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Wheel lateral stiffness. WHat makes it stiff?

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Wheel lateral stiffness. WHat makes it stiff?

Old 07-31-15, 01:19 PM
  #76  
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@FBinNY - LOL, I only continued reading because I wanted to see if you would make an additional contribution!

I appreciate your efforts to educate the masses. It is a systemic problem that people over simplify problems and are not able to think at a system level (many engineers of all disciplines), therefore missing the root cause or understanding how the whole works. The system is greater than the sum of the parts. It is difficult for some to grasp. I applaud your attempts and greatly appreciate your tenacity!
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Old 07-31-15, 01:31 PM
  #77  
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Originally Posted by McBTC View Post
Although it is worth analyzing, stiffness is not an important consideration in wheel design... A wheel that is strong enough to withstand the loads of its intended use is also stiff enough. ~Jobst Brandt (ibid.)
Well, maybe also not rubbing the frame might be important.
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Old 07-31-15, 04:13 PM
  #78  
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Originally Posted by Yellowbeard View Post
Pretty much, yeah. Barring any more complicated effects from the interaction at the crossing, which I've yet to see anyone try to quantify.

Spokes in a 3x build are slightly longer, which means they elongate slightly more under the same load. They also meet the flange a bit farther from the rim, which (for the same flange spacing and diameter) makes the bracing angle a bit smaller.

Of course, it also becomes slightly less torsionally stiff.
This is correct, but when discussing details like this it pays to have a sense of context or scale. So for a typical front 32h hub, the difference in spoke length is roughly 6mm, or 2% of the length. So reducing crosses does increase stiffness, but by an order of 2% or so, which isn't exactly a sea change, and is highly unlikely to be noticed in the real world.
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Old 07-31-15, 05:05 PM
  #79  
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Originally Posted by FBinNY View Post
This is correct, but when discussing details like this it pays to have a sense of context or scale. So for a typical front 32h hub, the difference in spoke length is roughly 6mm, or 2% of the length. So reducing crosses does increase stiffness, but by an order of 2% or so, which isn't exactly a sea change, and is highly unlikely to be noticed in the real world.
Very much agreed.

I'd love to see the carnage that would ensue if the bicycle market could somehow be subjected to a rash of double-blind testing. Everyone thinks they can feel every little nuance. I can barely register where my toes are pointing from one ride to the next, let alone make any kind of precise mechanical judgement.
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Old 07-31-15, 05:33 PM
  #80  
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Originally Posted by Yellowbeard View Post
Very much agreed.

I'd love to see the carnage that would ensue if the bicycle market could somehow be subjected to a rash of double-blind testing. Everyone thinks they can feel every little nuance. I can barely register where my toes are pointing from one ride to the next, let alone make any kind of precise mechanical judgement.
Never under estimate the power of the placebo effect. Eons back when I wrenched for a racing team, we discovered that they rode faster if their bikes looked worked on, whether we did anything material or not. The opposite was also true. We could make a meaningful improvement, but if the bike didn't have that worked on and loved look, they weren't happy.
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Old 08-01-15, 06:06 AM
  #81  
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Originally Posted by McBTC View Post
Although it is worth analyzing, stiffness is not an important consideration in wheel design... A wheel that is strong enough to withstand the loads of its intended use is also stiff enough. ~Jobst Brandt (ibid.)
Tell that.. to someone who can really supply some POWER to a rear... a strong sprinter.

JB is the piper for those who do not get the practical side of wheel building concepts. Graphs and endless 'theories' are not real world mileage
and the lessons learned actually building and riding different designs.

ONE size does not fit all... when weight & cost are factored into a wheel build. Main thing is good execution of the build and it staying 'put'.
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Old 08-01-15, 04:05 PM
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Originally Posted by McBTC View Post
For what it's worth, using finite element analysis, this author's model corroborated Jobst Brandt's results, leading to the conclusion that, the average compressive spoke [apparently 5 out of the 32 spokes analyzed] contributes 133 times as much lift force as the average tensile spoke.

See: Ian's Bicycle Wheel Analysis
Wow, I just read that whole webpage because of that clickbait quote. I deeply regret the total waste of time.
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Old 08-01-15, 05:19 PM
  #83  
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Originally Posted by AnkleWork View Post
Well, maybe also not rubbing the frame might be important.
Did you not understand him?
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Old 08-02-15, 10:03 AM
  #84  
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I read most but not all of this.
My question to the OP - Why are you asking? What are you trying to accomplish?
Is there a particular problem you need to solve?
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Old 08-03-15, 09:48 AM
  #85  
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Originally Posted by Jiggle View Post
Wow, I just read that whole webpage because of that clickbait quote. I deeply regret the total waste of time.
You may find engineers' support from the bottom up about hanging around, 'n round, 'n round...
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Old 08-03-15, 09:58 AM
  #86  
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Originally Posted by Aladin View Post
JB is the piper for those who do not get the practical side of wheel building concepts. Graphs and endless 'theories' are not real world mileage
and the lessons learned actually building and riding different designs.
Whatever your real-world experience, an accurate mechanical model will support it (unless the experience is a product of placebo effect and confirmation bias).
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Old 08-03-15, 10:04 AM
  #87  
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Originally Posted by tanguy frame View Post
I read most but not all of this.
My question to the OP - Why are you asking? What are you trying to accomplish?
Is there a particular problem you need to solve?
Reduce the amount of flex laterally. My OEM wheels did not rub the brakes but the new ones do when given the same spacing. Should the wheels need adjusting or spoke replacement, I would like to improve things when the opportunity arises or just do a complete spoke replacement now. not sure if this will do it or not. Could be, these wheels are not for me but riding, they really rarely rub. Adding a mm or two is OK but I already added a shim to the brifters due to reach and do not have as much room for braking as I would like. Plus I like my brakes to grab as soon as the slightest movement of the brifter is made meaning that the brakes need to be close to the rims.
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Old 08-03-15, 11:14 AM
  #88  
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Under what circumstances does the wheel rub the brakes?
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Old 08-03-15, 11:51 AM
  #89  
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Is the hub flange width the same between the two wheel sets --e.g., did you add more gears (as that would affect the flange spacing -- the distance of the hub flanges from the center of the hub)? Otherwise, the only other factors affecting lateral stiffness in addition to the flange spacing are rim strength and the number and thickness of spokes.
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Old 08-03-15, 12:05 PM
  #90  
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Call PETA!

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Old 08-03-15, 01:49 PM
  #91  
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Originally Posted by tanguy frame View Post
Under what circumstances does the wheel rub the brakes?
AS I have posted earlier, Front wheel only during turns, tighter and slower more often.
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Old 08-03-15, 05:48 PM
  #92  
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Originally Posted by Fly2High View Post
AS I have posted earlier, Front wheel only during turns, tighter and slower more often.
This is when I notice my front wheel (ref. post 29) deflecting laterally. I did run a different wheel set on the bike for some light touring experiments that didn't flex and seems to validate what @FBinNY stated in post 25. That wheel set is a CXP22 (very similar to the CXP23) with 32 14 ga. spokes on Sora hubs and it does not deflect at all.

Brad
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Old 08-04-15, 08:20 AM
  #93  
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Originally Posted by bradtx View Post
This is when I notice my front wheel (ref. post 29) deflecting laterally. I did run a different wheel set on the bike for some light touring experiments that didn't flex and seems to validate what @FBinNY stated in post 25. That wheel set is a CXP22 (very similar to the CXP23) with 32 14 ga. spokes on Sora hubs and it does not deflect at all.

Brad
This thread is so long that I may have missed the answer to a relevant question: Does your wheel possibly have excess play in the bearings? That, rather than "flexing" of the wheel, could account for the rubbing of the brake. Sorry if this was already addressed.
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Old 08-04-15, 09:25 AM
  #94  
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My first thought was that when you do a slow tight turn, your brake cable is affected due to cable routing and the caliper closes slightly. Slight out-of-true variations could explain the brake shoe rubbing on one wheel vs another. I am not so familiar with the wheel sets you are using, but modern rims are really stiff and if spokes are properly tensioned, the wheels should not deflect laterally by any appreciable amount.

My recommendation is to look really carefully at your brake cable routing and see if your calipers move when you turn the handle bars. If so - you've got your root cause.

Check that the wheels are true and properly dished with a good truing stand and dishing gage.
You should be able to get the wheels true within around 1 mm of side to side variation on high quality wheels. Lower quality wheels or damaged rims will wobble more and there's not much you can do about that (except get new wheels).

Open the calipers using the barrel adjuster is another way to make the rubbing disappear. I know you don't like to do that, but sometimes we gotta just make it work....
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Old 08-04-15, 09:32 AM
  #95  
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It is also possible that the width between the braking surfaces of the two rims you are experimenting with are different. A wider rim will need more caliper clearance...
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Old 08-04-15, 12:06 PM
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One problem with the thread is that the OP asked about stiffness in general without specifying that he had a problem of any kind. So we had a general discussion about wheel stiffness, and wheels in general.

Had the OP said, "I have a front brake rub problem in turns", wheel stiffness might jot have been brought up at all, and we'd be discussing how to diagnose and solve the brake rub issue.

This is something that everybody with a problem can learn from.

If you have a problem ask about the problem Don't diagnose it, then ask about something you suspect might be the cause, because you'll limit the discussion and all the responses might be unrelated to the actual cause and remedies available.
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Old 08-04-15, 04:06 PM
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Originally Posted by Fly2High View Post
Reduce the amount of flex laterally. My OEM wheels did not rub the brakes but the new ones do when given the same spacing. Should the wheels need adjusting or spoke replacement, I would like to improve things when the opportunity arises or just do a complete spoke replacement now. not sure if this will do it or not. Could be, these wheels are not for me but riding, they really rarely rub. Adding a mm or two is OK but I already added a shim to the brifters due to reach and do not have as much room for braking as I would like. Plus I like my brakes to grab as soon as the slightest movement of the brifter is made meaning that the brakes need to be close to the rims.
I'll try another shot at this: Have you checked for too much bearing free play in the offending wheel? As long as the wheel spins freely with no discernible drag in the bearings, then ANY play felt in the bearings is excessive. If you can wiggle the rim from side to side such that it moves even a millimeter or two closer to one fork blade or the other, that could be the source of your brake rubbing.
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Old 08-04-15, 08:02 PM
  #98  
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Originally Posted by habilis View Post
This thread is so long that I may have missed the answer to a relevant question: Does your wheel possibly have excess play in the bearings? That, rather than "flexing" of the wheel, could account for the rubbing of the brake. Sorry if this was already addressed.
Both hub sets are adjusted properly and the flex is noticeable just on the rim section. My rims don't unintentionally rub the brake pads, but the OP's do.

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Old 08-05-15, 04:44 AM
  #99  
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I wonder.. if a few VIAGRA wouldn't make the 'rear' stiffer........
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Old 08-05-15, 06:34 AM
  #100  
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Originally Posted by habilis View Post
I'll try another shot at this: Have you checked for too much bearing free play in the offending wheel? As long as the wheel spins freely with no discernible drag in the bearings, then ANY play felt in the bearings is excessive. If you can wiggle the rim from side to side such that it moves even a millimeter or two closer to one fork blade or the other, that could be the source of your brake rubbing.
Will have a look and report back.

Viagra? LOL. The real trick is getting it in the wheels. Of course, I would have to call a bike mechanic if the stiffness lasts over 4 hours
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