Lacing triple cross 28h

[Mark McM]

Originally Posted by oldpotatoe

Oh yeah? Take this.

What's scary is one or both of these guys will look at this and know what it means..

That's the formula for spoke length, where d = radius of rim (ERD/2), r1 = flange radius, r2 = flange offset, a = spoke angle (= 720 degrees x number of crosses / number of spokes), and r3 = radius of the flange spoke hole.

[cribbit]

Originally Posted by Mark McM

That's the formula for spoke length, where d = radius of rim (ERD/2), r1 = flange radius, r2 = flange offset, a = spoke angle (= 720 degrees x number of crosses / number of spokes), and r3 = radius of the flange spoke hole.

I thought spoke length came from the magical all-knowing website calculator.

[ergott]

Originally Posted by Mark McM

The vertical load can be magnified when hitting a bump to a very large value (consider - hitting a sharp edge bump can compress the tire enough to pinch flat it, which takes a very large instantaneous force). But perhaps more importantly, the vertical force only affects a few spokes near the LAZ (Load Affected Zone) at the bottom of the wheel, whereas torques are distributed nearly evenly across all crossed spokes.

I know I read this in his book too, but I have a bone to pick with that theory. What about the tire and air? If you compress the tire before the point the rim comes in contact with the other side of the tire/tube (pinch flat) that air cushion is spreading the load across a far greater area than the LAZ. Seems to me that the FEM drawing depicts a rim hitting the ground, not tire/tube.

[oldpotatoe]

Originally Posted by cribbit

I thought spoke length came from the magical all-knowing website calculator.

Works for me...

https://leonard.io/edd/

https://www.wheelpro.co.uk/spokecalc/

https://bikeschool.com/index.php/res...oke-calculator

Who remembers the ''good' old days' with Sutherlands 5th edition?? Chapter 11..kinda like celestial navigation..but harder..

[speedevil]

I put together a post about spoke length calculations on my blog. Take a look at this.

Calculate bicycle spoke lengths the old way

[oldpotatoe]

Originally Posted by speedevil

I put together a post about spoke length calculations on my blog. Take a look at this.

Calculate bicycle spoke lengths the old way

L = sqrt(R^2 + H^2 + F^2 – 2RHcos(360/h*X)) – shd/2

Check it out, it’s not really that complicated.

REALLY?? Thanks for this but for this business major..I'll stick to measuring the hub and rim and use an online 'program'...

[speedevil]

Originally Posted by oldpotatoe

REALLY?? Thanks for this but for this business major..I'll stick to measuring the hub and rim and use an online 'program'...

I get it - I was mainly curious about how the lengths were calculated. With a minor in mathematics, seemed reasonable. it's nice sanity check for the online calculators.

[Mark McM]

Originally Posted by ergott

I know I read this in his book too, but I have a bone to pick with that theory. What about the tire and air? If you compress the tire before the point the rim comes in contact with the other side of the tire/tube (pinch flat) that air cushion is spreading the load across a far greater area than the LAZ. Seems to me that the FEM drawing depicts a rim hitting the ground, not tire/tube.

Modeling the force at the ground as a single point load was of course a simplification to make the FEA easier (Brandt originally did this work in the 1970's when FEA was less developed). His analysis was mostly to demonstrate general principles of how wheels work. Since then, direct measurements of spoke tensions changes in actual wheels (with tires installed) have shown the general principles shown in Brandt's analysis apply in the real world.

Below is a link to paper by Henri Gavin of Duke University, who studied stress/strain in bicycle spokes to see how lacing pattern (number of crossings) influenced spoke fatigue. In this paper, Gavin compared mathematical models of spoke loads to direct measurements on wheels (tires installed) with the spokes instrumented with strain gauges. He measured the strains in the instrumented wheels both statically and dynamically (actually riding the wheels on the road). He found that the tire did act to spread the load over a short span of rim, and the peak spoke strains on the real wheel were a bit smaller than in the models that used a point load; but just like the numerical analyses predicted, the vertical load was distributed only among a small number of spokes at the bottom of the wheel, and was especially concentrated on the bottom most spoke.

http://people.duke.edu/~hpgavin/pape...heel-Paper.pdf

[Mark McM]

Originally Posted by speedevil

I get it - I was mainly curious about how the lengths were calculated. With a minor in mathematics, seemed reasonable. it's nice sanity check for the online calculators.

Using on-line pre-programmed spoke length calculators is fine when using standard components and lacing patterns, with equally spaced spoke holes on hubs and rims. But some wheels use non-standard patterns or non-standard spoke spacing. In these cases, you have to go back to the fundamental formulas and make the necessary adjustments for the non-standard geometries. This may be case even when starting with 'standard' components, such as making a 24 spoke triplet laced wheel with a standard 32 hole hub and 24 hole rim.

[oldpotatoe]

Originally Posted by speedevil

I get it - I was mainly curious about how the lengths were calculated. With a minor in mathematics, seemed reasonable. it's nice sanity check for the online calculators.

Why I use 3..I check thru all 3 before I start to cut spokes..

But as an aside..one thing that is really vexing these days is the YUGE variableness of spoke holes in the hubs..I try to 'predict' those which has a big effect on spoke length(for this guy who is picky about 1mm differences) but, altho not really 'bitten' yet, I have built 2 shimano rear hubs and found the spoke holes bigger than previous iterations(SLX and XT)..Why I tend to 'round down' with shimano, Bitex, Dynamo type hubs(Dynamo cuz the holes are counter sunk..)...

[Dasarbule]

Originally Posted by oldpotatoe

Why I use 3..I check thru all 3 before I start to cut spokes...

...for everything else, there is Mastercam...

[oldpotatoe]

Originally Posted by Dasarbule

...for everything else, there is Mastercam...

??

[Dasarbule]

For some combinations, especially when reusing proprietary straightpull hubs, i like to do a simple centerline 3D Drawing using Mastercam to check spoke length calculations.