[Got f1?]

Have an opportunity to get some titanium studs at a great price. Several people have mentioned galvanic corrosion and general brittleness (my word not theirs) makes them not ideal.

Anyone have first hand experience with titanium studs? How has the longevity been? Any issues?

[doughboy]

I've got PSD Ti stud kit, had it for 3 years.

Titanium is regarded highly for its outstanding corrosion resistance and very high strength / weight ratio.

Steel is more brittle (ie stretches less before breaking) than titanium.

It is softer than steel, so don't use impact tools and use a light graphite lube on the threads.

[RbBugBitMe]

I do not like them, I think they're very misunderstood and that is due to a lack of online information as well as a lack of belief in those that experienced failures were actually following OEM wheel installation directions. I don't doubt anyone that hasn't had issues for years but you're getting away with it while operating within a smaller margin than you'd like if you really knew.

There are a couple issues for me. By switching to titanium, you're changing the spring couple in the joint and I don't believe for the better. You're also changing the friction coefficient the joint was designed to to an unknown value then adding graphite lube further changes the friction in the direction of higher than intended clamp load. This is risky business for a few grams and some bling.

1) Titanium is not considered brittle but it does behave like brittle material and it is subject to oxygen embrittlement which was only really figured out in 2019. A single oxygen atom embedded in between layers of Ti atoms will destroy all the fancy quoted material properties. This alone is reason enough for me to stay away. I don't know enough about this but I think aerospace gets away with it by throwing money at processes to protect against this as well as way more thorough inspections and maintenance than the average motor head.

2) By reducing the bolt stiffness by 45-50% switching to Ti from steel, your joint stiffness is reduced too much. This means it takes less external load to separate your joint. When the joint separates, 100% of the load goes into the bolt and it will likely fail and for lug bolts/studs that would likely be in shear as I have seen a few pics of. If there was a torque to angle spec for the steel bolts (I know there isn't) then it would be way way off for the titanium and no one in the aftermarket would know what to do because OEMs don't sell cars with Ti wheel bolts, I think for good reason.

3) Reducing friction with graphite lube will increase the resultant clamp load for the same torque spec. This is good for countering #2 but also pushes the bolt/stud closer to yield just at installation torque. Perfect (no oxygen atoms, see #1) Grade 5 Titanium is still weaker or slightly stronger depending on what website you look at than a Class 10.9 bolt of the same geometry that you're replacing. That's like increasing the torque on your dry OEM bolts 20+%, would you do that cause the effect is the same?

4) Being less stiff than steel, there will be more relaxation that occurs after torqueing to spec compared to steel due to the twisting that occurs over the length of the stud. This is why even BMW recommends retorquing everything after you're done. This is less of a problem with a stud than a bolt of any material, you should always torque the nut and hold the stud/bolt steady to limit thread wind up that quickly relaxes and reduces clamp load.

5) Galling sucks. Mechanics suck. Everyone makes mistakes. Too risky. If you could safely dry torque everything like the steel bolts then it would be a much better trade assuming issue #1 is avoided. I did read that $1500 Mclaren MSO titanium bolts are dry threaded though.

I think there is a place for Ti bolts/studs in properly designed joints but not as a direct swap for a dry 10.9 steel bolt.

Final data point on steel vs Ti stretch... This is a force-displacement graph of identical bolts taken all the way to failure. A286 is a fairly commonly used high performance bolt material. The study is called Ductility and Use of Titanium Alloy and Stainless Steel Aerospace Fasteners.

• A286 yield is lower but safely stretches waaaay more than Ti up to nearly identical loads. This is what a curve looks like for a bolt an engineer would be very comfortable spec'ing torque to yield (TTY) for a higher clamp load than the Ti bolt.
• The margin shown on this graph between Ti yield and ultimate failure is why you'll never see a mass produced OEM wheel lug bolt/stud.

[doughboy]

Mine are PSDesigns Grade 5 Titanium Ti6Al4V, does that grade mean much?

That all makes sense to me, sounds like you know what you're talking about in this area?

I hadn't really heard about failures, they were a late night online purchase a few years ago.

Also, I was a little concerned about lubricating threads (as per instructions) as I know that increases clamp force/load for a given torque, but it only used it very sparingly on the threads to prevent galling.

The taper seat is still dry of course and that seems to grab quickly, the degrees turned from seat contact to 120nm click are very similar between OE steel and the Ti studs so I was happy that seemed ok.

But it's a pain to tell shops not to use impact tools.

[RbBugBitMe]

Grade 5 is the most common alloyed Ti.