I keep breaking rear wheels - advice?

90kgs is quite heavy. Unless I'm on an MTB I dont ''drop off a few gutters'' on a road bike.

Try straight gauge (14g) spokes and long brass nipples.

hd reynolds said:

90kgs is quite heavy. Unless I'm on an MTB I dont ''drop off a few gutters'' on a road bike.

Try straight gauge (14g) spokes and long brass nipples.

You're probably right about the gutters, although a majority of my roadie friends drop off gutters and suffer no adverse consequences, even those of a similar weight to me.
Straight 14G spokes with long brass nipples is what I used on the most recent wheel, and it hasn't helped me. For what it's worth, they almost always break at the elbow, not the nipple.
Have a look at Dave Ornee's long post on this thread:
http://www.cyclingforums.com/showthread.php?t=336952

Straight gauge spokes DO NOT build a stronger wheel. But making the middle of the spoke thinner, the spoke becomes more elastic allowing loads to be spread over more spokes rather than concentrate loads causing the threads or elbow to fatigue. Yes it is less stiff by a small amount, but the strength of a spoked wheel is shared loads.

Where are you're spokes braking? If at the threads then longer brass nipples will help support these loads. You can also get spokes with thicker butts on each end. If the elbows are braking look at a wheel set with straight pull spokes.

I have campy zonda wheels with quite a few 1000kms on them. I currently weigh 98kg but no sprinter, and these wheels have been bomb proof. But I'm not you!
I'd suggest easton circuit or tempest. Straight spokes, good spoke counts, deep rims, good hubs, and not too heavy.

Phill P said:

Straight gauge spokes DO NOT build a stronger wheel. But making the middle of the spoke thinner, the spoke becomes more elastic allowing loads to be spread over more spokes rather than concentrate loads causing the threads or elbow to fatigue. Yes it is less stiff by a small amount, but the strength of a spoked wheel is shared loads.

I disagree in this case. What I suggest is a stiffer wheel than an elastic one.

A straight gauge 14 spoke has a higher tensile strength than a thinner gauge spoke, say 15g, or even a butted spoke (14/15).

The difference is, thinner spokes stretch more under a given load. That is not always a bad thing, but it can lead to fatigue failue if over done (which usually occurs at the elbow), and may be a disadvantage for certain applications that require very stiff wheels. They also have a lower absolute yeild strength- like thin string vs thick rope, they just can't take the same load.

No, no, no. The modulus and yield strength of a spoke does not change because it is thinner. Therefore its elasticity does not change. Furthermore, this has nothing at all to do with fatigue failures.

The spokes are breaking at the elbows. This is an area that has a high amount of residual stress from the making of the spoke. Due to that added stress, the stress cycles of unloading and loading the spoke as you ride cause that area to fatigue more rapidly.

Experienced wheel builders will oftern correct for the residual spoke stresses during the build process. After lacing, they will grab the spokes and stress the hell out of them. What this does is yield the spoke (permanently bend it a bit more) at the elbow and relieve those residual stresses. Now that are of the spoke will be in a much more favourable regime to handle stress cycles. The fatigue life will be much better. The wheel will last longer.

However, at your weight and with your riding style, it may not be unreasonable to expect fatigue failures after 5000 - 7000 km.

Phill P said:

Straight gauge spokes DO NOT build a stronger wheel. But making the middle of the spoke thinner, the spoke becomes more elastic allowing loads to be spread over more spokes rather than concentrate loads causing the threads or elbow to fatigue. Yes it is less stiff by a small amount, but the strength of a spoked wheel is shared loads.

Where are you're spokes braking? If at the threads then longer brass nipples will help support these loads. You can also get spokes with thicker butts on each end. If the elbows are braking look at a wheel set with straight pull spokes.

I have campy zonda wheels with quite a few 1000kms on them. I currently weigh 98kg but no sprinter, and these wheels have been bomb proof. But I'm not you!
I'd suggest easton circuit or tempest. Straight spokes, good spoke counts, deep rims, good hubs, and not too heavy.

ScienceIsCool said:

No, no, no. The modulus and yield strength of a spoke does not change because it is thinner. Therefore its elasticity does not change. Furthermore, this has nothing at all to do with fatigue failures.

The spokes are breaking at the elbows. This is an area that has a high amount of residual stress from the making of the spoke. Due to that added stress, the stress cycles of unloading and loading the spoke as you ride cause that area to fatigue more rapidly.

Experienced wheel builders will oftern correct for the residual spoke stresses during the build process. After lacing, they will grab the spokes and stress the hell out of them. What this does is yield the spoke (permanently bend it a bit more) at the elbow and relieve those residual stresses. Now that are of the spoke will be in a much more favourable regime to handle stress cycles. The fatigue life will be much better. The wheel will last longer.

However, at your weight and with your riding style, it may not be unreasonable to expect fatigue failures after 5000 - 7000 km.

Thanks for replying. What is your recommendation: straight or DB spokes? Is it worth going to some trouble and expense to obtain a high-quality, straight spoke wheel (I'm not counting the R-550)?
I'm treating adequate stress relief of the spoke during building as a given.

I'm reluctant to give recommendations. I like to deal in facts, but I'm also open to the possibility that I'm wrong. My opinion, though, is that straight or DB won't make a difference to fatigue life. I would, however, go with the highest quality spoke you can afford. Remember that Sapim has fairly skinny spokes, but boasts some of the best fatigue characteristics. It's all in the material quality and how well they were made.

You might also want to consider a higher spoke count. That way, a smaller portion of rim is left unsupported and the depth of stress cycle is smaller. This will help with strength and fatigue. A heavier rim could also help with strength, though won't do anything for fatigue.

I'm being a bit evasive, but I hope that helps.

John Swanson

artemidorus said:

Thanks for replying. What is your recommendation: straight or DB spokes? Is it worth going to some trouble and expense to obtain a high-quality, straight spoke wheel (I'm not counting the R-550)?
I'm treating adequate stress relief of the spoke during building as a given.

hd reynolds said:

I disagree in this case. What I suggest is a stiffer wheel than an elastic one.

A straight gauge 14 spoke has a higher tensile strength than a thinner gauge spoke, say 15g, or even a butted spoke (14/15).

The difference is, thinner spokes stretch more under a given load. That is not always a bad thing, but it can lead to fatigue failue if over done (which usually occurs at the elbow), and may be a disadvantage for certain applications that require very stiff wheels. They also have a lower absolute yeild strength- like thin string vs thick rope, they just can't take the same load.

Give a read on Sapim's information on "Manning Good Wheels":
http://www.sapim.be/index.php?st=checklist&taal=uk
Tensile strength difference between Sapim 14 g straight and Sapim's 14/15 DB Race spoke is 7.3%; with the straight 14 g being stronger by the 7.3% mostly due to the 19% larger cross section compared to the 15 G cross section. Tensile strength numbers I used in these calculations come from Sapim and are available on their web pages. 14 G spokes will also make the wheel stiffer.
However, the the additional tensile strength and stiffness are only part of the wheels ability to deal with dynamic loads.
Longer nipples usually don't help anything and may cause the spoke alignment issue to be worsened.
The reference to an earlier response I made to a 300 lb rider applies.
Spoke alignment and stress relieving make a significant differnce in the durability of the wheel.
A couple of the other issues that are addressed in the Sapim "check list" is the diameter of the spoke and the hub flange thickness. A sloppy fit between hub and spoke elbow will quicken fatigue failure.
As Sapim mentions, some hubs particlularly benefit from their Strong spokes which have 2.3 mm butted section at the elbow end and are 15.7% higher tensile strength than their standard Leader 14 G spokes in the 14 G "center" section. I don't have any direct experience with the Sapim Strong spokes, but I have extensive experience with Sapim Race 14/15 DB spokes. I have now built over 1,000 wheels with Sapim Race Spokes and have never had a report of a broken spokes.
I have no connection with Sapim other than being a satisfied customer of their US distributor.

artemidorus said:

I've just broken a spoke on the fourth wheel in two years on my TCR and anticipate a slippery slope of further breakages, as this has happened with all previous wheels.
So far:
1st wheel: 32H 105 hub/ generic DB spokes /CXP-22 (best so far, lasted 4000-5000km then started to break spokes, killed by crash)
2nd: same hub, DT 14/15 spokes, OC Aerohead (lasted 1000-2000km then broke 10 spokes in rapid succession)
3rd: R-550 (lasted ~1000km then broke one spoke so repaired and relegated to shelf)
4th: original hub, DT 14 straight, same OC Aerohead, built by highly reputed wheelbuilder (~800-1000km)
I'm a lean 90kg, average fitness, no racing, like to sprint a bit during commutes, ride on relatively rough roads, use 23mm tyres and drop off a few gutters. I work pretty hard at avoiding bumps and "lightening the load" over obligatory bumps. The breakages usually happen taking off from traffic lights.
Options as I see them:
1. Replace the spoke and keep riding. (I'll do this in the short term)
2. 36 spoke wheel +/- deep-V rim +/-DB spokes
3. Throw a whole lot of money at the problem and get an allegedly bombproof wheel such as a ksyrium ssc sl

Advice?

Can you get Velocity Synergy OC 700C rim in either 32 or 36 hole?
Can you mount a 28 mm wide tire in the rear and have it clear your frame and brake?
Can you find a wheel builder near you that knows how to deal with spoke alignment and stress relieving and uses DT or Sapim spokes?
Can you find a Dura Ace FH7700 hub that will match the 32 or 36 hole Synergy OC rim?
The reason I suggest the Dura Ace FH7700 hub is that I find the spokes fit correctly and tend to have better elbow support.
The reasons I sugggest the Velocity Synergy OC rim is that it provides more even sharing of the load between the left and right side spokes, plus the eyelets allow for better spoke alignment at the rim. I also like the Sapim Polyax nipples for their inherent ability to improve spoke alignment at the rim, especially when the spoke hole (eyelet) allow them the space they need to take their effect.
28 mm wide tire will also improve shock absorption by around 20% over a 23 mm wide tire while protecting more from "snake bites" due to their taller profile. They usually last about 25% longer and cost the same, while not significantly increasing rolling resistance.
The one riding suggestion I have is to avoid the gutter drops if at all possible. Drops like that significantly decrease the fatigue life of any wheel.

artemidorus said:

Thanks for replying. What is your recommendation: straight or DB spokes? Is it worth going to some trouble and expense to obtain a high-quality, straight spoke wheel (I'm not counting the R-550)?
I'm treating adequate stress relief of the spoke during building as a given.

We ride tandems and that means lots of weight on two wheels. Our minimum rolling weight is about 160kg so the wheels have a lot of stress on them and if we hit a bump we cant bunnyhop that well. When we are touring the weight can get to about 190kg depending on how much wine and food we are carrying.
We've broken heaps of parts over the years.
Use DB spokes. This is what Jobst Brandt recommends and other top wheel builders like Peter White.
The number one factor is having the wheel built by someone that knows what they are doing. Steve Hogg at Pedal Pushers in Roseberry used to build the neutral support wheels for Mavic before the days of Krysiums. He will give a long guarantee with any wheel he builds.

Cheers

Geoff
Co-motion Mocha Copilot
Santana Sovereign
Titanium road
Blom Track
Vortex Fixie
Dean MTB
Klein Panache

artemidorus said:

I've just broken a spoke on the fourth wheel in two years on my TCR and anticipate a slippery slope of further breakages, as this has happened with all previous wheels.
So far:
1st wheel: 32H 105 hub/ generic DB spokes /CXP-22 (best so far, lasted 4000-5000km then started to break spokes, killed by crash)
2nd: same hub, DT 14/15 spokes, OC Aerohead (lasted 1000-2000km then broke 10 spokes in rapid succession)
3rd: R-550 (lasted ~1000km then broke one spoke so repaired and relegated to shelf)
4th: original hub, DT 14 straight, same OC Aerohead, built by highly reputed wheelbuilder (~800-1000km)
I'm a lean 90kg, average fitness, no racing, like to sprint a bit during commutes, ride on relatively rough roads, use 23mm tyres and drop off a few gutters. I work pretty hard at avoiding bumps and "lightening the load" over obligatory bumps. The breakages usually happen taking off from traffic lights.
Options as I see them:
1. Replace the spoke and keep riding. (I'll do this in the short term)
2. 36 spoke wheel +/- deep-V rim +/-DB spokes
3. Throw a whole lot of money at the problem and get an allegedly bombproof wheel such as a ksyrium ssc sl

Advice?

FWIW. You don't mention the lacing ...

Regardless of the spokes, consider a x3 lacing on the drive side and a x2 lacing on the non-drive side ...

OR, a x4 lacing on the drive side with x3 lacing on the non-drive side ...

OR EVEN, a x4 lacing on the drive side and a x2 lacing on the non-drive side.

All three options should result in a stronger wheel.

I prefer a laterally stiffer wheel, so very few of my wheels are laced with double-butted spokes, now.

Buy yourself a tensiometer and do the build yourself.

Periodically, check your spoke tensions (here's where the tensiometer will be handy ... and, since you will have it, you may as well build your own wheels) ... particularly, after riding episodes where you drop off gutters.

Consider going to a 700x25 to reduce some of the road shock.

Maybe one of those spoke tensionometer would help you diagnose the problem. Or try one of those web sites that claim you can determine uniform spoke tension 'musically'. I personally blew the money on a tensionometer after years of failed music lessons.

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