K2 / Proflex Riders Group
General => Tech Forum => Topic started by: fyrstormer on August 21, 2011, 09:33:08 pm
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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. 8)
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What was the total number of bolts?
Yamabiker
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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.
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*yawn*
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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.
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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.
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Yep, safe until the rebound...
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Yep, safe until the rebound...
Launch mode? :D :D
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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.
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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.
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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.
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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
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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.
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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.
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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
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Okay, time to revise the estimate upward. I've now spent $100.15 on titanium bolts, and I think my tithe to the bike is paid in full for the year. It's not really a riding season if I don't upgrade something, and as it stands the only original part left is the front derailleur. I love how modular bikes are.
The last batch of bolts I installed were a single M6x60 bolt to hold the swingarm pivots in-place, and 12 M5x10 bolts for the brake rotors. I wasn't originally going to change the rotor bolts because every new rotor comes with new bolts, thus making rust a non-issue...but what the hell, there's 12 of 'em and the new ones are nice and shiny.
So, I saved 42.2g total. That works out to $2.37 per gram saved, which is a bit high according to the sages at WeightWeenies.com, but really my goal all along was to replace rusting steel bolts with something that would never ever rust ever. Titanium fits that bill. I'm happy.
Pics!
New hex bolt to replace the cheesy Philips-head screw that used to hold the cable guide in-place:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4897.jpg)
New swingarm pivot clamp bolts; note the heads are just the right size, no sanding necessary to make them fit:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4898.jpg)
New bottle cage bolts:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4900.jpg)
New lower strut pivot bolts; the heads are slightly smaller than the originals, but that's not a big deal:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4901.jpg)
New upper shock pivot bolt; same story with the slightly smaller head, but again it's not a big deal:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4902.jpg)
New rotor bolts:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4899.jpg)
The tail-end of the new swingarm pivot bolt, to prove 60mm is long enough to fully capture both pivot cups:
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4903.jpg)
...and a pic of the gnarsty old steel bolts I replaced.
(http://i5.photobucket.com/albums/y186/deusexaethera/bikes/CIMG4904.jpg)
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I retapped the front derailleur to accept a ti bolt from my Boeing surplus stash. Whyn't you cut off the excess cable guide on the BB as well since it isn't doing anything except weighing you down.. ::)
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I'll say again, saving weight was a secondary benefit of this project; the main goal was to replace rusty old bolts with shiny new ones.
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Looks nice man!
Terry
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Whyn't you cut off the excess cable guide on the BB as well since it isn't doing anything except weighing you down.. ::)
exactly - it is what I did on my Scott Spark and am using a black nylon bolt to save even more weight - there is no major load on that part and after maybe 3 or 4 rides, all is well.
.... but back to the topic - I have spent probalby similar if not more on Ti bolts, mainly rotor bolts and to hold non-critical parts e.g. brake levers and shifters - also brake callipers (ok, those can be termed as critical). Bolts I have are from Taiwan - seller is manda someting and so far no problems.
re: Ti rotor bolts - it is the clamping force that holds the rotor to the hub i.e. using friction between the two sufaces so as long as they are done up tight (and I always use loctite to prevent unscrewing), then that should be fine. Some of the WW are using 3 Al bolts and 3 Ti bolts to hold on rotors, not sure I want to risk that..... :o
Oh, and none of this Ti goodness has been put on my proflex, that is weigh ::) too heavy for that.
PS Are you the guy who has the rear swing arm with TIG welded brake calliper mount?
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Saving weight by replacing pretty much any bike part, bolts to bottom brackets, is a waste of time. You can drop as much weight by taking a dump before you ride. My primary concern was corrosion resistance.
I have a rear disc caliper mount, yes. Shovelon was the one who installed it.
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Saving weight by replacing pretty much any bike part, bolts to bottom brackets, is a waste of time. You can drop as much weight by taking a dump before you ride.
nonsene :P unless you can you guarantee you can do one before each ride.
If you have ridden a 12 kg full suspension bike and then a 9 kg full suspension, you will notice a huge difference in the responsiveness and effort needed to shift the bike.
My primary concern was corrosion resistance
Stianless steel would have done that for you for much less cost. :P
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Saving weight by replacing pretty much any bike part, bolts to bottom brackets, is a waste of time. You can drop as much weight by taking a dump before you ride.
nonsene :P unless you can you guarantee you can do one before each ride.
I don't need to. The point was to demonstrate that the most effective way to shave a substantial amount of weight from a bike is for the rider to lose weight. I drink two glasses of water before every ride, to increase my blood volume so I don't get lightheaded. That works out to 710g "extra" weight I'm carrying with me; there is nothing I can do to the mechanical systems of my bike to add or remove the same amount of weight.
If you have ridden a 12 kg full suspension bike and then a 9 kg full suspension, you will notice a huge difference in the responsiveness and effort needed to shift the bike.
I have ridden full-suspension bikes lighter than mine, and yes they feel snappier, presumably because the bike itself has less inertia -- but the heaviest part of the bike is always the rider. Shaving off a half a kilo here or there will make zero difference in the actual performance of the system, compared to the mass of my body which is both the heaviest and highest-elevated component. Physics is physics.
I'd be interested to know where you found a bike that weighs 25% less than another comparable bike without having super-thin tubing that gets dented when you sneeze on it.
My primary concern was corrosion resistance
Stianless steel would have done that for you for much less cost. :P
No, it wouldn't have. Titanium may be more elastic than carbon steel, but stainless steel is much easier to permanently deform. That makes it a bad choice for load-bearing bolts. Also, while I have no intention of riding my bike in the ocean, stainless steel does discolor when exposed to saltwater. By comparison, titanium is so corrosion-resistant it can be used to store chemicals that are so nasty they'll even burn sand. (Google "chlorine trifluoride" if you're curious.)
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quote]
I'd be interested to know where you found a bike that weighs 25% less than another comparable bike without having super-thin tubing that gets dented when you sneeze on it.
My Whyte PRST-1 , without pedals weighs 14.03 kg, compare that to my lightest full suspension bike, Scott Spark that weighs no more than 10.89 kg, inc pedals (I put on lighter wheels since so is about 400 g less), not super thin tube but carbon fibre goodness.
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Ah, okay, yes, carbon fiber does save a lot of weight. Personally I don't like it as a frame material, because it feels "dead" compared to metal frames, but that's personal preference more than anything else.
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The Ti bolts that came on my 5500 have had no problems dealing with my 220lb frame.
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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
Just to follow up on this: Almost 5 years later, the titanium bolts (including the upper shock eyelet bolt) are still in pristine condition. Not a problem with a single one of them.
Also, my god, I only spent $100 on bolts for my bike and I felt like it was a fortune. Nowadays I drop that much on one of my RC cars every couple weeks. (I wonder if smoking would've been a cheaper hobby *including* the eventual cancer treatment, honestly.) Times sure do change.
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Saving weight by replacing pretty much any bike part, bolts to bottom brackets, is a waste of time. You can drop as much weight by taking a dump before you ride. My primary concern was corrosion resistance.
I have a rear disc caliper mount, yes. Shovelon was the one who installed it.
Just reading back a little... I was told this by my local wheel builder. I wanted
tie dye titanium spokes snow flake laced to go with my hope titanium hub's
(Purple) with campagnolo mirox rims.......he wouldn't do it,he said I'm wasting
my money and I should just take a dump instead. With the difference in cost
I treated myself to U.S.E bar's, bar ends and seat post. He fitted me double
butted spokes and said if I buckled them he would tru them for free....I rode
them for 2 years on two bikes (pro-flex 552 cracked)trouble free every day until my
bike was stolen. 15" Park pre scepter comp with girvin forks....would love to
know if it's still out there. :'(
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Holly thread revival!!!!!!!!!!!!!!!!!!!!!!!!! :o :o :o :o :o :o
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Things are kinda slow around here. ;)
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ahhh the ninetys were a purple kind of decade
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I missed mountain biking in the 90's. My Pro-Flex was made in '96, but I bought it in '98, and it was the first adult-sized bike I ever owned. I remember how big and ungainly it felt compared to my Huffy Sonic 6, which was way too small for me at that point, even though I kept riding it like it was a BMX bike until well after I bought the Pro-Flex. In any event, neither one ever had any purple-anodized aluminum parts.