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Rear Wheel & rack weight question

  • 27-09-2010 1:30pm
    #1
    Ole Rodrigo
    Closed Accounts Posts: 3,013 ✭✭✭


    Hi,

    I'm planning to mount a rack+rack bag on my bike for a week long tour, covering about 7/800 km and am wondering if I should change the tyre to accommodate the extra weight. At the moment its a 700X26 racing tyre and the rack + bag weight will be about 4.5 KG. Its not a touring frame, but has lugs for the rack and clearance for a 28mm.

    I have a Schwalbe Marathon 28mm. My question is whether the extra rolling resistance would be a worth the trade off for additional strength/ puncture protection ? Or would I get away the 26mm...

    Any advice would be appreciated, cheers :)


Comments

  • #2
    rp
    Users Awaiting Email Confirmation Posts: 1,227 ✭✭✭rp


    rocstar wrote: »
    I'm planning to mount a rack+rack bag on my bike for a week long tour, covering about 7/800 km and am wondering if I should change the tyre to accommodate the extra weight. At the moment its a 700X26 racing tyre and the rack + bag weight will be about 4.5 KG. Its not a touring frame, but has lugs for the rack and clearance for a 28mm.
    )
    I use a rear rack for commuting, with laptop, I'd guess I've 10kg on the back (spares, tools, clothes, shoes...), and run on a 23mm Schwalbe Durano Plus. Tyre hasn't burst yet.


  • #3
    Lumen
    Registered Users, Registered Users 2 Posts: 31,142 ✭✭✭✭Lumen


    Since your rear tyre takes ~60% of your weight, 4.5kg directly over the rear wheel is just the rider being 7.5kg heavier, from the perspective of the tyre.

    Arguably your own weight is slightly better "sprung" than that of a rack bolted to the frame, but there's not much in it.


  • #4
    Ole Rodrigo
    Closed Accounts Posts: 3,013 ✭✭✭Ole Rodrigo


    Hi Lumen

    How do you mean Sprung ?


  • #5
    Lumen
    Registered Users, Registered Users 2 Posts: 31,142 ✭✭✭✭Lumen


    rocstar wrote: »
    How do you mean Sprung ?

    Your body is a big squishy meatsack. When you hit a bump it doesn't jolt the bike the same way as a load directly bolted on to the frame.

    For instance, when you see a big pothole you'll instinctively take the load off your end and on to your feet and arms. This acts to suspend your bodyweight and cushion the impact. A rack/pannier can't do the same thing.

    Therefore your bike can take more rider weight than it can directly attached load.


  • #6
    Ole Rodrigo
    Closed Accounts Posts: 3,013 ✭✭✭Ole Rodrigo


    gotcha :o

    thanks !


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  • #7
    blorg
    Registered Users, Registered Users 2 Posts: 15,995 ✭✭✭✭blorg


    26 will be fine for 4.5kg on the back. 28 would not in itself have noticably different RR (although it would be more comfortable and protect the bike better) but the standard Marathon isn't great that way compared to a race tyre.

    Bear in mind that 4.5kg is no ta lot. I am at about 3.5 with a saddlebag sans rack. I would suggest a Tortec Ultralite at 400g. Personally I would go for either a single pannier (there is no balance issue) or a pair of very small ones over a rack pack, the weight is better lower down.

    @Lumen- the fact the weight is strapped to the frame makes a major difference. Going over a pothole most riders will instinctively get out if the saddle and transfer their weight forward once the front wheel is over. It is far worse than 7.5kg more on the rider in my experience.


  • #8
    Lumen
    Registered Users, Registered Users 2 Posts: 31,142 ✭✭✭✭Lumen


    blorg wrote: »
    @Lumen- the fact the weight is strapped to the frame makes a major difference. Going over a pothole most riders will instinctively get out if the saddle and transfer their weight forward once the front wheel is over. It is far worse than 7.5kg more on the rider in my experience.

    That's what I said, in a needlessly complicated fashion. :)


  • #9
    blorg
    Registered Users, Registered Users 2 Posts: 15,995 ✭✭✭✭blorg


    I should have been more clear myself; I got that you understood why, my issue was with your statement that there was not a lot in it- there IS a lot in it!


  • #10
    Ole Rodrigo
    Closed Accounts Posts: 3,013 ✭✭✭Ole Rodrigo


    blorg wrote: »
    I would suggest a Tortec Ultralite at 400g. Personally I would go for either a single pannier (there is no balance issue) or a pair of very small ones over a rack pack, the weight is better lower down.

    .

    Thats actually the rack I have, Blorg. Interesting about the weight being better lower down the rack rather than on top. I wouldn't have considered that tbh, the bag I have has folding side panniers so thats grand. Thanks.


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