# 20 or 24 spokes for front wheel



## DeLuz (Aug 1, 2008)

I weigh 135 and I keep debating in my head if should use 20 or 24 spokes on my next front wheel. I tend to be conservative and that leads me to 24 thinking the wheel will be stronger and more reliable and easier to ride home in the event of a broken spoke. But when I look around a lot of front wheels are 20 spokes or less and most of those riders weigh more than me so maybe 24 is overkill. Help me decide.


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## ergott (Feb 26, 2006)

Depends on the components. I'm 165 and I've been using a 16 spoke front with no worries. It even survived a head on crash with a piece of a catalytic converter in the road last week. Wish I faired as well.

-Eric


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## Kerry Irons (Feb 25, 2002)

*20*



DeLuz said:


> I weigh 135 and I keep debating in my head if should use 20 or 24 spokes on my next front wheel. I tend to be conservative and that leads me to 24 thinking the wheel will be stronger and more reliable and easier to ride home in the event of a broken spoke. But when I look around a lot of front wheels are 20 spokes or less and most of those riders weigh more than me so maybe 24 is overkill. Help me decide.


At your weight, unless you are some sort of pothole magnet, 20 spoke front would be fine if properly built. I rode 24 spoke front for 60,000 miles with no problems, and I weigh 175-180.


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## rruff (Feb 28, 2006)

DeLuz said:


> I weigh 135 and I keep debating in my head if should use 20 or 24 spokes on my next front wheel.


If it is a fairly stiff rim, 20 is plenty. On a road bike, front wheels have a much easier time than rear ones.


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## DeLuz (Aug 1, 2008)

OK I am convinced 20 for the front.
How about the rear 24 or 28? 2x DS, radial NDS?

Now I am going back and forth between Kinlin 270 or 300.
The weight difference does not matter to me at all I think it is negligible.
If there is an aero advantage to the 300 then that might be a reason to choose it over the 270.
From a looks standpoint I think I prefer the 270, the 300 might look freakishly deep to me.


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## rruff (Feb 28, 2006)

DeLuz said:


> How about the rear 24 or 28? 2x DS, radial NDS?


With the 27s, 20f and 24r would generally be fine for someone of your size. 24h should be laced 2x on the DS... 28h could be 2 or 3x.


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## Kerry Irons (Feb 25, 2002)

*One more point*



DeLuz said:


> OK I am convinced 20 for the front. How about the rear 24 or 28? 2x DS, radial NDS?


Just be aware, that whether front or rear, a 20 or 24 spoke wheel (and maybe a 28) will become unrideable if you break a spoke. Even after working with a spoke wrench, you'll have a serious wobble if you're missing a spoke in such a wheel.


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## eddie m (Jul 6, 2002)

rruff said:


> On a road bike, front wheels have a much easier time than rear ones.


Don't be so sure of that. The maximum load on a rear wheel is about 60% of the weight of the rider and bike, plus the pedaling load, which is only large when standing in low gears. Braking loads are low, even with a hub brake. 
OTOH braking load and related weight transfer can increase the loads on the front wheel to more than the weight of the bike and rider. Also, it's easy to put the front wheel down a little sideways if you hop at all, and wheels are relatively weak laterally. Given the fact that a front wheel collapse is more dangerous than a rear wheel collapse, maybe the front needs more spokes.
Rear wheels need more spokes because they are so offset that half the spokes can't be sufficiently tensioned, not because the loads are greater than front wheel loads.

em


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## jmlapoint (Sep 4, 2008)

I am a heavy rider at 180 and have broken a few REAR spokes in my time.
Remove the broken spoke if you can to avoid frame scratches/damage.
I always carry a spoke wrench.
Tighten the 2 spokes before and after the broken one.
Open the brake quick release and leave it open.
This will usually allow the wobbly wheel to turn without rubbing and you can usually ride home using the other brake if needed.


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## rruff (Feb 28, 2006)

eddie m said:


> Rear wheels need more spokes because they are so offset that half the spokes can't be sufficiently tensioned, not because the loads are greater than front wheel loads.


All I said was that front wheels have an easier time... not that the loads were greater (even though they are). Front wheels have significantly better lateral strength and stiffness even with fewer spokes.


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## eddie m (Jul 6, 2002)

rruff said:


> All I said was that front wheels have an easier time... not that the loads were greater (even though they are). Front wheels have significantly better lateral strength and stiffness even with fewer spokes.


I not sure what it means the "front wheels have an easier time," but it's obvious that front wheel loads are greater. It's also clear from measurement and from analysis that virtually all wheels are more than strong enough to support typical loads in the radial direction. It's not obvious how large the lateral loads on a wheel are, and what margin for safety is built into either a front or rear wheel. Every catastrophic wheel failure I have ever seen was a saddle failure (a taco) caused by lateral loads, and every one of those was a front wheel.

em


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## rruff (Feb 28, 2006)

eddie m said:


> Every catastrophic wheel failure I have ever seen was a saddle failure (a taco) caused by lateral loads, and every one of those was a front wheel.


It's easy enough to check how much lateral force it takes to make the spokes go slack in a wheel... and for most builds that will be far easier on the rear (force towards the NDS) than the front, even if the rear has more spokes. The two tacoed road wheels I've seen were rears. I'd also wager that riders have more issues with rear wheels (spokes breaking, wheels coming out of true) than fronts.


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## Kerry Irons (Feb 25, 2002)

*Empirical evidence*



eddie m said:


> I not sure what it means the "front wheels have an easier time," but it's obvious that front wheel loads are greater. It's also clear from measurement and from analysis that virtually all wheels are more than strong enough to support typical loads in the radial direction. It's not obvious how large the lateral loads on a wheel are, and what margin for safety is built into either a front or rear wheel. Every catastrophic wheel failure I have ever seen was a saddle failure (a taco) caused by lateral loads, and every one of those was a front wheel.


There can be all kinds of thinking about front wheel loads (braking loads are very minor compared to full out pedaling forces), but there's a real simple way to think of it. For most people who have broken multiple rear spokes, they have never had the experience of breaking a front spoke. Likewise trashing a front wheel (short of an accident). The real life loads on a front wheel, compared to the wheel's ability to take those loads (due to the symmetric nature of the wheel) are minor compared to the rear.


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## eddie m (Jul 6, 2002)

Kerry Irons said:


> There can be all kinds of thinking about front wheel loads (braking loads are very minor compared to full out pedaling forces), but there's a real simple way to think of it. For most people who have broken multiple rear spokes, they have never had the experience of breaking a front spoke. Likewise trashing a front wheel (short of an accident). The real life loads on a front wheel, compared to the wheel's ability to take those loads (due to the symmetric nature of the wheel) are minor compared to the rear.


I don't know how you can know that. If you exert 1000 newtons (225 lbs) on the pedals in a 34X25, you put 125 nt-m torque on the hub. If that's distributed equally over 28 spokes, that's changes the tension in each spoke by 100 nts, or about 10% of the preload. That only happens in low gears when you are standing. In a 53X12, you apply only 30% of that torque, and if you are sitting you can't exert 1000 newtons, unless you are really big. Of course, it's not clear which spokes exert most of the torque. 

On the other hand, braking loads can equal the full weight of the rider and more.
http://www.youtube.com/watch?v=fQV9wpNfMk0
That kid has the rear wheel off the ground while he's braking. The load on the front wheel is the vector sum of the total weight of the bike/rider and the braking force. That's the maximum load on the front wheel, and it's taken mostly by a small number of spokes at the bottom of the wheel. I know one guy who does that with his road bike (mostly only when there's some girls around), but maybe for me the maximum is a little less.

em


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## eddie m (Jul 6, 2002)

rruff said:


> It's easy enough to check how much lateral force it takes to make the spokes go slack in a wheel... and for most builds that will be far easier on the rear (force towards the NDS) than the front, even if the rear has more spokes. The two tacoed road wheels I've seen were rears. I'd also wager that riders have more issues with rear wheels (spokes breaking, wheels coming out of true) than fronts.


It's easy to know how much force a wheel can resist. The hard part is determining how much force is exerted in actual use, and how transient loads and impacts affect the wheel. 
I haven't seen any analysis or data that convinces me that fewer than 32 spokes is safe for a heavy rider. Most of the actual experience of road bikes is on 36 spoke wheels. It's like there's this giant experiment going on to find the minimum safe number of spokes, and we are the guinea pigs.

em


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## Kerry Irons (Feb 25, 2002)

*One more time, with feeling*



eddie m said:


> I don't know how you can know that.
> 
> On the other hand, braking loads can equal the full weight of the rider and more.


When braking, the forces are between the tire and the road and the rim and the brake pads. Yes, the wheel takes the full load of the rider's weight, but I can do that in my driveway just by putting all my weight on the handlebars. Doesn't seem that stressful to me. And I ask you again: How many front spokes have you (or your friends) broken vs. how many rear spokes. That tells the tale. Full stop.


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## flanman (Jul 7, 2006)

Just from my experience,

I regularly retrue rear wheels and have occasionally broken rear spokes. I have trashed a couple of wheels and they were all front wheels, never significantly damaged a rear.


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## raymonda (Jan 31, 2007)

These brainiacs make things so complicated. At 135lb ride the lightest wheels you can afford from a reputable builder and don't worry about it. I wish I weighed 135. Just wait for me at the top of the climb, please!


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## eddie m (Jul 6, 2002)

Kerry Irons said:


> When braking, the forces are between the tire and the road and the rim and the brake pads.


Of course there are braking forces at the rim and brake pads, but there is still a reaction force at the hub which is transfered to the rim through the spokes. 



Kerry Irons said:


> Yes, the wheel takes the full load of the rider's weight, but I can do that in my driveway just by putting all my weight on the handlebars. Doesn't seem that stressful to me. And I ask you again: How many front spokes have you (or your friends) broken vs. how many rear spokes. That tells the tale. Full stop.


It's not about breaking spokes. Spoke failures seem to be much less frequent than in the past, and I think that's because builders learned that stress relieving and higher tensions improved fatigue life. I also think most of that was learned after 7s exposed the inherent weakness of the old separate hub and freewheel design and then after 8s pushed wheels to the maximum possible dish. Newer wheels seem to be much more reliable than the first generation of 8s wheels. I think the most frequent failure now is cracking around spoke holes in the rim.

Any bicycle wheel will hold the rider's static weight and more. What I am concerned about is whether it can support a side load. I think the side load on a front wheel is typically more than on a rear, and I think it might be possible to put significant side loads on a front wheel while cornering and braking at the same time. It's also possible to skip a front wheel an put it down a little side ways. That seems to me about the worst case scenario for a wheel. I never worry about my 32 spoke wheels, but now every wheel seems to be 24 or less, often 20 sometimes 18 or even 16. I'm not sure I want to be riding those. 

If you search the google you can find academic papers about bicycle wheels. I assume that means that the large companies like Shimano, Mavic, Trek and others are concerned enough to fund studies of these same issues. Maybe they understand this better than me, but no one yet has explained to me why I needed 32 spokes for the last 35 years, but now 20 are fine. 

em


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## eddie m (Jul 6, 2002)

raymonda said:


> These brainiacs make things so complicated. At 135lb ride the lightest wheels you can afford from a reputable builder and don't worry about it. I wish I weighed 135. Just wait for me at the top of the climb, please!


If I weighed 135 I wouldn't be worried about this stuff at all. 

em


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## rruff (Feb 28, 2006)

eddie m said:


> Maybe they understand this better than me, but no one yet has explained to me why I needed 32 spokes for the last 35 years, but now 20 are fine.


Stiffer (deeper) rims are the biggest reason. Nothing wrong with putting in more spokes... gives you a bigger margin plus breaking a spoke doesn't take the rim very far out of true. 

But like all high-end bike parts, we are pushing the envelope for light weight and aerodynamics, so "strong enough" is what most people seem to want... strong enough to probably last 20k miles or so with a normal rider... or at least until the warranty runs out. IMO stuff like stems, forks, and bars are the places where I really want some margin.


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## eddie m (Jul 6, 2002)

rruff said:


> Stiffer (deeper) rims are the biggest reason. Nothing wrong with putting in more spokes... gives you a bigger margin plus breaking a spoke doesn't take the rim very far out of true.
> 
> But like all high-end bike parts, we are pushing the envelope for light weight and aerodynamics, so "strong enough" is what most people seem to want... strong enough to probably last 20k miles or so with a normal rider... or at least until the warranty runs out. IMO stuff like stems, forks, and bars are the places where I really want some margin.


That's all true, but deeper rims add strength mostly in the radial direction. Rims need to be wider to make them laterally stronger, and it's lateral loads that cause catastrophic failures.

The concern I have with all the light stuff is that I think it's designed for 140 lbs racers, not for guys my size.

That's a good point about stems and forks. I wonder if all the new carbon stuff will be as durable as steel and alloy. 

em


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## rruff (Feb 28, 2006)

eddie m said:


> That's all true, but deeper rims add strength mostly in the radial direction. Rims need to be wider to make them laterally stronger, and it's lateral loads that cause catastrophic failures.


Rims that are stiffer radially seem to have a significantly higher resistance to lateral buckling.


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## Blue CheeseHead (Jul 14, 2008)

eddie m said:


> That's all true, but deeper rims add strength mostly in the radial direction. Rims need to be wider to make them laterally stronger, and it's lateral loads that cause catastrophic failures.
> 
> The concern I have with all the light stuff is that I think it's designed for 140 lbs racers, not for guys my size.
> 
> ...


I ride some pretty light Rolf Elans, (1,300 +/-gms) with 20/24 spokes. I tip the scales at 195-200#. 4,000+ miles so far and no broken spokes and the wheels remain true. Someone 135# can ride on anything they wish.


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## eddie m (Jul 6, 2002)

rruff said:


> Rims that are stiffer radially seem to have a significantly higher resistance to lateral buckling.


That's true. If you double the depth, the lateral stiffness doubles, but the radial stiffness increases by a factor of 16. OTOH, the deflection in the span between the spokes increases as the cube of the span. So if you double the depth of the rim, but reduce from 32 to 20 spokes, it seems like you get a wheel that is more rigid radially, but twice as flexible laterally.

Of course, it might not be that simple. Lateral failures involve the rim twisting as well as bending, so maybe it is stable enough with fewer spokes. 

What's interesting is that BMX bikes use 20 inch wheels with 36 spokes or more. That should be as strong as a 54 spoke road wheel. I think they want all that because they jump, and they don't want to fold a wheel when they land a little sideways. I hop a little bit as well, and I'm a lot heavier than a typical BMX rider, so I'm not sure I want a wheel that's less than half as strong as a kid's wheel.

I've actually found academic papers on this stuff on the google, but I've never found anything about failure modes. Maybe that stuff is proprietary. 

em


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## Blue CheeseHead (Jul 14, 2008)

eddie m said:


> That's true. If you double the depth, the lateral stiffness doubles, but the radial stiffness increases by a factor of 16. OTOH, the deflection in the span between the spokes increases as the cube of the span. So if you double the depth of the rim, but reduce from 32 to 20 spokes, it seems like you get a wheel that is more rigid radially, but twice as flexible laterally.
> 
> 
> em



While I don't have the time to get into an in depth engineering analysis, I think you are simplifying way too much. Keep in mind that deeper rims are V shaped, not box shaped and as a V gets deeper it gets proportially narrower as the section changes, so does your equation and it is not a simple linear relationship.

While deflection of a simple beam is related to the cube of the span, a wheel is not a beam, but more of an arch. Again, not a simple deflection equation.

While I agree there is a relationship between lateral deflection and spoke count, it is not an easy equation. The triange formed between the nipple connection and the two opposite sids of the hub play a large role in lateral stiffness. You have way too many variables going on here to boil it down to 2x this and 16x that.

While you set forth the information in a very matter of fact manner, as an engineer, I'm not buying it.


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## eddie m (Jul 6, 2002)

Blue CheeseHead said:


> While I don't have the time to get into an in depth engineering analysis, I think you are simplifying way too much. Keep in mind that deeper rims are V shaped, not box shaped and as a V gets deeper it gets proportially narrower as the section changes, so does your equation and it is not a simple linear relationship.


I understand that, but if the rim gets narrower the increase in lateral stiffness is less. i was making a conservative assumption. If I were designing rims, i would have calculated the real numbers, but I'm just considering what factors might be important. 


Blue CheeseHead said:


> While deflection of a simple beam is related to the cube of the span, a wheel is not a beam, but more of an arch. Again, not a simple deflection equation.


Again, the arch should deflect more laterally than a beam, because the curvature creates another moment.



Blue CheeseHead said:


> While I agree there is a relationship between lateral deflection and spoke count, it is not an easy equation. The triange formed between the nipple connection and the two opposite sids of the hub play a large role in lateral stiffness. You have way too many variables going on here to boil it down to 2x this and 16x that.
> 
> While you set forth the information in a very matter of fact manner, as an engineer, I'm not buying it.


Of course it's not an easy equation. It's statically indeterminate, and I don't have the capacity to solve that problem. If it were simple, I wouldn't be asking what others experiences are.
I'm not selling anything, I'm just asking questions. The only answer I seem to get is that nobody has broken any 29 spoke wheels. That's a good thing, but the experience with those wheels is pretty limited.

em


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## Blue CheeseHead (Jul 14, 2008)

I can agree with your last post Eddie. Your earlier post just sounded very "definative". All is good. :thumbsup:


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