RE: the mechanics of a spoked wheel and reliability testing

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4/28/2018 7:48 PM

Couple of questions:

1. A Google search on whether the load seen at axle/Hub hangs more from the top spokes or stands more on top of the bottom spokes returned mixed results with some technical analysis seeming to support each argument. I realize the wheel assembly distributes the load with spokes at front and rear also helping to keep the wheel round but generally speaking does the load on a rolling spoked wheel like those found on a motorcycle not like a spoked wagon wheel moving along an even and smooth surface more so hang or stand etc.?



2. JA's broken spokes had me wondering if any teams have tested wheels to see how many spokes could be lost before the compromised wheel becomes too unsafe to not change it immediatly. Obviously rider safety is paramount and losing even a single spoke places more load on the remaining spokes not to mention if the missing spokes are random or sequential and if the wheel/spokes were properly tensioned to begin with and if the rim had any bends or dings but is there any accepted understanding with the teams that if the wheel has only lost X number of sequential spokes....although compromised they expect the wheel should last long enough to finish a moto?

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4/28/2018 7:49 PM

Winner for the longest thread title in Vital history?

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"Sorry Goose, but it's time to buzz the tower."

4/28/2018 7:52 PM

Yeah I was already shortening it as soon as I saw it sorry about that

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4/28/2018 7:53 PM

Holy shit

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4/28/2018 7:53 PM

Spokes are under tension, not compression.

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4/28/2018 8:04 PM

Ask Grant Langston about how many spokes can be missing for a wheel to survive or cost you a championship

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4/28/2018 8:04 PM

We should ask Grant Langston this question.

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2019 KTM 150 SX
2015 Yamaha YZ 250

4/28/2018 8:06 PM

Maybe some kind of front wheel clear lexan (thin) cover inside of the disc that runs the diameter of the inside of tge rim that protects the wheels spokes from something like this....yea it might look hokey but could be a good fail safe from taking a footpeg and ripping spokes out

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4/28/2018 8:07 PM

Photo

Under tension has always been my understanding as well but there's some differing opinions that make legitimate points.
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4/28/2018 8:12 PM

HighPlainsSquid wrote:

We should ask Grant Langston this question.

Lol why dont you try count them, go back and watch the race where his front wheel spokes failed and cost him a championship, then you wont have to bother him..

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4/28/2018 8:14 PM

I'd grab a bottle of wild turkey and lube up the brain stem before contemplating such a question

Be right back

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4/28/2018 8:20 PM

hillbilly wrote:

I'd grab a bottle of wild turkey and lube up the brain stem before contemplating such a question

Be right back

I look forward to this

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4/28/2018 8:23 PM

Think about it, how could you put a compression load on the spokes when the nipple will just push out? What about the straight spokes, where the spoke would just just push out the hub? Tension only. About 3/4 of the spokes are loaded at a time. Front, top, and back.

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4/28/2018 9:01 PM

Ummm... what about the broken spokes going into the brake rotor? That’s why the wheel needs to be changed.

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4/28/2018 9:19 PM

Xeno wrote:

Ummm... what about the broken spokes going into the brake rotor? That’s why the wheel needs to be changed.

Someone gets it !!

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4/29/2018 12:26 PM
Edited Date/Time: 4/29/2018 12:27 PM

You-n-Gs-town born & bred wrote: Photo

Under tension has always been my understanding as well but there's some differing opinions that make legitimate points.

This is mostly incorrect. The wheel is supported by spoke tension and the upper spokes are doing all the work supporting the hub. While the lower spokes may see a larger change in stress than the top, they are NOT supporting the load in compression. They are still in tension and simply can's support a compressive load.

Even if they lost all tension, the lower spokes couldn't support a compressive load as the nipple would just be pushed into the rim. And even if they lost all tension and the nipple somehow didn't press into the rim, they still couldn't support a compressive load as they are very long and thin and will buckle under a very small compressive force.

Regardless, broken spokes rattling about can cause all sorts of havoc and be unsafe. Changing the wheel was the right move for that alone, but the wheel would have also had serious structural issues missing that many spokes.

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Billy Wight
Luxon MX
@LuxonMX
https://luxonmx.com
Motocross Components Engineered for Performance

4/29/2018 12:53 PM

You-n-Gs-town born & bred wrote:

Couple of questions:

1. A Google search on whether the load seen at axle/Hub hangs more from the top spokes or stands more on top of the bottom spokes returned mixed results with some technical analysis seeming to support each argument. I realize the wheel assembly distributes the load with spokes at front and rear also helping to keep the wheel round but generally speaking does the load on a rolling spoked wheel like those found on a motorcycle not like a spoked wagon wheel moving along an even and smooth surface more so hang or stand etc.?



2. JA's broken spokes had me wondering if any teams have tested wheels to see how many spokes could be lost before the compromised wheel becomes too unsafe to not change it immediatly. Obviously rider safety is paramount and losing even a single spoke places more load on the remaining spokes not to mention if the missing spokes are random or sequential and if the wheel/spokes were properly tensioned to begin with and if the rim had any bends or dings but is there any accepted understanding with the teams that if the wheel has only lost X number of sequential spokes....although compromised they expect the wheel should last long enough to finish a moto?

It doesn't matter if anyone expects the wheel would finish the moto. Point is, the rider can feel a difference in the wheel, and would immediately lose confidence in said wheel. the number of spokes lost is not relevant...only what the rider perceives is relevant

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Many thanks to everyone helping me out this GNCC season: SRT Offroad, Acerbis, FCR Suspension, O'Neal Racing, Evans Waterless Coolants, Rekluse, Twin Air, Braking Brakes, Carbsport

Profile image credit Ken Hill Photography

4/29/2018 12:57 PM

Wasn’t it the rear on Langston’s bike? And I’m sure Anderson didn’t want to risk a catastrophic injury over a front wheel

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"Shifting gears and passing queers" GL

4/29/2018 12:58 PM

My question is how do you notice broken spokes. I had 2 broken for 3-4 rides. Did not notice until I washed my bike.

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4/29/2018 1:50 PM

You-n-Gs-town born & bred wrote: Photo

Under tension has always been my understanding as well but there's some differing opinions that make legitimate points.

This would be accurate for traditional wheels with “J” spokes, not like modern straight pull spokes on a mx bike. Upper spokes take the load, lower spokes will “push” in the hub vs break or punch through the tube. If excess play is in the wheel due to loose spokes or broken spokes, they wont have the tension needed to push in the hub and will instead push in to the tube causing a flat.

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4/29/2018 1:53 PM

r.sal923 wrote:

My question is how do you notice broken spokes. I had 2 broken for 3-4 rides. Did not notice until I washed my bike.

You notice them right away when you can hear them hitting your fork tubes.

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4/29/2018 2:11 PM

Yamaha spokes are best spokes...

Photo

Photo

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4/29/2018 2:27 PM

How do these spoke loads effect the physics of a seat bounce?

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4/29/2018 2:56 PM

Richard Tease II wrote:

How do these spoke loads effect the physics of a seat bounce?

DUDE!!!! I was just going to say that Teefus is reading this up above right now and wishing like mad he could chime in!

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4/29/2018 11:06 PM

r.sal923 wrote:

My question is how do you notice broken spokes. I had 2 broken for 3-4 rides. Did not notice until I washed my bike.

You only wash your bike every 3 to 4 rides? blink blink

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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

4/30/2018 12:51 AM

You-n-Gs-town born & bred wrote: Photo

Under tension has always been my understanding as well but there's some differing opinions that make legitimate points.

Luxon MX wrote:

This is mostly incorrect. The wheel is supported by spoke tension and the upper spokes are doing all the work supporting the hub. While the lower spokes may see a larger change in stress than the top, they are NOT supporting the load in compression. They are still in tension and simply can's support a compressive load.

Even if they lost all tension, the lower spokes couldn't support a compressive load as the nipple would just be pushed into the rim. And even if they lost all tension and the nipple somehow didn't press into the rim, they still couldn't support a compressive load as they are very long and thin and will buckle under a very small compressive force.

Regardless, broken spokes rattling about can cause all sorts of havoc and be unsafe. Changing the wheel was the right move for that alone, but the wheel would have also had serious structural issues missing that many spokes.

Agree. The author was just trying to be smart.
The bottom spokes probably do lose more tension because the rim is also flexing upwards under load. But the top ones continue to do the work. As do the side ones. It is a system.

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4/30/2018 4:07 PM
Edited Date/Time: 4/30/2018 4:08 PM

This is actually a good question. See my wheel below. A60 with excel spokes. Likely a similar setup to Andersons. 2013 at Comp Edge there was a double/tripple/quad. Cut the track to attempt the 4th gear quad 2 lanes away from the water truck/tower. Shorted it about 4 times. Then did a 5 lap moto. Pulled off and noticed my wheel in this condition. 8 spokes broke and wheel deformed. Im 220lbs and not smooth at all.

For JA 3 spokes broken, a perfectly round rim, and the remaining spokes tight - could it have made it? I wouldnt be suprised if it did.

Photo

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4/30/2018 4:57 PM
Edited Date/Time: 4/30/2018 5:00 PM

Of course it's distributed around the wheel once it's completely laced but all spokes run in tension. The answer your looking for is hanging. Spokes wouldn't support jack shit in compression, they are strong in tension. The spoke nipples aren't even supported from the backside, so there's no way for them to run in compression.

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4/30/2018 5:23 PM

I have another question. Was their tire change fast or slow by their standards? I honestly don’t know what would be considered fast for changing a front tire. Every time I’ve helped people do it, we were in no hurry obviously. Wasn’t sure what the standard was for SX/MX mechanics during a race like that.

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4/30/2018 8:03 PM
Edited Date/Time: 4/30/2018 8:56 PM

Looks like JA wasn't the only rider to experience spoke issues.

AJ Cantazaro lost 8 or 9 on his rear wheel....he believes it started out with only a few broken then progressed until it locked up.


By the way my question regarding if a rider can or should continue was with the understanding that any broken spokes would be cut and removed first. I didn't make that clear.

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