Calculate bicycle spoke lengths the old way

This is an interesting math exercise that has been largely replaced (hidden, actually) by web-based spoke length calculators, linked to nice databases for hub dimensions and rim ERD values.  I always measure rim ERD for myself and measure at at least 2 different points around the rim.  And I always check the supplied hub dimensions for myself.  Sometimes a bad value is stored, so checking is worth the extra few minutes it will take.  Some hubs and rims are rare enough that they aren’t in the databases at all, so once you’ve determined the measurements, sending them to the various calculator sites is a nice way to pay it forward.  Good karma from that can’t hurt.  Remember, you are the one that will pay for replacing spokes that are not the correct length, so measure at least twice.  Personally, I consider the correct length to be where the top of the spoke is level with the bottom of the slot in the nipple.

A couple of web-based spoke length calculators are:

Prowheelbuilder

EDD

2/3/4 cross lacing:

The basic formula is:

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

Where:

L = calculated spoke length
R = rim radius to nipple seat (ERD/2)
H = hub radius to spoke holes (spoke hole circle diameter/2)
F = flange offset from hub centerline
X = cross pattern (2, 3, 4…)
h = number of holes in one side of the hub
shd = diameter of spoke hole in the hub

Check it out, it’s not really that complicated.  Most any calculator can handle this fairly easily.  When you’re done, try one of the online spoke length calculators to see what lengths they calculate.  You can try more than one spoke length calculator and average the results (they will likely have slightly different results, depending on any fudging done during the calculations).

Since spokes are generally available in 2mm increments and some in 1mm increments, you’ll likely need to round the calculated values.  For me, I tend to round to the closest available length, but you’ll have to determine that on your own.  Experience with calculated lengths on successful wheel builds will tell you which way to go with different length calculators.

Definitely a math geek’s exercise, but sometimes it’s nice to see how the “behind the curtain” work is actually done.

Radial lacing:

For radial lacing it’s much simpler.  it’s just a right triangle and you’re solving for the hypotenuse.  The formula is:

L = sqrt((R-H)^2 + F^2) – shd/2

Where:

L = calculated spoke length
R = rim radius to nipple seat (ERD/2)
H = hub radius to spoke holes (spoke hole circle diameter/2)
F = flange offset from hub centerline
shd = diameter of spoke hole in the hub

Be aware that there are multiple places in the formula for rounding, and length calculators can and do round differently.  This accounts for the differences between methods.  All of them should deliver results within a mm +/-.

And you thought you’d never use trigonometry once you finished school.

2nd Annual Bourbon and Tobacco Tour – April 13, 2019

To help us with planning, please click here to register.

Saturday, April 13:

We will meet at the east side of LBL on US-68/KY-80, just west of the bridge over Lake Barkley.  Parking is on the north side of the highway, and there is plenty of parking available.  I will have some repair/adjustment tools, grease, chain lube, floor pump, work stand, and some spare tubes and patches.  Hopefully no major repairs will be needed before, during, or after the ride but we’ll be prepared for the usual (and some of the unexpected).  We’ll leave from the parking area around 10am.

There is no cost for these rides.  If you want to chip in a little for the Saturday post-ride cookout, that would be appreciated, but it’s neither expected nor required.  There is a nice surprise planned for the midpoint of Saturday’s ride.

The route:

The route is entirely within the LBL.  This loop starts and ends at the east entrance to LBL, and is a little less than 40 miles, with about 4 miles of well-compacted gravel.  The gravel should be fine for 23mm tires, but I will ride this section next spring and will alter the route if it looks at all iffy.  As of now, there are a small number of actual turns in this route, 8 by my count, in the entire ride, so there should be no issues with navigation or getting lost.  I will give my cell number to riders, should assistance be needed during the ride.

 

 

Click to Download Cue Sheet

Moonshine:

If folks are interested, we’ll head over to Casey Jones Distillery near Hopkinsville to sample some genuine Kentucky moonshine.  We can take a tour, or just try some samples.  I need to know if y’all would like a tour so I can let them know, OK?

Post-ride cookout:

We are planning a cookout after the ride.  LBL does not allow alcohol, and the Barkley Lodge pavilion is reserved.  We’ll just have it at my house.  It’s easier anyway as I can just leave everything is the fridge/freezer at home and not have to haul it to the Lodge.  If you’re local, just bring something to share.

Sunday, April 14 – ride the trails:

If folks are interested, we’ll take some fatter-tired bikes out for some trail riding on Sunday.  There’s a lot to choose from, the map links below will give you an idea of the variety available to us.

We’ll figure out when and where to meet during the cookout and I’ll update the information here.  Most likely will be one of two places.  Either at the LBL North Visitor Center, or the LBL Golden Pond Visitor Center.

LBL Hike and Bike Trails

LBL Maps – click the Trails tab.

I didn’t know there were 500 miles of trails and 200 miles of roads in LBL. It is great to have this area so close to home.  Not all of the trails are available for bicycling, so check the website while you scout a potential route.

Temperatures to expect:

The average high temperature in April is 66 degrees, so good riding temps, but plan on 10-15 degrees plus or minus from that.

Lodging:

Here are some options for lodging and some suggestions for restaurants in the area.

Kenlake State Resort Park Reservations

Lake Barkley Lodge reservations

Both are reasonably priced and are just a few minutes from our starting place.  Kenlake and Lake Barkley both have restaurants too.  For those folks arriving Friday, I have a place in mind for dinner.

Bike Shop:

Bikes and Moore in Hopkinsville is a shop that I’ve been to several times, and I couldn’t find a complaint if I tried.  Good folks and they’ll be happy to help you out, should you need more than a tweak or two.

Questions:

Contact me if you have any questions, I’ll do my best to help.

Some sponsors have graciously agreed to help out.  I have no right to expect anything and I’m immensely grateful for their support.

Chain-L – the best chain lube available

 

 

 

PRIZES – Yes, we have prizes too.  They won’t take you out of the amateur ranks, if you’re concerned about that – but they are good ones that will definitely see some use.

Prize #1 – for the rider traveling the farthest to attend the ride.

Prize #2 – for the oldest participating rider.

Prize #3 – for the youngest participating rider.

Prize #4 – for the best C&V bike, as voted on by the participating riders.

Prize #5 – for the Lantern Rouge on Saturday’s ride.

Please watch your speed while driving in LBL, it’s federal land, so speeding tickets are expensive – as Agent K said “the rangers do not have a sense of humor they’re aware of.”