Why do tandems use 40 or 48 spokes when DH bikes use 32 or 36 ?

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  • Why do tandems use 40 or 48 spokes when DH bikes use 32 or 36 ?
  • I’d have thought that one rider regularly jumping over rocks and stuff puts a lot more strain on the wheels than two riders hitting the occasional pot hole.

    My guess is that back in the good ol’ days, it wasn’t worth making a new rim profile just for a limited number of tandems, so the easiest way to make a stronger wheel was to put more holes in a normal road rim and hub.

    Now that manufacturing processes have improved and got cheaper, and there are more DH bikes around than there ever were tandems, it’s easier to make stronger rims and hubs.

    Any truth in that ?

    I’m curious because I’m building up another tandem and wondering what hubs, rims and tyres to use. There’s far more second hand MTB than tandem stuff out there.

    Premier Icon Northwind
    Subscriber

    I suppose rears are torqued more? 2 people pedalling, and more force resisting.

    jonk
    Member

    Think about the sideways flex too.

    Disc brakes put more torque load on a wheel than any two riders ever will.

    belugabob
    Member

    Disc brakes put more torque load on a wheel than any two riders ever will.

    If this is true, it will be doubly true on a tandem, due to there being twice as many people involved.

    aP
    Member

    I’d be very nervous about riding our tandem with less than 40 spoke wheels, we’ve done rather more than hit the occasional pothole on ours.

    Sideways flex; that’s what I was originally thinking of. Landing a jump bike at an odd angle must put more side load on the wheel than a tandem cornering.

    40/48 spoke tandem wheels started in the days of rim brakes, when there was no braking torque load at all.

    There are lots of tandems around with 32h Rohloff hubs, so you can’t just dismiss anything with less than 40..

    martinxyz
    Member

    The extra weight of the bike and riders effectively pushing down on the hubs/pulling the spokes above the level of the hubs out of the rim is the reason why. Out of the nipples above the hub taking the load, I’m not sure how many at any given time would be taking the majority of the load (5,6,8?, who knows) it really would help to increase the amount of nipples sharing the load by 30%+ by adding a 40 hole rim.

    Not to mention the stress of trying to stop a hub (disc braked) with the weight of two riders/heavier bike.

    Never thought about it before but I suppose magura hydro rim brakes would probably be the best option.

    Premier Icon porter_jamie
    Subscriber

    i have often wondered why touring bikes have more spokes than a dh bike for example. maybe it is fatigue – a 32h wheel might be strong enough, but will fatigue earlier because of the higher payloads

    cynic-al
    Member

    Peak loads on DH bikes may be comparable but a tandems wheels are under twice the stress all the time.

    That said it wouldn’t surprise me if tandem makers hadn’t caught up with new technology

    Both my current tandems have 32h wheels, so far so good, but the MTB has monster DH type rims and the road bike has deep section alloy 700c rims. Having said that they might break any second of course.
    If you go for more spokes you need tough hub flanges or they break, less spokes and the spokes become a weak spot (?)
    You limit your hub and rim choice with more than 36 spokes. I was only interested in the availability of cheap second hand hubs, or what I had lying about.
    Anyhow, I seem to see plenty riders on solo bikes who probably weigh more than me and my stoker put together.

    yesiamtom
    Member

    dunno if I posted on the super-awesome-bike-riders facebook group MTG but we use 32h for mildish XC stuff. Ours is full susser though so that takes a lot of the sting out of potholes etc.

    jonah tonto
    Member

    8 inches of travel, that is why

    Premier Icon bedmaker
    Subscriber

    In my limited tandem experience I think the wheels get a far harder time than on a DH bike. There is no way to effectively unweight so the wheels are just slamming into stuff with the weight of two people all the time.

    pdw
    Member

    Tandems are often built for touring, so are designed to support two people plus luggage, meaning the forces in the wheel are going to be more than double when you’re JRA. A DH bike may take bigger hits, but it’s also got suspension which will significantly reduce the peak forces.

    Premier Icon singlespeedstu
    Subscriber

    The rear rim on our tandem would tend to agree with what bedmaker up there is saying.
    Even with a dual ply tyre pumped up to 40psi the rim is battered half to death.

    Suspension’s got to help, but rigid dirt jump bikes seem to do OK with 32 spokes.

    Fatigue’s got to come in to it as well. DH bikes take some big hits, but for what, ten 5 minute runs in a day between uplifts ? Meanwhile, a touring tandem has done 100 miles.

    Stu, when you say the rims battered, do you mean dented ? More spokes wouldn’t help that.

    identicalbutlighter, thanks for the real world example.
    I’ve built a pair of wheels for the current tandem, Rohloff rear and Hope Bulb front, both 32h, on Spank Stiffy rims with Maxxis Larsen tyres.
    We haven’t used it much since I put them on, so I wanted to hear from anyone who has done it long term before deciding what to put on the new bike.

    We won’t really be doing “mountain biking” on it. We want to do longer road rides, but with the option of linking up tow paths, Sustrans routes and easier bridleways and forestry roads.
    The sort of thing that would best suit a CX or hybrid solo.

    martinxyz
    Member

    This is it. You might be wanting more spokes but you also have to ask yourself if you think you’ll be slamming into stuff. I’ve always seen a well built rim with less spokes tougher for hits than a wheel with a high spoke count. Less holes drilled out of the rim at the impact points!

    Premier Icon singlespeedstu
    Subscriber

    When I say battered I mean battered as in constantly needing trueing and dented.
    You’ll be fine with just towpath stuff though.
    It’s rocky trails that really do the wheels in as often the only way through is in a straight line and just hope speed carrys you over the square edged hits.
    We soon figured out there’s no finess to tandeming offroad. Speed, straight lines and hope for the best gets best results for us.

    TiRed
    Member

    700c touring bikes with twice the load, innit. Our Dawes Super Galaxy with Suzue hubs and freewheel bends/breaks axles. More recent 559 rimmed wheels with wider OLN and freehub are much stronger for the same number of spokes and often dishless, hence fewer spokes are required. Thank Santana for that.

    I see what you mean now, Stu. I’m not expecting any big hits on rocks. The new tandem will probably end up supplementing the existing one, not replacing it, so we can afford to bias more towards road use with limited off road ability.

    TiRed, I looked at 145mm hubs and was surprised at how many of them are just 135mm hubs with an extra 10mm of spacers. I really couldn’t see the point of them. If they are not using a wider hub body, then all it’s doing is putting more bending force on the axle.

    TiRed
    Member

    Santana and many other US tandem makers moved to dishless 160mm some time ago.

    http://santanatandem.com/Techno/160Spacing.html

    You can of course go a LOT lower than 40h, how about 16? (road only 🙂 )

    http://santanatandem.com/Techno/Sweet16.html

    Premier Icon aracer
    Subscriber

    I’m sure TJ will be along shortly with a definitive answer…

    thecaptain
    Member

    It’s history, habit and conservatism. Wheels used to be crap, due to a combination of components and build quality. These days 36H built up properly on a beefy rim is fine, for either 700C or 26″. I’ve lightly buckled a wheel in a crash (still rode out) but otherwise our MTB tandem wheels have held up fine over many years of use. We made the mistake of speccing 40H on the road tandem and it’s been a minor PITA maintaining. I’m actually going to get a new set of 36h now the hubs and rims are all bit **** together.

    Of course, two real pie-eaters might still feel that they need something a little more solid.

    It’s history, habit and conservatism

    From 15 years of mountain-tandeming I’d agree with that. Our rear wheel was replaced last month after 15 years service. 36hole Mavic D321 on Hope Big Un. Never touched it with a spoke key since it was built by Leisure Lakes @ Breaston, Nottm, but found a broken spoke the month before it was retired. And that was hammered round the Peaks on the hardtail Cannondale for the first 7+ years, and has since done Scotland, Lakes, Glencoe red on the Ventana with 4″ travel. It only got replaced because the ratchet ring has no teeth left and Hope have no more spares. We aren’t a light team, and I’ve always gone for the most bombproof components possible, but my conclusion is that the wheel was overkill.

    After much deliberation have replaced it with a Stans Flow EX on a 32hole Pro2 with a 10mm bolt thru axle. Ill health has stopped us getting out on the new wheel but will report back.

    Rob & Sandy

    Alex FR32 rims,32 spokes and 25mm wide, 2.4 tyres. Don’t know who made the hubs for Lapierre but they could be Formula.

    Tandem Pic

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