Asymmetric rims on a Scalpel Si

[michaelbiker]

Any expert wheel builders out there that have an opinion on whether an asymmetric rim will work on the rear of a Scalpel Si? 

 

I am mainly wondering if the spoke tension will be symmetric on both sides of the rear wheel. I've had various mixed answers from bike shops. Some say it depends very much on the hub and flange distance, which I am having trouble understanding. 

[Captain Fastbastard Mayhem]

Any expert wheel builders out there that have an opinion on whether an asymmetric rim will work on the rear of a Scalpel Si? 

 

I am mainly wondering if the spoke tension will be symmetric on both sides of the rear wheel. I've had various mixed answers from bike shops. Some say it depends very much on the hub and flange distance, which I am having trouble understanding. 

it will, but seeing as the rear has already been designed to give a more evenly dished wheel, it may be counter-productive as a standard non-asymmetric rim will likely sit in the middle of the hub due to the way the rear has been designed. 

[michaelbiker]

Yeah this is what I've been thinking. This store sells custom asymmetric wheels with an Ai offset option.

 

http://bikeonline.it/en/wheels-29/1544-rocky-as33-carbon-29er-carbon-ti-x-hub-sp-wheelset-from-1275g-2000000000000.html#/nipples_colour-black/compatibility-sram_xd_xx1/front_hub_standard-lefty_2_0_supermax/rear_hub_standard-x12x142mm_through_axle_12mm/hubs_colour-black/rear_wheel_camber-for_cannondale_si/number_of_spokes-28_front_28_rear/spokes_type-alpina_blade_hyperlite

 

Here is the reply I got from them when asked the same question.

 

The use of asymmetric rims on SI frame allow to reach almost the same spokes tension on both sides of the wheel, if hubs with large distance flanges (like Carbon-Ti) are used.

This way the wheel reaches the best level of lateral stiffness.

Using hubs with narrow distance flanges (like American Classic) asymmetric rims are not necessary.

 

 

I've asked them to elaborate to clear up any confusion.

 

[Captain Fastbastard Mayhem]

no elaboration needed. The wider the distance between the hub flanges, the more the asymmetrical nature of the rims helps, in reference to the Si, because of the rear triangle.  

 

What hubs are you going to use?

[michaelbiker]

no elaboration needed. The wider the distance between the hub flanges, the more the asymmetrical nature of the rims helps, in reference to the Si, because of the rear triangle.  

 

What hubs are you going to use?

Thinking of going with the Carbon-Ti SP hub or DT-240s SP.

[Jewbacca]

I have a set of the WTB i29 rims and they built up really easily and the spoke tension was so easy to manage. I really don't know if there is any other advantage or disadvantage to having the rim other than the wheel building.

 

It rides like a nice sturdy wide rim......

[michaelbiker]

I have a set of the WTB i29 rims and they built up really easily and the spoke tension was so easy to manage. I really don't know if there is any other advantage or disadvantage to having the rim other than the wheel building.

 

It rides like a nice sturdy wide rim......

 

 

Ah right, so to clarify, it simplifies the rim building process by making the tensioning part of it easier.

[michaelbiker]

Finally got feedback from the shop, and this seems to make sense, if anyone else is interested:

 

1) Hubs with large flange distance like Carbon-Ti X-HUB SP: flanges distance 55.1mm

2) Hubs with narrow flange distance like American Classic: flanges distance 47.5mm

 

On standard rear wheels with symmetric rims you always have an higher spoke tension on cassette side. The tension difference between cassette side and disc side depends on how large are the flanges. Narrower flanges allow for an higher spoke tension disc side tension, larger flanges give lower spoke tension disc side.

 

With narrow flanges distance and a symmetric rim the bracing angles of the spokes, left side and right side are close, but the spoke tension is higher on the cassette side, so with a F-SI design and a symmetric rim you reach almost the same tension on both sides of the hub.

 

With large flanges distance and a symmetric rim you have far more tension on cassette side. With an asymmetric rim tensions difference decrease but with F-SI and asymmetric rim you reach almost the same tension on both sides of the hub.