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  • Mine is a bit battered and one of the rack mounts has a thread stripped along with other dodgy mods otherwise I'd offer it

  • What size? I have no issues fixing problems

  • I've built my partner a rather large trailer and now need to add a surface.

    The surface needs to carry a multitude of kids bike and an adult bike, in all weathers. The frame is made of 30mm wide aluminium profiles with 8mm slots and I have nuts with M6 threads.

    The overall dimensions of the surface need to be 2040 x 1000mm and I'll cut out where the wheels go. In the photo below, I've mounted the axles on the wrong side of the frame, but now I've corrected that and the crosswise supports are level with the side rails. The width between the inner rails (inboard of the wheels) is 680mm, so 710mm between mounts, and along the length of the trailer the longest gap is 550mm.

    I'm thinking a sheet of HDPE, Nylon 6 or 66 or polypropylene would work, but I don't know how to calculate how thick a sheet of each material would need to be to support about 120kg of unevenly distributed bicycles, without adding an extra 5pk just for the surface. I've run out of bolts, so can order button-head screws if the sheet is too thin to countersink.

    There is a supplier about 20 miles away so it'll cost be about ÂŁ5 to fuel my van to collect from https://www.visionplastics.co.uk/

    Any engineers feeling curious and helpful?


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  • Ahh, too small. Thanks though!

  • No prob, if you end up with a 135 rear spacing I also have an old Day One wheel for ya đź‘Ť

  • I'd use buffalo board it's very high quality weather resistant ply with a tough, durable non slip coating on the front / back. I've used it the past for all kinds of applications including boarding out my old trailer bed and it lasted years sat in wind/rain/snow when not in use and being heavily abused when in use.

  • Not an engineer, but I think you should be looking at this:

    https://www.engineersedge.com/calculator­s/flat-plate-deflection.htm

    The dimensions should be 700 x 550mm
    HDPE has a tensile modulus of about 1200 and a poisson ratio of 0.46.

    You'll probably want it to survive a sizable child standing on one foot in the center of a gap. Let's say a child's foot has a contact patch with a radius of roughly 30mm and at 50kg that would give (500N/(pi*30mm^2) 0.2N/mm2.

    A sheet of 15mm thick would then give you a displacement of ~4mm, which sounds acceptable. But that sheet would weigh about 30kg, which is a bit much. If you reduce that weight to 20kg by making the weight 10mm you'd get a displacement of 15mm, not sure if it'll survive that and don't know how to tell. Perhaps tell your children not to climb on the trailer, you'd get away with a far thinner sheet.

    These are static loads though, riding over rough roads will introduce all sorts of vibrations but I had switched to the design faculty by then so I don't have a clue.


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  • Looks like it would work, but heavy if the thinnest they do is 9mm, which is probably overkill given the spans and loading. Also couldn't find a vendor near me, so that'd add 30-50% onto the price.

  • Thanks, I'll throw some numbers into that for the various materials. It'll only be carrying bikes, no humans, and each 10-15kg bike will be upside down spreading its weight over 3 points.

  • Given this datasheet: https://www.aiplastics.com/media/amari/d­atasheets/Nylon-6%20Datasheet.pdf

    Is there enough information to get the Modulus of Elasticity and Poisson ratio? There is a tensile modulus of elasticity, but the unit is MPa. and there's no mention of Poisson.

    edit: google says 1 MPa = 1 N/mm^2... and typical poisson ratio for Nylon 6 is 0.42

    I'm assuming that calculator is for a plate just supported at the edges, whereas my sheet will be bolted down to a rigid frame, so different calc needed? Taking advantage of the tensile strength to compensate for a lack of rigidity?

  • I know the answer is carbon fibre, but I don't thing anyone sells sheets this big at a reasonable price.

  • the rims wear out and people can't find replacement rims at a sensible cost.

    That is true, we quote a Shimano RS81 time; they’re a couple hundreds!

  • I know the answer is carbon fibre

    I think the answer is probably Aluminium. Your 2040Ă—1000 sheet in 2mm 5-bar treadplate would be just over ÂŁ150 delivered and 11kg

    The advantage over plastic is high elastic modulus and high strength, so you can use a much thinner sheet.

  • honeycomb

    Obvs., but I looked a couple of months ago and it's hard work getting small quantities at anything like a reasonable price. In this lightly loaded and well supported application, there's no real advantage over solid aluminium treadplate.

  • Fair enough. I guess if it was less well supported than it is, you'd be looking at thicker and heavier chequer plate to reduce bowing / flex..

  • I'm not sure whether the price or weight is most disturbing, but my expectations of cheap plastic sheet were probably a tad optimistic. Smooth sheet is about ÂŁ25 cheaper than treadplate though.

    More contemplation due.

    Ta.

  • Foo, that is way different than the buffalo board I've always known, basically a lightly heat pressed fibreboard made from whatever garbage was hanging about that day after all the real composite materials had been manufactured.

  • Freehub on my Dura Ace 9000 rear hub is shot.

    Had this problem recently. Bike had this maddening clicking, I thought from a dry or pitted hub. Turned out to be a broken 11sp centrelock freewheel on a nearly unused wheel, which can’t be serviced only replaced. How or why is a mystery.

    Wondering if a cheaper freewheel model would work? I don’t particularly want to cheap out, but is there really a big difference between a titanium and alum freehub?

  • The cheaper Shimano freehubs are steel not aluminium, so will be heavier than the titanium freehubs used on Dura Ace models.

  • But I don't think that's a problem for a lot of people if you're talking about a ÂŁ200 freehub replacement compared with ÂŁ30 Ultegra one. But are they compatible?

    EDIT

    I just found a YouTube clip
    https://youtu.be/e6Z5QcngH6A

    In the comments someone asks the same question and the mechanic replied saying as long as they are both 11 speed you can use a Ultegra hub - heavier but almost 10 times cheaper!

    EDIT 2

    SJS Cycles also state it is compatible on their website

    https://www.sjscycles.co.uk/hub-spares/s­himano-ultegra-wh6800-cassette-freehub-b­ody-y49398060/

  • I posted this elsewhere but didn't get a reply, hoping someone in here will be able to help out!
    My Look S Track pedals are starting to get really crunchy, they don't run smoothly at all. I've had a quick google and it seems like they're pretty tricky to service, has anyone had a go at it? I bought them secondhand and had them on my work bike for a long time so they've taken a bit of a beating and have done a lot of miles. If they're not worth servicing I wouldn't feel like I hadn't got my money's worth.

  • Replacement chainrings for shimano m569? What are the options?

  • I have these (but am going to replace soon, in case you're after some cheap spares down the line) and have found them pretty easy to open for cleaning and greasing. Grip this bit with pliers and unscrew. The RH pedal has a LH thread. Mine are a plastic thread, so are easy to over-tighten.


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Any question answered...

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