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talking of steel, how about bolts?

Old 07-27-15, 01:51 PM
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elcruxio
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talking of steel, how about bolts?

As I have a 2 bike project going on currently I recently went to buy replacement and installation bolts for the bikes. I bought m5's and m6's in various lengths as stainless bolts. Also got myself some loctite 243 (gotta love the hidden pro hardware store). I had no idea about various grades of bolts but have since learned that there are in fact different steels used for bolts.

The bolts I got are stainless grade 8.8 which I suppose works well enough for any standard bicycle applications such as stem or bottlecage bolts. But I started thinking whether or not I should upgrade our rack and brake mount bolts to grade 12.9? Or is 8.8 sufficient for that and just carry spares? Getting broken bolts out can be a chore however...

Also, anyone had bolts loosen when using loctite? I suppose retightening every week or so on tour is recommended but it also wears the threads in the frame/bolts so I'd rather get away with minimal retightening. Using nylock nuts is a possibility with front racks but those won't fit either of our frames in the back.
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Old 07-27-15, 02:56 PM
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I didn't know they even made 8.8 stainless bolts. If you are thinking of 12.9 I don't think they exist in stainless steel ( I could be wrong ). If you are carrying heavy loads on your racks I would certainly consider getting something higher than 8.8 grade bolts. M5 bolts of 10.9 or 12.9 grade are easy to find, but like I said I don't know if they exist in stainless. For brakes, whatever comes with the bike is fine, I've seen broken rack bolts but never any broken bolts on brake mounts.
I've never seen a Loctite fail.
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Old 07-27-15, 02:59 PM
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I have occasionally heard of a M5 bolt failure on a rack bolt, but it is rare and the type of bolts are rarely described. An M6 seatpost bolt can also fail. But I can't remember hearing of any other bolts that have broken. I however prefer a threadless stem with four bolts, not two, that hold the front plate on because I am always nervous that I might strip the threads on an Aluminum stem.

Locktite, I usually use blue but not sure what number. Sometimes I use a competitor to Locktite. I think it a good idea to use Locktite (blue) on rack and kickstand bolts. Some cantilever brake mount bolts come with a blue locktite already on them.

Other bolts I almost never use Locktite, but I often use grease instead. Using grease (a lubricant) to prevent bolts from coming loose and falling out is not intuitively obvious, but it works rather well because grease is a very viscous fluid. Thus, the viscosity will often help prevent a bolt or nut that is loose from vibrating.

A friend had a rack bolt from the seat stay mount fall out. No grease or Locktite was used on that bolt. I am aware of that episode because I loaned my friend a bolt to replace the one he lost.

If a bolt feels tight, there is no need to make it tighter, thus no wear occurs on the threads. I do not make a habit of checking all bolts on my bikes on any form of schedule.

But, if tightening a bolt will cause plastic to deform, then the bolts can loosen as the plastic deforms over time. Three examples come to mind, (1) Greenfield kickstands that mount on the rear chain and seatstays compress the plastic that wraps around the stays, (2) shoe cleat bolts initially loosen as the plastic shoe sole deforms under pressure from the cleat, and (3) brake levers that use a plastic body (Cane Creek, Tektro drop bar levers) will need to be retightened after initial installation. Thus, I do specifically check these bolts soon after installation and retighten as necessary. And I use Locktite on the kickstand and cleat bolts.
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Old 07-27-15, 11:24 PM
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Last year I went to LBS for some fender/rack bolts & they barely had any. Mech half-heartedly suggested chain hardware store. But Home Depot/Lowes metric bolts aren't really designed for tough bike use, they seem prone to rust. Cheapo black finish. Must be somebody selling nice chrome-plated bolts for bike use. Rack bolts would seem to be the weak link & thus important to ensure using a good quality esp w/disc-compatible mounting that uses long bolts.

I like that component makers are using Loctite but I never had much problem with nuts loosening unless under-torqued. Seems that w/heavy use one should check all bolts anyway.
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Old 07-28-15, 01:08 AM
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Originally Posted by DropBarFan View Post
Last year I went to LBS for some fender/rack bolts & they barely had any. Mech half-heartedly suggested chain hardware store. But Home Depot/Lowes metric bolts aren't really designed for tough bike use, they seem prone to rust. Cheapo black finish. Must be somebody selling nice chrome-plated bolts for bike use. Rack bolts would seem to be the weak link & thus important to ensure using a good quality esp w/disc-compatible mounting that uses long bolts.

I like that component makers are using Loctite but I never had much problem with nuts loosening unless under-torqued. Seems that w/heavy use one should check all bolts anyway.
You might want to try to find out the bolt grade in your local hardware store. The 12.9's (almost 2x the strength of 8.8 bolts) I'm going shopping for today are in black finish.
I'm going to solve the rusting issue on those by using loctite in the threads and frame saver on the bolt head.
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Old 07-28-15, 01:30 AM
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Originally Posted by DropBarFan View Post
Last year I went to LBS for some fender/rack bolts & they barely had any. Mech half-heartedly suggested chain hardware store. But Home Depot/Lowes metric bolts aren't really designed for tough bike use, they seem prone to rust. Cheapo black finish. Must be somebody selling nice chrome-plated bolts for bike use. Rack bolts would seem to be the weak link & thus important to ensure using a good quality esp w/disc-compatible mounting that uses long bolts.

I like that component makers are using Loctite but I never had much problem with nuts loosening unless under-torqued. Seems that w/heavy use one should check all bolts anyway.
Go to Ace Hardware. They have a much better selection of bolts. (They tend to also have someone in the store who knows bolts and can help you find the right one for the job.) The local Ace has been my goto for bike bolts for years. Don't be fooled by rust. Many of the strongest bolts rust as they are made from stronger and harder steels than most stainless. Grease the threads liberally. It will take years or decades for rust to do damage that matters to the heads (assuming you keep salt away).

Ben
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Old 07-28-15, 01:54 AM
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The thing I find a bit strange is the fact that rack bolts are M5's. I mean ok, most bolts in a bicycle are m5's but one would think that a heavy duty application such as carrying a lot of weight would warrant an M6. Brakes and especially disc brakes use M6's as mounting bolts.

I swear when I build my dream tourer frame the rack eyelets are going to use M6's all around and if possible, double boltable, although I don't think there are many racks out there that allow for double bolting.
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Old 07-28-15, 02:30 AM
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I would caution against using high-strength bolts to attach things such as racks. Even though the weight on a rack may be high, I would suggest that most ordinary bolts have lasted very well for many touring riders, and certainly in my own case.

Bolts in those situations usually break because they haven't been torqued properly. However, and here is the point of my post, if you use high-strength bolts and there is a "need" for a breakage, it will be your frame that breaks, not the bolt.

elcruxio, just what do you intend to carry that would create so much weight on a rack that is has you so concerned you have to use M6 bolts and even double-bolt? As I alluded to above, your rack and/or frame are going to fail before the bolts, and I know that I would prefer the bolt to fail first.

Stainless M5 are fine if you are concerned about rust. So are zinc-plated bolts.

I would suggest further that you invest in some nickel based thread prep; it's black and not as "clean" as grease (the stuff I have is black), but it is meant to prevent corrosion between threads of different metals and so far for me, so good.

However, if bolts continue to undo, Loctite 243 (definitely not the red variety) is a solution. But if proper lockwashers and flat washers have been used, Loctite shouldn't really be needed.
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Old 07-28-15, 02:47 AM
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I'm not sure of the grade, but I get my M5 and M6 stainless allen head bolts at Fastenal and after dozens of bolts on several bikes, I can say I have yet to have one break. I use Loctite blue on rack, fender and bottle cage bolts and have never had one come loose or seize.
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Old 07-28-15, 03:01 AM
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Originally Posted by Rowan View Post
I would caution against using high-strength bolts to attach things such as racks. Even though the weight on a rack may be high, I would suggest that most ordinary bolts have lasted very well for many touring riders, and certainly in my own case.

Bolts in those situations usually break because they haven't been torqued properly. However, and here is the point of my post, if you use high-strength bolts and there is a "need" for a breakage, it will be your frame that breaks, not the bolt.

elcruxio, just what do you intend to carry that would create so much weight on a rack that is has you so concerned you have to use M6 bolts and even double-bolt? As I alluded to above, your rack and/or frame are going to fail before the bolts, and I know that I would prefer the bolt to fail first.

Stainless M5 are fine if you are concerned about rust. So are zinc-plated bolts.

I would suggest further that you invest in some nickel based thread prep; it's black and not as "clean" as grease (the stuff I have is black), but it is meant to prevent corrosion between threads of different metals and so far for me, so good.

However, if bolts continue to undo, Loctite 243 (definitely not the red variety) is a solution. But if proper lockwashers and flat washers have been used, Loctite shouldn't really be needed.
We'll be using pretty standard touring weights on the racks we're using.

But the point you make is not actually a bad one. I was of the opinion that it be better that the frame break since then I'll get a new one from warranty buuuut waiting for one while being stranded somewhere in eastern europe might not be an optimal solution.

The thing I'm worried about is riding bad roads or gravel roads with loaded racks and the abuse the bolts will suffer as a result. Thus a stronger 12.9 bolt would resist said stresses better than an ordinary stainless 8.8 bolt (although apparently 8.8 is already relatively high strength)
I'm not worried about the bolts coming loose since I'll use loctite 243 and nyloc nuts where possible, and I'll be periodically checking the tightness of the bolts. I might add lockwashers as well just as a precaution.

I seriously don't want anything to break on tour so I'm trying to eliminate breakage variables beforehand. A broken bolt can be quick fixed with a bunch of ways but it most likely cannot be extracted By the tools I'll have handy (I won't be taking reverse drill bits with me that's for sure) so I'll need some kind of autoshop to do it for me which is a major pain... A logical solution to this is to use bolts that don't break even if you show them a little abuse in the way of bad roads.
The rack will not fail as it's the Tubus Cargo. It see it as a very unlikely scenario for it it break without an actual accident.
The Frame on my bike will likely fail before the bolt anyways since it's aluminum, but luckily the eyelets are positioned in such a way that failure is unlikely as well (dropout embedded)
IF the bolt fails this then creates a dangerous scenario which can possibly destroy the wheel / frame as well.

Decisions decisions...

I'm also thinking stronger bolts in terms of a possible expedition bike which may or may not have racks. Those cannot be nearly as loaded as in road touring but it would be handy to put the bulky stuff, such as sleeping bags and tent on carriers so I'd have more space for heavy stuff in frame bags / backpack.
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Old 07-28-15, 04:27 AM
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What did the rack manufacturer supply as mounting hardware?
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Old 07-28-15, 04:51 AM
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I use decent quality M5 allen bolts on my aluminium commuter frame. I had a problem with rack bolts working lose, no matter how they were tightened. I replaced the std washer with an anti-rotation star washer and resolved the issue.
I never get this problem on steel frames.

Tubus racks some with good bolts, but most other racks seem to use stainless-cheese hardware.
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Old 07-28-15, 06:04 AM
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Originally Posted by Darth_Firebolt View Post
What did the rack manufacturer supply as mounting hardware?
Tubus provides stainless bolts for the racks it sells, apparently A2 steel. Those have almost as good numbers as the equivalent 8.8 high tensile bolts
BUT
Apparently stainless bolts have the shear strength of only about 1/3rd of the 8.8 grade coated high tensile bolts.
Shear strength is probably the most important factor in rack bolts.

Tubus bolts have been known to snap even though their racks are the shiznit

I've decided to stick with the 8.8 grade bolts as they are actually not stainless but high tensile carbon steel with zinc plating. Together two 8.8 grade M5 bolts have a shear strength of upwards 1000kg (2200lbs for the imperials), and that added with the support the upper bolts give and what aid clamping friction gives we should be ok with those. The 8.8 bolts are actually a bit stronger than Cromo bolts so I'm cool with that.

I decided to stick with the 8.8 because the stronger 10.9 and 12.9 also have a higher hardness, which gives more strength but also makes the steel more brittle. Considering that a rack bolt needs to cope with a lot of vibration and banging, brittle is not the adjective I'm looking for in that context.

But I'm still going to get the 12.9 grade bolts for my front disc brake and as disc brake bolt spares as that is where the absolutely huge shear strenght of a 12.9 grade bolt shines. Considering I'm a big heavy dude and I'll be riding down mountains at some point with a loaded bike, I consider the added strenght a bonus.
a 12.9 m5 bolt has double the shear strength of a 8.8 bolt but discs are bolted with M6, so that's even more PAWAAAH!! (as Jeremy Clarkson would say)
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Old 07-28-15, 06:05 AM
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I have used everything from real good milspec bolts, to black M5 Internal Hex Socket Cap machine screws from home depot, to whatever junk came with racks and water bottle cages. The only ones I really avoided was the aluminum ones that came in the frame of some bikes. The only rack bolt problems I have seen on my bikes and the bikes of friends and family is vibrating loose. Even with heavy loads on rough surfaces I have not seen any broken rack bolts.

So my take is that unless you get some really poor quality bolts they aren't going to break or cause problems if properly installed and subjected to normal usage. If they do cause problems it is most likely that it will be because they vibrated loose not because they broke.

On the other hand I really don't see any harm in using better bolts. If I had them on hand when I was installing the racks I would use them, but I wouldn't bother seeking them out or swapping out bolts that are already installed.
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Old 07-28-15, 06:17 AM
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Second the suggestion of Ace for finding bolts; they have a fine selection of bolts. Also second the suggestion of using grease. I grease every bolt on a bike and have never had an issue with a bolt coming loose on a tour. Still after reading this thread, I might just switch to loctite to fasten the rack to my bike.
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Old 07-28-15, 06:43 AM
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Ive never had a broken bolt, but have had bolts loosen during trips. I have used heavy duty anti-seize grease on bolts since reading of this suggestion a while back and it does seem to help with the "coming loose a bit from vibrations" thing that invariably happens (to me anyway). I have an unopened blue loctite small tube that I will use on rack bolts in the future, figure a little bit of it can't hurt.

re broken or lost bolts--I am pretty much convinced that broken bolts happen when folks dont notice that a bolt is getting loose, and it makes sense to me that as a bolt loosens up on a loaded rack, the forces on the bolt go up incrementally the more loose and the more play appears. I have the habit of checking the rack bolts once in a while when I do a drivetrain clean when on tour (less so when I commute , but still check once in a blue moon).

I have also gone too far the other way and broken bolts from over tightening, seat post bolts, so have been guilty of this and have learned from mistakes to be more careful and attentive to how much I tighten stuff (its kinda like you overdo it worrying about stuff becoming loose.....)
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Old 07-28-15, 07:03 AM
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Tighten your bolts properly and they won't shear. Load bearing is by friction first, then shear. Friction is a function of the normal force times the coefficient.

Bolt Mechanics

Grease doesn't help prevent bolts from coming loose. They help you tighten the bolt to a higher torque, which in turn prevents them from coming loose.
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Old 07-28-15, 07:03 AM
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oh yeah, re rust. I did some cursory work on a really cheap bike of a friends friend recently, and this bike had been kept in a shed with a pool water pump etc that was running salt water in the pool. It was amazing how the cheap steel bits were rusted all to rat poop. One of the bolts holding down a brake cable was so rusted that after I cut the cable to replace it, I found I couldnt even get the allen key in it because of the rust, and had to use a pointy metal pawl and a small screwdriver to dig out the rust enough to open up the allen key shape enough to be able to get the key in enough not to round it out....
Was the worst rusting I'd ever seen, and it was all from the salt water mist etc from inside the shed.
All other rusting I've had on parts has been really slight surface stuff, not a concern at all, so I'm not sure its really a concern unless bolts are really really cheap.
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Old 07-28-15, 07:47 AM
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black steel 8.8, tightened down firmly, then applied paint.
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Old 07-28-15, 08:10 AM
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Originally Posted by elcruxio View Post
The thing I find a bit strange is the fact that rack bolts are M5's. I mean ok, most bolts in a bicycle are m5's but one would think that a heavy duty application such as carrying a lot of weight would warrant an M6. Brakes and especially disc brakes use M6's as mounting bolts.

I swear when I build my dream tourer frame the rack eyelets are going to use M6's all around and if possible, double boltable, although I don't think there are many racks out there that allow for double bolting.
Thorn rates their heavy duty expedition rack as:
Max load when used on surfaced roads:- When fitted with 6mm screws = 60Kg…when fitted with 5mm screws = 40kg. These figures should be halved when being used on South American Ripio.

Above from:
Thorn Expedition Steel Rear cycle pannier rack - B - 89.99

Even if off road or bad roads where they suggest cutting the weight rating in half, 20kg with M5 bolts on a rear rack is more than most people would typically carry.

If you build your bike with M6 rack bolts, you will find that some racks need to be drilled out to fit.
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Old 07-28-15, 08:44 AM
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And I would add that even on paved roads, tire width and pressures play a big part in the actual level of harshness of jarring when going over rough surfaces.

which to me it seems that along with if you bash into stuff regularly at higher speeds than someone else, is also a factor of the stresses going into rack bolts and the rack itself. Some people ride over rough stuff like a bull in a China shop and are regularly hard on their equipment anyway.
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Old 07-28-15, 10:24 AM
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I try to baby my gear on rough surfaces as much as possible because it's not comfortable and I absolutely hate truing wheels. I love building them, but if I have to true a wheel that _should_not_need_truing_ I get all nervous because I then think the whole wheel has been compromized
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Old 07-28-15, 02:24 PM
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We really overthink things don't we? Just don't use aluminum or Ti bolts, and on the bolts you do use grease them properly and check them before every tour.

BTW that Thorn rack is hideous.
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Old 07-28-15, 04:57 PM
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Originally Posted by elcruxio View Post
I swear when I build my dream tourer frame the rack eyelets are going to use M6's all around and if possible, double boltable, although I don't think there are many racks out there that allow for double bolting.
With a dream tourer, you can have your rack custom also. There are some guys out there who tour full time who just drill out the M5 and convert to M6. on some eyelets there is the beef for that though I haven't tried it.



A2 isn't a stainless to pick up on another point, but it is sure tough stuff and doesn't rust as badly as plain steel. It's a chromoly tool steel.

The problem with rack is that the hardware and BOs were never really designed for what we do with them. For fenders, fine, but for other stuff it is stretching the use.

Another thing to get them properly specked is to cut them to correct dimensions and use high end bolts as discussed here. Just as important as the bolts is the design and execution of the BO, which is pathetic. I like what they do for the pegs on some BMX bikes That's a fitting.
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Old 07-29-15, 10:09 AM
  #25  
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Originally Posted by veganbikes View Post
...
BTW that Thorn rack is hideous.
My point really was that they felt that off road, 20kg was the limit with M5 bolts. On smooth pavement, twice that.

In the very rare chance you are hauling more than that, then maybe the M6 bolts would be worth it.
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