Wheelbuilding / Wheel Building / Wheel build help

that's not really how engineering works

It's certainly not how practical bicycle wheels are designed, mostly because of the problems in computational analysis which we're talking about. What actually happens is that people take some known good design and progressively shave bits off it until it fails endurance testing, then send the last version which passed endurance testing to market 🙂

the tension in spokes being different is not what second-order effects refer to, that's just what happens due to the preload you mentioned earlier, and the way any wheel is built

Spoke tension dropping to zero is a second order effect, it can only happen if the rim moves quite a long way from its starting point relative to the hub, because the spoke is elastically strained by up to 0.3% under "no load" conditions.

you don't want to be that close to failure anyway

Mostly you don't. In a competitive environment, you sometimes do; I'd rather win all the races I finish than finish all the races I start 🙂

my method is to build it and if you aren't dead within 3 days (insert arbitrary number here) then things are ok. i'm not dead yet but someday i may be.

Spoke tension dropping to zero is a second order effect, it can only happen if the rim moves quite a long way from its starting point relative to the hub, because the spoke is elastically strained by up to 0.3% under "no load" conditions.

Fair enough, that is a good point.

But otherwise, no, you definitely don't want to be that close to failure, and no one is, even in pro cycling. Otherwise, you'd get a LOT more incidents of parts failing in a catastrophic way, and a LOT more riders getting seriously injured, or killed. Especially things like wheels are certainly always overengineered quite a bit. And you mentioned another good point - it doesn't just have to withstand one load cycle, but many many many of them. However, how many exactly is a bit of an arbitrary decision of course, in the grand scheme of things. But especially big brands are usually extremely keen on their name not becoming indelibly connected to randomly failing hardware, so they tend to be on the generous side as far as I know. I will definitely follow them in that in stuff I make...

i'm not dead yet but someday i will be

ftfy

Since very few people continue to cycle for more than about 80 years after they get their first adult bicycle, any design which is intended to last for longer than that is needlessly over-built 🙂

Now that's an upper limit I can get behind...

Need new rear wheel for the ultra bike. Currently thinking of blowing my wad on:
DT Swiss 240S hub 12mm TA
HED Belgium Plus 32h
CXRaysalways

Alternatives: (using another 350 hub to save some coin)
Kinlin XR31T rim (very similar to HED but slightly skinnier, 19mm vs 21mm)
DTSwiss 511db (same as my front wheel, deeper, 18mm internal compared to 21 for HED)

Anything else I should consider that's as wide as HED and decent?

EDIT: JRA don't do HED Belgium any more but they do have a Lark rim that looks wide as:
http://www.justridingalong.com/jra-wheels/jra-road-wheels/jra-lark-road-wheelset.html

EDIT EDIT: hmm they have braking surface, wonder if they do non-braking surface version.

EDIT EDIT EDIT:
The JRA disc rim is the MAP not the Lark:
http://www.justridingalong.com/jra-wheels/jra-map-road-disk-wheels.html
JRA Map rims: 24,28 or 32 hole front and rear. Width 19mm internal, 24mm external, depth 25mm.

Ooh, there's a DTSwiss 521 for disc brakes that's wider than the 511db (20mm vs. 18mm internal)

https://www.chainreactioncycles.com/dt-swiss-rr-521-disc-brake-20mm-road-rim/rp-prod168804

I can get these in disc version if they don't have them

Kinlin TL-23 ?
23mm/28mm:

https://thecycleclinic.co.uk

What size tires will you be using?

edit: dt swiss 521 is only 23mm wide on the outside (the drawing is wrong), but i guess you are only interested in the inner width.

Wow, they're massive. What's the minimum tyre width you can run on those? I normally race on 25/28 but I'd go higher if I could find something fast and reliable in say a 32mm.

As a mtb rim wouldn't the tl-23 have a very low max pressure rating for the tyres, possibly unsuitable for something as small as even a 32c tyre.

What's the minimum tyre width you can run on those?

You probably want a true width of at least 28mm. In practice, that means any "25" which is 25mm on a 15mm rim will be fine, as it will come up to more like 30mm on that rim.

As a mtb rim wouldn't the tl-23 have a very low max pressure rating for the tyres

Stress on the rim from tyre pressure rises as the tyre width rises. In practice, that means rims which will take a pressure suitable for the load with a fat tyre will also take the correspondingly higher pressure required to support the same load with a narrower tyre.

Very useful info!

usually tire size on wide rims is: size on a 15mm rim + half the difference between rims:

a measured 23mm tire@15c on a 23mm wide rim becomes ((23-15)/2=+4mm) = 27mm...

edit: tldr: tire size changes with half the rim width difference

a 23mm tire@15c on a 23mm wide rim becomes ((23-15)/2=+4mm) = 29mm

23+4=27

Using your formula:
25+((21-15)/2)=28, but really my 25C GP4000S comes up to 30mm on a 21mm internal Mavic Crossride

25+((16.5-15)/2)=25.75, but really my 25C GP4000S comes up to 26.5mm on a 16.5mm internal Mavic MY2016+ Aksium

If I were trying to guess at a rule of thumb for estimating the width of a tyre on a rim bigger than the one on which it manifests its nominal width, I'd divide the difference by π/2 (about 1.6) rather than dividing by 2.

25+(2(21-15)/π)=29
25+(2(16.5-15)/π)=26

Because the extra width is actually a chord rather than an arc, this formula will always come up with an answer smaller than the correct result, but it will be closer than your version 🙂

Are tyre widths as they are sold usually meant to be correct on a rim with 15mm internal width?

Are tyre widths as they are sold usually meant to be correct on a rim with 15mm internal width?

That seems to be about right for skinny road tyres, obviously not for 4" fat bike tyres. I expect there's some sort of table in the ETRTO standard relating tyre sizes to rim sizes. There are also tolerances, so if it says "25C tyre must be nominal size on 15C rim", that means something like "between 24mm and 26mm"

yes thanks I was trying to make it simple :)
also it was meant for measured width on a given rim. 25c gp4000s count as 26mm or 27mm tires on a 15mm rim

Maths thread >>>

So, assuming I'm running 25mm+ all the time, can you think of any disadvantage to running one of these sillywide™ Kinlin rims on the back of my ultra bike?

Only thing I can think of is small weight penalty and I'm already a big weight penalty.

That seems to be about right for skinny road tyres, obviously not for 4" fat bike tyres.

Yeah of course, that makes sense. That's very useful to know though, thanks! Makes it easier to estimate which rim / tyre / fork combinations should actually work on my bike.

@svenhöek

25c gp4000s count as 26mm or 27mm tires on a 15mm rim

So now you're confusing me again, why do they count as 26 or 27mm? Is that just what they come up as, or do you mean 'count as' for a specific reason?

Anyone got any experience with http://www.carbonal.com.cn for rims? Seem to sit in the middle of FarSports and Light Bicycle for price/weight. A few Ebay wheel builders use them but can't see much else in way of review.

Is that just what they come up as

yes!

Ah ok. I currently have Gatorskin 25mm tyres on a Miche XPress wheelset (which btw is holding up surprisingly well for my commuting purposes), and it's just about 26mm. The problem is, I can't find info about what the inner width of the XPress rims is, and I'm not quite curious enough to take a tyre off for that purpose... they look pretty 'standard' though.

I can't find info about what the inner width of the XPress rims is

Aluminium hook bead rims don't deviate very far from outer width-5mm, certainly not enough for any differences to have a material effect on tyre width.

Fair enough, standard 15mm then seeing as the outer width is 20mm.