Titanium Rotor Bolts......

[DukeDesmo]

Interested in Ti bolts for front brake rotors but have a few questions;

I know Ti is lighter than steel but is it as strong? I have heard that some titanium parts are prone to failure under use, any info?.

What's the difference between Titanium Gr5 and 6Al-4V Titanium Alloy - which is best, strongest, most suitable etc.

Does Ti 'Gall' to Aluminium unless fitted with anti-seize Grease? or can Loctite be used and removed without issue?

On a related issue I see that according to 'Desmotimes' website 'older' Ducati's used M8 x 20mm rotor bolts and that from 2000 they used M8 x 15mm, presuambly they were changed to reduce weight but was anything changed in the wheel? I ask because my 1998 916 had the shorter bolts.

Concerning bolt length, is there any reason why I should not be using the shorter bolt in an aftermarket Marchesini 10-spoke (5y) forged Aluminium wheel?

Any advice?

[Neil996R]

Ti is stronger than steel by wiehgt NOT by volume i.e. if you had 2 componenets made xactly the same, the steel one would be the stronger but more heavier.

If the Ti part was scaled up in size to weigh the same as the steel part than it would be stronger.

Puting the Ti grades aside the weight difference for 2 parts the same size is roughyl 30% lighter for the Ti part. If the Ti part is scaled up to weight the same it will be very roughly (and I emphasize very roughly but for the purposes of this discussion sufficiently accurate) 16% stronger.

To answer your question - yes, Ti rotor bolts of either grade you referred to will be absolutely fine.

Will it gall against Al? Yes, it most certainly will - apply some copper slip or similar anti-sieze compound to the thread and all will be just fine, no prob's at all.

Bolt length - now you are getting into serious engineering theory!

I the stress on rotor bolts and similar types bolts - is a radial load as opposed to an axle load. For the purposes of this discussion, you are fine with I guess 10%-15% length reduction in the Ti bolt so long as that 105-15% does not exceed the diameter of the bolt. If it does, then do not reduce the length of the bolt by more than the diameter across the thread.

Again, as far as bikes goes it is my opinion that the above would be a perfectly safe application of the theory in the exmple you illustrate, but I would be hesistant to apply it in the case of torqueing down cylinder heads, where the strength fluxuates not only as a function of radial loading, but also as a function of axial loading and temperature variation, on top of which is added the differances in coefficient of expansion between botl thread and hole thread .....!! - you see the subject can get seriosuly complicated, but as said - for the purpsoes of your application, abide by the above and ye shall be safe.

Oh, and how do a know all this - I is an engineer for Boeing, doing material and stress calcs day in day out.

Good luck

Neil996R

[DukeDesmo]

Thanks for the info........

[Neil996R]

And thank you for the courtesy of addressing my question regards lighting - anyidea where I can get said relfector from?

Neil996r

Originally Posted by DukeDesmo

Thanks for the info........