Spoke tensions - disc brake wheels vs rim braked

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Svetty
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Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty

Instinctively I feel that spoke tensions should be higher on disc braked wheels as the spokes have to transfer the braking force. On the other hand I guess a properly built wheel will have correct tensions and be appropriately stiff whether it is rim or disc. What do more experienced builders think?

DamonRinard
in the industry
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by DamonRinard

Ideally, no spoke ever reaches "zero" tension in use.
Normally spokes decrease tension due to rider weight (radial or less often lateral) and torque transfer.
Torque transfer is either due to pedaling (rear wheels) or braking (hub braked wheels only).
Deceleration (braking) can be about double acceleration (pedaling). So in maximum braking situations, potentially there could be a greater tension decrease with hub brakes.

In 1896 (not a typo) Archibald Sharp published the formula which calculates tension change due to hub torque. See page 342 in his book: https://books.google.com/books?id=leq7A ... el&f=false

Theoretically hub braked wheels could use a little more spoke tension, but in practice most well-tensioned wheels have enough already.

So unless something else is unusual (extremely low flanges, extremely low number of spokes, etc.) then I don't recommend higher spoke tension on disc brake wheels.
Last edited by DamonRinard on Tue May 22, 2018 11:49 am, edited 1 time in total.
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

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Beaver
Posts: 420
Joined: Wed Aug 18, 2004 6:06 pm
Location: Lower Saxony - Germany

by Beaver

DT Swiss runs a little more up front: https://dycteyr72g97f.cloudfront.net/up ... DE_002.pdf (sorry, German, but it's chapter 4.1)

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kavitator
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Joined: Sun Sep 21, 2008 9:07 pm
Location: Slovenia---that forest land

by kavitator

Disc brake wheels often has more spokes than rim brake.

Also there are more tubless /clincher wheels - those need higher tension because of tension drop when tire is infalted
Tubulars hasnt got that effect.

More important is even spoke tension - so complete wheel is balanced

Front wheels 80-100kg and rear 100-120kg max tesnion will be ok

pushstart
Posts: 445
Joined: Sat Jun 16, 2012 3:12 am

by pushstart

I always prefer to build my front disc-brake wheels to at least 110kgf (but usually closer to 120) and rear to at least 120kgf (usually 120-130). (Unless rim has lower max tension, though I prefer to find rims that don't.). Majority of braking force will be up front. But rear does have to support more rider weight. I figure doing about the same tension front and rear makes sense, though this might be a bit more than the front needs (?)

As long as you do a good job relieving tension during the build (so that the final tension is a "true" tension and won't drop when you start riding it), I am sure you could get away with a bit less. -- But I'm also not sure what the benefit would be to using less tension.
Last edited by pushstart on Thu May 24, 2018 4:14 pm, edited 1 time in total.

joejack951
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Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

I have thousands of miles on hand built disc wheelsets, built by me the same way I'd build non-disc wheels. Never had any spoke tension related issues on those wheels, but I tend to not have wheel issues in general starting with a properly built wheel at least. As noted above, get your tension even and stress relieve that wheel during the build and you'll be good to go.

NovemberDave
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Joined: Sat Oct 09, 2010 11:42 am
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by NovemberDave

Our disc front wheels have a higher tension than non-disc wheel builds. Rim brake front builds get 90kgf nominal tension, where most disc brake fronts wind up around 115 on the disc side in order to have enough drive side tension. Rear wheels are the same because I don't want to go much past 125kgf anywhere in the wheel, though most disc rear hubs allow slightly better non-drive tension than rim brake rear hubs.

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