Titanium front rotor bolt. Head size?..

Hey guys. What do you think about these rotor bolts.? I picked up some titanium bolts for the front end of the bike, and figured I'd try the rotor bolts too. Although when I got em, I noticed the head size of the bolts are significantly smaller than factory. The bolts are from Ti64.com and are rated at 140kpsi. My thoughts are the brake force will be more torsional than pulling, so head size might not be a major factor..?..

Any thoughts?

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Ahhh, all the real important stress on the bolts is sheer. Considering the adapter plate only has three bolts and consequently twice the sheer stress, run them, you'll be just fine. (Not accounting for friction between surfaces of course.)

 

Should actually be any torsional I think if it were ideal. Should be an all axial load when tightening and sheer on the thread. Then sheer front he braking force. Learning all about bolts and their applications in class right now and this stuff interest me. But yea like said, your good.

 

Cool, Thanks! I agree, I guess it would be sheer stress, and in that case head size wouldn't matter, just thread strength, which the titanium is greater than the factory stainless. So. I'll go with em

 

Shear.

 

People love correcting spelling and grammar for the sheer fun of it.

 

Just trying to learn a bit here, I'm not a mechanical engineer or anything. Isn't the bolt there to create friction between the mating pieces, thus keeping them in place? I get the clamped items will be shearing together, but once the bolt is clamped I wouldn't think the stress would be much in shear for it (fastener) as it would be in tension if it were doing it's job? Enlighten me please.


I guess the way my thinking is, is the bolt does the clamping to make friction, the friction is what holds the pieces together. I guess I don't see why the bolt sees stress from shearing unless it's not adequate in it's job at tensioning.

Maybe the line isn't black and white as im taking it? Maybe both forces are involved and way over my understanding?

 

No bites? This is the shit that keeps me awake thinking about at night.

 

Trying to follow you here:
As the bolt is tightened it creates shear in the threads (which is why if you over torque something you can strip threads off) and an axial stress in it as well.

Once installed and torqued to spec if there wasn't friction between the threads and mating piece it would just back itself out. This friction is what keeps bolts in place, not the torque we apply to it.

Then your left with a preload axial load on the bolt and shear stress on the threads, say in the X direction.

Under application in the Y direction as the caliper resist rotation it creates a shear stress as well.

After rereading your post, yes you are correct that preload on bolts will cause a friction between the two pieces. Under certain conditions it can be high enough that the bolts don't ever experience this shear in the Y direction. I seriously doubt that is factored in to this equation though.

 

This reminds me why I won't take any of my engineering classes online, way to difficult to communicate.

 

Your question really depends on the CoF of the two parts being clamped which is based on the surface area, textures, clamping force and the external forces being applied. In many cases the SHEER strength of a fastener normally exceeds the frictional resistance of two clamped pieces. The frictional resistance should be enough to keep the piece from moving which can abnormally wear and stress the SHEER component. Luckily the movement in a brake system is in one direction, so heavy shock loads are normally a one time event. Basically once the frictional resistance is over come the sheer strength of the fasteners is the important factor, if that is exceeded then bad shit happens.

On a motorcycle the force applied to the front brake rotor bolts will very rarely exceed the traction available between the tire and the road surface, which isn't very high.

 

Shear = a strain in the structure of a substance produced by pressure, when its layers are laterally shifted in relation to each other.

Sheer = nothing other than; unmitigated (used for emphasis).

Don't know if you were trying to be funny or correct me after I was corrected on being corrected but this is googles definitions.

 

Your good, I was just being a poor spelling american ass.

 

I guess that's the main question, if the bolts are doing what they are supposed to be doing, which is clamping the two pieces together, what does it matter what the shear rating of the bolt is? I see movement between the pieces as failure and something the needs to go back to the table as far as an engineering standpoint then. If the rotor carrier can rotate on the hub because of the forces and then the bolts become the fail safe, that doesn't seem quite right..? Maybe they need a different surface texture, serrations etc. Or even more bolts for more clamping area.

I guess i could see a shouldered bolt shank carrying a shear load, but one that's threaded to the head doesn't seem designed for that load bearing on just the threads.

Again, i'm just doing this for learning and discussion, interested in what i don't know.

 

So basically it IS the failsafe and i'm reading too deep into it.

 

Sounds like you have some fun math ahead of you. Compare the surface friction of a rotor and rim plus clamping forces vs. the shear strength of x# Ti or steel bolts. I'm glad I have engineers to do this for me with really expensive computers and software because engineers make me laugh.

Only very silly people use Al bolts on brake systems even though the same clamping force can be achieved Just a thought.

 

Why not ask the rotor mfr? They'll probably say not OK due to liability of an unknown brand but they may say yes and then you can not worry about it.

 

Mind if I ask what it is you do besides sell bike parts?

I see movement between the pieces as failure and something the needs to go back to the table as far as an engineering standpoint then.

Movement between the rotor and wheel? That would be a failure.

 

That depends on how and when. Is it engineered into the components or not? Does an aftermarket supplier meet the OEM specification?

I definitely don't sell bike parts. That was 25 years ago. But all the keyboard engineers are going to be waiting on your MATLAB or Solidworks results and calculations. So, time for you to learn a bit.

And "failures" are unexpected engineering results, which involves cycles,environmental factors, and other constraints. Keep this simple. We are just talking about breaking a bolt/s.