Pacenti PL23 rims

[velomann]

I've been following with interest the concerns with these rims and premature failures in the 650b rear rims, as confirmed by the new (beautiful color!) BQ. I built a set of these for my Ocean Air Rambler which have yet to see the road. But I'm hopeful that my use of the White Industries T11 rear hub with the high/low flange configuration will reduce the drive side forces that seem to be causing the failures. Anyone here experienced a PL23 rim failure using one of these high/low flange hubs? Maybe Kirk Pacenti could chime in on whether he's heard of this?

Mike

[WMdeR]

Hi, Mike,

 

For a given rider, the rear rim issue will come down to 1. relative dish and 2. spoke tension on the drive side. You want enough spoke tension on the drive side that the nds doesn't go slack when side-loaded.  Low tension in the NDS will increase the frequency of maintenance and probably reduce the spoke life, and the NDS spoke tension is a function of the wheel geometry and how high you can run the drive side without damaging the wheel.

 

The PL23's I've put together start puckering at the eyelets at pretty low tensions, well under the 90Kgf I've seen as a recommendation.

 

All the rim knows is spoke tension and bracing angle of the spokes.

 

For a given placement of the flanges relative to the centerline, the bracing angle of a tangent-spoked wheel  isn't significantly different for various hi-lo setups (it is different for radial-lacing setups)  Hi-lo hubs look cool, I like them, but I wouldn't expect them to do anything significant concerning the forces acting on the rim.

 

Cheers,

 

Will 

 William M. deRosset

Fort Collins, CO

On Monday, September 23, 2013 10:41:09 PM UTC-6, velomann wrote:

[Bubba]

Mike

I have a rear wheel with a 32 hole White T11 and a PL23 rim.  I've been a shop mechanic for 15 years and normally build all my own wheels, but I do spoke tension by feel only.  I don't have a tensiometer.  For that reason I had a pro build this wheelset.  My builder consulted directly with Kirk and went up to the recommended tension but no higher, and confided to me that normally he'd like to go tighter.  I agree with him that the non-drive side feels quite loose.  So far, so good, but I've only put about 200 miles on them.  I think that any 11-speed compatible 130mm OLD hub is probably the worst possible choice for these rims.  Whether I will experience a failure or not is TBD.  

I had a second set of PL23s and chose a 135mm OLD 9/10 speed rear hub for that set, and the tension feels much more equal.  That rear wheel has not seen the road yet.

Can you share any detail about what exactly is "confirmed in BQ"?  I haven't gotten my copy yet.  Is there a failed P23 report in there?  What's the backstory?

[Anton Tutter]

Indeed, haven't received my copy either, and this vague but suggestive statement has peeked my curiousity. 

Anton

[Bubba]

I assume Anton has received his copy by now.  I read the article last night.  There is the black and white objective report:  two different riders reported that drive-side spoke holes developed cracking on the PL23.  There is a photo confirming one failure, and apparently a reader wrote in about the other.  

Beyond that there are two important pieces that are merely implied:  

First off, in the title of the article, it states that this article is in reference to BOTH the 32 hole and the 28 hole PL23 rim.  So, the implication is that one rider had a 32 hole rim fail in this way, and another had a 28 hole rim fail in this way.  Can BQ state clearly if that is the case?  I think that would be an interesting distinction.  I, for one, had already concluded that I will not be building a high dish 28-hole rear wheel from the PL23 rim.  My builder told me to avoid the 28, even for the front, because he'd want to go to higher spoke tension and heavier spokes, which would result in a slightly heavier wheel.  

Second is the qualitative reference to spoke tension.  Kirk made a max tension recommendation of 100kgf to my builder.  Did the builders of the two wheels that failed follow that recommendation?  Or did they tension the wheel to what they thought was right?  What was that tension?  I think that quantitative data point would be really useful.  The implication is that they were tensioned much higher, with the quote from the article "They were used with modern, high-dish rear wheels, which must be built with high spoke tension on the drive side".  If these wheels failed at 100kgf, that would be very valuable information to all of us.  If they failed at 150kgf, that also would be valuable.  I can only assume we don't know, because BQ usually shares numbers when they have them.  

[Jan Heine]

We tested two rims. The 28-hole rim was used on the front wheel, and the 32-hole rim on the rear. As the article explains, the rear rim cracked. The front rim has lower spoke tension, since it's not asymmetric. It is fine.

Regarding the spoke tension, the builder of the test wheels contact Pacenti and asked for recommendations, then followed those. There is a small concern that spoke tensiometers do not remain calibrated for long, so what you think is 100 kgf may be something quite different. All this information was included in the original review, where we talked about the bulging of the rims and hoped that this would be a cosmetic concern only.

I very much hope that the cracked rims remain the exception, but considering the product has been available for only a year, the failure rate is high. Unfortunately, removing the design flaw of the flat bottom would require a new mold for the extrusion, which is a significant investment.

Jan Heine
Editor

Bicycle Quarterly

http://www.bikequarterly.com

Follow our blog at http://janheine.wordpress.com/

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[Bubba]

Thank you Jan for clearing that up.  Now the black and white observation is that two 32 hole PL23s had failures around the drive side spoke holes.  

At least one of those two wheels was built to the manufacturers recommendation of 100kgf, provided we trust the accuracy of the tensiometer, and still failed in under a year.  

I think that is a much clearer picture of the situation.  Like you, I'll probably use the rims I have and continue to keep my eyes open for the perfect rim.  When I next need another 650B wheelset, I'll almost certainly try out the O/C A23 or the forthcoming Pacenti SL23.  

[Anthony King]

There is a small concern that spoke tensiometers do not remain calibrated for long, so what you think is 100 kgf may be something quite different. 

Usually tensiometers register higher rather than lower if they go out of calibration. The spring the deflects the spoke loses some of its uumph, making tension appear higher than it really is.

100kgf on the driveside of a 130mm hub would result in very, very low non-drive side tension. Especially if it was 11 spd. Was the rear hub 11 speed compatible? Those hubs have sub 17mm drive-side center to flange measurements that make the spoke tension between the side disparity greater than 10 speed hubs.

What gauge spoke were used on the drive side of the PL23 that cracked, Jan?

By the way, here's how I keep my tensiometer (I use an FSA) calibrated. 1) I keep a reference wheel that isn't used and periodically check my tensiometer to make sure a designated spoke on the wheel still gives me the same reading. 2) I have a second tensiometer that I use on every wheel one time to make sure the reading matches the reading of the FSA.