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I'm currently building a front wheel based on a WTB i35 rim. This is an asymmetric rim, and you can see a picture of it below.

As you see, one side is larger than the other, and I was wondering which side of the wheel that this side is supposed to be on. Should I place it so that the largest side point to the right or the left? Or does it not matter since the spoke length of both sides are identical?

enter image description here

Originally from http://southernwheelworks.com/wp-content/uploads/2015/07/FullSizeRender-30.jpg

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    I'm not a MTBer, but I would have thought the asymmetric rim is for rear wheels. It is for road bikes. – andy256 Sep 28 '16 at 22:07
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    @andy256 Front disc wheels have a lesser version of the same angle/tension disparity that rear derailer wheels have. – Nathan Knutson Sep 28 '16 at 23:08
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Asymmetric rims are trying to do a couple different things to increase the strength and durability of a wheel built with a hub that's got unequal center-to-flange measurements, such as all common disc and/or derailer wheels.

  • The lateral bracing angle of the spokes becomes closer to equal, creating a wheel less likely to buckle or warp from side loads.
  • Bringing side-to-side tension of the built wheel closer to equal, which is always a side effect of equalizing the angle.
  • Increasing the total amount of spoke tension the built wheel can have, creating a stronger wheel. Modern wheels are often bottle-necked in spoke tension by the rim's ability to resist fatigue cracking if the tension were any higher. Say both the normal and asymmetric version of a rim have a maximum spoke tension of 110kgf before fatigue cracking is an issue. Both wheels get built so the tight side (the left in the case of a disc front) is at 110kgf. If the other side's tension is 70kgf on the normal rim wheel and 90kgf on the asymmetric, that extra tension is "free" in a way and will make the wheel quite a bit stronger.

So, orient it taller (or positive offset, or however you want to say it) side right in front and left in back.

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    The first sentence is very difficult to parse. – RoboKaren Sep 28 '16 at 22:43
  • @Robo It's all difficult. – andy256 Sep 29 '16 at 0:13
  • @Nathan From your earlier comment to me, maybe the way to explain it is in relation to the disk brake mount on the hub. – andy256 Sep 29 '16 at 0:15
  • Much better :-) The last sentence is still tricky; does in front and in back refer to the front and rear wheels? – andy256 Sep 29 '16 at 7:17
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For the sake of clarity and a simplified answer: Typically MTB front and rear have the asymmetric rims opposite from each other.

Put the 'fat' side of the rim towards the the hub flange closest to the axle center (this pushes the holes towards the center of the flanges so to speak).

On a disc front wheel, the rotor mount takes up the most space, pushes the flange in and therefor takes the 'fat' side of the rim. Opposite for the rear, where the driver typically takes more space that the rotor mount, so the 'fat' side goes to the cassette.

Below left is what you are after for rear, opposite for front. enter image description here

Seeing you asked this question, I think you will benefit from this build guide. It goes through a few concepts, and then later the specifics that would apply to get it right for an asymmetric build.

This is the reason for my answer as the wheel will be flipped and flopped as you are finding your way with the spokes and then it's easier to recall "fat side - sort flange" logic IMO.

  • Thanks for the guide. Should drive side in the guide be substituted with disc side when building a disc brake front wheel? – user1049697 Sep 30 '16 at 17:41
  • that's how I would read it @user1049697 . 'Drive side' can be see as the part that takes up the most of the flange offset. - Still for all those weird and non/new-standards it's still best to measure the flanges to make sure which is closer to the middle of the axle. – piet Oct 3 '16 at 7:35
  • I did some more research and found out that it is actually wrong. Drive side is always drive side, even on disc brakes. I'll just quote Roger Musson's "Professional Guide to Wheel building" p. 67: "The lacing starts on the right side hub flange. For rear hubs this will be the drive side flange. For front disc hubs this will be the flange opposite the disc brake fitting." – user1049697 Oct 3 '16 at 16:06
  • Let us know if you get more info; That sounds like the reference as a staring point meaning that if you start on the right side, the wheel rotation will be the same and then the lace pattern will follow the same method. - To me that statement especially out of context doesn't infer anything re the dish. Look further through his advice and see what he says about the dish. The dish id what your asymmetric rims are about, not which side we want to reference as drive side. – piet Oct 4 '16 at 22:17
  • The book states that the offset will be placed on the right hand side for disc brake wheels. – user1049697 Oct 6 '16 at 18:38

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