How would I go about lacing a 36H hub motor into a 32H rim? I need a way to calculate the spoke width. I have the ERD and flange diameter, but the grin spoke length calculator only takes a single spoke count. I understand that the tension would be spread out unevenly because the holes won’t match and I’d have to skip 4 holes on the hub. So should I just buy a set of spokes according to the grin calculator and add a few millimeters for safety?
Lace 32H rim with 36H hub motor
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briangv99
1 kW
I've redrilled the spoke flange on a bafang bpm to be a paired 32h single cross. It was quite easy to do with just a ruler, a marker, a centre punch and hand drill.
All the spokes are the same length and had no problems truing or with spoke tension.
All the spokes are the same length and had no problems truing or with spoke tension.
Chalo
100 TW
Was it easier than finding a 36 hole rim for the job?
I've done mixed patterns before (28h rim/36h hub, 48h rim/32h hub)-- but having done that, I would go to great lengths to find an appropriate rim. There are a lot of them out there, and they don't even have to be currently available if you only need one.
16h and 32h have got to be the easiest patterns to lay out yourself, though. I think you came up with the best solution for your problem, and now you can even switch to a 36h rim in the future if it suits you.
I've done mixed patterns before (28h rim/36h hub, 48h rim/32h hub)-- but having done that, I would go to great lengths to find an appropriate rim. There are a lot of them out there, and they don't even have to be currently available if you only need one.
16h and 32h have got to be the easiest patterns to lay out yourself, though. I think you came up with the best solution for your problem, and now you can even switch to a 36h rim in the future if it suits you.
briangv99
1 kW
All things considered, yeah it was easier. I had the 32h rim and the only rims I could find at the time were well over $100 shipped compared to the rim I had on hand. Re-drilling the spoke flange only took about half an hour.
As a heavier than average cyclist, I've had regret after flat spotting 32 hole rims on potholes, I wish I had gone with 36 hole hubs and rims.
On a bike with a heavy hub and the ability to sustain high speeds when a human cyclist would slow down, I can't think of a good reason to not use all the spokes.
Just sayin'
On a bike with a heavy hub and the ability to sustain high speeds when a human cyclist would slow down, I can't think of a good reason to not use all the spokes.
Just sayin'
I've experimented with this idea aswell. The reason being lack of availability of decent 36H rims. I'm sure the 50-kilowatt crowd will soon tell me to just use the same 23 lb rims they use, but that wasn't an option for me.
See the attachment. It certainly is possible. Red/blue are front spokes, magenta/cyan are the back ones. Skipped holes are marked green (front) and yellow (back). I've ensured that the skipped holes are evenly spaced.
The problem with this approach is that you get lots of different spoke angles at the rim, possibly requiring many different spoke lengths and making it harder to true the rim. Still doable tho.
Myself I ended up having custom Carbon rims with 36 holes made. With extra Carbon and closed rim bed they're much tougher than alloy rims while still being lighter.
See the attachment. It certainly is possible. Red/blue are front spokes, magenta/cyan are the back ones. Skipped holes are marked green (front) and yellow (back). I've ensured that the skipped holes are evenly spaced.
The problem with this approach is that you get lots of different spoke angles at the rim, possibly requiring many different spoke lengths and making it harder to true the rim. Still doable tho.
Myself I ended up having custom Carbon rims with 36 holes made. With extra Carbon and closed rim bed they're much tougher than alloy rims while still being lighter.
Attachments
Chalo
100 TW
1N4001 said:
That sounds cheap and convenient and easy to replace when damaged. Is there some kind of proprietary solution for connecting spokes, since the rim bed is closed?
Let's go back to something the OP said:
So how much did you pay for your custom plastic rims, so we can make an informed comparison? My most relevant point of comparison is the 42mm wide, 36 hole double walled rim that I've used most often for pedicab hub motor builds at the bike shop. $40 retail.
There are lots of good 36 hole rims available. If you're are hung up on here-today, gone-tomorrow trendy features, I can see how you'd maybe find selection somewhat lacking. But you don't have to tolerate parts incompatibility or disproportionate expense.
You're partially correct. It costs more than alloy rims, but Chinese Carbon can be had for reasonable prices. Don't be fooled, the quality is excellent. I got mine from Light Bicycle, they have a fairly good reputation among MTB riders, and they'll do customizations such as 36 holes or weird spoke hole angles for larger hubs. They'll even lace your motor for a small fee if you ship it to them.Chalo said:
Expect to pay around 200 USD per rim. That's expensive, but not insanely so.
As for lacing these rims, you have to insert the spoke nipples through the valve hole and guide them into position with a magnet. It's not as bad as it sounds. By not having holes in the rim bed you eliminate one of the main weak points of most rims, and you can run tubed or tubeless without needing any rim tape.
They can be had with regular drilled rim beds aswell if you prefer that.
Of course if weight is not a factor, then there is little point in considering Carbon.
999zip999
100 TW
Buy a 36h hole rim and make it ez and strong. Strength . K.I.S.S
Chalo
100 TW
1N4001 said:
It's a lot less than I expected. All the carbon rims in my distributors' catalogs have MSRPs of $450 and up.
I think you'd have to be using a very, very light hub motor before a few ounces of weight difference between a carbon rim and an aluminum rim becomes a significant part of the overall picture. If that's what floats your boat, I recommend using 14-17ga spokes as well. They're light, but they also increase wheel reliability compared to thicker spokes. They work effectively at modest tension levels that won't risk damaging laminated composite rims.
DeluxeMC
100 µW
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Hey guys, I just did an analysis of spoke lengths for a project I was doing using the pattern provided above. There is an insane amount of different spoke lengths, especially on the magenta/cyan side because on that side there is ONLY 1 axis of symmetry, and that is perpendicular to the spoke across the axis running through the center of the hub. I have done a lot of research on this, and although it is VERY VERY difficult to find any 14mm width 700c rims that have 2.5mm spoke nipple holes, I would suggest that just buying a wheel is the best option, since you have to buy over 10 different lengths of spokes. I know you could combine some because some of them are close, but the spokes that I need are 2.5mm 12 Gauge spokes for an e bike and they all come from china, and I am in a time crunch. SOOOOO, guess I'm going with the option of just selling the current rim and seeing if I can find a new rim with 36 Holes that AT LEAST has a 15-17mm outside width. Inside preferably 14-16mm. I know turning a road bike into an e bike is a bad idea, since you are sacrificing all the good things about a road bike. This is the last one I am going to do. They are just too much of a hassle to convert to e bikes.https://cad.onshape.com/documents/e...374ed0621016e27242/e/29223d6fa508d5dd4267d1a1
DeluxeMC
100 µW
- Joined
- Feb 22, 2020
- Messages
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I also didn't mention that you have to take into account the camber of the spokes, so I modified a program I found to calculate the spoke lengths. You will need to install GNU Octave to run it, as it is written in MATLAB. Also change the file extention from .txt to .m
View attachment spokecalc.txt
View attachment spokecalc.txt
Code:
function [length] = spokecalc(T, hub_diam, rim_diam, flange_spacing, ...
hole_diam)
%% Function to calculate spoke lengths given spoke angle, and optionally
%% other rim and hub dimensions. T may be a vector of spoke angles.
%% Equations from The Bicycle Wheel (3rd Edition) by Jobst Brandt, p. 127
%%
%% USAGE
%% length = spokecalc(T, hub_diam, rim_diam, flange_spacing, hole_diam)
%%
%% INPUT
%% T: (vector of) spoke angle in degrees
%% hub_diam: diameter of hole circle in flange
%% rim_diam: effective rim diameter
%% flange_spacing: centre-to-centre flange spacing
%% hole_diam: diameter of flange holes
%%
%% OUTPUT
%% length: length of spoke required (round down!)
%% T = put something here;
th = T*2*pi/360;
d = 146.5; % diameter of hole circle in flange
D = 605; % effective rim diameter
W = 69; % flange spacing (centre to centre)
S = 2.5; % flange hole diameter
if nargin > 0
T
end
if nargin > 1
d = hub_diam;
hub_diam
end
if nargin > 2
D = rim_diam;
rim_diam
end
if nargin > 3
W = flange_spacing;
flange_spacing
end
if nargin > 4
S = hole_diam;
hole_diam
end
%% pythag time also the one above is refference
%% A = (hub_diam/2)*sin(th);
%% B = rim_diam/2 - (hub_diam/2)*cos(th);
%% C = flange_spacing/2;
%% length = sqrt(A.^2 + B.^2 + C.^2) - hole_diam/2;
A = (d/2)*sin(th);
B = D/2 - (d/2)*cos(th);
C = W/2;
length = sqrt(A.^2 + B.^2 + C.^2) - S/2;DeluxeMC said:
There's your problem. If you use motorcycle spokes with a bicycle rim, you'll either have spokes that chronically loosen, or you'll crack your rim, or both. If you somehow avoid both these things, you'll get broken spokes from the elbows chafing against the hub holes.
Rim strength and spoke stretch work together as a system. Ideally, they match. But there's no significant downside to using spokes that are thinner than necessary for your rim, whereas using spokes that are too thick for your rim is inviting all kinds of problems.
Dealing with the same issue 32h rim and 36h hubs (non motor hubs, normal bicycle wheel hubs is what I'm talking about)
This is what I found for the quick minute I searched
https://www.instructables.com/Lacing-Bike-Wheel-36-Holes-Hub-to-32-Holes-Rim/
Notice how some holes are skipped.
This is what I found for the quick minute I searched
https://www.instructables.com/Lacing-Bike-Wheel-36-Holes-Hub-to-32-Holes-Rim/
Notice how some holes are skipped.
Chalo
100 TW
calab said:
That's a great way to spend all kinds of effort building a sucky wheel. Don't bother. Your spoke tension will be all over the place if you manage to make the wheel round (which you probably won't).
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