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mounting best practices and carrying capacity of rear racks

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mounting best practices and carrying capacity of rear racks

Old 07-07-13, 04:49 PM
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seafood
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mounting best practices and carrying capacity of rear racks

I have an oldish road bike outfitted with fenders and a rear rack. Both of those I purchased separately and the rear fend and the rack are sharing the same eyelets for mounting. I had to go and get longer 5mm bolts, threw some lock washers on as well and all seems to be well. What worries me slightly is that fender stays naturally want to be on the inside (closer to chain stays), while the rack stays are stacked on the outside, closer to the bolt cap. So far, all's good (been carrying all kinds of cargo and just had about 40lbs of groceries and chain on a short trip without issues), but mechanically this isn't ideal.

The reason it's not ideal is because the really heavy bit is pushing down on the whole assembly further away than perhaps it was designed for from the point it wants to bend/pivot the bolt around. Attaching a crude diagram, if the text isn't clear:


My question is whether these kinds of installations are common and if people are having any issues with heavy cargo placing large stresses on 2 relatively skinny little bolts. I hope to take a multi-day tour alone with this bike in the months to come and am wondering if I need to buttress this configuration or just bring some spare hardware with me.
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Old 07-07-13, 04:59 PM
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I think you are over worrying. I've had some pretty hefty loads on there, without issue.
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Old 07-07-13, 05:01 PM
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Basically your concern is well founded and the rack stay should be placed inboard of the fender stay to reduce the load's leverage on pretty thin 5 mm bolts. I'd "customize" (read: bend) the stays as needed to get the rack supports inboard.
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Old 07-07-13, 05:03 PM
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There nothing wrong with your set up , people do it all the time . Just make sure the bolts are tight . If in drought use some blue loc-tide on the bolts .
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Old 07-07-13, 05:13 PM
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Whichever way you go, keep an eye on the screws to make sure they remain tight.

I have double eyelets on my 86 Rockhopper and a rack & fender set up is still a pain.
Maybe get a set of fenders for bikes with no eyelet mounting? I'd hate to see you "wallow out" the eyelets.
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Old 07-07-13, 05:29 PM
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Originally Posted by seafood View Post
. What worries me slightly is that fender stays naturally want to be on the inside (closer to chain stays), while the rack stays are stacked on the outside, closer to the bolt cap. .... but mechanically this isn't ideal.
.
You're right -- this is less than ideal because the heavier leg is outside imposing a bending moment on the screw, rather than against the eyelet where it would be pure shear.

If there's any way you can reverse these, do so and you'll have a more secure arrangement. Otherwise use heat-treated chrome-moly cap screws, or at least quality stainless once, instead of the typical standard hardware. If you're planning a long tour carry spares.

One trick, if you cannot pass the fenders outside the rack, is to place the left leg of the rack inside the dropout, with the fender outside. If you do this pass the bolt from the inside outward with a nut to retain the fender stays. That way your rack won't fall down if the nut loosens and falls off.

The beauty of this is that at least one leg of the rack is better secured.
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Old 07-07-13, 06:21 PM
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When in doubt head over to the Auto Parts store , ask for the same sized bolt in 8.8 type,
a high strength heat treated alloy steel .. It will be stamped on the hex head.

get properly tight and use a threadlock compound.
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Old 07-07-13, 06:31 PM
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Thanks for the ideas, folks! Looks like my worry isn't needless, though the sky isn't falling just yet. I'll try to reverse rack and fender stays and if that doesn't work, I'll get some stronger bolts and some spares.
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Old 07-07-13, 08:36 PM
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Originally Posted by seafood View Post
Thanks for the ideas, folks! Looks like my worry isn't needless, though the sky isn't falling just yet. I'll try to reverse rack and fender stays and if that doesn't work, I'll get some stronger bolts and some spares.
Do both, you can never go wrong with high quality hardware.
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Old 07-08-13, 04:19 PM
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You could also carry some p clips and hardware for back up. But under normal use scenario ( let's say 30 pounds riding on paved roads) I don't think you would need them.
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Old 07-08-13, 06:18 PM
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Was looking at the assembly today and realized there would be no easy way to swap the stays in place due to the available length of fender stays and where they want to intersect with the rack. But then I got another idea.

The holes in the frame let the bolts come out the other side and it looks like it'll be possible to have the bolt cap squeeze the rack stays to the frame, while the fender stays can be squeezed to the frame from the other side (from the inside of the bike) by a nut and washer. Think I'll try that next time I can make it to a hardware store.
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Old 07-08-13, 06:24 PM
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Originally Posted by seafood View Post
Was looking at the assembly today and realized there would be no easy way to swap the stays in place due to the available length of fender stays and where they want to intersect with the rack. But then I got another idea.

The holes in the frame let the bolts come out the other side and it looks like it'll be possible to have the bolt cap squeeze the rack stays to the frame, while the fender stays can be squeezed to the frame from the other side (from the inside of the bike) by a nut and washer. Think I'll try that next time I can make it to a hardware store.
This is what I suggested earlier, but a bit of safety advice. If bolting to the inside of fender eyes, put the head of the bolt on the inside, and nuts and washers on the outside. This provides minimum possibility of stuff getting loose between the frame and wheel, thereby lessening the chances of something slipping into and jamming the wheel.

While a locker rear wheel isn't as critical as a locked front wheel, it's no picnic if it happens at speed.
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Old 07-08-13, 06:40 PM
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Originally Posted by FBinNY View Post
This is what I suggested earlier, but a bit of safety advice. If bolting to the inside of fender eyes, put the head of the bolt on the inside, and nuts and washers on the outside. This provides minimum possibility of stuff getting loose between the frame and wheel, thereby lessening the chances of something slipping into and jamming the wheel.

While a locker rear wheel isn't as critical as a locked front wheel, it's no picnic if it happens at speed.
Ah, sorry. Missed your comment somehow. Thank you.

I was thinking about that too. What I like about having the bolt cap on the outside is that if a nut gets loose, the fender will likely rub against the tire, but will not cause much other trouble because the bolt itself will still be tight against the rack stay. On the other hand, if a nut on the outside gets loose, it may cause the loaded rack to slip off the bolt and tweak itself, dislodge the luggage or who knows what else. But your concern is valid and what I think I'll do to mitigate that risk of wheel entanglement is to put some reasonably tight plastic zip ties around fender stays and frame so as to keep them close to their intended position in case of nuts coming loose.
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Old 07-08-13, 07:05 PM
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Originally Posted by seafood View Post
Ah, sorry. Missed your comment somehow. Thank you.

I was thinking about that too. What I like about having the bolt cap on the outside is that if a nut gets loose, the fender will likely rub against the tire, but will not cause much other trouble because the bolt itself will still be tight against the rack stay. On the other hand, if a nut on the outside gets loose, it may cause the loaded rack to slip off the bolt and tweak itself, dislodge the luggage or who knows what else. But your concern is valid and what I think I'll do to mitigate that risk of wheel entanglement is to put some reasonably tight plastic zip ties around fender stays and frame so as to keep them close to their intended position in case of nuts coming loose.
Your thinking makes sense, the tire itself will keep the fender form settling too far, and a loop between the fender stay and carrier leg, will absolute assure that neither will jam the rear wheel.
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Old 07-08-13, 07:22 PM
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I have seen aluminum machine screws/bolts included with racks in the past. Make sure to use steel, as previously mentioned.
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Old 07-08-13, 10:13 PM
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On the two bikes I have with racks, I mount the racks to the seatpost binder bolt. With a 16 inch frame (c-c), it allows me to not bend the supports at all (which I think has to be stronger than bending them down to hit the seatstay mounts). Furthermore, when I carry my cable lock, I can wrap it twice around the seatpost and those rack supports hold it high enough to keep it from interfering with the cantilever brakes. Someone remarked to me the other day that the setup looked 'strange' but to me it seems a better alternative than bending the supports to mount on the seat stays.
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