Wheel stiffness
 

Interesting article about wheel stiffness: LINKY

Thoughts? Comments?

I use my "old school wheelbuilder" experience and my years as an aerospace engineer to arrive at a best bang for your bucks set of wheels: a Shimano 105 32H or 36H hub with aluminum Deep V rim and 2.0 mm SS spokes/brass nipples. I prefer higher spoke tension between 260 and 300 lbs. Have never encountered a broken spoke due to high cycle fatigue.

The Open Pro and other highly regarded boxed rims cannot compete with modern Deep V rims (Velocity Deep V, Velocity Chukker, or Weinmann DP18), both in lateral and radial stiffness. Hopefully, others will learn from this report and step up to Deep V.

The major variable that kills speed is air/wind, not a few hundred grams at the wheels. There is no reason to lose sleep over a pair of 2000 g wheels unless you're a world class cyclist. The extra rotating mass may require an extra 2-3 watt to cruise at 18 mph, but that's such a tiny fraction of the total watt needed to overcome air resistance.

Very interesting article. I have been annoyed by brake rub when sprinting on my 50mm carbon tubular race wheels. The front wheel only. I noticed that it has radial spoking elbows out, which means that the spokes go from the hub to the rim on the inside of the hub flange. I have considered rebuilding them with the elbows in, thereby widening the brace angle slightly. It may be enough to eliminate the brake rub. Or it may be a huge hassle for nothing....

I'd be very interested to hear about how that turns out for you.

I thought the article was very timely in that it seems lateral stiffness and rub aren't talked about all that much these days. I also thought the comment about the strength of brass nipple strength as relating to high spoke tension was also insightful.

Good stuff!

Set your brakes wider.

Are you sure it's not the fork? I had a buddy who thought his wheel was flexing, causing rub. I looked it over carefully, then showed him how much his fork flexed. The wheel was perfectly fine.

so are you suggesting that everyone should be cruising around on 80mm carbon rims. ;)

I build high tech LOX pumps and thrust chambers, but only deal with old school Shimano 32H or 36H hubs and deep V aluminum rims (30-40 mm nominal).

Don't believe in selling high-tech "sex" out of my garage. This is a hobby to fund my hobby...not to put food on the table. Therefore, I can afford to be very selective with my work.

I build my own wheels as I have a couple of powertaps. at #165 I find the 24/28 spoke combo works a charm and wish more rims were available with these counts. Having said that, you can build a 28 hole deep carbon rim (enve and others) or Hed Jet4 come in 28 along with FF, its sometime more difficult to get a 24 hole alloy front (mavic dont make one for example). In my opinion 90% of normal size blokes could ride a 24/28 and be happy whether they go deep carbon or shallow alloy. I have also found if you break one it is still rideable.

the only time I ever got brake rub was using HOPE steel rod skewers - junk skewers!

I am generally interessted in this but that was way more than I could want to know.

definitely not the fork, as I have had 2 other wheels (Ksyriums and a 32 spoke 3x standard) and no flex. I will try a different skewer, though.

My comment is...thanks for the article. Maybe the best wheel article I have read.

One of the more interesting statements, "As you can see, the deeper and stiffer rims deflect less at the point of load (the road surface). However, they deflect more on the opposite side – where the brake caliper sits on a normal road frame. "


I never thought about the above but it makes a lot of sense. Deep rims overall don't elastically bend/deflect much...so the spokes are more challenged. Deep V's don't bend at the road...therefore the 'whole rim' displaces laterally and can rub brake pads more if the spoke count isn't high enough...and we all know that many deep V rims don't have high spoke count to optimize weight and aerodynamics...per Rob's response to the article.

Lastly, I have never counted grams on wheels. Also, I find uber light high end wheels to have high radial stiffness which compromises ride quality.

Very interesting article and thanks OP for posting the article.

Leave it up to Psimet to go all 41 on the guy!

Great article showing once again how complicated wheel engineering is. Also counterintuitive. Learned a lot, especially the part about stiffer rims transmitting the flex all the way across and causing brake rub. Fascinating.

First, I think you made an error. I think you mean "heads out" or "elbows in" (the same thing, but not what your said) which is the lower bracing angle setup. Then I think the point of the article was that making a stiff carbon rimmed wheel stiffer with spokes can't usually address a problem brought on by too stiff a rim. The force causing the deflection is at the road and hub. If you can isolate the flex there because the rim is not too stiff, then the part of the rim near the brakes doesn't have to move. If the rim is so stiff that it stays straight and just tilts at the hub instead of actually bending, then you get the movement at the brake and rub. I wouldn't think the small increase in "build" stiffness due to turning the spokes around would fix the problem. Besdes, elbows out (heads in) looks just awful. We do have to keep up appearances, after all.:)

Robert

What I don't like is how the author separates the stiffness of the rim from the "spokes". Yes - deeper rims are stiff, but if you don't have enough spokes you end up with a flexy wheel. Want a stiffer wheel - add more spokes.

yeah...you can take the boy out of the hood but can't take the hood...;)
He's right of course...though I believe his criticism was addressed in the article...or the article explained the relative contribution of how rim stiffness
relates to spoke stiffness. He is quite right in that it is a 'system'. In fact because it is a system, I believe adds further credence to factory wheels which are developed as a system. But...Rob points out that many high end carbon deep V wheels have insufficient spoke count.
The other thing is...each set of wheels are rider dependent in terms of weight and watt output. So one size never fits alls. A stiff wheel to a lightweight maybe a noodle to Boonen.

Rob...if you are around...do you have a universal standard i.e. tolerance you build to for spoke tension?...or is it spoke shape and gauge specific?

Not to mention many hubs have a nice lip on them - keeping them from being easily laced elbows out.

You can easily overcome a "stiff rim" with spokes. You have to add more. It's simple and works great. It's why my builds have been as popular as they are.


caloso - because you can't add any spokes to your current setup - simply change the spokes and lace 2X over over radial. Small changes that will add a lot to the feel of the system.

Actually due to the nature of a spoke being a tension member - it strictly transmits tension to the rim - so gauge and shape are meaningless (outside of having to know them so that you can interpret the readings on your tensiometer). The optimal tension for a build is determined strictly and solely by the rim itself.

Each rim is different, but in general most modern rims can withstand upwards of 120kgf or even higher. I tend to shoot for more in the 100-120kgf range....again - dependent upon the rim itself. In general the tension does nothing to stiffness or any other property of the wheel, but the appropriate tension will support the rim and allow it to endure longer.

While..in bold makes sense...I guess my question is...why start with an uber stiff rim to begin with?...if you end up adding a lot of spokes anyway. Enter short height flexible rim Open Pro. Can't wheel stiffness be achieved with 'any rim' with enough spoke count? So why not start with a lighter flexible rim?..if objective is to run high spoke count.

Thanks...makes sense...appreciate it.

That makes sense. My guess is that some Carbon wheels are prone to low spoke count for cost reasons stemming from manufacturing.

Also I would think that there is more shear force acting at the spoke nipple with a deeper rim both latteraly and radialy causing an increased feel of flex. This theory is based on the fact that the connection point is further from contact with the ground where the forces are acting. I think if it is far enough it can act almost as a pivot point and the rim becomes a lever, so the deeper the rim the more leverage it is putting at the spoke nipple.

Folks wanna be aero.

+1

The way you make a wheel aerodynamic is by eliminating all of the spokes. Short of that you limit them to the fewest that you can. Radial is more aero than 2x, etc.

It's all a balance. Weight, aero, stiffness. Pick two...eh ;)

Will continue...

You can compare a 32H Open Pro vs. 32H Velocity Deep V at similar spoke tension. Deep V can take more radial punishment from the road before giving in. Neither will see much lateral flexing due to the spoke counts.