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  1. #1
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    Mounting bike racks on wagon rear hatches. Dangerous?

    Hi Folks,

    I'm new to this forum; I hope I can tap your experience. We need to purchase a bike rack and are leaning towards a trunk-mounted model because it could be more easily swapped between our cars (a Jetta and a Subaru Legacy wagon). Plus, we're contemplating a minivan in the near future, so a roof rack could become more of a hassle with a taller auto. At a retail store (LL Beans) this morning, we were told that one should never mount a rack on the glass of a rear hatch (i.e., our Subaru) because it places too much stress on the glass. I'd never heard that before, I routinely see people doing precisely that, and I've never heard of any problems. But what do you think? Should I heed this warning? Have you ever heard that this is a concern?

    Many thanks for your thoughts.

  2. #2
    Senior Member Retro Grouch's Avatar
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    Check the Thule or Saris fit guides. They have model-by-model instructions for installing strap on bike racks.

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    Senior Member DieselDan's Avatar
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    You can mount a strap rack onto a rear door of your cars. Do not allow the lower supports of the rack to rest on the glass, as that supports the load and will break the window. Make sure the lower supports are on the bodywork of the hatch. I've done this with minivans many times without ever breaking a window.
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    I mount a Saris Bones 2 on a Ford Escort wagon, top (middle) arm on the glass. No problems. The instructions say the two lower legs are to rest on the bumper, but mine rest on the licence plate indentation so I can more easily open the hatch with the rack on.

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    Much like passenger doors without a frame surrounding the window, there are hatches where the upper part of the rear window isn't surrounded by a metal frame. It's a bad idea to hook the upper straps around the edge of the glass in this case. I'm car shopping myself and there was a 2004-ish Hyundai Elantra I had to walk away from because I couldn't put a rack on it.

    I recommend checking the fit guides for Yakima and Thule too. There could also be notes saying it's ok if the lower bar is resting on the bumper. In you don't do that the straps could be left carrying the entire load and I'm not sure they're rated to do so. Same thing goes for a mini-van.

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    +1 on the Saris Bones.

    I have a Bones 3. I bought it because of its versatility. I don't own a car, so I never know what sort of car I'll have to attach it to.

    I know from experience that it works just fine on a Subaru Outback and Subaru Tribeca. The online installation guide video shows it being mounted on a Ford Explorer. I've also used it on regular cars with trunks.
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    Straps can break

    Quote Originally Posted by Retro Grouch View Post
    Check the Thule or Saris fit guides. They have model-by-model instructions for installing strap on bike racks.
    I dumped my bikes on the interstate yesterday (no one hurt, minor damage to car behind me, bikes severely damaged, $300 ticket for me) because the straps running up to the Prius hatchback top edge broke spontaneously. Next time I use that kind of rack I will incorporate a safety "leash" from the car frame to the bikes and rack (as with a car trailer) to minimize damage. Maybe the rack manufacturers should consider incorporating this safety feature.

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    consider adding a trailer hitch receiver to the under side of the car, then you can fit a multiple bike rack in,

    or tow a light trailer for your bikes and gear..


    BTW sunlight , UV , damages the plastics in Nylon and other polymer Plastics , so replace your straps every few Years with New ones .

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    Most of the rack companies have fit guides that indicate what will or will not work for most cars. E.g., my small SUV won't take a trunk rack because it has a built-in spoiler on the hatch. Some car models allow a rack to be attached to glass, but there is a special kit for that - most will not allow it (from a liability perspective). I'm with the LL Bean guy in regard to hooking a rack on glass unless the fit guide says it's OK.

    Check the Thule site to see what will work for your cars. Yakima also has online fit guides.

    Buyer's Guide - Thule

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    Quote Originally Posted by PDenton View Post
    I dumped my bikes on the interstate yesterday (no one hurt, minor damage to car behind me, bikes severely damaged, $300 ticket for me) because the straps running up to the Prius hatchback top edge broke spontaneously. Next time I use that kind of rack I will incorporate a safety "leash" from the car frame to the bikes and rack (as with a car trailer) to minimize damage. Maybe the rack manufacturers should consider incorporating this safety feature.
    rigging anything requires an understanding of a simple but often overlooked physical principle.



    As the strap angle becomes flatter the load increases dramatically. that's going to happen on the flat back of a Kia Soul like I drive or the flat profile of something like a Prius even though the straps and rack are in a much more horizontal plane. In fact it may be worse on a Prius since a rack in a more vertical position would tend to unload either the top or the bottom and almost flat stretched out straps on a hatchback would convert vertical shock loads, (bumps) into center loading on the two straps like the most extreme end of the chart..

    It's impossible to rig a strap mounted rack to a flat back or hatchback without getting strap angles under 20 degrees or so.
    Last edited by TGT1; 07-26-15 at 09:56 PM.

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    Senior Member Nermal's Avatar
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    Quote Originally Posted by TGT1 View Post
    rigging anything requires an understanding of a simple but often overlooked physical principle.

    As the strap angle becomes flatter the load increases dramatically. that's going to happen on the flat back of a Kia Soul like I drive or the flat profile of something like a Prius even though the straps and rack are in a much more horizontal plane. In fact it may be worse on a Prius since a rack in a more vertical position would tend to unload either the top or the bottom and almost flat stretched out straps on a hatchback would convert vertical shock loads, (bumps) into center loading on the two straps like the most extreme end of the chart..

    It's impossible to rig a strap mounted rack to a flat back or hatchback without getting strap angles under 20 degrees or so.
    Yep! That's one of the first things I had to learn as a journeyman machinist when I hired on at a coal fired power plant that used chokers almost every day. Strange, the things most machinists never even heard of.
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    I have a thule rack that goes on the hatch. I use on my Subaru Impreza and Kia Soul. Check the fit guide and you will be good to go. I put roof racks on my Subaru. I prefer the roof racks.

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    +1

  14. #14
    Senior Member tarwheel's Avatar
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    TGT1,

    Please explain your chart or add a graphic. It is not clear to me what the angles are measuring. Are these angles in relationship to the roof line, the back window or what?

    To the OP, I would recommend a hitch rack. I have used roof racks, rear window/trunk racks and hitch racks. Hitch racks are far superior in terms of strength, ease of use and safety. Roof racks are an accident waiting to happen, and many many cyclists have destroyed their bikes and serious damaged their cars by driving into garages or hitting overhangs. They also create a lot of wind drag and noise, lowering gas mileage. With rear window/trunk racks, you are much more likely to scratch the paint on your bike or car, and they are a hassle to use. Hitch racks are out of the windstream, so do not add noise or affect gas mileage much. They are the simplest for mounting bikes as well.

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    The issue is with the angle the straps make with each other.

    While the nylon straps have plenty of overkill strength to handle any forces that even a hundred pounds of bikes on a removable rack could place on them, the forces on the anchor points/clips get incredibly high as the angle of the straps gets flatter and flatter even with low weights.

    From the chart a five degree strap angle multiplies the forces by over eleven times.

    That's not to say you can't safely rig one on say a flat back or top car, just don't flatten out the rack to where the straps are also almost flat too.

    That's kind of counter intuitive. I think most people who haven't dealt with rigging would assume that adjusting the rack so that it stands out a bit more and the straps make a sharper angle would increase the load on the straps. The opposite is true.

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