Why aren't fat bike wheels spoked like car wheels?

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  • Why aren't fat bike wheels spoked like car wheels?
  • On fat bike rims where there are two rows of spoke holes offset from the centre, why are they laced left of hub to left of rim and vice versa, when car wire wheels are laced so that the spokes cross over, left to right and right to left?

    aP
    Member

    Weight saving.

    Surely the whole point of wire wheels on a car is weight saving over stamped disc wheels?
    I wonder if it’s something to do with the extra side loads when cornering with a four wheeled vehicle?

    scotroutes
    Member

    There was loads of stuff on mtbr about this. It was for offset builds where one side of spokes otherwise ended up in very poor tension. IIRC, some folk did it and it resulted in a noodly wheel. I imagine a car rim (like the one shown above) has more inbuilt rigidty than a single-skin fatbike rim.

    Isn’t that more of a problem with derailleur rear hubs?
    Front or Rohloff hubs should end up fairly well evenly tensioned.

    Premier Icon Pickers
    Subscriber

    I’d guess the loads on the car rim are quite different. Bike wheel loads are all pretty vertical (ground to hub?). Car wheel loads are sideways from the road (in cornering at least) as well as vertical. Probably. Not an expert though

    Premier Icon ampthill
    Subscriber

    Bike wheels have fairly low lateral loads

    Car wheels have huge lateral loads

    Ilove the way the spoking isn’t symetrical as the outer wheel has greater lateral load

    I expect on fat bike they are going for the shortest lightest spoke

    trail_rat
    Member

    ive built wheels like that MTQG .

    they were far from noodly scotroutes – more like STIFF AS **** and took a beating.

    i did it because 100mm alaskan cycles rims spoke holes were wider than the flanges on a rear hub – now THAT results in a noodly wheel.

    Premier Icon thisisnotaspoon
    Subscriber

    Surely the whole point of wire wheels on a car is weight saving over stamped disc wheels?

    Wire wheels on a car are for asthetics. They weigh a ton (about 30% more than pressed steel) and still flex.

    Premier Icon shaggy
    Subscriber

    The nipples are designed to sit pretty well perpendicular to the rim wall. That spoke pattern makes the angle too acute. I guess you could use semi-circular cup washers, dimple the rim (like on that car wheel) or similar but I don’t think the spoke angle is really a limiting factor in the strength of these wheel.

    trail_rat
    Member

    “dimple the rim”

    i forgot about that …. thats an experiance i never want to repeat.

    manually dimpling a rim inner with a punch is a fooking ballache

    Premier Icon AlexSimon
    Subscriber

    manually dimpling a rim inner with a punch is a fooking ballache ballpein

    ftfy

    Premier Icon thisisnotaspoon
    Subscriber

    Some actual weights.

    TR-3 stock disc wheel, 4″ tire seat width = 14.25 Lb.
    TR-3 48-spoke original wire wheel, 4″ tire seat width = 15.25 Lb.
    TR-3/4 60-spoke original wire wheel, 4.5″ tire seat width = 16.6 Lb.
    Morgan Supersport original 72-spoke wheel, 5.0″ tire seat width = 19.2 Lb.

    http://www.britishcarforum.com/bcf/archive/index.php/t-85684.html

    And that doesn’t include the additional weight of the knock on or the much heavier splined hub Vs the 4 nuts holding the wheel onto a modern hub.

    Premier Icon cookeaa
    Subscriber

    Next Question then;

    Why are Fat bike wheels still constructed using the traditional spoked method?

    If ever there was a candidate for reintroducing some version of mag wheels to bicycles it must be fat bikes, Low pressure tyres, great way of making a closed profile for tubeless use, and it’s not like anyone is using rim brakes so no need ot try and mould a braking surface into the rim profile, it’s not like using reinforced plastics and laminates in bicycle construction is frowned on these days is it…

    I now fully expect someone to show me a picture of a Fat-Mag wheel and a list of reasons why it’s a shite idea…

    Premier Icon cookeaa
    Subscriber

    Some actual weights…

    Fair enough, I’d always assumed they were used on old sports cars before the days of magnesium wheels because they were lighter than steel disc wheels and that Classic Motorsports page seemed to confirm it.
    I can see why people use them now, to give a car a classic look, but why were they used back in the days when classic cars were current if they were heavier than the alternative?

    Premier Icon epicyclo
    Subscriber

    Speaking from experience, old time car wheels used to crack from the bolt holes to the rim if you cornered enthusiastically (eg on two wheels) whereas wire wheels could handle it. 🙂

    I have always built my fat wheels with a crossover. It makes for an extremely stiff wheel. Disadvantages are the steep angle the spokes leave the rim, and the necessity to get the wheel perfectly true before putting any tension into it – it’s just about impossible to pull them into true. The steep angle puts a lot of the pressure on just one side of the spoke hole and can cause a localised crack.

    I would prefer to drill my own rims because then they could be dimpled first – although I’m not sure the alloy used in the rims would take kindly to dimpling, so that would depend on the alloy. Spoke washers are another option, but most of those I have are steel and I’m not keen on the dissimilar metals in a wheel that is likely to get dunked in salt water.

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