Jason Curtiss

Hello all, I have a 10-speed 24H (12H per flange) rear wheel that is laced in a 2X pattern. The rim is true, but it will shift slightly to the left (non drive side) when I sit on the bike with my weight of 187 lbs. I've tightened the drive side spokes as much as a I dare to, but the rim will still shift some .030" (0.7mm) with my weight applied. Is this a typical phenomenon with a 24H (12H per flange) rear wheel?

Thanks!

Jason

AnkleWork

The elastic modulus of metals is linear, so tightening the spokes above the optimum value will not help. Monitor the rim for cracking.

Steelman54 

In my opinion, 187ish lbs is a bit too heavy for 24 spokes and your wheel seems to be telling us that. You have tightened spokes as much as deemed feasible, not sure where else to go. I guess you could check tension with a gauge and see if you can go tighter, but i think you need 28 or preferably 32 spoke wheel for durability.

pdlamb

Just out of curiosity, how do you measure the 30 mil shift? Seems like it'd be hard to measure that small a shift while you're sitting on your bike.

fietsbob

At 187 pounds ? have you considered a 24 spoke 700c wheel is inappropriate for your riding ??

+1) saying you measured to .030" (0.7mm) defection, suggests you are obsessive.. How did you measure that while riding?


(I have a 16" 349 rim wheel with 24 spokes , and had a Brompton with a front wheel with 20) whole different story with smaller wheels ..

Andrew R Stewart 

Are you equally balanced on the bike when measuring the shift? (and like pdlamb I'd like to see a shot of that feat). Or are you placing one foot on the ground during the measurement? What about when you support the bike with a trainer stand? Andy

Koyote

I'm not sure how I would measure a .7mm shift, especially when ON the bike.

But I will agree with some other posters. I prefer 32h 3x wheels, as they will be only marginally heavier but much stronger.

Jason Curtiss

Thank you all for the responses!

AnkleWork: Regarding the modulus of elasticity, it is indeed linear, within the proportional limit that is. My thinking was that I could preload the drive side spokes such that the horizontal force component from the non-drive side spokes when loaded with riser weight would not pull the rim to the left. But it seems I can't get there, especially with the same quantity of spokes on each side. Regarding the question about how I measured the 0.7mm shift, I used different thicknesses of stiff paper as feeler gauges and measured the gap statically, not while riding. I would set the right-hand brake pad so that it just touched the rear rim. Then I would sit on the bike and have my wife insert the "gauges" in the resultant gap between the right brake pad and rim. It's not a dead-nuts accurate way of measuring the deflection, but it's close.

In the end, I think the symmetrical pattern, 12H per side, combined with my weight is the problem. I have another rear wheel that is 24H, but it has 16H on the drive side and only 8H on the non-drive side. This arrangement with the greater quantity of spokes on the drive-side offsets the greater horizontal component on the non-drive side spokes as a result of the larger spoke angle on that side. There is no perceptible shifting of this rim when I sit on the bike.

Thank you all again for responding to my query.

Best,

Jason

seattle29er

I've built wheels.... +1 on using 28 spokes... or at minimum heavier gage spokes on your 24h set-up for a heavier rider. Some manufacturers "wheel systems" will even specify rider weight... have you looked into whether you have a custom wheel or whether it's a brand "system" (eg Shimano or Mavic hub/spokes/rim, etc) and whether it has a recommended rider weight limit?

Jason Curtiss

Hello seattle29er.

Installing heavier gauge spokes on the drive side would be a elegant solution, except the hub will only accommodate a maximum spoke diameter of 2mm and the spokes I have installed are 2mm straight gauge.

The wheel was built from bits and pieces: the hub is a Novatec F172SB-11S, the rim is an Oval Concepts model 327 and the spokes are 2mm diameter stainless steel straight gauge from Wheel Builder. As you can see, it's a Frankenstein wheel and does not have a "published" weight limit.

So, it appears I either live with the slight rim shift, or buy or build a better/stronger wheel.
Best,

Jason

pdlamb

With a sealed bearing on that hub, I'd be wondering if the (very very small) shift was due to spoke tension asymmetry or to a little bit of bearing looseness.

TimothyH

I don't know much about wheel building but have had rims shift around when hub bearings are bad.

Bad enough bearings and the wheel could be moved laterally by hand.


-Tim-

Jason Curtiss

Thank you for the bearing suggestion, but the hub is brand new and the bearings are nice and tight.

seattle29er

Some rear wheel flex can be built-in to a wheel as a solution for comfort, etc, but seems that just by sitting on a bike the rear wheel flexes... sounds like the wheel is overloaded...which to me is a safety concern and totally not worth cutting corners. I'd seriously encourage you to look for a stronger wheel.

ljsense

The spoke count doesn't matter -- the physics are the same whether there are 24, 28 or 32 spokes.

When you load the wheel by sitting on the bike, some spokes lose tension, some gain. Depends on the existing tension, shape of the rim.

I wouldn't mess with it, sounds like you've figured out how to have a great time with your wife. And 187 isn't too heavy for a good x spoke wheel.

Jason Curtiss

Ha, I'm not too sure my wife agrees with you!

Best,

Jason

fietsbob

Or if radial contact sealed bearings the problem is user obsession not mechanical ..

Time weighing on your hands ??

Jason Curtiss

Here's the deal there fietsbob: I have two (2) 24H wheels, one (1) with 16 spokes on the drive side and one with 12 spokes on the drive side.
The 16-spoke drive side wheel has virtually no perceptible rim shift when I sit on the bike. However, the 12-spoke drive side wheel shifts noticeably to the left when I apply my weight of 187 pounds.
So, I'm trying to figure out a solution to this wheel shift. As you pointed out, one solution is to ignore it. In my mind, this is similar to applying black electrical tape to the "check engine" light on your car. This may in fact be the best solution, all things considered, but I'm still working on a more physics-based solution.

Thank you for your input.

Jason

fietsbob

As I said my 24 spoke wheels are 349 16" on my bike Friday Tikit Folding bike , rear built on a 36 spoke gear hub , Company used 2/3 of the holes in the hub..

may I , a Bike touring and commuter type with decades of riding and mechanics, recommend a wheel with a lot more spokes?

I don'r understand the modern trendy minimal spoke ing.. if you want to cut rear wheel spoke induced turbulence get a full disc time trial rear wheel

pdlamb

Not necessarily grounds for dismissal. Look at the tolerance stackup and the lever arm. Press-fit bearings will have some clearance so you can get them into the shell, and the axle into the bearing. Also, you're going to have some manufacturing tolerance in the bearing itself. Assuming a 1" diameter bearing, the radius at the outside of the bearing is 0.5"; the rim is ~12" from the centerline, so for any slop in the axle-bearing-shell assembly, the slop at the rim is 12/0.5=24 times greater.

So your next question is, can you have 0.03/24" of slop around the axle from clearance and manufacturing tolerance? That question is left for the reader.

If it were my bike, it looks like a nice one, I'd go ride it instead of using it for a metrology project.

easyupbug 

I (188#) agree, and have a good history as do my sons-in-law (180&223#) with 20/24 wheels. The long term fatigue effect of cyclical loading is increased with rider weight and lower spoke count but major factors like the environment, increased preventive maintenance, larger volume tires, etc., are significant enough to make low spoke count a trivial issue with a quality wheelset, with rider weights under the manufactures limit. Low quality wheels are another matter.
All the new Campagnolo wheelsets from what I have seen are 16/21 with a 240# limit and ask if you are over 180# to look for increased maintenance.