ATSR

Hey everyone,

A few weeks ago at a track day my titanium lug bolts came loose after running just 33 miles at the track. Towards the end of the warm-up lap for the third session, I started hearing a thumping noise coming from one of the rear tires, and my initial though was that a tire had developed some type of bump due to the high temperatures. I slowed to a crawl and went into the pits.

I started looking for any visible problems with either one of the rear tires or suspension, but I couldn't see anything. So I asked someone to look around the tires as I drove VERY slowly to see if he could find something wrong. As I started moving I was also looking carefully with my head poking out of the car looking at the left rear tire. As soon as the tire went around once, I could see it wobble a bit. A stopped immediately and checked the lug bolts just in case, and to my absolute shock, I could remove ANY of them with my fingers!! I then checked the right rear tire and found the exact same thing. Of course the next step was to check the front ones, and to a lesser shock at this point, they were also loose. The front ones where not as loose as the rear ones, however they are longer since I have 5mm spacers at the front.

Some background:

I installed the titanium bolts from World Motorsports in November of last year when I got my new wheels, and I have them checked regularly for torque since one of the Porsche techs at my dealership mentioned "they look awesome but make sure to check them periodically since titanium lug bolts tend to come loose over time". I honestly didn't believe him 100% since I never heard of this while researching to buy the bolts, but I still had them checked and re-torqued if necessary to the factory spec of 96 ft/lbs every time the car went in for any service or warranty work (3 times since November). Every time the lug bolts where checked, they were perfectly fine. I also purchased a torque wrench to do periodic checks on my own.

Two days before the track day, I had my brake fluid flushed and replaced with Motul RBF600 at my Indy, and I was standing right next to the tech as he torqued each one of the bolts to 96 ft/lbs. Due to the fact that I was going to the track, I made sure that this was done correctly. My Indy is 70 miles away from my home and the track is 30 miles away. I also drove the car for approx. 50 miles between coming back from my Indy and going to the track.

Another important thing to mention (I believe), is that I was pushing the car quite strongly during the track day, and thanks to the Motul brake fluid, I could keep going for longer stints. At the end of each session, you could literally see the heat coming from the brakes/wheels.

The track day was a bit over 3 weeks ago, and I've checked the torque on the bolts 3 times since then. The first time was 1 day after the track day, the second time was 1 week after, and then third time was 2 weeks after that. All the bolts where perfectly tight during each one of my checks. During these three weeks I've put a few hundred miles on the car, including a 140 mile round trip at highway speeds.

My non-engineer mind tells me that the reason why this happened is due to the thermal coefficient of expansion of titanium (bolts) vs steel (hub). Here's a good thread about the expansion of different metals: http://www.ferrarichat.com/forum/tec...us-metals.html

My guess is that the holes in the hub expanded more than the bolts due to the very high temps achieved during the track day, causing the bolts to loosen up.

Does my theory make sense? Has anyone else experienced this? Are there any other possible causes for this to happen?

Thanks in advance for your insight with this troubling issue that could've had a very tragic ending.

jhbrennan

Porsche changed the spec sometime between 2011 and 2012 - maybe try the higher number?? Did you use anti-seize? Also, you say you watched the tech - are you sure his wrench is calibrated properly and that he used ft/lbs and not Nm? Is your wrench calibrated? Lots of variables - hope it gets sorted.


Optional on older cars.
From the service manual (2012 version)...
Silver wheel bolts (up to model year 2011) = 96 ftlb. or 118 ftlb. also permitted retroactively.
Silver wheel bolts (as of model year 2012) = 118 ftlb.)
Black wheel bolts = 118 ftlb.
Center Lock wheels - 444 ftlb. (that's right four-hundred-forty-four foot pounds.)

snethss

Torque them yourself.

Devil Boy

As the safety chair for our region, this is why we check lug torque on all the cars coming through tech each HPDE track day.

alexisthemovie

You should always check lug bolt torque before every session. I use aluminum Rays lug nuts on my track car - this expands from heat at a much higher rate compared to titanium or steel.

ATSR

Thanks for all your replies!

So it seems that the culprit could be an out of calibration torque wrench from my Indy instead of the rate of expansion of titanium vs steel.

I'm going to have my torque wrench calibrated to make sure it's accurate. By the way, this is the one that I bought:



So once I have my torque wrench calibrated and I re-check the torque before each session, I should be ok? Not necessary to use regular steel bolts for the track?

My next track day is in a few weeks.

ATSR

I'm a bit confused regarding these torque numbers. The dealer said that the correct value was 96 ft/lbs for my car. Should I try the 118 for the track? Sounds quite high.

I didn't use anti-seize.

stronbl

Agree with many above ... always check and re-check your torque throughout the day. Also agree you may have experienced some sort of differential expansion due to dissimilar metals / alloys - you can look up the expansion coefficients in chemical properties reference book if really interested. Probably the OEM wheel bolts (hardened steel) match the wheel hubs expansion best, but they can still become loose after or during tracking - so check OEM bolts too.

Torque data from jhbrennan is the most current I could find as well in looking at the workshop manual. It is now permissible to torque all OEM wheel bolts on 997 to 118 ftlb as per Porsche technical bulletin and current workshop guidance. 991 has always been 118 ftlb I believe. Torques should be made and measured with the wheels off the ground (to be most precise) but that often requires an auxiliary device to prevent wheel rotation so most people simply torque 5 bolt wheels with the car's wheels resting under load (i.e. on the ground). 5 bolts can get away with it, center locking wheel bolts cannot.

nwGTS

The 96 to 118 figure is because Porsche changed to a different material for the lug bolts. in my 2012 car the manual says to use 96 for a few type of lugs and 118 for another type... mostly dependent on color. Titanium nuts are probably even more different which is why most guys who track just use steel or steel teflon coated nuts.

Buddhamonk

I always torque them myself the morning of the track day...that's for any car, any wheels, any bolts/lug nut. It's like checking your tire pressure before you go on track...

Lvt19672

Your expansion rate for titanium vs steel theory is so much more interesting than a out of calibration torque wrench

Backmarker

I like studs. Simple and bullet proof.

Why do people try to mess with things that keep the wheels on the car? Those light lugs are not impacting lap times...

Recommend studs for the OP, and checking torque every session and at end of day

porscheaddicted

+543423423

ATSR

Haha I agree

Thanks for the recommendation. I will check the torque before and after every session during my next track day. I might also get a set of regular steel bolts in case the titanium ones start coming loose again.

The main reason why I got the titanium bolts was for their lack of rust compared to the oem ones. I agree that weight savings are too small to make a difference.

user 72902

Just as a reference I've had titanium lugs for a few years and always use anti-seize on them. Torque to 96ft-lbs and they are always tight. Wheels are removed 6 to 8 times a year.