Disc brake wheelset longevity

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modcon
Posts: 15
Joined: Sat Apr 07, 2018 8:32 am

by modcon

Hi all

Disc brake wheelset. How should the rear wheel go in terms of spokes compared to rim brake wheels? On two wheel sets I've broken spokes in a relatively short time frame and wondering how much of it is to do with being disc rather than rim brake?

If so would a particular build improve this, or a rim brake wheelsets just stronger or more durable due to being exposed to less forces through the rear? Or do disc brake wheelsets need more care?

Cheers



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by Weenie


Squashednuts
Posts: 502
Joined: Tue Apr 25, 2017 11:12 am
Location: Christchurch New Zealand

by Squashednuts

I think that wheels built specifically for disc brake bikes are designed and built to manage the specific forces and stresses caused by using disc brakes.

Disc wheels should last a long time, the discs will need replacing periodically, but the actual wheels should go on....
Disc brake wheels shouldn’t need any more care than rim brakes
I’ve worn down the brake rim on a few sets of wheels but never had an issue with discs

What make are the wheels with the broken spokes?
Do they have a weight limit?

I had a disc brake bike and did about 17k km’s on one set of wheels with no broken spokes, and a couple thousand kms on tubulars with no issue
Fuji SL 5.8kg - viewtopic.php?f=10&t=157704

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Focus Izalco Max Disc - Final Weight 6.7kg - http://weightweenies.starbike.com/forum ... o+Max+disc

TobinHatesYou
Posts: 4025
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Which wheels, how much do you weigh and what can you tell us of your riding style / roads?

ducman
Posts: 118
Joined: Fri Jan 07, 2011 12:49 pm

by ducman

Surely the spokes have to handle a lot more stress. I had the sane issue. Braking a couple of cx ray spokes on several wheelsets.

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pdlpsher1
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Location: CO

by pdlpsher1

I had a Spinergy tandem rear disk wheel that broke on me after a few thousand miles. The rim cracked around the spoke holes on half of the spoke holes. The wheel was specially designed for tandems (it has a 160mm hub so it can only be used on tandems) but only has 24 spokes. Foolish on my part in believing in marketing crap. The front wheel has 18 spokes and there was no sign of fatigue. But the front wheel is rim brake only. So I drew the conclusion that the disk brake forces caused the rear wheel’s demise. On tandems the weight distribution is closer to 50/50 as the heavier rider is up front. Spinergy warrantied the wheel and I promptly sold the set. I replaced it with a custom build, Hed Belgium + in 32 spokes (24 front but it’s rim brake-only), 160mm tandem specific hub with symmetrical braced spokes, and Pillar CX-Ray equivalent spokes. After a few thousand miles no stress cracks on the rim but broke one spoke at the spoke elbow. Upon inspection I found about 8-10 spokes with low tension. I retentioned all of the spokes and thus far so new issues. I suspect disks add a lot more stress to the wheels than people realize.


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modcon
Posts: 15
Joined: Sat Apr 07, 2018 8:32 am

by modcon

Squashednuts wrote:I think that wheels built specifically for disc brake bikes are designed and built to manage the specific forces and stresses caused by using disc brakes.

Disc wheels should last a long time, the discs will need replacing periodically, but the actual wheels should go on....
Disc brake wheels shouldn’t need any more care than rim brakes
I’ve worn down the brake rim on a few sets of wheels but never had an issue with discs

What make are the wheels with the broken spokes?
Do they have a weight limit?

I had a disc brake bike and did about 17k km’s on one set of wheels with no broken spokes, and a couple thousand kms on tubulars with no issue
Hmm hed ardennes and fulcrum racing 3 dB.... I thought they would be good but both have popped rears. I'm 83kg and reasonably forceful on the bike, but even still I thought theyd go further. Both sets popped around 10k? Whereas I have a range of fulcrum rim wheelsets that lasted much longer no spoke issues...

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modcon
Posts: 15
Joined: Sat Apr 07, 2018 8:32 am

by modcon

TobinHatesYou wrote:Which wheels, how much do you weigh and what can you tell us of your riding style / roads?
Weight and riding style above. Live near hills so do a fair bit of vertical, and sometimes commute with a backpack. Race and train on the same bike.

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modcon
Posts: 15
Joined: Sat Apr 07, 2018 8:32 am

by modcon

pdlpsher1 wrote:I had a Spinergy tandem rear disk wheel that broke on me after a few thousand miles. The rim cracked around the spoke holes on half of the spoke holes. The wheel was specially designed for tandems (it has a 160mm hub so it can only be used on tandems) but only has 24 spokes. Foolish on my part in believing in marketing crap. The front wheel has 18 spokes and there was no sign of fatigue. But the front wheel is rim brake only. So I drew the conclusion that the disk brake forces caused the rear wheel’s demise. On tandems the weight distribution is closer to 50/50 as the heavier rider is up front. Spinergy warrantied the wheel and I promptly sold the set. I replaced it with a custom build, Hed Belgium + in 32 spokes (24 front but it’s rim brake-only), 160mm tandem specific hub with symmetrical braced spokes, and Pillar CX-Ray equivalent spokes. After a few thousand miles no stress cracks on the rim but broke one spoke at the spoke elbow. Upon inspection I found about 8-10 spokes with low tension. I retentioned all of the spokes and thus far so new issues. I suspect disks add a lot more stress to the wheels than people realize.


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That's what my hypothesis is too.... Do I need to go back to rims? There my problem was wearing out rims in a season!

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pdlpsher1
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by pdlpsher1

For sure a custom build will easily handle it. I’d recommend 32 spokes rear. Using more, lighter weight spokes is better than fewer, heavier weight spokes. A radially stiff rim (i.e. deeper profile) will help distribute the braking forces to more spokes.


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NickJHP
Posts: 255
Joined: Wed Feb 14, 2018 2:22 am
Location: Canberra, Australia

by NickJHP

Spoke problems sounds like a bad wheel build. I have several sets of disc wheels on different bikes, and haven't broken a spoke in any of them. That includes a tandem using 203mm disc rotors, so far more stress on the spokes there than on a single bike, and those wheels are built using CX-Ray spokes, 32-spoke front wheel and 40 spoke rear wheel. So far they've lasted more than 15 years without any problem. I also built a 24/28 set of disc wheels for one of my own bikes using CX-Ray spokes, LightBicycle carbon rims, and DT Swiss 240s hubs. No problems with those wheels either, though they've only been on the bike for about a year, so only a few thousand km on them so far.

moyboy
Posts: 444
Joined: Thu Aug 18, 2016 12:19 am

by moyboy

Have a wheelbuilder check it out if you have an independent wheel builder in your city / town.

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Alexbn921
Posts: 207
Joined: Wed Apr 10, 2019 6:39 pm

by Alexbn921

Rim stiffness plays a huge roll in wheel longevity. Spoke do experience loads under braking that rim brakes do not impart. Any high quality build should be able to take year and years of abuse. I use 28 cxray spoke wheels on my mountain bike and Huck 10 foot drops. 24 spokes on my road wheel should be able to handle anything I throw at them.

Squashednuts
Posts: 502
Joined: Tue Apr 25, 2017 11:12 am
Location: Christchurch New Zealand

by Squashednuts

I’m not happy with my initial post as it was an “I think, I feel” post.
These are never very helpful other than to muddy waters and help entrench positions
So I slept on it, did a bit of internet research and these are two interesting posts that don’t rely on supposition

From looking at disc brake and rim brake bikes from the same manufacturer, such as Giant, the wheels are laced differently to accommodate different forces

“amount of torsion about the hub seems like it is enormous. It also seems like using a disc brake can introduce a large amount of angular acceleration in the opposite direction of the motion which means that the spokes are transferring torques in directions they are not designed to.”

https://forum.cyclinguk.org/viewtopic.php?t=120117


“disc brakes do indeed create very high stresses in the spokes when the brakes are used hard. These do vary but are always larger than the stresses in otherwise similar rim-braked wheels. Depending on the design of the front hub the torque is or isn't shared appreciably between the flanges, and depending on the size of the flanges the net change in leading tension vs trailing tension can be large (small flanges) or smaller (large flanges).

Disc braked front wheels are dished, too, which makes them quite a bit weaker than rim braked wheels. There are also much greater loads on the disc-braked hub bearings than is 'normal' with a rim braked wheel.

In addition to the torque loading there is (because of weight transfer) an increased thrust loading on the wheel when the brakes are on whether rim or disc braked. To a first approximation this can (depending on rim stiffness and a few other things) cause a ~25 to 50% reduction in tension in those spokes below the hub at any one time, eg in a rim braked wheel (with a ~100kg rider braking as hard as possible) ~four spokes might each lose 25kg tension and this creates a net upthrust of ~100kg.

If you take a 'worst case' for disc brakes (which is in fact by no means uncommon) then you might have a 28 spoke front wheel with medium-sized flanges and poor torque sharing between them. This can leave just seven spokes on the left side of the wheel that see a tension increase because of the brake torque loads, of which at least one will be running almost slack anyway because of the thrust load (which isn't shared with other spokes in the same way as for a rim-braked wheel). This leaves just six leading spokes doing all the work, basically. These spokes could see tension differentials of ~170kg (or more) vs the trailing ones on the same flange, i.e. if those spokes started at 120kg tension, then trailing and leading spokes could see tensions of ~35kg and ~205kg respectively. The slack spokes will be in danger of simply having the nipples unscrew and the tighter ones are about 2/3 of the way towards yielding in tension; they will undoubtedly accrue significant fatigue damage whenever the brakes are used in this way.

Under the same braking loads there can be a thrust load at the disc caliper of about 500kg. The fork needs to be considerably stiff and stronger in order to safely withstand this load. This load is also reacted through the hub bearings in (vector) addition to the thrust loads that would be present anyway. The net result of this is that a LH disc hub bearing will see a thrust load of at least 500kg under heavy braking, in contrast to a rim brake hub which sees a load increase of ~100kg in each front hub bearing under the same braking loads. 500kg is at or beyond the relevant (static) load rating of many front hub bearings.

In a nutshell the loading in (all parts of) a disc braked wheel and fork is considerably more aggressive than in a rim-braked wheel at the same braking loads. That this doesn't more often cause big trouble is, I suspect, largely because heavy braking does not occupy a very large proportion of the duty cycle of the wheel.”
Fuji SL 5.8kg - viewtopic.php?f=10&t=157704

Sold -
Focus Izalco Max Disc - Final Weight 6.7kg - http://weightweenies.starbike.com/forum ... o+Max+disc

bm0p700f
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by bm0p700f

Tandem wheels need more than 24 spokes even its rim brake. The minimum I would do is 32 spoke but 36 is ideal. The front wheel has less load on it as is symmetrical so that will.last longer.

Disc brake wheels can last a long time. One set I did for myself on a bike with panniers and I'm not light either had 24 cx ray spokes on a 27mm deep alloy rim and it did 25000km before I sold them as a beater set as they had several dents.

I suspect build issues for the OP with the hed rims might be a 24 spoke build with cx Ray's which for.some will be fine but others will pop spokes. The fulcrums are weird with triplet lacing. Also there work be the odd fulcrum not built right.

However in general most disc brake wheels on the market are not stiff enough in my view to be reliable for all. Radial and lateral loads will be the same but torsuonal loads are higher. That lends itself to higher spoke counts. The fulcrum racing 3 db wheel will have the similar torsional stiffness as the rim brake model which may or may not be the problem. Hard to say really.

The deeper the rim the lower the spoke count. Rims of the depth the op is using need 28 spokes front and rear to be reliable for the more aggressive riders. I have learnt that the hard way.

This is why the disc hubs I use are large flange which reduce spoke loading and 28 spoke wheels are laced 3x both sides and deep 24 spokes 2x both sides. Thicker spokes also help with shallower disc brakes wheels. Deeper rims seem to get away with cx Ray's.

shallower disc wheels also benefit from asymmetric rims. Deeper ones do too but it messes with the aero.

by Weenie


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Alexbn921
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by Alexbn921

The answer is yes. Disks do need a different and stronger build.

If you are breaking spokes then I would recommend getting a stronger set of wheels. It all depends on riding style, weight and quality of the build. A perfectly built wheel with the same parts might stand up better or you may just be pushing it past it's limit.

Mountain bikes impart far more hub force from braking and the huge rear cassettes. Wheels can easily withstand these forces if the are designed too. I have tens of 1000's of miles on King and DT hubs without a single broken spoke. I do check and adjustment my wheels regularly as I love the feel that perfectly tentiontion, trued wheels give.

Crap builds of expensive parts will still be crap wheels.
Great builds of weak parts will not stand up over time. Not necessarily cheap parts either.
Stock wheels are where bike manufacturers save the most money. They need attention or replaced almost immediately.
If your heavy or strong your wheels need to be too!
If you have to replace more than a couple spokes on a wheel then they all need replacing.

Wheels bend and flex far more than most people give them credit for. They are a dynamic system and the stresses are high.

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