# 20 24 Hole Cyclocross Disc Hubs?



## kk5551 (Jul 4, 2010)

Hi all- I have a couple of sets of 50mm Gigantex carbon tubulars that I have raced CX on for a couple of years. 

I would like to make the move to disc brakes so I will be buying a disc frame. The problem is that both sets are 20 24 hole rims. I don't have the money to buy two new sets and would like to buy some inexpensive hubs and have them re-laced. 

Are any 20 24 hole hubs starting to pop up now that disc CX frames are becoming so common?

Thanks!


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## Randy99CL (Mar 27, 2013)

I've seen disc hubs with 24 holes but not 20, and lots of companies make disc wheelsets with 24 spokes.

I'm sure you realize that disc wheel stresses aren't the same as with rim brakes. Could you trust 20 spokes, especially on the front?
I've read here that some carbon rims aren't certified for use with disc brakes and that the nipples might pull through the spoke holes. I don't have a link but you can do a search.


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## tednugent (Apr 26, 2010)

As far as I know. No hubs you can buy off the shelf 

Mavic Crossmax wheel set is 24/20 though


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## sanrensho (Jan 2, 2003)

Circus Monkey disc hubs are available through eBay in 20 and 24H drillings.


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## atpjunkie (Mar 23, 2002)

20 hole front wheel, discs, hard off road braking. Sounds like an awesome idea


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## tednugent (Apr 26, 2010)

sanrensho said:


> Circus Monkey disc hubs are available through eBay in 20 and 24H drillings.


CIRCUS MONKEY

I don't see 20H front hubs for disc


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## pretender (Sep 18, 2007)

atpjunkie said:


> 20 hole front wheel, discs, hard off road braking. Sounds like an awesome idea


Just for sake of argument, I'm not sure that the braking load adds much stress to the spokes and nipples, compared to what they already undergo.

That said, if I were building those wheels I would for sure use brass nipples and DT Comps (or equivalent).


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## tednugent (Apr 26, 2010)

pretender said:


> Just for sake of argument, I'm not sure that the braking load adds much stress to the spokes and nipples, compared to what they already undergo.
> 
> That said, if I were building those wheels I would for sure use brass nipples and DT Comps (or equivalent).


The loading will be on the hubs more (which the spokes will help disappate) . It may also effect the durability of the spokes, at the J-bend, as naturally, the bend will be a stress riser.


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## atpjunkie (Mar 23, 2002)

pretender said:


> Just for sake of argument, I'm not sure that the braking load adds much stress to the spokes and nipples, compared to what they already undergo.
> 
> That said, if I were building those wheels I would for sure use brass nipples and DT Comps (or equivalent).


putting the braking force at the center of the wheel greatly increases the torque at the spoke/nipple/rim junction. The center of the wheel is slowing and the rim has to catch up. So instead of the rim slowing, the hub slows and that is transferred to the rim via the spokes

good read

https://fernandoj.wordpress.com/2013/11/01/a-20-spoke-disc-wheel-for-cyclo-cross/


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## Randy99CL (Mar 27, 2013)

Disc hubs change everything when considering the stresses spokes endure.

On a rim-brake front wheel the spokes only need to keep the wheel centered. I'm sure they get some extra stress when braking but not enough to be concerned with. That's why 16 and 20 (and fewer) spokes can survive on the front with rim brakes.
With discs the brake is trying to stop the hub and the spokes have to transfer 100% of that considerable force to the rim/tire. 

On the rear the spokes have always had to transfer the force as the hub was powered by the pedals but now they also need to withstand as much (or more) opposite force when braking.

As an example of the enormity of the problem, there have been incidents of spokes being ripped from the rims on disc wheels. Rim manufacturers have strengthened the spoke bed to compensate.

Just imagine a 300lb bike/rider/load trying to stop from 40mph with a 180mm front rotor. Those spokes are going through hell.


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## Randy99CL (Mar 27, 2013)

Another quick point: when I was shopping for disc CX wheelsets I saw that many were (surprisingly) laced with only 24 spokes. Most of them use straight-pull hubs to eliminate the weakness of the J bend.


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## sanrensho (Jan 2, 2003)

tednugent said:


> CIRCUS MONKEY
> 
> I don't see 20H front hubs for disc


Search eBay for "Circus Monkey HDW-F CX Front disc hub 20 hole Black."


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## pretender (Sep 18, 2007)

Randy99CL said:


> Just imagine a 300lb bike/rider/load trying to stop from 40mph with a 180mm front rotor. Those spokes are going through hell.


OK so I'm guessing you'd recommend a 300lb guy use 36 spoke front. That is proportional to a 170 pound guy and 20 spokes.


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## ms6073 (Jul 7, 2005)

kk5551 said:


> Hi all- I have a couple of sets of 50mm Gigantex carbon tubulars that I have raced CX on for a couple of years.
> 
> I would like to make the move to disc brakes so I will be buying a disc frame. The problem is that both sets are 20 24 hole rims. I don't have the money to buy two new sets and would like to buy some inexpensive hubs and have them re-laced.
> 
> ...


Not as budget friendly, but I would use the rears to build a 24 hole disc brake wheels et while selling the two front wheels so you can purchase two new 38 or 50mm, 24 hole rims to build up as the second wheelset.


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## ACree (Feb 5, 2006)

White industries makes disc compatible hubs at least down to 24 hole.


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## foto (Feb 7, 2005)

Randy99CL said:


> Disc hubs change everything when considering the stresses spokes endure.
> 
> On a rim-brake front wheel the spokes only need to keep the wheel centered. I'm sure they get some extra stress when braking but not enough to be concerned with. That's why 16 and 20 (and fewer) spokes can survive on the front with rim brakes.
> With discs the brake is trying to stop the hub and the spokes have to transfer 100% of that considerable force to the rim/tire.
> ...


The makes no sense to me. The spokes are supporting the rider, and slowing the rider under braking, no matter if the frame has disc or rim brakes. The rim and tire must be about 0.05% of the total mass of the bike/rider system.

The only difference is: does the rim pull on the hub (through the spokes) or does the hub pull on the rim (through the spokes).


hmm...or maybe not? maybe I need to think about this a little more...

With a rim brake, the force applied to the rim is the same as the force applied to the ground which is equal to the force the hub applies to the fork dropouts. (It must be that way otherwise the rim would just pivot around the brake). Thus, there must be force being transfered through the spokes.

Yeah, I don't get what you are trying to say.


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## CapitalCrewBiker (Aug 24, 2011)

This works.. Cannondale Wind Disc Center Lock 24H Front Hub New | eBay


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## Randy99CL (Mar 27, 2013)

I'm not an engineer and can't define what forces are acting on the spokes in a rim-brake front wheel, but I don't think they add up to much.
The fact that there are 12 or 16-spoke radially-laced wheels shows me that they don't have to be especially strong.

Simply put, with disc hubs the front wheel now has to be as strong as the rear. 

Since an estimated 70% of braking power is in the front that wheel has to withstand as much (or more) than the pedaling force on the rear.
Radial lacing will fail and it's best to spread the load over a number of spokes.


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## foto (Feb 7, 2005)

Think about it this way.

Forces act on a mass, and looking at just a wheel, the mass is pretty much concentrated at the axle (this is where the rider's weight is applied). The mass of the rider is transferred to the ground through the spokes. Under braking, the ground is applying a force to the rider, which similarly must travel through the spokes. Where that force is generated doesn't really matter, the spokes are still the only mechanism transferring force from the ground to the rider.

Thus disc, rim, shouldn't really matter as far as the tensions the spokes are under.

As for 12 spoke radially laced wheels, those are appropriate only for the lightest people, riding pretty much just up hill. Wheels that light aren't designed for everyday use, and definitely not for cross.


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## haikalah (Oct 5, 2004)

foto said:


> Think about it this way.
> 
> Forces act on a mass, and looking at just a wheel, the mass is pretty much concentrated at the axle (this is where the rider's weight is applied). The mass of the rider is transferred to the ground through the spokes. Under braking, the ground is applying a force to the rider, which similarly must travel through the spokes. Where that force is generated doesn't really matter, the spokes are still the only mechanism transferring force from the ground to the rider.
> 
> ...


Are you an engineer?

The weight bearing load on spokes is the same with either type of brake, but to take it out of the equation, imagine this: Clamp two bikes upside down. One with rim brake and one with disc. Both with same rim and number of spokes and spoke pattern. Lock down the brakes so that the wheel cannot spin. Tie a rope to the top of the wheel (bike is upside down). Pull tangentiallly on the rope (so the rope is horizontal to the ground). Which wheel do you expect to fail first?


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## foto (Feb 7, 2005)

haikalah said:


> Are you an engineer?
> 
> The weight bearing load on spokes is the same with either type of brake, but to take it out of the equation, imagine this: Clamp two bikes upside down. One with rim brake and one with disc. Both with same rim and number of spokes and spoke pattern. Lock down the brakes so that the wheel cannot spin. Tie a rope to the top of the wheel (bike is upside down). Pull tangentiallly on the rope (so the rope is horizontal to the ground). Which wheel do you expect to fail first?


The disc brake wheel. Now I get it, I just had to draw a picture...


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## atpjunkie (Mar 23, 2002)

aka--there's a reason why most disc hub builders have minimum spoke numbers
their engineers have already done this


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## pretender (Sep 18, 2007)

Is it the spoke, the rim, or the hub that is the limiting component?


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## atpjunkie (Mar 23, 2002)

pretender said:


> Is it the spoke, the rim, or the hub that is the limiting component?


my guess is spoke or spoke/rum junction


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