Trunk Bags and Center of Gravity- Mtbr.com
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  1. #1
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    Trunk Bags and Center of Gravity

    I recently changed jobs, and my new commute gives me the chance to mix in a few miles of singletrack each way Unfortunately I really should be carrying my laptop to and from work also (don't really want to pollute my home computer with work stuff). If I'm going to do this I would like to keep the weight off my back.

    I mostly ride a single speed 29er now, but I have an old trek with 26" wheels that I'd like to try using as a commuter. I've looked at some laptop specific panniers but it looks like heel clearance could be an issue because of the compact wheelbase. After a bit of searching I found this Topeak MTX Office Bag that seems like it could do the trick, but I have some concerns about it raising the center of gravity (though to be honest the old bike is so heavy that it would probably just raise the center of gravity to about where it is on my other bikes ). I plan to carry

    Has anyone ridden off road with this style of bag? Do they make for any balance issues? I'd be riding relatively tame singletrack but with a lot of log-overs and a few really steep downhills and creek crossings with it.
    Yeah I only carry cans cause I'm a weight weenie.

  2. #2
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    You sure you want to jolt your laptop on the trail? I use a cheap Sette brand trunk bag on my commuter. I've loaed it to it's max and don't feel any adverse affect as far as center of gravity is concerned. Only thing I noticed is the weight it adds! Btw, the Sette bag is around $5 at PricePoint. I actually have a spare I bought when PP had free shipping. So cheap and works great.

  3. #3
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    For singletrack, I'd keep the laptop on your back.

  4. #4
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    I'm not terribly worried about the jolt - the drive will not be spinning and I will probably end up replacing it with a solid state drive anyways. I'd rather wreck the laptop than my back anyway

    AlmostGreenGuy, are you recommending keeping the laptop on back for the laptop's sake or for mine? I know it would get a lot less jolt on my back, but I'm more concerned about my already bad back than the computer.
    Yeah I only carry cans cause I'm a weight weenie.

  5. #5
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    I'm concerned about the laptop. A trunk bag on a rear rack seems like the worst possible idea for a laptop.

  6. #6
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    Are your concerns centered around any parts other than the hard drive?

    Do you think a pannier mounted to the rear rack would be a better choice?
    Yeah I only carry cans cause I'm a weight weenie.

  7. #7
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    Quote Originally Posted by AlexCuse View Post
    Are your concerns centered around any parts other than the hard drive?

    Do you think a pannier mounted to the rear rack would be a better choice?
    Continual vibration and jarring can effect many parts on a computer, and laptops are by far the toughest and most expensive to repair.

    A pannier is a much better option. If your Trek has a suspension fork, a front mounted rack might even be a decent option. But keeping the laptop on your back is definitely the safest option for your laptop.

    if the weight on your back is an issue, maybe consider a Built backpack. Very light.

  8. #8
    Fat-tired Roadie
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    Even if you still carry the laptop itself on your back, I think a pannier or trunk bag is a great idea. If you're only carrying a laptop on your back, it's not that bad anymore. It's the laptop AND battery AND everything else that sucks.

    I've run into the laptop/vibration discussion before. Personally, I wouldn't be hugely worried about putting one in a pannier, especially wrapped in a sweat shirt or something, if it didn't have any drives with moving parts. Yeah, there are some fans. But everything else is solid-state. How often do you replace this thing? I'd be even less worried about computers I just used for a few years and threw out. Which I know is the use pattern for a lot of people's work computers. (And, do you even pay for it in the first place?)

    I haven't used a trunk bag, but I found attaching things to the top of a rack to be a pretty crappy way to carry them - I definitely notice the weight more than if it's in a pannier.

    I've also found it's a lot harder to get the rear wheel up with a couple pounds of dead weight back there.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  9. #9
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    I use the Topeak MTX DX system on my rigid commuter and I haven't noticed that my laptop HDD's fail any more frequently than before (over three years). This system works fine for road commuting, there is plenty of give in the beam rack suspended from the seatpost which absorbs / damps vibrations. I also use the DXP pannier bag and have had this up at 9kg (it's design limit) and haven't found it causes any stability issues and much less than 9Kg in a rucksack.
    I backup my HDD weekly and dump the backup on the server at work and on a desktop HDD at home or a USB stick when traveling - I also wrote a windows script that will auto detect either the desktop, the server or USB and when saving documents will auto save a copy in those locations - so it doesn't really matter if the LT breaks - I do that anyway regardless of whether commuting or not - it's a pain in ass when any HDD fails full stop!

    I have tried this system out on my full sus (2010 Epic), with the DXP bag and it is not good and wouldn't recommend it for use on single track / off road generally:
    1) The rack can and does rotate around the seat post when ridden on trails.
    2) At moderate loads it upsets the COG and stability of the Epic, for some reason it seems to cause front wheel traction issues,
    3) It has too many potential single point failures - the QR bolt, the hinge and the welds on the rack any one of these goes its going to hit the ground which would be very likely to damage the LT.

    If you are only carrying a laptop you could carry it on your back for the terrain you are talking about in a good pack, it is not going to weigh much more than a 1.5 Litres of water in a Camelbak. Would it fit in the front triangle? - if so you could get a custom bag made up and cut out some foam to hold the LT and PSU in there would be better there in terms of COG / Stability than any where else and won't cost much if any more than the Topeak set up

    EDIT: Scratch the front Triangle Idea unless it's a tiny LT - just took my LT down to my XL 700c commuter to see and there is no way it will fit - nice idea though!!!

  10. #10
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    Thanks for the ideas guys. The build backpacks look a bit sparse for my needs (I'd like to be able to carry a little extra) but this Deuter giga flat looks promising.

    I found some parts around the house over the weekend that have potential to change my commuting setup significantly. I will update as things take shape.
    Yeah I only carry cans cause I'm a weight weenie.

  11. #11
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    I recommend keeping it in a backpack for a couple reasons:

    Weight on your back probably has less effect on bike handling than weight on the bike. My commuter bike has a rack and milk crate, so the bike's center of gravity is higher. I've noticed if the front wheel leaves the ground or loses traction for some reason (usually while I'm pushing the bike), it is unstable and forcefully tips over because of the extra top weight. I've had a few close calls while riding if I lift the front wheel up while going around a turn.

    The one time I made the mistake of putting my laptop (which was in my backpack) in the milk crate, it ended up with a dent in the side, and a jar of mango chutney exploded all over my backpack. I was coming back from the store with some groceries, and I was feeling lazy and didn't want to carry the backpack. My lock was resting at the bottom of the milk crate, and the backpack with my laptop and groceries in a separate compartment was on top of the lock. I figured it would be OK since the backpack has a slightly padded laptop sleeve, but no. It turns out, since the rear of the bike is rigid, any bumps it hits are directly transmitted through the rack to any cargo. All I did was hop down a curb and go over some small potholes, but the bumps were enough that the U lock dented my laptop and broke the jar of mango chutney.

    Riding single track with a laptop on the bike would be the equivalent of dragging it on the ground behind you. It's much better to keep it on your back where the weight won't affect the bike's handling and where your body absorbs the bumps.
    Matt

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