Front disk motor hub spoke length-different results

[mihai230]

Hi, I made some calculation with Sapim spoke calculator for Mxus XF15F. Total length 100mm, non gear side length is 34mm, gear side is 19 mm, 143mm hub flange diameter both sides, number of crossings 3, ERD of rim is 587, but I used 585 + 2 mm thickness- Sapim gave me 267 and 268mm spokes length. No offset of rim

I used also ebike.ca calculator same data and the result is 264 and 265 mm.

I missed something? I want to mention this is my first build.

Regards,
Mike

 

[E-HP]

3 cross seems impossible. When I laced my hub into my 24” rim, I used 1 cross. I probably should have used radial lacing, since 1 cross was barely doable. I’ve only laced the one rim and maybe yours has some very angled eyelets.

 

[mihai230]

Thanks for the answer. Regarding different spokes lenght calculator, what should I use? You are saying that I shoud use only one cross? Radial lacing is not strong!
Thank you

 

[E-HP]

Thanks for the answer. Regarding different spokes lenght calculator, what should I use? You are saying that I shoud use only one cross? Radial lacing is not strong!
Thank you

2 cross seems more than enough for that motor and rim as far as strength goes. I put 7kW through 1 cross, so 2 cross and 1kw should be fine. What are the prelaced hubs using?

 

[mihai230]

2 cross seems more than enough for that motor and rim as far as strength goes. I put 7kW through 1 cross, so 2 cross and 1kw should be fine. What are the prelaced hubs using?

Understood, I'll use Sapim and Ebikes.ca with only 2x to see if the results are the same!

 

[docw009]

I have compared DT swiss calculator with Grin calculator using 1X crossing, Also saw small differences in the 1-2 mm range. I use the Grin calculator,

More times than I like, the resulting spokes come back 1-2mm too long, but double wall rims and washers hide those errors. I find it hard to measure ERD. My last build, I used the manufacturer's ERD and the spokes were too long on the non-drive side. They protruded past the rim holes,

 

[mihai230]

That is a great idea to use washers to compensate the ERD! I just wached online the Grin tutorial how to use the calculator. I will use today Sapim, ebikes.ca and Grin with only one cross. Will post the results!
thanks

 

[mihai230]

I want to use grin technologies as a spokes calculator. The only issue I have is that I do not know how to input the offset. I have Mxus XF15 front. This hub motor has disk brake and I do not know what is the offset? Can you suggest something? From what measurements I can see the offset?
Thank you

 

[docw009]

Offset is a property of the rim, With a centerline down the middle, if the spoke holes are staggered, it's their distance from the center line. Makes a big difference on fat tire rims.

Good way to measure ERD.

 

[mihai230]

Understood, but my holes from the rim are aligned. It is a cross 622 rim. On that I want to install mxus xf15f . It has disk brakes. What I meant is spoke calculation has resulted equal spoke lenght drive side and non drive. How the offset for disk brake mount is achived?

 

[E-HP]

I want to use grin technologies as a spokes calculator. The only issue I have is that I do not know how to input the offset. I have Mxus XF15 front. This hub motor has disk brake and I do not know what is the offset? Can you suggest something? From what measurements I can see the offset?
Thank you

Rim or dishing offset?

Dishing looks like 6.9mm

but you should check a few diagrams to make sure.

 

[mihai230]

Dishing offset. That value of 6.9 mm is the offset? didn't new that! but, I watched the grin tutorial for measuring hub at home with no specialized tools. I measured left side 34mm and right side 19. Subtracting 19 from 34 I got 15 and dividing by 2 I got 7.5 mm. And considering errors in manual measurement, that is about right. 6.9mm should be!
P.S. What diagrams you want me to check?

 

[E-HP]

Dishing offset. That value of 6.9 mm is the offset? didn't new that! but, I watched the grin tutorial for measuring hub at home with no specialized tools. I measured left side 34mm and right side 19. Subtracting 19 from 34 I got 15 and dividing by 2 I got 7.5 mm. And considering errors in manual measurement, that is about right. 6.9mm should be!
P.S. What diagrams you want me to check?

I just did a search on your motor, and it displayed several drawings of both the front and rear versions but not clearly marked for front vs rear. The one above had 100mm dropout measurement, for a front hub. I didn’t check them all but if this one is close to your measured value, it’s probably right. I quadruple checked everything before ordering spokes, since it’s a costly mistake if you get it wrong.

Edit: Make sure you use the same width washers, inside the dropouts on both sides (“3” in the diagram).

 

[mihai230]

Hello E-HP. Your effort is much appreciated! You got this right! The one above is labeled Xf 15f . It is the front motor hub. You said it yourself, this is a probability . So you are right 100 mm for the OLD is the front. I will make all the calculations regarding the spokes. I will replay later.
Best regards,
Mike

 

[amberwolf]

Radial lacing is not strong!

Works on my SB Cruiser heavy heavy-cargo trike's rear wheels (that carry almost all the weight and do all the motor work and have all the lateral stress).

Have broken axles and rims without breaking the spokes (sapim (strong?) 13/14g singlebutted radial laced in 20" rims on old Stromer and A2B ultramotors (and have used the same configuration in other hubmotors on it before these).

But I have seen and had radially-laced wheels fail, when not built correctly of the right parts to handle the loading placed on them.

 

[offGridDownUnder]

shoud use only one cross?

Open your chosen spoke calculator in two pages at the same time. In both, set the same rim.

In one, set a regular bicycle hub that you would use 3 cross with for strength. This has a small diameter for the spoke ends.
In the other, set your chosen motor as the hub. Change the cross setting until you get similar spoke angles.

What you will see is that due to the size of the motor hub, the angles result in 0 or 1 cross for the same spoke angles. It's due to the much greater size of the motor hub and has the same physical dynamics.

It's obvious if you do this side-by-side. On the motor page, you'll see that 1 or 2 of the crosses needed on the bicycle hub actually fall within the outer diameter of the motor hub, so what seems to be a 1 (or 0) cross on the motor is actually the same physics as the 3 cross on the much smaller standard bicycle hub.

As mentioned in the Grin page, motor makers also use a tactic of grouping the spoke holes on the motor flanges rather than spacing them equally around the hub as most bicycle hubs do. This has the effect of providing an offset and angle on the spoke that mimics a cross lacing even when the spokes physically don't cross with that motor.

I don't know if your motor has equally spaced spoke holes, but the size difference still applies.

 

[mihai230]

Open your chosen spoke calculator in two pages at the same time. In both, set the same rim.

Hi, I just did what you suggested. I used my motor with only one cross and the angle of the spoke to the rim is 84 degree and used the same rim settings with a hub shimano hb-tx 505 and with 3x I have the angle of the spoke to the rim 85 degree.
If I set 3x to the hub motor I got an odd angle of 77.
What do you suggest for the motor crossing 1x or radial?
Thank you

 

[docw009]

I have always done 1x. What does Justin say at the bottom of his calculator page?

"Most hub motors are laced with a single cross pattern. There is no point at all in having 2 or more crosses with the large flange diameters of most hub motors, and doing so will usually result the spoke entering the rim at a very difficult angle."

For your motor and 700cc rim, the spokes are around 262mm for 3X and 224mm for 1x. It's tough enough bending the shorter spokes so they can go under the rim and around each other when you start crossing them. Can't imagine it with an extra 40 mm length.

 

[mihai230]

Hi,
I think I will do 1 cross pattern. This calculation of the spokes is correct?
best regards

 

[docw009]

You wrote 587 for ERD in the first post and now you're using 596. This really is the most critical parameter in the calculator.

This is when Chalo would tell us what for, if not earlier.

 

[mihai230]

Yes, after that I measured exactly with two spokes and a caliper. I measured the spokes with a ruler and added the 3 mm x 2 off the nipples + what was the caliper. Spokes 267x2+nipple 2x3mm + caliper 56mm.
If the measure is 2 mm more, I can add some washers between the nipple and rim. Better extra than less.

 

[E-HP]

You wrote 587 for ERD in the first post and now you're using 596. This really is the most critical parameter in the calculator.

This is when Chalo would tell us what for, if not earlier.

If Chalo were here we’d already be warned to use 14 gauge spokes with washers at the flange holes.

#free_chalo

 

[mihai230]

I'm very confident about my measurements. I'll use anyway washers because I should install 13G spokes and I will use 14G.

 

[docw009]

I like and suggest Sapim Strong spokes. 13G at the elbow and 14G at the end. Easier to flex a thinner spoke thru the rim when lacing. Cost more though,

For your measurement, the nipple is there to hold the end of the spoke at the perfect height above the hole and its edge thickness isn't used. I think you're adding 4-6mm too much.

 

[mihai230]

The rim is Euroline Schurman. What is usually the ERD of an 622 rim? Can I compensate those 4-6mm with washers at the elbow and nipple? Regards. I Kind of stretched the elbows when I measured with the caliper!