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Be careful with titanium fasteners of any kind. The reason is that titanium is particularly prone to galling and if you've ever had to remove a fastener that has galled in the threads you'll know what I mean. Titanium has twice the friction coefficient compared to steel so the chance of galling a fastener is greatly increased. ALWAYS make sure that the tapped hole and the threads are clean and that you start the bolts by hand to make sure you don't get any chance of cross threading or damaging the threads. NEVER use an impact wrench or drill to run in the fastener because you can generate heat which can start the galling process. If the manufacturer of the fastener recommends a lubricant use what they recommend and ALWAYS use the torque that is recommended, which may well be different than what was used for the steel fastener due to the difference in friction as well as the different material strength. NEVER use a titanium fastener with a stainless steel threaded mating part. Stainless and titanium are horrible and gall together and frequently make a mess of things. Other than looking cool there really isn't much benefit from going to ti lug bolts. As someone above noted the lug bolts are so close to the center of rotation that there isn't much rotational inertia improvement, and if you could notice the difference of 6 pounds in the car, even with a stop watch you're ready to be an F1 driver. If you are a track rat and are changing tires often you're asking for more trouble than they are worth because you're running those lugs in and out a lot and that's when you stand a chance of galling a fastener. In that case I'd be using a thread lubricant (tiny amount of neversieze) and adjusting torque accordingly.
Good point about dissimilar metals there. Nothing beats the stock setup for strength and longevity. Looks are up to you. Also, the taper at the mating surface has a lot to do with the torque feel. I try to keep that area clean and dry so they cinch up consistently. Never over tighten with aluminum wheels.
I would wager that 0.005 PSI of air pressure in one tire would have a greater change in lap time than steel versus titanium bolts.
0.36 divided by 0.31 equals 1.2 ... where does 2x come from? Steel-on-Steel is 0.31 Titanium-on-Titanium is 0.36 Titanium-on-Steel is 0.48 For our application, the third number is the most representative of titanium bolts threaded into a steel hub. Static and Kinetic Coefficient of Friction Reference Table for COF Values of Common Materials
How much does the coefficient of friction have to do with the "resistance" to the bolt "loosening ?" I usually use "Never Seize." Thoughts ?
Engineering tables list coefficients of friction for static and dynamic conditions, with the latter always being less than the former. Why? Because after the two objects in contact with each other (a box sliding down a ramp or in this case, a wheel bolt turning in the threaded hole of the hub) begin moving relative to each other, that movement requires less force or torque to continue. Therefore, the static friction relates to the break-away torque and the dynamic friction has to do with continuing to turn the wheel bolt in the hubs threads.
Would that be true for center lock racing style wheels as well? I watched some mechanics lube up a challenge car when they were changing tires in the paddock.
You're referencing smooth metal on metal contact which is not what happens in a threaded fastener. Here is a quote from the link below relative to threaded fasteners.... The coefficient of friction of commercially pure titanium is given in the range .30 -.34, with lower figures in the range .25 - .30 for titanium alloys. Practical tests can indicate much higher figures, into the range .8 - .9 for rubbing contact of untreated surfaces without lubrication. Three fundamental factors combine to give titanium its high coefficient of friction and cause the poor tribological behavior of the metal. The first arises from titaniums atomic structure, and this can be marginally improved by bulk or surface alloying to form a harder and more wear resistant structure. Here is the entire article... Titanium and Titanium Alloys - Wear Behaviour and Lubrication Bottom line is that friction coefficients in the real world can be much higher and that causes potential galling and high wear rates in titanium threaded fasteners. Some titanium fasteners are improved by anodizing and have a dry film lubricant applied. I don't know if the factory fasteners are treated or not. That is why I said to follow the recommendations of the manufacturer as far a lubrication goes. If they are treated for wear resistance they will last a lot longer and be relatively trouble free, but untreated fasteners have a very limited life in terms of the number of times they can be removed and reinstalled. Uncoated fasteners have a life of around 30 removals before they typically wear out due to high thread wear. Here is an article no thread wear in titanium fasteners that you may find interesting as it goes into the wear mechanism for titanium fasteners.... http://www.ewp.rpi.edu/hartford/users/papers/engr/ernesto/lessam/FWM/Project/Research%20Materials/Tribological%20properties%20of%20titanium%20alloys.pdf As I said I don't know if the factory Ti fasteners have been treated to improve the life and this will also change the installation torque requirements so one has to know what he has and how it should be used. If you are buying aftermarket ones I'd be very careful if you plan on removing and reinstalling wheels frequently. I would not touch aftermarket ones that were not anodized and treated with some kind of dry film lubricant if I were changing tires frequently like you do if you're doing track days and then shifting back to street tires every other weekend. I've been designing titanium parts in turbine engines for over 40 years and have lived through or seen first hand most of the horror stories that are in the textbooks concerning the use of titanium at one time or another. That includes everything from common thread galling to having an engine burn like a roman candle from a titanium fire in a supersonic test chamber. Titanium is great stuff and if you use it properly it is a wonderful material. But titanium can bite you in the butt if it is not used properly and that includes the person putting the parts on and taking them off.
I have no idea. F40 and F50 are clean and dry as well. Many have lubed them and it has led to some train wrecks.
I accept everything you say but just FYI as far as Ferrari goes: No lubricant No rated life by cycles And as far as I can tell the bolts are untreated but I may be wrong if the treatment had no effect on the appearance of the fastener. I will say that for the steel bolts factory torque is rather low for a fastener of this size. The Ti bolts are a little lower still. I have yet to see a wear or galling issue and they have been in use a number of years now. On steel fasteners in ti, as on the rod bolts there are very special recommendations as far as lubricant is concerned both on the threads and on the head shoulder and I have seen problems there. As far as I am concerned I think we would be better off with steel bolts on street cars and if a different look is desired get allen bolts with black chrome or some phosphate treatment. Titanium bolts on Ferraris are getting to be pretty commonplace. Soon people will pay extra for chrome.
I agree with all of the above also. The manufacturers know what they have and make recommendations accordingly. It could well be that the OE bolts are anodized, as with aluminum unless you use a color process anodizing isn't visible. Also note that alloys like 6-4 (which are actually much more commonly used than pure Ti) are better than pure Ti, and while better still isn't very good, it's still better than pure Ti. Every application is a little bit different. No manufacturer would use Ti bolts if they felt they had a serious safety issue and if a bolt takes the recommended torque it's not likely to come loose. Most of the problems with Ti fasteners that I have seen wasn't related to wear, jet motors don't get taken apart that frequently. Most problems were due to galling and the threads binding up and then having to drill out or cut off the offending hardware to get it apart. Clean threads are very very important for Ti fasteners. If you get some junk in the threads you can cause higher friction and galling if any tiny bits of machining junk or garbage in the threads. Even worse if you try to run in the bolt with a drill or a impact wrench. In places on aircraft or in engines that I have seen, they strictly prohibit the use of air driven or any kind of high speed wrench to even "spin down" a Ti fastener.
This is well thought out, and I am now searching for some answers........ 1) If we assume that both male and female threads are very clean, and that the fastener turns in with no perceivable "extra" resistance, and the "manufacturers recommendations" are unknown: A) Is using a lubricant "wrong?" B) What is the default lubricant choice ? C) What characteristics are we looking for ? 2) I often use Never-Seize (Permatex brand) in demanding applications, like the Bonneville salt flats, where salt intrusion is a given. Titanium usually will not corrode in that situation, but the mated steel part will degrade, especially galvanic corrosion. When Titanium bolts are tightened into Carrier airplanes, is there a special lubrication for the salt spray, that is not used in land-based applications ? If the steel mated part corrodes, that often makes the fastener hard to remove. In the absence of other information, is it better to lubricate the Titanium fastener ? Thanks in advance, Scott
I believe there is a dry film lubricant on the Mil-Spec hardware as supplied. There is general data available for modifying torque specs (using less torque) when they are installed wet (lubricated). You should be able to do some searching with these terms I have used to get up to speed on how different applications deal with this kind of thing. I am not advising that you do any of this to your Ferrari though, that will be up to you. What I follow is clean and dry threads and use the torque values from the manual.
I have said it before and evidently it was ignored. Install dry. Unambiguously stated in every direction on the subject.......dry. If you want to over stress the bolts and risk failure then by all means ignore that.
Look..if it's the look your after go and buy a set of STEEL Allen head wheel bolts ( they are very available) and have them plated to look like the ti bolts. Be done with it already. Ti bolts are a gimmick..and your being suckered into it. If you want them, it's your dollar, buy them. There is ZERO,ZIP,NADDA NOTHING of an advantage to haveing them on a street car other then bragging rights. If you want to deal with all this mumbo jumbo everytime you wanna pull a wheel to clean brake dust, be my guest. But gall a Ti fastener in a hub, you are replacing the hub assembly and the wheel bolt. Do as you will, just my very humble opinion.
If you don't know what you have you probably shouldn't be using Ti since most manufacturers spend time and money figuring out what is right for each application. If you really need to use Ti and don't have the specs from the manufacturer that is a different animal. I'm assuming that you are designing your own bolted joint and if it is a critical joint then I would see what the bolt manufacturer recommends for torque and lubrication. If you're buying surplus Ti fasteners (great prices on some of them), then you are on your own. The only good thing about getting surplus stuff is that if you have the MS part number you can look up the drawing for the bolt and it will give you the strength, material specs, and also whether or not it is a coated bolt. Mil spec bolts are also consistent quality and are good stuff, you just have to put the extra work into researching what you have and use it accordingly. Relative to lubricants and whether to lubricate or not, it isn't so much a matter of right or wrong, but for each lubricant you use the the torque will be different and you could very well over torque a bolt or it may not be properly tightened if you don't know what you have or are doing. Some companies, like Mettec recommend a molydisulphide paste (like neversieze) other do not. Mettec also has a torque chart for their fasteners with and without lubrication. Mettec Makers of Quality Titanium Fasteners, Motorsports Products, and Motorcycle Accessories. This is good info, but it is only applicable to their fasteners since they don't tell you the alloy they are using or whether or not they anodize their parts first. Both of those are pretty big variables and without knowing what your bolts are it is not a good idea to just use just any torque value that looks right. If I'm in a situation where I'm using a lubricant I tend to use a dry film lubricant, but there are actually tons of them, depending on the temperature of the joint you are bolting. I've used Neversieze also and there are also tons of them from copper to nickel to just graphite.. Again, it depends on the temperature of the parts. You don't want a thread lube to coke up and make a mess of things if you use the wrong one and the joint is at 1000 degrees F. A grease or neversieze is better to prevent corrosion, unless there is a lot of water and then it can trap water inside and cause more trouble than it solves. Also, flat fasteners have different torque relationships than conical fastener surfaces like lug bolts and that changes the torque required. Bottom line is that you shouldn't use the same table values for wheel lugs that you would use for normal 90 degree headed fastener. Galvanic corrosion is always an issue as is corrosion of a steel threaded hole with a Ti fastener in it. If that's what you have stay with steel and stay away from stainless. Stainless doesn't corrode, but the potential for galling with stainless on TI is just plain nasty. If you have anodized surfaces on the Ti that is better from a corrosion resistance standpoint. I don't have any experience with carrier specific applications, The joints I've done were for USAF engines and I have done engines for Navy applications, but didn't do any Ti bolted joints for Navy that I can recall. To give you an idea of what it takes to get it right, at P&W we made up mockups of the bolted joint and used strain gauges and lots of calculations to measure the stretch in the bolt and determine what the proper torque (or in some cases angle of twist from "snug") Then we developed a procedure for torquing the fastener for the lubricant used and the particular bolt length and joint stiffness. If the joint is very stiff (like a wheel bolted on hub) then calculating the correct angle of twist that will give you the right bolt loading is a fairly accurate way of doing it. That is, knowing the length of the bolt that isn't in the threads and the thread pitch if the bolt you can calculate how much angle of twist from "snug" that will give you the stretch you want in the bolt. Less accurate for really short bolted joints though. In some applications we did angle of twist because it was more repeatable than torque wrenches. If you torque the fastener in the clean and dry condition, and use the same angle of twist from snug, you will have the same tension in the bolt no matter if the threads are lubricated or not. The only difference is that the torque will be lower. We used to use dial type torque wrenches that had tell tales, and measured angle of twist to get a specified strain and then recorded the torques and that was a consistent way to derive the proper torque for the bolt in that specific joint.
