Cornering Forces Breaking Spokes?

[safe]

Right Hand Turns

I was out riding the old bike today and in the middle of my smooth right hand high speed sweeper turn I heard that terrible sound of a spoke popping. To my knowledge EVERY spoke I've broken has been the result of high speed turns to the right. Has anyone broken a spoke on a straight away over something like a bump when you were not turning?

The spokes that break are always on the rear and usually on the side of the wheel that is trued such that the spokes are nearly vertical. (the bad side is near the freewheel) The result is that spokes tend to break the must while turning to the right.

Have people noticed this?

Or is this just me with my big tires (and big traction) and freewheel cluster that makes the alignment off center for the rear wheel?

Another argument for a multispeed hub in the rear... no uneven tensioned spokes...

 

[Lowell]

What kind of spokes are you using?

 

[safe]

What kind of spokes are you using?

Standard spokes... the type you get on a cheap bike. An improvement in the spoke quality could help. Money can buy better stuff most of the time. I just wanted to point out the fact that it's the right hand turns that break spokes and not left hand turns because the left hand turns don't seem to put the same level of stress on the right hand spokes. I'm not sure why.

Maybe it's just a coincidence... :?

 

[Lowell]

How much tension are you running? I just saw a wheel yesterday with 6 broken spokes, and the owner said they were loose and creaking for a while.

 

[xyster]

Has anyone broken a spoke on a straight away over something like a bump when you were not turning?

Yup. Broke one 13ga spoke in my x5/24" going over a bump. I think the spoke had been loose for awhile. I broke another spoke while fixing that spoke. :?

 

[safe]

You're not supposed to do this, but I managed to bend a spoke through the freewheel cluster (there was a hole in the sprocket) and then unbend it and attach it to the rim.

So I'm thinking:

"Hey, great, a five minute repair!"

So I get out on the bike again and go around another right turn at some pretty nice speed and "pop"... yep, another spoke went and it was a different spoke but on the same side in the rear. This means that I've got some kind of fatigue situation developing (I'm right around 2000 miles) with the spokes and I'm going to have to think this out a little more.

I have plenty of spokes laying around so I could simply take the wheel off and replace ALL the spokes on the right hand side. (18 spokes) That way I'm starting "fresh" with a new batch and maybe I'll get 500 miles worth out of them before they start breaking again.

Another issue is the heat.

When I first got these tires on the bike I was still reluctant to use all the traction they allow, but now they are fully worked in and with the higher temperatures on the road they're sticking like glue. I'm finding myself going faster pretty much everywhere. The new transaxle seems to have much less friction induced drag than the older ones. All those old versions forced the bearings into the relatively soft mild steel cups and all that deformation not only wore out the transaxle bearings, but slowed me down. Now I'm getting the full 1000 watts everywhere and I've got traction everywhere... so the general rule is that once you fix one thing (which increases your speed) then something else breaks in response to it.

With the traction I'm getting now I can envision some SERIOUSLY intense cornering speeds... on a par with a good quality motorcycle. This concept... the electric "Road Racer"... has enormous potential in the top end... and all these techinical issues are just blocking the way.

So the best thing would be to go to a "centered" hub where the spokes on both sides carry the load equally. The problem is with the freewheel cluster concept. So I'm in a sort of circular logic where the path forward "should" involve no transaxle and a direct drive to a multispeed hub. Do that and ALL the problems get fixed. (but it requires a redesign of the frame and a complete teardown, repaint, rebuild) The other direction is to try more "patchwork" repairs.

Money and time, both are factors in this decision. The "free" solution is to simply replace all the spokes... which is probably what I'll do.

Any other ideas?

 

[safe]

How much tension are you running? I just saw a wheel yesterday with 6 broken spokes, and the owner said they were loose and creaking for a while.

I always keep the spokes tight... maybe too tight. A tighter wheel will be more rigid, but also will be more likely to break the spokes at the hub which is where they are breaking. The rim is simply not very strong and I'd probably be better off with a wider rim because that would distribute the stress more evenly and allow for less spoke tension to achieve the same rigidity.

Again... money... time... hard to know if it's worth an extra $50 for a custom wide rim when the other option to switch out of the transaxle and into a multispeed hub is available. (solves many problems at once)

 

[knightmb]

All of my e-bike spokes have been back spokes that break. The front spokes are 12 ga on a double wall rim. In the 3 years that I've had it, a spoke has never broken. The rear wheel has gone through 2 spokes. Both times broken while going fast (30+ MPH) and hitting a dip in the road. I think it's a combination of both speed and stress. The good thing, you can still get home on a broken spoke, but fix it before it starts a fail over process of the others since with one missing spoke, the others are taking more pressure now.

 

[Geebee]

Possibly a combination of too small a spoke gauge and to much weight?
Some of those cheapo bike spokes are like noodles strength wise and you bike is not exactly what they were designed for.
The spokes you are describing take a heavy load as when you dish a wheel the shorter spokes ie the ones that are breaking tend to wind up a lot tighter (to get the offset) than the longer ones.
What about fitting the next gauge or quality spokes up, to just that side? cheaper that way.

 

[rhubarb]

This guy seems to know everything about building wheels- it's worth the 8 quid to download his e-book.

http://wheelpro.co.uk/

 

[oatnet]

safe, were your broken spokes on the left side or right side? Sheldon's website gives his opinion on breakage in dished wheels. I have been wanting to try the half-radial spoking sheldon mentions below, haven't figured out what the spoke lengths would be.

I like the 'crows foot' approach as well.

-JD

http://sheldonbrown.com/wheelbuild.html

Wheels with hub brakes and drive wheels should never be radially spoked. Due to the near perpendicular angle of the spoke to the hub's tangent, any torque applied at the hub of a radial spoked wheel will result in a very great increase in spoke tension, almost certainly causing hub or spoke failure.

More and more rear wheels now are built "half-radial" with semi-tangent spoking on the right side and radial spoking on the left. Radial front wheels offer mainly esthetic benefits, but half radial rear wheels can be substantially more durable than conventional ones, in cases where the wheel is highly dished. The high amount of dishing called for to make room for more and more sprockets has caused an increase in spoke breakage on the left side of rear wheels. This is caused by metal fatigue.
A spoked wheel relies on having all of the spokes in constant tension. A highly dished rear wheel starts with very light tension on the left side spokes. The torque of hard pedaling combined with cyclical weight loading can cause the left side "leading" spokes to occasionally go completely slack momentarily.

Repeated cycles of tension and slackness cause these spokes to fatigue at the bends, and ultimately break.

With half-radial spoking, the amount of dish is very slightly less to begin with if you run the radial spokes up along the inside of its flange ("heads out.") In addition, since there are no "leading" spokes, no amount of torque on the hub can reduce the tension on any of the spokes. In fact, if you have an old wheel that has been breaking left side spokes, "half rebuilding" the wheel into a half radial will solve the problem once and for all.

I used to think that this was exotic, cutting edge technology, until I happened to look at a couple of Model A Fords in a local parade. Their wheels were highly dished inward, and were laced in the same half-radial pattern, for the same reason.

 

[safe]

I did a complete teardown of the rear end of the bike:

1. Cleaned the chain in paint thinner. (lubed it once back on)

2. Replaced the rear disc brake. (a part broke on it)

3. Replaced a bearing cone on the axle that had pits.

4. Cleaned and repacked the rear wheel.

5. Added three layers of extra nipple tape over the top of the nipples so that the tube will be less prone to pop if I tighten the spokes.

6. Replaced ALL the spokes on the right hand side of the hub.

7. Added an extra washer so that I didn't need to dish the wheel as much (or at all... it's nearly perfectly centered now)

8. While replacing the rear disc brake I also added new spacers to compensate for the wheel realignment.

9. Tried out one of my other tires as the rear tire. (something I think I will reverse because the other tire was better)

10. Trued the rear wheel both up and down and sideways with high tension.

This time I'm going to go with more tension than I was using before just to see what the result will be. If the breakage is due to slack (as many seem to say) then this time I'm starting with a clean slate testing environment and I'll see how the thing works out. It's very possible that I was not using as much spoke tension as is possible. (or that the tension had gradually gotten to be less while I didn't notice)

That was my day... that's it...

Time to drink a beer...