# Wheel building - What is your tension/roundness tolerance ?



## boisvertdom (Dec 1, 2009)

After having built sets with various rims brands and models now (alloy, carbon, low, high profile, open pro, alex, kinlins, velocity, ambrosio ...) I realize that aiming for an all around strictly equal tension doesn't necessarily lead to the roundest wheel.

I build my wheels on a park stand with deflection gauges and a park tensiometer and put each spoke's tension in an Excel spreadsheet when fine tuning the wheel. I sort of try to finish within a 0.1 mm error radially/laterally and under 0.5 notch (of the tension meter) of standard deviation for all spokes.

With some rims (usually higher profile/stiffer rims) it's fairly achievable, but with some others (open pros, for example), the compromise between roundness and equal tension has to be stretched a bit more. I think the closest to perfect I was able to get was with a pair of 60mm chinese carbon rims on a paire of hubs from BikeHubStore (rear triplet) and cx-rays (race on NDS) : 0,25 notch standard deviation for tension and 0.1mm radial/lateral deflection. But usually, the std. deviation is closer to 0.4 - 0.5 notch.

I know that the error coming from the tire will be way more than 0.1 mm and that the tire deformation while rolling will absorb the radial variation easily, so it's better to lose a bit of roundness in order to keep more equal spoke tension, but how much do you guys compromise ?


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## CleavesF (Dec 31, 2007)

As long as my brakes wear out evenly, I don't mind a deviation or two. Then again, I'm not OCD with my wheels. 

I true my wheels about once every 2 years. I'm so lazy, and I'm also not very good at it. I've only replaced all 32 nipples to brass after my alu ones were cracking once, and I'd care not to do any "pseudo" wheel building anymore. 

I find the time to perfect the art very time consuming, and for some reason it is one of the few mechanical things on the bike that I certainly do not enjoy. Dishing is also something I hate to do. 

Sometimes, I'm so lazy I just drop them off at the LBS.


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## boisvertdom (Dec 1, 2009)

Well, for me it's the opposite. I enjoy building a wheel and trying to get as close to perfection as I can. It takes time the way I do it with the XL spreadsheet but it allows me to monitor the increase of tension in the whole wheel and which spokes are getting a bit too much out of rank compared to their neighbors. 

Takes me a whole afternoon for a set, but I watch movies/races/tv shows at the same time.


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## TomH (Oct 6, 2008)

If they're my wheels, a couple mm out of round or true is fine. I get DS tension under 1 notch on the park tensionmeter. You cant feel it while riding, and it doesnt impact reliability. 

Equal tension and true comes first, then I get it as round as possible while keeping tension even.


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## boisvertdom (Dec 1, 2009)

A couple mm ?? Wouldn't 4mm out of round make the bike shake on a 70 km/h descent? Seems like a big margin to me.


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## bytewalls (Feb 14, 2010)

I will first get them all very close to the right tension using a park tensiometer. Since these have an inherint amount of inaccuracy, I then compare each spoke to the one on either side of it by plucking the spoke and using a guitar tuner to get the frequency. Get each one very close to the same frequency this way then go do all the truing and round stuff. I've had a couple where with almost perfectly even tension audibly there was no need to truing, tensiometers just kinda suck.


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## TomH (Oct 6, 2008)

boisvertdom said:


> A couple mm ?? Wouldn't 4mm out of round make the bike shake on a 70 km/h descent? Seems like a big margin to me.


2mm total, like from the hop on the joint. But no, you wouldnt get a shake. I had a cheapo sun rim I built up a couple years ago that absolutely wouldnt go round with any reasonable tension. Rode perfect, still in use today. 

Most good rims will go round and true pretty easy, but a little (or sometimes a lot) of hop at the joint isnt going to make a difference. Looks bad, and I wouldnt want to sell a wheel like that, but its really fine. I think you'd have to build a wheel intentionally oval on purpose to feel it.


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## jnbrown (Dec 9, 2009)

I have not built that many wheels and mostly with Velocity rims which tend to have a hop at the joint. 0.1 mm is not realistic or possible with most rims. As you stated, trying to achieve this tolerance can result in the tension being uneven. I have had a few rims that were bad enough I had to send them back. 0.1mm is 0.004 inches or about the thickness of a sheet of paper.


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## Zen Cyclery (Mar 10, 2009)

Well, there really is no magic number you should be shooting for. You should be focusing predominantly on having uniform tension throughout the system. If you can achieve this, chances are your hoop will be pretty darn true.


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## boisvertdom (Dec 1, 2009)

So for example, these are the tension readings of the DS of a rear wheel :

14,25
15
14
14
14
14
15
15
13
13,5
15
14,75
14
14
14
14,5

Average: 14,25 (notches of the park tension meter)
Standard deviation : 0,58 notch

This gives me a round and true wheel with 0.1mm margins laterally and radially.

So if I just blindly bring the two 13.x spokes (they're at the joint) to 14.5 and that brings the radial error to 0.5 mm, you're saying that it's better than having a rounder wheel.

Which brings me back to my initial question: at how many mm of radial deflection will you stop trying to get the tension absolutely equal all around ?


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## jnbrown (Dec 9, 2009)

The answer is yes. 0.5mm radially is more than good enough.
To summarize, you are being way too anal. 
Just be done with it and ride the wheel.
If it makes you feel any better, I am an engineer and frequently agonize over trivialities.
I am working on changing this.


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## jwk (Jun 17, 2011)

Folks, I have a question regarding this topic. Is it possible to build a wheel or take my existing wheel and make it absolutely perfectly round and perfectly tensioned or will it be always slightly off? And one more question. Before mounting my inner tube and tire, it seemed my wheel spun perfectly and I felt no hop in the wheel. But now after mounting the inner tube and tire, I feel it pulsating like it has a hop in it. I am thinking maybe it is the 90mm extension valve that is sticking out so my 80mm deep dish wheels can have a pump attached to it. So do you all think the valve can cause that to feel unbalanced?


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## TomH (Oct 6, 2008)

boisvertdom said:


> So if I just blindly bring the two 13.x spokes (they're at the joint) to 14.5 and that brings the radial error to 0.5 mm, you're saying that it's better than having a rounder wheel.


Yes, absolutely. 

Radial runout kinda is what it is. You get the tensions even and make a minor adjustment to get it as round as possible. If its too far out, its a rim issue (still not really an issue).


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## ergott (Feb 26, 2006)

±0.1-0.2mm laterally and ±0.1-0.3mm radially with uniform tension is typical. I can't promise that with some rims. Carbon rims have imperfections that make radial tolerances misleading. The wheel can be very true, but have hops that are just excess material. A good wheelbuilder knows the difference between imperfections and being true.

As already mentioned, get the tension ±5% of average for the side.


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