want an improvement in strength, it has to be done in size. Increasing the diameter from M12 to M14 increases strength by 30%.
- There is no such thing as an unbreakable stud. Regardless if it is pressed in or threaded in, there is always a greater force that can and may be introduced that will exceed the limits of the strength. If you're only doing street driving or even HPDEs, you are usually in control of your environment. In wheel-to-wheel racing, this may not be the case. Sometimes you may get an unsuspecting car that runs into you, bumps your wheel, or just doesn't see you. Now what?
- Press-in studs are best for endurance racing. Oh, really? If this is the case, and you encounter a situation not within your control, and you do break one of those unbreakable press-in studs, now what? How long will it take to change a front hub? How long will it take to change a rear wheel bearing? Simply put, your car (and team) would be out of contention of the race. Our HEX design studs allows for the broken piece of stud to be removed quickly and efficiently without the need for drilling or extracting. This means minutes to make a simple change rather than hours.
- Potential flange damage/loose studs. The idea of a press-in stud is that the hole of the flange is to be precisely bored to allow for the stud to be accurately pressed into place. What happens when the stud is continually hit from the face (ie. with the back of the rim face), it can loosen from the flange. After that, the stud will no longer be securely "seated" and be prone to fall out. Once an unsecured stud is loose in the flange, then what? The head of the stud could be spot welded in place, however, it makes replacement just that much more difficult.
- There is no replacement for maintenance. A claim to press-in studs is that they do not have to be replaced. Our experience is that logging parts usage, regardless on how trivial the item may be, can eliminate potential failures when it is least expected. From harmonic engine balancers, spark plugs and coils, fuel injector service and to wheel studs, if they're expecting 100% performance of out all the parts on your car, make sure they're being properly maintained.
How To Make A Better Stud
After seeing many people break studs over the years, we were determined to look at the science of "why" this was happening. With input of many drivers, customers, racers, and dealers, we continued to develop the best (and safest) stud possible.
When vehicles start breaking studs, a lot of questions arise such as:
- How old are the studs?
- What material are the studs made from?
- When were they changed?
- How many track hours (if a track driven car) do the studs have?
- Are you using wheel spacers?
- What torque are you using for the nuts?
- When were you torquing them (hot or cold)?
- Are you using a torque wrench (when was it calibrated)?
- What wheels are being used?
Choosing the Material
Regular laboratory testing of the material alone (nothing to do with stud design) has shown that our PRO studs and MOTORSPORT studs exceeded Grade 12.9 yield strength by an average of 14.6% and tensile strength by 10.6%. What does all these numbers mean? This means one of the strongest studs money can buy. For reference, a factory BMW wheel bolt is a Grade 10.9 in strength.
Rogue Engineering stud strength vs. other grades of studs
Details in the Design
Material choice alone does not define the stud. As we started looking at obvious data, we then started looking at the design of specific studs and potential issues. Mechanical issues to address were a top priority.
Based on where the studs were breaking (near the hub face), it did not make sense why studs made from high quality material were sheering. After looking more carefully, there was an issue when impacting lug nuts onto studs, as they would actually drive the stud down into the hub MORE, because there was no defined "shoulder" to stop the stud from moving. The hub was actually cutting into the portion of the unthreaded stud, weakening the stud near the hub.
The Rogue Engineering MOTORSPORT stud has an very pronounced and defined shoulder (red arrow) for the stud to bank up to and terminate on the hub face. This defined shoulder ensures that the stud does not move when the wheel nuts are being driven on and torqued in place.
Another engineered specification on the new MOTORSPORT stud is a clearly defined undercut behind the shoulder (blue arrow). This very minute detail ensures that the stud's shoulder will absolutely bottom out on the hub face during the installation. Granted a small detail, but preventing the stud from moving after install is important to its strength.
Another detail is the unthreaded area (green arrow) portion of the stud. In actuality, this portion of the stud resides under the brake rotor hat and wheel pad, so no threads are actually required in this area. Not having threads reduces the risk of failure because of stress risers from unnecessary threads.
Patent-Pending machined HEX portion of the stud allows for easy installation and emergency removal.
HEX portion protrudes just enough from the flange to be accessible with hand tools.
Rogue Engineering MOTORSPORT Studs (standard) Technical Specifications
- For street, track or race cars
- Machined from Chromoly Alloy Steel, hardened and tempered to beyond Grade 12.9 class to DIN/ISO 898 (independent lab testing shows much higher strength)
- Max Torque Recommendation: Recommended torque on BMW applications maximum is 90 ft. lbs. (M12 size) or 105 ft. lbs. (M14 size) COLD torque. DO NOT HOT TORQUE WHEELS!
- New! Trivalent Chromium Black Zinc coating much more resistant to rust over previous finishes
- Bullet nose design allows for easier wheel installations
- Studs are available as M12 and M14 (1.5mm thread pitch) configurations.
Rogue Engineering MOTORSPORT HEX Studs Technical Specifications
- ONLY for trailered track/racecars WITHOUT rear ebrake assemblies. The protruding hex portion of the stud can interfere with the rear ebrake hardware.
- Machined from Chromoly Alloy Steel, hardened and tempered to beyond Grade 12.9 class to DIN/ISO 898 (independent lab testing shows much higher strength)
- Max Torque Recommendation: Recommended torque on BMW applications maximum is 90 ft. lbs. (M12 size) or 105 ft. lbs. (M14 size) COLD torque. DO NOT HOT TORQUE WHEELS!
- New! Trivalent Chromium Black Zinc coating much more resistant to rust over previous finishes
- Bullet nose design allows for easier wheel installations
- HEX back end (8mm for M12 studs and 10mm for M14 studs) prevents studs from being over torqued during installation. In the case of breakage, removal is extremely efficient without the need for drilling and using extractors.
- Studs are available as M12 and M14 (1.5mm thread pitch) configurations. F-Series not available.
How much torque is too much torque?
A common question we get is how often should studs last? Perhaps a better answer is the actual inspection of the stud itself. Although a stud may appear "fine", closer inspection may show otherwise.
Below is a picture of a new stud and a yielded stud with a thread pitch gauge, showing that a stud has clearly been over stretched beyond its yield point. It would be a matter of time before this yielded stud would break while being used.
Stud Service Life
When is the time to replace studs? Unfortunately, most decide to do it when it is too late, when they've already broken one or more studs. We have surveyed and asked many racers and drivers and it would be the consensus that approximately 10 hours of track use would be a safe interval for a stud change. Driving to the track event does not count as "interval time". If you attend the average HPDE, generally speaking, a driver will get 1.5 hours of track time. With this in mind, the studs should be changed after 7 track events. This also means NO nut torquing while in the "hot pits" as the actual temperature of the stud can increase by 30%. This is generally for M12 stud users. Our experience with M14 studs is much longer!
Fits the following vehicles:
- M12 x 1.5 will fit E36, E46, E39, E60, E63, E9X, E82, E88, E85, E89
- M14 x 1.5 will fit E53, E65 (and 3-series cars with our hub conversion kit)
- M14 x 1.25 fit F-series and G-series vehicles.
Installation Notes: We recommend the use of Loctite 262 on the base of the threads of the stud during installation. Installation of the studs into the hub only requires 15 ft. lbs. We find the "double-nut" method to be the best way to install these.
