H Plus Son - Spoke Tension

[Tony T]

What are the dimensions for Sapim CX-Ray?
Sapim lists as: 2.0 - (0.9x2.2) - 2.0 mm,
Wheelbuilder.com lists as 0.9x2.3
Park list as 2.1m x 1mm bladed steel (Sapim® CX Ray) (with an old post saying "The CX-ray was used to calibrate the chart. The CX-ray does not measure 2.3mm by our caliper, but 2.1. The 0.9 was rounded to 1mm. Use the 2.1 x 1 column on the CX-ray. Again, that was the spoke we used for that column..")

I guess in the "old days" before Park set up the parktool.com/wta website, the printed chart had to be used, but now any measurement can be added to the conversion, so what the caliper reads is what should be used in the on-line wta tool.

I measure 0.9x2.2 with my caliper.
Curious as to what dimension others are getting (to check against my measurements).

Edit: More info on spoke dimensions here: http://www.wheelfanatyk.com/blog/tension-inaccuracy/


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[yashcha]

Originally Posted by Tony T

Nice wheels. What Hubs?

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Thank you! Hubs are bikehubstore sl79 and sl210. Surprisingly nice hubs. I have been buying from those guys for years.

[Tony T]

Kgf v. Psi, part 1
Here’s first of a 2-part discussion of this phenomenon, that is reaching a worrying scale in today’s wheels. Inflate a clincher to 90psi (6 bar) and you may see tension drop 20-50%. Why? Is tension drop bad? Should wheels be over tightened to compensate?

Read more: http://www.wheelfanatyk.com/blog/kgf-v-psi-part-1/

[Mark McM]

Originally Posted by Tony T

Kgf v. Psi, part 1
Here’s first of a 2-part discussion of this phenomenon, that is reaching a worrying scale in today’s wheels. Inflate a clincher to 90psi (6 bar) and you may see tension drop 20-50%. Why? Is tension drop bad? Should wheels be over tightened to compensate?

Read more: http://www.wheelfanatyk.com/blog/kgf-v-psi-part-1/

The WheelFanatyk article appears to ignore the affect of the bias ply casing constriction, which also causes spoke tension loss with inflation pressure. Since tubulars are also constructed with bias ply casings, tubulars will also cause tension loss with inflation.

[Tony T]

Originally Posted by Mark McM

The WheelFanatyk article appears to ignore the affect of the bias ply casing constriction, which also causes spoke tension loss with inflation pressure. Since tubulars are also constructed with bias ply casings, tubulars will also cause tension loss with inflation.

Maybe in Part 2 (not posted yet)? "Next on tension drop concerns tires themselves"

[Tony T]

Kgf v. Psi, part 2
Here in Part 2 we explore how tires, independent of inflation, affect this dynamic.

[Tony T]

Kgf vs Psi, part 3
"Here in Part 3, let’s ask what builders can do to minimize negative influences of tension drop. After all, builders invest spoked structures with tension and answer for wheel performance"

[weisan]

Tony pal, I want to commend you for taking such a strong interest in wheel building and going a lot further than I could or would. Good for you!

[MaraudingWalrus]

I really am interested in part3 on that about "what to do."


On my wheels on my gravel bike, White Industries CLD to Velocity Ailerons with Sapim Force spokes, I built to 110kgf rear ds and disc side front, and then with somewhere around ~8% variance in tension.

Once tires mounted, rear ds and disc side on front are down around 60kgf.

A ~50% loss in tension is huge and mind blowing.

[Formulasaab]

I really am interested in part3 on that about "what to do."

Unfortunately, there wasn't much in Part 3 that was immediately useful to someone sitting at the bench building a wheel. Rather, it seemed like a "call to arms" of sorts, which I found odd considering the lead-ins to the articles. It was still worth reading I think.

But that's neither here nor there...

What I came here to report and what I thought might be useful was my observation of tension drop after tire installation/inflation on a wheel build I did this weekend.

The rim and tire combo is American Classic ACRD 2218 road tubeless rims with IRC Formula Pro Tubeless RBCC tires, 25c, @100 psi. These tires were recommended to me by American Classic customer support as being a good match for their bead profile and their preferred ride.

Overall, the build with these rims was a satisfactory experience. They were round and I was able to get an exceptionally even spoke tension on the front and reasonably even readings on the rear. This wheel build was a departure for me. Usually I insist on things like directional spoke hole drilling but this wheelbuild had a different goal. I wanted:

* classic low-profile (box section) look
* modern-light
* modern-wide
* tubless compatible
* with muted graphics/branding

These (mostly) fit the bill.

Anyway, I started with a bit-too-tight pre-build before installing the tires and recorded my tensions.

Pre-build average tension FRONT: 119 kgf.
Pre-build average tension REAR NDS: 85 kgf.
Pre-build average tension REAR DS: 185 kgf.

Then I installed the tires and inflated to 100 psi.

Tire installed FRONTaverage tension: 71 kgf. (a 40% drop)
Tire installed REAR NDS average tension: 50 kgf. (40% drop)
Tire installed REAR DS average tension: 128 kgf. (31% drop)

I then did a final re-tension to my preference rate and called it done. However, after sleeping on it, I think the rear wheel DS tension crept up higher than I want it. I am going to go back and tune it down.

Still, I was surprised at just how big the tension drop was. A front wheel that I considered a fair bit over-tight ended up significantly low after tire installation. A rear wheel (which I over-tightened even more extremely after the experience with the front) ended up damn close to where I wanted it, but the dish had moved a bit (necessitating some additional fiddling).

Tire installation was easy, for what it is worth. Yes, I used a compressor.

I haven't ridden them yet, and won't for a while as I am still recovering from the flu (precisely why I had time to do a wheel build).

Add that to the collective knowledge base.