I spent $75 on titanium bolts.

[fyrstormer]

After 14 years, the steel bolts on my 756 were starting to show their age, so I swapped them out for rustproof titanium bolts. TorontoCycles hooked me up with all the bolts I needed.

Oh, and I shaved 27.8 grams of weight, if that matters to anyone. 

[Thunderchild]

What was the total number of bolts? 

Yamabiker

[fyrstormer]

Hmm...

1x Upper shock pivot bolt (M6x45 shallow-round cap)
1x Lower shock mount bolt (M6x20 non-taper cap)
2x Strut pivot bolts (M6x30 shallow-round cap, cut down to M6x23)
2x Swingarm pivot clamp bolts (M6x15 non-taper cap)
4x Accessory mount bolts (M5x15 non-taper cap)
1x Derailleur cable guide bolt (M5x10 shallow-round cap, cut down to M5x5)

Still waiting on the swingarm pivot bolt which I ordered from SRP instead of TorontoCycles. SRP is *not* getting my "Best Customer Service" award. I might just order an M6x60 bolt from TorontoCycles instead; technically that's long enough to fully secure the swingarm pivots, even though the OEM steel bolt is M6x65.

[fyrstormer]

*yawn*

[shovelon]

A little worried about the upper shock bolt.  Ti bolts are not as strong as steel machine bolts.

 The others look the schnizle.    Toronto Cycles is great.

[fyrstormer]

A little worried about the upper shock bolt.  Ti bolts are not as strong as steel machine bolts.

 The others look the schnizle.    Toronto Cycles is great.

In theory they're not as strong as steel, but they say the same thing about the titanium Salsa skewers I have which are supposedly "for road use only" or some nonsense like that. Part of the reason for having suspension is to reduce the force applied to the load-bearing parts at each instant, by extending the duration of each impact. What's good for my tailbone is also good for the bolts. If the upper shock bolt were to break, it would break in the middle of an impact, which would cause the end of the shock to be captured by the junction between the top tube and seat tube. That's a pretty safe failure mode all in all.

[w2zero]

Yep, safe until the rebound...

[shovelon]

Yep, safe until the rebound...

Launch mode?   

[timboiow]

Gents,
From what i remember, there was a "analysis" of Ti skewers a long time ago (might have been MTB Pro magazine) and the problem with Ti skewers was to do with the "elastic" properties of the material itself (ther's is proabbly a technical term for this  ) and that they "stretched" slightly under load compared to the traditional steel skewers and therefore weren't helping keep the base of the shocks "locked" together (the brace at the top of the forks and the securely clamped axle help to ensure both legs of the forks move together, especially when the fork structures moved to asymetric internals). The arrangement of the vector forks may be better in that respect and the Ti skewers can revert to being just another lovely blingy finishing touch (those touches that when you look over a bike make you think "Niiiiiiiiiicccccceeee").
Looking forward to the piccies when they're posted.

[fyrstormer]

Yep, safe until the rebound...

Even if the upper shock bolt instantly snapped into three pieces at the two interface points between the shock eyelet and the frame -- which is very unlikely given the elastic coefficient of titanium -- that still wouldn't change the rebound damping setting on the shock. Just because the upper shock eyelet would no longer be firmly attached to the frame doesn't mean the shock would respond after the impact by shooting off like a firecracker. It would still do its job such as it could without a fixed mounting point.

In any event, you guys are vastly overestimating the likelihood of such an occurrence. The upper shock mount is a suspended part; the force of impact necessary to snap the mounting bolt in the method you're envisioning would almost certainly be enough to break my tailbone as well. In the most likely scenario, the rear wheel (which is made of aluminum) would collapse under the direct application of the force necessary to bottom-out the shock and snap the mounting bolt, and that collapse would further dampen the impact with respect to the top half of the bike.

In reality the only way to apply the necessary force to snap the upper shock bolt would be a direct impact of the top half of the shock against a hard, immovable object, which it's pretty well protected from because it's positioned directly above the swingarm. Basically you'd have to hit the top of the shock with a sledgehammer to get that kind of catastrophic failure; any "naturally-occurring" scenario that could transfer that much force to the bolt would seriously endanger the rider's life for reasons other than the shock breaking loose.

If you really want to look for a potential failure point, look at the frame itself; it's made of aluminum, which doesn't have a "stress floor" -- it will crack eventually if you tap on it with your finger enough times.

[fyrstormer]

Gents,
From what i remember, there was a "analysis" of Ti skewers a long time ago (might have been MTB Pro magazine) and the problem with Ti skewers was to do with the "elastic" properties of the material itself (ther's is proabbly a technical term for this   ) and that they "stretched" slightly under load compared to the traditional steel skewers and therefore weren't helping keep the base of the shocks "locked" together (the brace at the top of the forks and the securely clamped axle help to ensure both legs of the forks move together, especially when the fork structures moved to asymetric internals). The arrangement of the vector forks may be better in that respect and the Ti skewers can revert to being just another lovely blingy finishing touch (those touches that when you look over a bike make you think "Niiiiiiiiiicccccceeee").
Looking forward to the piccies when they're posted.

I remember a similar article. There are two problems with the analysis presented:

1. The weight of the bike doesn't rest on the skewer, it rests on the ends of the steel axle passing through the center of the hub. The steel axle is the only part of the wheel assembly that directly seats into the notches in the end of the fork/swingarm. The skewer ONLY provides clamping force on the horizontal axis.

2. The greater elastic coefficient of the titanium skewer can be compensated for by tightening the skewer a little more than a comparable steel skewer, and even if it does stretch horizontally, there is no way it will stretch enough to allow the teeth on the skewer and the hub to let go of the fork/swingarm without the skewer permanently deforming from the strain.

I like bike magazines, but remember the vast majority of them are not engineers, whereas I am. I actually read in Bicycling magazine that spoked wheels support weight through the compression of the spokes at the bottom of the wheel, instead of tension of the spokes at the top of the wheel. After I read that, my estimation of their engineering expertise dropped dramatically. I very nearly wrote a letter to the editor to correct them, but I figured it would probably be wasted effort.

[shovelon]

No, it is all good.
I am just thinking that the upper swingarm pivot has the most leverage of any on the entire frame. And given the lower shear strength of a hardened machine bolt, I personally would be a little worried. But I have never tried it, so this is a good test.

I do remember that there has been controversy regarding Ti rotor bolts.

Terry

[w2zero]

I assumed you bought a longer bolt so as to cut off the extra threads and move the larger diameter unthreaded portion of the bolt closer to the threaded side of the frame.  To insure more contact with the sleeve in the upper end of the shock being the purpose, yes?  I did much the same by buying higher quality machine bolts that were significantly larger diameter where they are in contact with the shock mounting sleeve but I am not concerned with the weight. 

Your bolt will likely never fail as Ti is nothing short of amazing compared to other readily available materials.  In the event that the upper shock mount bolt on the rear did fail, it would likely be at the end of the threaded shank on the bolt.  That should have some noticeable tell-tale noise involved unless it were a completely gnarly downhill or your tunes were cranked to eleven.  Even with that, you might actually feel the bolt working its way out on your leg or more likely, it would be bent and jammed in place, bulging the sheet aluminum out where the shock is mounted. 

You should have written to the bike mag about the tension and compression aspect of the wheel spokes.  They were assuming that since the spokes below centerline had less tension it amounted to compression.  But then they are in the business of pimping for the suppliers of the parts du jour and sales trump facts.  I used to run into that crap regularly in my car mags so I don't waste my money there.

I'm no engineer, I just break stuff and fix it.

[fyrstormer]

The bolt is 45mm long, with 9mm of threads at the end. I bought it that way; it was specially made for the Cannondale Scalpel but it fits my 756 also.

Titanium is pyrophoric, which makes cutting it an extremely sparkly and fumy affair, so I only did that for the bolts I couldn't buy at the right length to start with. There were three: two for the lower strut pivots and one for the front derailleur cable guide.

[fyrstormer]

I do remember that there has been controversy regarding Ti rotor bolts.

If I believe the conversation at the other end of this link, some brakes come with Ti rotor bolts from the factory: http://weightweenies.starbike.com/forum/viewtopic.php?f=1&t=72474