Front brake discs

What Pete said

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Stainless bolts and the correct tool

eeyore wrote:

I hope Piaggio or Brembo have based their specification on calculations and lab testing.  

The calculations were probably done by the bean counters, not on strength, but price

There is no (extra) force on the bolts under breaking, friction between disc and hub does the job.

Fit what you want to your bike.
Read my second post - not disputing that the braking force is transferred to the wheel by the clamping force but your photo shows a stainless cap head screw without a flange or thick washer. This is poor practice and combine this with the thermal elongation of stainless (almost 2x that of steel) and you have compromised the design.

Then I first compromised the design in 1988 on my Le Mans, did it again in 1997 on my Sport 1100i, and in 2008 the GRiSO, I should be dead by now

Bit like roulette just waiting for green.
It would only take a single occurrence and it could be game over.

Based on your personal knowledge and experience are you happy to recommend this modification to others?

If you want to shed weight and change the odds I can supply composite screws or if you want fancy colours anodised alloy both options would accept 25Nm for a while.

Bit like roulette just waiting for green. Nonsense

It would only take a single occurrence and it could be game over. Bull, I check their torque every winter, no problem so far on any of the bikes mentioned

Based on your personal knowledge and experience are you happy to recommend this modification to others? Yes, provided they check them on a yearly base or mark them.

If you want to shed weight and change the odds I can supply composite screws or if you want fancy colours anodised alloy both options would accept 25Nm for a while. Shed weight?    Fancy colors? no thank you.

25Nm for a while

How do check the torque on a fixing secured with threadlock?
If you don't use threadlock and torque up every year you compensate for the creep and eventually the fixing fails.
Marking position on the head doesn't show any creep.
I do this sh*t all day for a living (engineering - not pis*ing people off on forums). Not saying your brakes are going to fall off but the safety margin has been reduced. If you can live with it fine but it's not wise to encourage others to do the same without understanding the risks or possible increased maintenance or checks required.

As I seem to piss you off (sorry if you feel that way), Just one more thing: How many customers from this well known company have passed away because they bought their products you think? Pro-bolt

Wasn't game to mention Ti bolts ............................................

Titanium is nice to mount the calipers to the forks Ghezzi, I use SS for that as well but please don't tell anybody, sssshhhh

Ti

WOW.It looks like there are plenty of diverse opinions on this! Thanks to all for your input.

I finally got back to the garage and removed the rotors. A big yawn. Bolts came out soooo easily with 10mm 6pt and breaker bar. I think I could have also used a 1/4" drive if I put an extension on it. Sounds like not all rotors are secured with the same fasteners from the factory. The ones I removed  are alloy steel, cad plated with an integrated flange which eliminates the need for a washer, similar to a JIS (Japanese Industrial Standard) that rice burners use all over.

Regarding strength of SS fasteners:

The strongest commonly available SS fasteners can only compare up to about a Grade 5 alloy fastener strength wise.

316 ss =70,000 psi
18-8 (Same as A-2) = 70,000 psi
Bumax 88 = 110,000 psi   This is close to a Grade 5 (120,000 psi). This is as good as it typically gets and these fasteners are not commonly available. Bumax also produces even stronger SS bolts if you want to send them a drawing and have a few thousand made...
Alloy steel socket head cap screw = 170,000 psi This is a typical Grade 8.

Typically if you buy a specialty SS fastener it will be made out of 18-8 stainless which works to a little better than a Grade 2. This has no relationship to a class 8.8 alloy fastener which is nearly twice as strong.

SS is pretty, just ask her.  

18-8 may work fine in many applications but the safety margin is dramatically smaller than using a modest Grade 5 fastener.    
In my humble opinion, brake rotor attachment is no place for an 18-8 fastener but it also doesn't surprise me that it has been done many many times with success. The designers of these types of mechanical joints typically tend to use many more fasteners than is required in order to proved a wide margin of safety which is the proper way to approach it.  

FYI, If you use ss nuts and bolts without anti-seize and tighten them up the chance of galling is very high and the only way to get them apart will be cut/grind/drill or just break it apart. Ask me how I know this.

Thanks everyone.

Tim

Found this guide on ebay.
The non believers don't understand the message and fail to comprehend the relationship between the properties of the fastener, torque requirements and clamping force required to hold the disc in position.

There are several misconceptions about stainless steel bolts and other fasteners. This guide is intended to clear up some common misunderstandings, but in a format that that is short and simplified.

1. Stainless Steel is Stainless Steel.
Not at all true. Steel is an alloy of Iron and trace amounts of Carbon, with some other elements in the mix, too. Making stainless steel requires the addition of other alloying agents, among them are chromium, manganese, molybdenum, nickel, phosphorous, silicon, and/or sulfur. Depending on the amount of these and other elements, many different grades of stainless steel can be produced and there are several grades suitable for making bolts and other fasteners with. The most common stainless steel is some version of "18-8"--that is, using approximately 18% chromium and 8% nickel. Common grades of stainless steel are 410 (Also called C1), 302, 304 (302 and 304 are also called A2), 305, and 316 (Also called A4). ( a version of 316 with additional molybdenum is labeled "2343") I've listed those grades in bold ordered from lowest corrosion resistance to highest corrosion resistance. Of the boltmakng alloys listed above, 302, 304, 305 are all based on "18-8" stainless. Put another way: If you ask the seller what kind of stainless steel his products are made from, and he says "18-8" or "A2", he hasn't told you much because there are various versions of 18-8, and at least two versions of "A2" stainless steel. F593C is an American Society for Testing and Materials (ASTM) specification for 304 stainless steel.

2. Stainless steel bolts are stronger than ordinary steel bolts
This is clearly not true for the majority of stainless steel bolts. Stainless steel in general has very little carbon, and because of that, most grades of stainless steel cannot be hardened by heat treatment. Stainless steel bolts are, in most cases, just slightly stronger than Grade 2 hardware store junk bolts, and in nearly all cases, significantly less than Grade 5. You do NOT want to use common-grade stainless fasteners in any application that would call for a hardened (Grade 5 or Grade 8, or stronger) fastener. ARP makes a fine line of stainless bolts that have a tensile strength of approximately 170,000 lbs per square inch. This is greater tensile strength than a typical Grade 8 fastener, but keep in mind that tensile strength is not the only measure of bolt quality/strength. Common grades of stainless steel may have reasonable tensile strength, but significantly less yield strength than a "regular" steel bolt--the stainless bolts are more "stretchy". Those ARP-made bolts are the ONLY stainless fasteners I'm aware of that are suitable for general use. There may be others--if you know of any, please let me know!

3. Stainless steel doesn't corrode
Stainless steel is more correctly called "corrosion resistant" steel. Some grades are more resistant to corrosion than others, and grades have been developed that are highly resistant to corrosion caused by specific uses: for example, 304 is subject to pitting when used in an environment heavy in chlorides, while 316 is less reactive to chloride.

4. Stainless Steel is not magnetic
Stainless in general tends to be LESS magnetic than "ordinary" steel, and some grades are non-magnetic. Stainless steel bolts can become slightly magnetic when processed by cold working. Even though the "raw material" going into the boltmaking machines is non-magnetic, the process of forming the head and threads may cause the bolts coming out of the machine to be somewhat magnetic.

5. Rolled threads are somehow "special".
It is absolutely true that rolled threads are better than cut threads in terms of strength and accuracy. But since NOBODY produces common-sized bolts by cutting the threads, it's kind of pointless to brag about rolled threads! In a production environment, it's actually cheaper to roll the threads rather than cut them, and it produces better results because the threads are "forged" and the grain of the metal is pressed into shape, while with cut threads the grain of the metal is disturbed by the cutting process. Huge diameter fasteners of low production volume, or "ready rod", long lengths of threaded rod, may--or may not--have cut threads. Still, ordinary-sized bolts will have rolled threads.

I received a communication of interest from eBay member alleygnat. In it, he told me:
"I would add one additional item to your discussion regarding rolled threads: Though it it correct that rolled threads are stronger due to the residual work left in them, residual stress can be relieved at prolonged exposure to elevated temperatures thus eliminating any benefit. However, more important to the topic is that threads with residual work (Rolled Threads) are far less corrosion resistant than cut threads. I've seen many a boat with rust running down the hull from bolts with oxidized threads with still bright heads."
I have not verified his claim that rolled threads are susceptible to corrosion more than cut threads.

Another issue with common grades of stainless steel is that the threads often seize ("gall") between the bolt and the nut. I suggest the use of an anti-seize compound, coupled to CAREFUL USE OF THE TORQUE WRENCH when tightening stainless steel. You MUST use a torque setting on the wrench suitable for the mechanical limits of the fastener, as adjusted for the reduced thread friction inherent when using a thread lubricant like anti-sieze compounds. As a rule of thumb, and unless the manufacturer says otherwise: Consider a stainless steel fastener to be capable of Grade 2 torque loads, and then adjust the torque DOWNWARD by 20% because of the lubricant properties of the anti-sieze.

Example: A common 304 (A2) 3/8-16 stainless bolt should accept the same torque as a 3/8-16 Grade 2 bolt--only about 20 ft/lbs. But since you've lubricated the threads with anti-seize compound, you'd reduce the torque by 20%, for a torque-wrench-setting of 16 ft/lbs. That is NOT VERY MUCH for a 3/8 bolt!!! There are stronger stainless bolts--some but not all 316 alloy bolts will take almost but not quite Grade 5 torque specs, but again you must adjust downward when you use anti-sieze. If you're used to working with hardened fasteners (Grade 5 and Grade you won't believe how little torque is the maximum acceptable amount.

Generally, a manufacturer will put a trade mark of some sort on the bolt head. For example, many stainless steel bolts have the initials " THE" in raised letters on the bolt head. The THE signifies the bolt was made by Tong Hwei Enterprises, somewhere in the Far East--most likely Taiwan, although THE has factories in China and Malaysia as well.

You are missing the point, in this application the clamping force (friction between rotor and hub) is what keeps the rotor in place. There is no sideway stress on the bolts during braking.

You are missing the point, in this application the clamping force (friction between rotor and hub) is what keeps the rotor in place. There is no sideway stress on the bolts during braking.

The friction between the rotor and hub is caused by the spring properties of the fastener used. In general, an alloy fastener is capable of creating significantly more force than a SS one. The shear strength of the fastener may not be an issue here but the tensile strength is. That doesn't mean that using SS fasteners will fail but it does mean the margin of safety is reduced by nearly half. (70,000 psi vs. 120,000 psi).

Correct!

Just out of interest, what torque settings are you using for these stainless cap-heads?

Now you want to start a discussion about max. recommended torque for SS?

Looking forward to this one (not)

Me either Paul

Oh well, I must be dead.
Plastic wheels.
Home made axle & hubs
Ti axle nuts & disc bolts.
SS caliper bolts.

I'm out....

Well I understand that opinions can be right and wrong - and facts also can be. However I have been enjoying the discussion side of things and have in fact, learnt some things about bolts (never too old to learn) even though "I knew it all before"!

In for a penny, in for a pound...

If we are to discuss the torque, let it be as a sort of educational training document for all, rather than a "my dick is bigger than yours" type discussion.

Wayne (Ghezzi) you are not dead, you just smell funny. As for the plastic in your wheels, you are at the bleeding edge of this, and if you F**K up, you will bleed. But even bad things can serve as a bad example. Not that I wish this upon you or anyone else, but it is seat of the pants engineering that thrills me, at least as a spectator sport.

Mind you, I did lots of very dodgy engineering when I was racing bikes a few yesteryears ago - it only had to pass scrutineering, not abide by design rules. We all "run what ya brung" in those days. Most of us are still kicking.

Edumecation, bring it on!

And lighten the f**k up you lot - now ducks for cover....

I suppose the one saving grace for all us numpty's who want to re-invent the wheel, the OEM have to err so far on the side of caution with what they do, so as not to get sued.
ie. Takata air bags

So if we take a guess at doing something not too far from stock, we may still be in the ball park safety wise. I too have enjoyed the education in metallurgy here.
In one sense, it scares me when I think of past modifications, but then I'm also encouraged by the fact I haven't fucked up ................ yet.

Tony, standby. That smell might get a lot worse.

I think its time to remove my splined rear axle and disc carrier and see if I can reduce the unsprung weight by another kg.