Alloy wheels and flex?

[dddd]

I'll second (third?) the recommendation to first verify uniform high spoke tensions.

As noted, thinner and fewer spokes of course allow more flex.

But what of the rim itself?
A rim gets stressed laterally where the tire meets the road, and of course a flexier rim will allow more flex between the hub and the tire's contact patch.
But, a stiffer rim will more effectively mirror an (albeit reduced) amount of lateral flex up from the roadway, to the brake pads.
The flex between the hub and the roadway is reduced, because the spoke stresses are less localized to the "lower" spokes, but again, the lateral movement down there is also more effectively transmitted upward through the stiffer rim, pivoting about the hub.

Theoretical considerations (that I hadn't yet considered) aside, I was actually surprised by this effect after changing one bike's 40h single-walled rim to a very sturdy touring rim having double-wall construction, then began experiencing brake rub that required a looser brake adjustment.

[slowpoke]

Originally Posted by ridethecliche

I'd say that rebuilding the wheels with thicker spokes is a waste of time, money, and effort. Just sell the wheels to a lighter rider and get them again in a 24/28 count.

If these are the HED Ardennes Black rim brake wheels, they have that special textured brake track and only come in 18/24, and 20/28 ("stallion" version).

[David Kirk]

I've spent a long time on HED Ardennes Blacks with the textured brake surface.

I think it's possible that the OP isn't flexing the HED wheels more than his other wheels and that his other wheels also rub the pads....but with the distinct sound that the rim surface makes that you can for the first time hear the pad rub.

dave

[ridethecliche]

Originally Posted by David Kirk

I've spent a long time on HED Ardennes Blacks with the textured brake surface.

I think it's possible that the OP isn't flexing the HED wheels more than his other wheels and that his other wheels also rub the pads....but with the distinct sound that the rim surface makes that you can for the first time hear the pad rub.

dave

Hah, the plot...twists?

[Mark McM]

Originally Posted by dddd

I'll second (third?) the recommendation to first verify uniform high spoke tensions.

As noted, thinner and fewer spokes of course allow more flex.

But what of the rim itself?
A rim gets stressed laterally where the tire meets the road, and of course a flexier rim will allow more flex between the hub and the tire's contact patch.
But, a stiffer rim will more effectively mirror an (albeit reduced) amount of lateral flex up from the roadway, to the brake pads.
The flex between the hub and the roadway is reduced, because the spoke stresses are less localized to the "lower" spokes, but again, the lateral movement down there is also more effectively transmitted upward through the stiffer rim, pivoting about the hub.

Theoretical considerations (that I hadn't yet considered) aside, I was actually surprised by this effect after changing one bike's 40h single-walled rim to a very sturdy touring rim having double-wall construction, then began experiencing brake rub that required a looser brake adjustment.

Actually, tension spoke wheels have two lateral flex modes - a "tilting" mode, as described above, which causes the top of the wheel to deflect in the opposite direction as the bottom of the wheel; and a "buckling" mode, which causes the wheel to bend int a saddle ("potato chip") shape, and in which the top of the wheel deflects in the same direction as the bottom of the wheel.

Here is a article on the SlowTwitch web site that describes the tilting deflection mode, which includes this diagram:




Measurements of wheel deflection showing the buckling mode are shown in Question 4 of the Rinard Wheel Deflection Test:




The deflections of the top of the wheel (at the rim brake caliper) for the tilting and buckling modes are in opposite directions, and the amount of deflection in each mode will depend on the relative difference in stiffnesses of the rim and the spokes. It is conceivable that with the certain combinations of rim and spoke stiffnesses that the two deflection modes will cancel each other out, resulting in no lateral deflection at the brake caliper.

[carpediemracing]

I haven't had issues with my Bastognes, which are sort of poor man's Ardennes. I chose them because they were the cheapest 18/24 spoke count wheels at the time. All the other wheels were 20/28 or something like that, except the Ardennes, and I wanted a low spoke count, especially considering the heft (and presumably the stiffness) of the actual rim. I was coming off regularly using 300-330g tubular rims, 28h, and 16/20 Reynolds carbon wheels (clincher and tubular). I was looking to keep spoke count low.

I did find the Bastognes loosened up over time. I think I've retensioned the wheels twice since I got them in 2010.

I've weighed as much as about 185-190 on them. That's an...err "unladen" weight, aka no clothes. I'm sure I was at least 5-7 lbs heavier with my kit, phone, spare tube / tools, etc. Same bike since then. Max peak power about 1600 repeated, 1800w PR, 1000-1200w pretty much every time I rode, for outdoors. FWIW I used 175 cranks for most of those years.

(I use the same wheels on the trainer, depending on what has a good tube or not, so either the Bastogne or the Jet 9, same tire as outdoors, significant trainer use since 2014 or so).

Incidentally they are 18/24. They might have changed them since 2010 but the various ones I've looked at are 18/24.

I have noticed that stiff rims (they tend to be heavier ones) tend to tilt about the hub, and flexible rims (old school light rims, like 300-350g) tend to flex like a potato chip. The Bastognes (which uses a cheaper alloy than the Ardennes) seem to tilt about the hub. I have no objective data on that.

[br0qn]

i have these wheels, picked up second hand, on my brand new build and also am experiencing rub in the rear when I stand. i'm 135 lb and I don't know what my power is but it's got to be low.

[Xrslug]

Originally Posted by David Kirk

I've spent a long time on HED Ardennes Blacks with the textured brake surface.

I think it's possible that the OP isn't flexing the HED wheels more than his other wheels and that his other wheels also rub the pads....but with the distinct sound that the rim surface makes that you can for the first time hear the pad rub.

dave

Thanks, Dave — definitely agree with this (I’m the OP). I’m thinking of all the town line sprints I’ve unwittingly lost due to unknown brake rub in the past . I love the braking on the RA Black wheels and as someone mentioned they’re not available in a higher spoke count (or even as separate rims) from HED, so my options are: (1) confirm proper spoke tension; (2) if spokes are tensioned properly, then deal with the rub (not ideal); (3) rebuild with stiffer spokes and hopefully stiffen the wheels up sufficiently; or (4) sell them and buy stiffer wheels.

On my ride this morning I was experimenting and I can pedal out of the saddle without rub if I keep the bike fairly vertical, but when I start rocking the bike side to side to put more power into the pedals (i.e. subjecting the wheels to lateral flex) I get rubbing. This was pedaling hard out of the saddle uphill, but not a sprint.

Appreciate everyone’s input — thinking the safe solution for my weight, power (such as it is), and riding style is 24 front (radial or 2x?) and 28 rear (2x?) with CX-Sprint spokes and either the HED Belgium R or the Boyd Altamont (assymetric rear rim, which I gather is a positive). Both the Belgium and the Altamont are 21mm internal width, which seems to the widest alloy rim currently available (for rim brake).

[Mark McM]

Originally Posted by Xrslug

Appreciate everyone’s input — thinking the safe solution is 24 front (radial or 2x?) and 28 rear (2x?) with CX-Sprint spokes and either the Hed Belgium R or the Boyd Altamont (assymetric rear rim, which I gather is a positive).

Contrary to common belief, assymmetric rims actually reduce wheel stiffness. This is because the contribution of the spokes to lateral stiffness is proportional to the square of the sine of the bracing angle*. Which means stiffness lost in the reduction in the bracing angle of the NDS spokes is not fully regained in the stiffness gained in the increasing bracing angle of the DS spokes. That's not to say that assymmetric rims are a bad idea - they do improve wheel durability by producing less differential between right/left spoke tensions.

As it sounds like you are looking at entirely new wheels, also consider the hubs, and in particular the flange offsets. Flange offset has a major affect on wheel lateral stiffness, and the more widely spaced the flanges, the stiffer the wheel will be.

*This assumes that the spokes are tight enough that they don't completely slacken in use. If the hub has a very large difference in flange offsets, then the NDS spoke tension may be so low that the easily slacken in use.

[Tandem Rider]

Wheel flex is not anything new, I'm not sure it can be attributed to low spoke count or a poor build either. I have seen pro team wheels flex to the point of appearing to hit the frame during a sprint, they were definitely slapping the pads because the caliper was moving. It didn't seem to slow them down. These would have most likely been 32 holes, 14-15 butted spokes, probably GP4, SSC, or equivalent rims. I guess the point is, does it really matter all that much?

[reuben]

Originally Posted by ridethecliche

Hah, the plot...twists?

As my wonderful Aunt Lucy used to say, "The thick plottens."

[oldpotatoe]

Originally Posted by marciero

Does anyone use straight gage spokes anymore?

I just rebuilt an E-Bike rear wheel that came with straight gauge spokes, 36h and laced 1 cross. I rebuilt with Sapim Strong spokes and laced 2 cross(HUGE flange)...BUT, considering the cost of double butted spokes, no real reason to use straight gauge spokes..they make for a less reliable wheel, all else being equal.

Low end, OEM, machine built wheels, lots come with straight gauge spokes..They are cheap along with the low end bike.

[oldpotatoe]

Originally Posted by Xrslug

Thanks, Dave — definitely agree with this (I’m the OP). I’m thinking of all the town line sprints I’ve unwittingly lost due to unknown brake rub in the past . I love the braking on the RA Black wheels and as someone mentioned they’re not available in a higher spoke count (or even as separate rims) from HED, so my options are: (1) confirm proper spoke tension; (2) if spokes are tensioned properly, then deal with the rub (not ideal); (3) rebuild with stiffer spokes and hopefully stiffen the wheels up sufficiently; or (4) sell them and buy stiffer wheels.

On my ride this morning I was experimenting and I can pedal out of the saddle without rub if I keep the bike fairly vertical, but when I start rocking the bike side to side to put more power into the pedals (i.e. subjecting the wheels to lateral flex) I get rubbing. This was pedaling hard out of the saddle uphill, but not a sprint.

Appreciate everyone’s input — thinking the safe solution for my weight, power (such as it is), and riding style is 24 front (radial or 2x?) and 28 rear (2x?) with CX-Sprint spokes and either the HED Belgium R or the Boyd Altamont (assymetric rear rim, which I gather is a positive). Both the Belgium and the Altamont are 21mm internal width, which seems to the widest alloy rim currently available (for rim brake).

Why 24h front? Why not 28h? For you? (I'm guess not 32h since they are hard to find from HED)And laced 3 cross, both ends. Additional 8 spokes front and 4 spokes rear..12 additional CXSprint spokes weigh about 60 grams...

For your about 96,000 gram or so 'package'..rider and bike..don't think you'll notice those 60 grams..a little more than 2 ounces...

[Spoker]

Originally Posted by marciero

Does anyone use straight gage spokes anymore?

IIRC Greg Gaulzetti recommended straight spokes for some carbon wheels (forgot which) to correct flex problems.

[dddd]

Originally Posted by Spoker

IIRC Greg Gaulzetti recommended straight spokes for some carbon wheels (forgot which) to correct flex problems.

Must be because straight 14g spokes are the stiffest to be commonly found while still fitting the drillings, being locally/immediately available (in black, jeez), having less wind-up ...and of course no sticker shock.

And the stiffest spokes might be the way to go when the spoke count is perhaps seeming to come up short?

Rims with a "service history" and even some of today's "warpier" carbon rims often leave me despising low spoke counts, even as there are fewer spokes to deal with and copious knuckle clearance.